Emeritus Faculty, Acad Council, Medicine
Multimorbidity-the presence of multiple chronic conditions in a patient-has a profound impact on health, health care utilization, and associated costs. Definitions of multimorbidity in clinical care and research have evolved over time, initially focusing on a patient's number of comorbidities and the associated magnitude of required care processes, and later recognizing the potential influence of comorbidity characteristics on patient care and outcomes. In this article, we review the relationship between multimorbidity and quality of care, and discuss how this relationship may be mediated by the degree to which conditions interact with one another to generate clinical complexity (comorbidity interrelatedness). Drawing on established theoretical frameworks from cognitive engineering and biomedical informatics, we describe how interactions among conditions result in clinical complexity and may affect quality of care. We discuss how this comorbidity interrelatedness influences the value of existing quality guidelines and performance metrics, and describe opportunities to quantify this construct using data widely available through electronic health records. Incorporating comorbidity interrelatedness into conceptualizations of multimorbidity has the potential to enhance clinical and research efforts that aim to improve care for patients with multiple chronic conditions.
View details for DOI 10.1007/s11606-013-2616-9
View details for PubMedID 24081443
The extent to which chronic kidney disease (CKD) affects achievement of blood pressure targets is not comprehensively understood. We evaluated the effects of CKD (estimated glomerular filtration rate: <60 mL/min per 1.73 m(2)) on achievement of blood pressure control (nondiabetic: <140/90 mm Hg; diabetic: <130/85 mm Hg) using data from the Guidelines for Drug Therapy of Hypertension Trial. This 15-month study obtained outpatient blood pressures from 3 Veteran's Affairs institutions. Among 9985 subjects with hypertension, we evaluated the association of CKD with achieved control and antihypertensive medication use. We also explored the association between the number of antihypertensives and systolic, diastolic, and pulse pressure. After 15 months, 41% of participants met blood pressure targets. CKD was not associated with control (adjusted odds ratio: 1.04; 95% CI: 0.93 to 1.15). However, CKD was associated with higher odds of use of >or=3 medications among nondiabetic subjects (odds ratio: 1.46; 95% CI: 1.25 to 1.71) and diabetic subjects (odds ratio: 1.40; 95% CI: 1.17 to 1.66). A significant interaction was observed between CKD and the number of antihypertensives as determinants of diastolic and pulse pressures. Among non-CKD participants, a greater number of antihypertensives (0 compared with 4) was associated with wider pulse pressure (Delta5.2 mm Hg; P<0.001), mainly because of higher systolic pressures (Delta3.6 mm Hg; P=0.001). Among participants with CKD, although greater numbers of antihypertensives were associated with even wider pulse pressures (Delta8.3 mm Hg; P<0.001), this was primarily because of lower diastolic pressures (Delta4.8 mm Hg; P<0.01). Among participants with CKD, greater use of antihypertensives was associated with lower diastolic pressures. Given recent evidence suggesting adverse effects of diastolic hypotension, these results suggest potential risks in patients with CKD from aggressive attempts to control systolic blood pressure.
View details for DOI 10.1161/HYPERTENSIONAHA.107.088088
View details for Web of Science ID 000248945100010
View details for PubMedID 17664397
End stage renal disease (ESRD) is associated with altered hemodynamic regulation as a result of the pathophysiology or treatment of renal failure. Hypertension, common among dialysis patients, is a recognized complication of recombinant human erythropoietin (rHuEPO) therapy. We determined vascular adrenergic and nitric-oxide-mediated responsiveness in 7 patients with established ESRD on rHuEPO treatment and in 13 healthy volunteers using the dorsal hand vein technique. Sensitivity to the alpha1-adrenergic selective agonist phenylephrine was significantly increased in patients with ESRD on rHuEPO. The mean dose of phenylephrine producing 50% venoconstriction (ED50) was 38 +/- 1.6 ng/min in patients with ESRD and 135 +/- 1.3 ng/min in healthy volunteers-almost a 4-fold increase in dose, P = 0.01. In contrast, maximal venodilation mediated by bradykinin, an endothelium-dependent vasodilator, was not different in the 2 groups. To determine whether rHuEPO has a direct vasoconstrictor effect, we studied venous responsiveness to local infusions of rHuEPO in healthy volunteers. Increasing concentrations of rHuEPO produced no vasoconstriction in hand veins of healthy volunteers. These results suggest that vascular responsiveness to alpha-adrenergic stimulation in patients with ESRD on rHuEPO is increased whereas bradykinin-mediated venodilation remains intact. This increase in vascular alpha-adrenergic responsiveness may contribute to the increased peripheral vascular resistance and hypertension seen in patients with ESRD on rHuEPO.
View details for PubMedID 17890929
Only 31% of Americans with hypertension have their blood pressure (BP) under effective control. We describe a study that tests 3 different interventions in a randomized controlled trial using home BP telemedicine monitoring.A sample of hypertensive patients with poor BP control at baseline (N = 600) are randomized to 1 of 4 arms: (1) control group--a group of hypertensive patients who receive usual care; (2) nurse-administered tailored behavioral intervention; (3) nurse-administered medication management according to a hypertension decision support system; (4) combination of the 2 interventions. The interventions are triggered based on home BP values transmitted via telemonitoring devices over standard telephone lines. The tailored behavioral intervention involves promoting adherence with medication and health behaviors. Patients randomized to the medication management or the combined arm have their hypertension regimen changed by the study team using a validated hypertension decision support system based on evidence-based hypertension treatment guidelines and individualized to patients' comorbid illnesses. The primary outcome is BP control: < or = 140/90 mm Hg (nondiabetic) and < or = 130/80 mm Hg (diabetics) measured at 6-month intervals over 18 months (4 total measurements).Given the increasing prevalence of hypertension and our inability to achieve adequate BP control using traditional models of care, testing novel interventions in patients' homes may improve access, quality, and outcomes.
View details for DOI 10.1016/j.ahj.2007.03.004
View details for Web of Science ID 000247540600005
View details for PubMedID 17540191
Factors contributing to low adherence to clinical guidelines by clinicians are not well understood. The user interface of ATHENA-HTN, a guideline-based decision support system (DSS) for hypertension, presents a novel opportunity to collect clinician feedback on recommendations displayed at the point of care. We analyzed feedback from 46 clinicians who received ATHENA advisories as part of a 15-month randomized trial to identify potential reasons clinicians may not intensify hypertension therapy when it is recommended. Among the 368 visits for which feedback was provided, clinicians commonly reported they did not follow recommendations because: recorded blood pressure was not representative of the patient's typical blood pressure; hypertension was not a clinical priority for the visit; or patients were nonadherent to medications. For many visits, current quality-assurance algorithms may incorrectly identify clinically appropriate decisions as guideline nonadherent due to incomplete capture of relevant information. We present recommendations for how automated DSSs may help identify "apparent" barriers and better target decision support.
View details for PubMedID 17238390
ATHENA-HTN is a clinical decision support system (CDSS) that delivers guideline-based patient-specific recommendations about hypertension management at the time of clinical decision-making. The ATHENA-HTN knowledge is stored in a knowledge-base (KB). Changes in best-practice recommendations require updates to the KB. We describe a method of offline testing to evaluate the accuracy of recommendations generated from the KB. A physician reviewed 100 test cases and made drug recommendations based on guidelines and the "Rules" (descriptions of encoded knowledge). These drug recommendations were compared to those generated by ATHENA-HTN. Nineteen drug-recommendation discrepancies were identified: ATHENA-HTN was more complete in generating recommendations (15); ambiguities in the Rules misled the physician (3); and content in the Rules was not encoded (1). Three new boundaries were identified. Three updates were made to the KB based on the results. The offline testing method was successful in identifying areas for KB improvement and led to improved accuracy of guideline-based recommendations.
View details for PubMedID 17238399
To determine whether an intervention focusing clinician attention on drug choice for hypertension treatment improves concordance between drug regimens and guidelines.Cluster-randomized controlled trial comparing an individualized intervention with a general guideline implementation in geographically diverse primary care clinics of a university-affiliated Department of Veterans Affairs healthcare system.Participants were 36 attending physicians and nurse practitioners (16 in the general group and 20 in the individualized group), with findings based on 4500 hypertensive patients. A general guideline implementation for all clinicians, including education about guideline-based drug recommendations and goals for adequacy of blood pressure control, was compared with addition of a printed individualized advisory sent to clinicians at each patient visit, indicating whether or not the patient's antihypertensive drug regimen was guideline concordant. We measured change from baseline to end point in the proportion of clinicians' patients whose drug therapy was guideline concordant.The individualized intervention resulted in an improvement in guideline concordance more than twice that observed for the general intervention (10.9% vs 3.8%, t = 2.796, P = .008). Bootstrap analysis showed that being in the individualized group increased the odds of concordance 1.5-fold (P = .025). The proportion of patients with adequate blood pressure control increased within each study group; however, the difference between groups was not significant.An individualized advisory regarding drug therapy for hypertension given to the clinician at each patient visit was more effective in changing clinician prescribing behavior than implementation of a general guideline.
View details for Web of Science ID 000233132300002
View details for PubMedID 16268751
Studies of barriers to guideline adherence have generally surveyed clinicians temporally remote from the clinical scenario in which recommendations were delivered, potentially adversely biasing clinician observations. The user interface of ATHENA DSS, a guideline-based decision support system for hypertension, includes a point-of-care feedback window that accepts clinician-user comments during the display of recommendations. Analysis of this feedback has revealed a number of intriguing patient, provider, and technical barriers to adherence collected during real-time system use.
View details for PubMedID 16779202
Little is known about how well clinicians are aware of their own adherence to clinical guidelines, an important indicator of quality. We compared clinicians' beliefs about their adherence to hypertension guidelines with data on their actual performance.We surveyed 139 primary care clinicians at three Veterans Affairs medical centers, asking them to assess their own adherence to hypertension guidelines. We then extracted data from the centers' clinical databases on guideline-concordant medication use and blood pressure control for patients cared for by these providers during a 6-month period. Data were collected for patients with hypertension and diabetes, hypertension and coronary disease, or hypertension with neither of these comorbid conditions.Eighty-six clinicians (62%) completed the survey. Each clinician saw a median of 94 patients with hypertension (mean age, 65 years). Patients were treated with an average of 1.6 antihypertensive medications. Overall, clinicians overestimated the proportion of their patients who were prescribed guideline-concordant medications (75% perceived vs. 67% actual, P <0.001) and who had blood pressure levels <140/90 mm Hg on their last visit (68% perceived vs. 43% actual, P <0.001). Among individual clinicians, there were no significant correlations between perceived and actual guideline adherence (r = 0.18 for medications, r = 0.14 for blood pressure control; P > or =0.10 for both). Clinicians with relatively low actual guideline performance were most likely to overestimate their adherence to medication recommendations and blood pressure targets.Clinicians appear to overestimate their adherence to hypertension guidelines, particularly with regards to the proportion of their patients with controlled blood pressure. This limited awareness may represent a barrier to successful implementation of guidelines, and could be addressed through the use of provider profiles and point-of-service feedback to clinicians.
View details for DOI 10.1016/j.amjmed.2004.03.035
View details for Web of Science ID 000225232900005
View details for PubMedID 15541324
Information technology can support the implementation of clinical research findings in practice settings. Technology can address the quality gap in health care by providing automated decision support to clinicians that integrates guideline knowledge with electronic patient data to present real-time, patient-specific recommendations. However, technical success in implementing decision support systems may not translate directly into system use by clinicians. Successful technology integration into clinical work settings requires explicit attention to the organizational context. We describe the application of a "sociotechnical" approach to integration of ATHENA DSS, a decision support system for the treatment of hypertension, into geographically dispersed primary care clinics. We applied an iterative technical design in response to organizational input and obtained ongoing endorsements of the project by the organization's administrative and clinical leadership. Conscious attention to organizational context at the time of development, deployment, and maintenance of the system was associated with extensive clinician use of the system.
View details for Web of Science ID 000223898000005
View details for PubMedID 15187064
View details for PubMedCentralID PMC516243
View details for Web of Science ID 000221604400326
View details for Web of Science ID 000221125800916
alpha(2) adrenergic agonists such as dexmedetomidine generally suppress noradrenergic transmission and have sedative, analgesic, and antihypertensive properties. Considering the importance of the neurotransmitter norepinephrine in forming memories for fearful events, we have investigated the acute and chronic effects of dexmedetomidine on discrete cue and contextual fear conditioning in mice. When administered before training, dexmedetomidine (10-20 microg/kg, i.p.) selectively suppressed discrete cue fear conditioning without affecting contextual memory. This behavioral change was associated with a decrease in memory retrieval-induced expression of c-Fos and P-CREB in the lateral, basolateral, and central nuclei of the amygdala. Dexmedetomidine's action on discrete cue memory did not occur in alpha(2A) adrenoceptor knockout (KO) mice. When dexmedetomidine was administered after training, it suppressed contextual memory, an effect that did not occur in alpha(2A) adrenoceptor KO mice. We conclude that dexmedetomidine, acting at alpha(2A) adrenoceptors, must be present during the encoding process to decrease discrete cue fear memory; however, its ability to suppress contextual memory is likely the result of blocking the consolidation process. The ability of alpha(2) agonists to suppress fear memory may be a valuable property clinically in order to suppress the formation of memories during stressful situations.
View details for DOI 10.1038/sj.npp.1300324
View details for Web of Science ID 000188769600002
View details for PubMedID 14583739
Measurement of provider adherence to a guideline-based decision support system (DSS) presents a number of important challenges. Establishing a causal relationship between the DSS and change in concordance requires consideration of both the primary intention of the guideline and different ways providers attempt to satisfy the guideline. During our work with a guideline-based decision support system for hypertension, ATHENA DSS, we document a number of subtle deviations from the strict hypertension guideline recommendations that ultimately demonstrate provider adherence. We believe that understanding these complexities is crucial to any valid evaluation of provider adherence. We also describe the development of an advisory evaluation engine that automates the interpretation of clinician adherence with the DSS on multiple levels, facilitating the high volume of complex data analysis that is created in a clinical trial of a guideline-based DSS.
View details for Web of Science ID 000226723300026
View details for PubMedID 15360788
We have investigated sensitivity to the conditioned fear procedure of mice is influenced by the genetic deletion of alpha2A adrenoceptors (ARs). We observed a heightened freezing response in the discrete cue memory test in alpha2A AR knockout (alpha2A AR KO) mice and in D79N mice, a transgenic mouse strain with functionally impaired alpha2A ARs. No significant differences in contextual memory were observed between control and alpha2A AR KO or D79N mice suggesting a minimal role for the noradrenergic system in contextual memory. We speculated that the increased freezing response of the alpha2A AR KO and D79N mice in the discrete cue setting was due to increased release of norepinephrine evoked by the unconditioned footshock stimulus. In alpha2A AR KO mice we measured a doubling in the number of noradrenergic neurons in the locus coeruleus (LC) and a large increase in the cell volume of tyrosine hydroxylase positive neurons, likely due to selective preservation of large, multipolar neurons in the subcoeruleus. Hyperplasia of the noradrenergic neurons in the nucleus tractus solitarius, A5 and A7, was also observed. Alpha2A AR KO mice exhibit greater c-Fos expression in the LC compared to wild type mice suggesting that the LC neurons in the alpha2A AR KO mice were spontaneously more active. This study suggests that alpha2A ARs are involved in the development of the central noradrenergic system and raises the possibility that alterations in alpha2A AR expression may contribute to variations in fear and stress responses.
View details for DOI 10.1016/S0006-8993(03)03248-7
View details for Web of Science ID 000185454000017
View details for PubMedID 12965240
There is increasing evidence that G-protein-coupled receptors cross-talk with growth factor receptor-mediated signal transduction in a variety of cell types. We have investigated mechanisms by which the activation of beta-adrenergic receptors, classically GTP-binding proteins coupled receptors, influence the migration of cultured human keratinocytes. We found that iso-proterenol, a beta-adrenergic receptor-selective agonist, inhibited cell migration stimulated by either epidermal growth factor, or extracellular Ca2+ in a concentration-dependent manner. This was prevented by pretreatment of the cells with the beta-adrenergic receptor-selective antagonist timolol. Interestingly, isoproterenol, at a concentration of 1 nm, did not measurably increase intracellular cyclic adenosine monophosphate concentrations yet inhibited cell migration by 50%. To test further if isoproterenol's actions were mediated via activation of adenylyl cyclase, two inhibitors of its activity, 2'5'-dideoxyadenosine and SQ22536, were used. Both compounds significantly diminished iso-proterenol-induced increases in intracellular cyclic adenosine monophosphate concentrations but did not attenuate isoproterenol-induced inhibition of cell migration. Also, forskolin (1 microm) markedly increased intracellular cyclic adenosine monophosphate concentrations but did not significantly inhibit cell migration. As mitogen-activated protein kinases are known to signal growth factor-stimulated cell migration, we examined whether beta-adrenergic receptor-mediated inhibition of keratinocyte migration might occur via inactivation of mitogen-activated protein kinases. We found that isoproterenol inhibited phosphorylation of extracellular signal-regulated kinase mitogen-activated protein kinase in a concentration-dependent manner but had no effect on the phosphorylation of the stress mitogen-activated protein kinases c-jun N-terminal kinase and stress-activated protein kinase-2. Neither forskolin nor a membrane permeable cyclic adenosine monophosphate analog inhibited phosphorylation of any of these mitogen-activated protein kinases. These findings suggest that beta-adrenergic receptor-induced inhibition of keratinocyte migration is mediated through inhibition of the extracellular signal-regulated kinase mitogen-activated protein kinase signaling in a cyclic adenosine monophosphate-independent manner.
View details for Web of Science ID 000179803200008
View details for PubMedID 12485426
In vascular smooth muscle, increased expression of cyclooxygenase-2 (COX-2) has emerged as an important mechanism for regulation of prostanoid synthesis influenced by vessel injury, cytokines, and growth factors. We have investigated how COX-2 participates in angiotensin II (ANG II)-mediated cell responses in cultured human vascular smooth muscle cells (VSMCs). ANG II type 1 (AT1) receptors induce increased accumulation of COX-2, both at the mRNA and protein levels. ANG II increased transcription of the COX-2 gene; also, nuclear extracts from stimulated cells had increased NF-kappa B binding to its DNA consensus sequence. ANG II-induced COX-2 expression was markedly blunted by inhibition of mitogen-activated protein kinase. Furthermore, the ANG II-induced increase in COX-2 protein abundance was attenuated by both the peroxisome proliferator-activated receptor alpha (PPARalpha) activator Wy-14,643 [pyrinixic acid; 4-chloro-6-(2,3-xylidino)-2-pyrimidinyl) thioacetic acid] and the PPARgamma activator 15d-PGJ2 (15-deoxy-Delta(12-14)-prostaglandin J2). Not only did ANG II increase COX-2 expression and prostaglandin synthesis, ANG II-stimulated DNA synthesis and cell migration were dependent on COX-2 activity. PPARalpha and PPARgamma activators inhibited ANG II-stimulated DNA synthesis and cell migration. These results suggest that ANG II enhances COX-2 expression at the transcription level; also, COX-2 activity plays an important role in mediating ANG II- induced proliferation and migration of VSMCs, suggesting the possibility of magnification of ANG II effects over time due to the induction of COX-2 expression. These results also demonstrate that both the alpha and gamma type of PPAR activators inhibit COX-2 expression induced by angiotensin II in VSMCs which may have therapeutic significance in vascular diseases.
View details for DOI 10.1124/jpet.102.037705
View details for Web of Science ID 000178684800016
View details for PubMedID 12388637
Electronically available data, both administrative, such as outpatient encounter diagnostic data, and clinical, such as problem lists, are being used increasingly for outcome and quality assessment, risk adjustment, and clinical reminder systems.To determine the accuracy of outpatient primary care diagnostic information recorded in administrative and clinical files in a Veterans Affairs VISTA (Veterans Health Information Systems and Technology Architecture) database compared with medical chart notes.Cross-sectional medical chart review of 148 patients attending a general medicine clinic at a university-affiliated Veterans Affairs hospital for 9 diagnoses relevant to the choice of drug therapy for hypertension.An administrative file of encounter diagnoses, for a 2-year period, and a clinical file of the problem list maintained by the clinician were the sources of electronic diagnoses. We compared these sources with diagnoses abstracted by medical chart review. We estimated the sensitivity and specificity of each electronic data source for detecting medical chart note diagnoses.The sensitivity for 8 of the 9 study diagnoses was greater than 80% in the administrative file and 49% in the clinical problem list. The specificity was good for the administrative file (91% to 100%) and even better for the clinical file (98% to 100%).Outpatient encounter diagnoses relevant to hypertension recorded as electronic data had high specificity, and some codes had high sensitivity when collected over multiple visits. The administrative file was more sensitive but less specific than the clinical file. Administrative vs clinical files can be selected to minimize either the false-negative or the false-positive designations, respectively, as dictated by the needs of the quality assessment review.
View details for Web of Science ID 000173442700002
View details for PubMedID 11814171
The Institute of Medicine recently issued a landmark report on medical error.1 In the penumbra of this report, every aspect of health care is subject to new scrutiny regarding patient safety. Informatics technology can support patient safety by correcting problems inherent in older technology; however, new information technology can also contribute to new sources of error. We report here a categorization of possible errors that may arise in deploying a system designed to give guideline-based advice on prescribing drugs, an approach to anticipating these errors in an automated guideline system, and design features to minimize errors and thereby maximize patient safety. Our guideline implementation system, based on the EON architecture, provides a framework for a knowledge base that is sufficiently comprehensive to incorporate safety information, and that is easily reviewed and updated by clinician-experts.
View details for Web of Science ID 000172263400045
View details for PubMedID 11825183
View details for PubMedCentralID PMC2243380
Cigarette smoking is associated with impaired endothelium-dependent dilatation in human veins and arteries. An in vivo study in animals suggests that nicotine may contribute to this abnormality. We tested the hypothesis that local administration of nicotine at a dose reproducing the plasma concentration observed during smoking would impair endothelium-dependent vasodilatation in human veins in vivo.We studied 11 healthy nonsmokers with the dorsal hand vein compliance technique. After 70% to 80% preconstriction with phenylephrine, endothelium-dependent venous relaxation was assessed by infusion of bradykinin (1 to 278 ng/min), a potent vasodilator acting primarily in this model through endothelial release of nitric oxide and prostanoids. Sodium nitroprusside (0.0001 to 3166 ng/min) was used to test endothelium-independent relaxation. Dose-response curves were constructed before and during nicotine coinfusion at a rate of 40 ng/min, reproducing a plasma concentration of 15 ng/mL.After a 10-minute preinfusion, nicotine administration was associated with a loss in sensitivity to bradykinin (P < .001). After 30 and 60 minutes of preinfusion with nicotine, the venorelaxant effect of bradykinin was further reduced (P < .001). A similar inhibition of the response to bradykinin by nicotine persisted in the presence of indomethacin (INN, indomethacin). Coinfusion of nicotine did not attenuate sodium nitroprusside-induced venodiiation.The results show that acute local exposure to nicotine in vivo is associated with an impaired response to endothelium-derived nitric oxide in human veins. This finding may provide further insight into the pathophysiology of smoking-induced endothelial dysfunction.
View details for Web of Science ID 000086783100010
View details for PubMedID 10801248
Smooth muscle cells in vascular tissue, like tissue within the urogenital sinus, undergo growth and proliferation.This review attempts to compare and contrast the mechanisms and controlling factors involved in prostatic and vascular tissue. There is a particular focus on the role of catecholamines and alpha-adrenoceptors (alpha-ARs), and on the effects of alpha(1)-AR antagonists (blockers) on cellular dynamics. RESULTS AND CONCLUSIONS The situation in vascular tissue appears analagous to that in prostatic tissue. Certain AR-antagonists, in addition to altering smooth muscle contraction, may have other actions on cellular dynamics.
View details for Web of Science ID 000089999900007
View details for PubMedID 11056500
View details for PubMedID 10685409
An important aspect of the drug development process is prediction of efficacious and toxic side effects. Profiling of mRNA expression is a powerful approach to analyze the molecular phenotype of cells under various conditions, for example, in response to stimulation by compounds. We attempt to explore the approach of using expression profiling to identify patterns or fingerprints that are correlated with specific drug properties or behaviors. Identification of such expression patterns may also lead to revelation of the potential action mechanism of drugs and fingerprints indicative of certain drug efficacy or side effects. We describe here a strategy that was used to identify a set of genes whose differential expression pattern correlates with activation mode and target specificity of a specific group of drug compounds.
View details for PubMedID 11083092
The obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular disease and systemic hypertension. Because systemic arterial blood pressure is proportional to venodilation and venous return to the heart, we hypothesized that altered vascular responsiveness might exist in the veins of subjects with OSAS. We therefore investigated venodilator responses in awake, normotensive subjects with and without OSAS, using the dorsal hand vein compliance technique. Dose-response curves to bradykinin and nitroglycerin were obtained from 12 subjects with OSAS and 12 matched control subjects. Maximal dilation (E(max)) to bradykinin was significantly lower in the OSAS group (62.1% +/- 26.1%) than in the control group (94.3% +/- 10.7%) (p < 0.005). Vasodilation to nitroglycerin tended to be lower in the OSAS group (78.6% +/- 31.8%) than the control group (100.3% +/- 12.9%), but this effect did not reach statistical significance. When six of the OSAS subjects were retested after 60 d of treatment with nasal continuous positive airway pressure (CPAP), E(max) to bradykinin rose from 60.3% +/- 20. 3% to 121.4% +/- 26.9% (p < 0.01). Vasodilation to nitroglycerin also increased, but this effect did not reach statistical significance. These results demonstrate that a blunted venodilatory responsiveness to bradykinin exists in OSAS. This effect appears to be reversible with nasal CPAP therapy.
View details for Web of Science ID 000084820200032
View details for PubMedID 10619819
This paper describes the ATHENA Decision Support System (DSS), which operationalizes guidelines for hypertension using the EON architecture. ATHENA DSS encourages blood pressure control and recommends guideline-concordant choice of drug therapy in relation to comorbid diseases. ATHENA DSS has an easily modifiable knowledge base that specifies eligibility criteria, risk stratification, blood pressure targets, relevant comorbid diseases, guideline-recommended drug classes for patients with comorbid disease, preferred drugs within each drug class, and clinical messages. Because evidence for best management of hypertension evolves continually, ATHENA DSS is designed to allow clinical experts to customize the knowledge base to incorporate new evidence or to reflect local interpretations of guideline ambiguities. Together with its database mediator Athenaeum, ATHENA DSS has physical and logical data independence from the legacy Computerized Patient Record System (CPRS) supplying the patient data, so it can be integrated into a variety of electronic medical record systems.
View details for Web of Science ID 000170207500062
View details for PubMedID 11079893
To investigate whether heparin produces vasodilation in human veins and to explore the underlying mechanisms.Eleven healthy volunteers were studied with the dorsal hand vein compliance technique. Dose-response curves to heparin and enoxaparin were generated. Dose-response curves to heparin were also constructed before and after heparin was infused with the nitric oxide synthase inhibitor N(G)-monomethyl-l-arginine (L-NMMA) or combined histamine H1- and H2-receptor blockade.Heparin but not enoxaparin caused significant dose-dependent relaxation with an average apparent maximal response (at an infusion rate of 20 IU/min) of 47% +/- 23%. L-NMMA attenuated heparin-induced relaxation (P < .001). The combination of H1-and H2-receptor antagonists attenuated heparin-induced relaxation to a lesser extent (P < .05). Heparin-induced relaxation decreased by 52%, 73%, and 35% in the presence of L-NMMA, indomethacin (INN, indometacin) plus L-NMMA, and combined H1- and H2-receptor blockade, respectively.Heparin is an endothelium-dependent venodilator in humans. The mechanism of heparin-induced relaxation involves an increased availability of nitric oxide, possibly partially related to local release of histamine.
View details for Web of Science ID 000082744100004
View details for PubMedID 10511058
Signaling pathways of many G protein-coupled receptors overlap with those of receptor tyrosine kinases. We have found previously that alpha1-adrenergic receptors stimulate DNA synthesis and cell proliferation in human vascular smooth muscle cells; these effects were attenuated by the tyrosine protein kinase (TPK) inhibitor genistein and the mitogen-activated protein kinase (MAPK) antagonist 2-aminopurine. Experiments were designed to determine if activation of alpha1 receptors directly stimulated TPKs and MAPKs in human vascular smooth muscle cells. Norepinephrine stimulated time- and concentration-dependent tyrosine phosphorylation of multiple proteins, including p52-, 75-, 85-, 120-, and 145-kDa proteins. Increased TPK activity was demonstrated in proteins precipitated by an antiphosphotyrosine antibody, both in autophosphorylation assays and with a peptide substrate. These effects of norepinephrine were completely blocked by alpha1 receptor antagonists. A membrane-permeable Ca2+ chelator [1,2-bis(o-aminophenoxy)ethane-N,N, N',N'-tetraacetic acid tetra(acetoxymethyl)ester], completely blocked norepinephrine stimulation of phosphorylation of tyrosine proteins, suggesting that intracellular Ca2+ plays a critical role in alpha1 receptor stimulation phosphorylation of tyrosine proteins. Of the tyrosine-phosphorylated proteins, the results suggest that two of them are PLCgamma1 and adapter protein Shc. Also, alpha1 receptor stimulation caused a time-dependent increase in MAPK activity due to increased phosphorylation of p42/44(ERK1/2). The alpha1 receptor-mediated activation of MAPK was also attenuated by TPK inhibitors and intracellular Ca2+ chelator [1, 2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl)ester]. These results suggest that phosphorylation of tyrosine proteins and intracellular Ca2+ plays a critical role in alpha1 receptor-stimulated MAPK signaling pathways, potentially contributing to increased DNA synthesis and cell proliferation.
View details for Web of Science ID 000081039900005
View details for PubMedID 10381756
alpha1-Adrenergic receptors mediate mitogenic responses and increase intracellular free Ca2+ ([Ca2+]i) in vascular smooth muscle cells. Induction of c-fos is a critical early event in cell growth; expression of this gene is regulated by a number of signaling pathways including Ca2+. We wondered whether Ca2+ signaling plays a critical role in the induction of c-fos gene by alpha1-adrenergic receptors. Using stably transfected rat-1 fibroblasts, we confirmed that PE induced c-fos mRNA expression in a time- and dose-dependent manner, and also increased [Ca2+]i (measured with Fura-2 AM). These responses were blocked by the alpha1-adrenergic receptor antagonist doxazosin. Both intracellular Ca2+ chelation (using BAPTA/AM) and extracellular Ca2+ depletion (using EGTA) significantly inhibited PE-induced c-fos expression by alpha1A and alpha1B receptors. Brief (1-min) stimulation of alpha1A and alpha1B receptors with PE did not maximally induce c-fos expression, suggesting that a sustained increase in [Ca2+]i due to Ca2+ influx is required. The calmodulin (CaM) antagonists, R24571, W7, and trifluoperazine, but not the CaM-dependent protein kinases inhibitor KN-62, significantly inhibited c-fos induction by alpha1A and alpha1B receptors. Neither inhibition of protein kinase C nor inhibition of adenylyl cyclase modified c-fos induction by PE. These results suggest that alpha1-adrenergic receptor-induced c-fos expression in rat-1 cells is dependent on a Ca2+/CaM-associated pathway.
View details for Web of Science ID 000080471300026
View details for PubMedID 10336529
In arteries and veins smoking is associated with impaired nitric oxide-mediated relaxation to endothelium-dependent agonists such as bradykinin. We investigated whether acute local angiotensin-converting enzyme (ACE) inhibition, achieved by enalaprilat, could influence bradykinin-induced vasodilation in veins of smokers.We studied 7 smokers and 7 nonsmokers with the hand vein technique. After preconstriction with phenylephrine was performed, endothelium-dependent and independent relaxations were assessed by infusing bradykinin (1 to 278 ng/min) and sodium nitroprusside (0.0001 to 3166 ng/min), respectively. Dose-response curves were constructed before and during enalaprilat coinfusion (1 microg/min for 40 minutes).Smokers had impaired venodilation to bradykinin compared with nonsmokers (P < .01). Apparent maximal relaxation induced by bradykinin was 78%+/-9% in the control group and 48%+/-9% in smokers (mean +/- SD). ACE inhibition shifted the bradykinin dose-response curve to the left in both groups (P < .001) and was associated with a minimal increase in apparent maximal venodilation in nonsmokers (78%+/-9% to 83%+/-18%). In contrast, in smokers ACE inhibition augmented the magnitude of apparent maximal venodilation to values comparable to those observed in the control group (48%+/-9% to 102%+/-21%). In both groups the response to sodium nitroprusside was not affected by enalaprilat.This study shows that acute local ACE inhibition restores bradykinin-induced relaxation in smokers to values found in nonsmokers. This observation suggests that increased vascular metabolism of bradykinin exists in veins of smokers and that the vascular renin-angiotensin system may play a key role in smoking-induced endothelial dysfunction.
View details for Web of Science ID 000079197500009
View details for PubMedID 10096262
Recent studies in patients with cardiovascular diseases suggest potential for the use of orally administered L-arginine, the precursor of nitric oxide, as a therapeutic agent. This crossover study was designed to examine the pharmacokinetics of single i.v. and oral doses of L-arginine in healthy volunteers (n = 10).A preliminary control study (n = 12) was performed to assess the variation in plasma L-arginine concentrations when ingesting a normal diet. The observed variation was taken into account when interpreting the pharmacokinetic data obtained after exogenous administration.The mean baseline plasma concentration of L-arginine in the control study was 15.1+/-2.6 microg ml(-1). After intravenous administration (30 g over 30 min), the plasma concentration reached 1390+/-596 microg ml(-1). The disappearance of l-arginine appeared biphasic, with an initial rapid disappearance due to concentration-dependent renal clearance followed by a slower fall in plasma concentrations due to nonrenal elimination. The peak concentration after oral administration (10 g) was 50.0+/-13.4 microg ml(-1), occurring 1 h after administration. Renal elimination was not observed after oral administration of this dose. The absolute bioavailability of a single oral 10 g dose of L-arginine is approximately 20%.This study provides basic knowledge of L-arginine pharmacokinetics in healthy humans. Intravenous and oral administrations show at minimum a biphasic pattern. Further studies will assess whether a similar profile is observed when the drug is administered to patients.
View details for Web of Science ID 000079405200005
View details for PubMedID 10215749
Acute administration of L-arginine, the precursor of endothelial nitric oxide, has been shown to improve endothelial function in hypercholesterolaemic rabbits and humans. Animal studies suggest that this beneficial effect, which is thought to be related to the increased availability of nitric oxide, may not be sustained during chronic oral administration. Pharmacokinetic alterations may contribute to this observation. The present study was designed to examine the disposition of L-arginine in hypercholesterolaemic subjects during long-term administration. Plasma L-arginine concentrations were determined by HPLC in 10 patients (eight women and two men; mean age 46+/-16 years) after an intravenous dose of 10 or 30 g and an oral dose of 5 or 7 g. Pharmacokinetic studies were performed at regular intervals (4 weeks) during a 12-week period of oral L-arginine administration (14-21 g/day). The average plasma L-arginine concentrations before (baseline) and during administration were 16.1+/-1.2 and 22.5+/-1.3 microg/ml respectively (P<0.05). Plasma concentrations of L-arginine remained above baseline throughout weeks 2-12. The L-arginine exposure, expressed as a normalized area-under-the-curve for 8 h (AUC0-8) after oral or intravenous doses during the first visit, was 894.4+/-118.7 and 1837. 8+/-157.0 units respectively. There were no significant changes in peak plasma L-arginine concentrations or in the AUC0-8 after oral and intravenous doses during subsequent visits (P>0.05). The mean non-renal clearance of L-arginine during the four visits remained constant. Knowledge of the pharmacokinetics of L-arginine may be useful in the design of clinical trials involving this agent, as well as in the interpretation of the pharmacodynamics of this important precursor of nitric oxide.
View details for Web of Science ID 000078706000011
View details for PubMedID 9918901
The amino acid L-arginine is the precursor of nitric oxide (NO), a powerful vasodilator with antiplatelet properties. The availability of L-arginine has been suggested to be a rate-limiting factor in the production of NO in conditions such as hypercholesterolemia. It was speculated that fluctuations in plasma concentrations of L-arginine during the day may be dependent upon dietary intake of the amino acid, or other variables, and might modify the elaboration of endogenous NO. Over a 24-h period, the plasma concentrations of L-arginine and NO-related compounds (NOx) were measured during an L-arginine and nitrate/nitrite-free diet (diet A) or a nitrate/nitrite-free diet with a fixed amount of L-arginine intake (3.8 g/d) (diet B) in eight healthy volunteers during a 2-day crossover study. Subjects were randomly selected to begin with diet A or diet B and consumed the other diet on the second day. During diet A, plasma L-arginine decreased significantly from 09.00 to 16.00 (21.4+/-2.0 to 11.9+/-1.1 microg/ml), rose slightly in the evening (to 16.6+/-1.7 microg/ml) and gradually increased during the night. During diet B, plasma L-arginine showed a peak after each meal (approximately 23 microg/ml). Plasma NOx concentrations measured by chemiluminescence did not show any circadian variation on either diet. Plasma L-arginine concentrations change during the day and are influenced by dietary intake. Importantly, plasma NOx do not seem to vary with this pattern in healthy individuals.
View details for Web of Science ID 000081421400005
View details for PubMedID 10355867
Recent reports, largely in animal models, have suggested that either inhibition of nitric oxide (NO) synthase or endothelium removal in arteries inhibits the response to isoprenaline, a beta-adrenoceptor agonist, and also enhances the response to sodium nitroprusside, a nitrovasodilator. This in vivo study was designed to determine whether N(G)-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthesis, influences relaxation of human hand veins mediated by isoprenaline or by sodium nitroprusside.Using the dorsal hand vein technique, full dose-response curves to bradykinin (0.27-278 ng min(-1), n=6), isoprenaline (2.12-271 ngmin(-1), n=8) and sodium nitroprusside (0.01-634 ng min(-1) n=7) were generated on separate occasions before and after L-NMMA co-infusion (50 microg min(-1)).In veins preconstricted with the alpha1-adrenoceptor-selective agonist phenylephrine, the three vasodilators induced maximal responses (Emax) of 119+/-35, 72+/-18 and 103+/-17%, respectively. L-NMMA inhibited relaxation to bradykinin by 64% (P=0.014) but did not influence relaxation induced by isoprenaline. The sensitivity to sodium nitroprusside was significantly enhanced by L-NMMA co-infusion (concentration shift of 2.3, P=0.031). CONCLUSIONS; We conclude that in human veins, spontaneously released NO does not play a major role in isoprenaline-induced relaxation. Our results also suggest that the effects of sodium nitroprusside in this vascular bed may be attenuated by endothelium-derived NO.
View details for Web of Science ID 000078493800017
View details for PubMedID 10073745
Conversion of angiotensin I to angiotensin II likely occurs in human veins, supporting the existence of endothelial angiotensin-converting enzyme (ACE) activity in these vessels. Using the dorsal hand vein technique, we investigated the effects of 2 ACE inhibitors, captopril (single oral dose of 6.25 mg) and enalaprilat (local infusion of 1 microgram/min), on venous responsiveness in healthy subjects. Orally administered captopril induced a marked decrease in angiotensin I- but not angiotensin II-induced venoconstriction. This blunted response persisted for at least 4 hours. Enalaprilat and captopril increased the sensitivity to bradykinin, decreasing the dose producing half-maximal response (ED50) of bradykinin 18-fold and 5-fold, respectively, without changing the maximal venodilatory response. These results confirm that there is substantial rapid metabolism of angiotensin I in human veins and suggest that a single dose of locally infused angiotensin I can be used with the dorsal hand vein technique to assess the time-course effect of vascular ACE inhibition after oral administration. Our findings also extend previous in vitro observations in human veins by showing that these agents potentiate the venodilatory effects of bradykinin in vivo.
View details for Web of Science ID 000078293300007
View details for PubMedID 9951431
Cigarette smoking has been shown to impair endothelium-dependent dilation in arteries. We tested the hypothesis that cigarette smoking also impairs endothelium-dependent venodilation and evaluated changes in this response after smoking cessation in a time-course study using the dorsal hand vein technique. Dose-response curves were constructed in smokers and nonsmokers by infusing bradykinin (1-278 ng/min), an endothelium-dependent vasodilator, and nitroglycerin (0.006-1,583 ng/min), an endothelium-independent vasodilator, into hand veins preconstricted with the selective alpha1-adrenergic agonist phenylephrine. The maximal venodilation induced by bradykinin was 89 +/- 5% in controls (n = 16) and 61 +/- 7% in smokers (n = 18; P = 0.02). No difference in nitroglycerin-induced venodilation was observed between the two groups. Coinfusion of L-arginine (0.33 mg/min) markedly improved the bradykinin-induced venodilation in smokers (52 +/- 7 to 90 +/- 9%; P < 0.01). After acute smoking cessation (n = 7), restoration to normal bradykinin-induced venodilation was observed within 24 h, whereas no change in the response to a maximally effective dose of nitroglycerin (1,583 ng/min) was detected. In a human vein model appropriate for testing vascular functional alterations, this study demonstrates that smoking impairs endothelium-dependent venodilation in heavy smokers. Moreover, this endothelial dysfunction appears to be rapidly reversible after smoking cessation. This model may be useful in studies evaluating mechanisms of endothelial dysfunction and interventions to modify it.
View details for Web of Science ID 000075620800038
View details for PubMedID 9724311
View details for Web of Science ID 000072420300166
Hypotension induced by parenteral administration of chloroquine is a common and serious adverse effect of this drug. Our aim was to investigate whether chloroquine produces venodilation in vivo and to explore the underlying mechanisms.Vascular effects of chloroquine were studied in healthy volunteers with use of the dorsal hand vein technique at the Geriatric Research Education and Clinical Center, Veterans Affairs Palo Alto Health Care System. We studied 22 healthy volunteers (19 men and three women). Venous responsiveness was determined with the dorsal hand vein technique, which measures the diameter of the vein.Chloroquine was found to produce a dose-dependent relaxation of hand veins preconstricted with the alpha 1-receptor selective agonist phenylephrine. The venodilatory response to chloroquine ranged from 15% +/- 19% at an infusion rate of 0.75 microgram/min to 61% +/- 24% at 48 microgram/min. Venodilation was attenuated by the nitric-oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) so that the dose of chloroquine required to produce 20% venodilation was increased from 3.7 micrograms/min to 15 micrograms/min (p < 0.01). In the presence of a combination of histamine receptor antagonists, there was also a diminution of the vasodilatory response to chloroquine from 72% +/- 5% to 44% +/- 5% at the infusion rate of 96 micrograms/min. The response was further reduced to 33% +/- 7% by the coinfusion of H1-/H2-receptor antagonists with L-NMMA.Chloroquine produces venodilation at infusion rates that achieve local concentrations likely similar to those observed systemically after clinically relevant intravenous doses. The date also suggest a role for nitric oxide and histamine release in mediating this response.
View details for Web of Science ID A1997XG20900010
View details for PubMedID 9209251
Morphine has been extensively used in the treatment of pulmonary edema, and its action is believed to be mediated in part by its ability to produce peripheral venodilation. This study investigated whether opiates produce venodilation in human hand veins and explored the underlying mechanism(s). Fifteen healthy volunteers (11 men and four women) were studied with use of the dorsal hand vein compliance technique. After preconstriction with the selective alpha 1-adrenergic receptor agonist phenylephrine, dose-response curves were constructed to (1) opiate receptor agonists morphine (1 to 30 micrograms/min) or fentanyl (0.07 to 1 microgram/min), (2) a combination of morphine and the mu-opiate receptor antagonist naloxone, and (3) morphine and a combination of histamine (H1 and H2) receptor antagonists. Infusion of morphine caused venodilation in a dose-dependent manner, whereas fentanyl did not produce venodilation. Coinfusion of naloxone and morphine impaired the venodilation only slightly. Coinfusion of the H1- and H2-antagonists completely abolished the venodilatory effect of morphine. These results suggest that the venodilatory effect of morphine is mediated through histamine release and that mu-opiate receptors have little or no involvement in this process.
View details for Web of Science ID A1996VV59700008
View details for PubMedID 8941028
Hyperinsulinemia has been implicated as an important risk factor for the development of accelerated cardiovascular disease. We wondered if insulin or IGF-I induced expression of alpha1 adrenergic receptors in vascular smooth muscle cells (VSMCs) which could enhance smooth muscle contraction and cell growth activated by catecholamines. Rat aortic VSMCs were incubated with insulin or IGF-I for various times and expression of alpha1 receptors was detected using [3H]prazosin binding. Both insulin and IGF-I increased alpha1 receptor number; also, these peptides increased expression of the alpha1D receptor gene with no change in expression of the alpha1B receptor gene as detected by RNase protection assays. Using Western blotting, we found that these peptides increased expression of the alpha1D receptor subtype in these cells. Increased expression of the alpha1D receptor mRNA was inhibited by the receptor tyrosine kinase inhibitor genistein and the PI 3-kinase inhibitor wortmannin but was not inhibited by protein kinase C inhibitor H7 or the L-type calcium channel blocker nifedipine. Preincubation of cells with insulin or IGF-I enhanced subsequent norepinephrine stimulation of mitogen activated kinase activity. These results suggest that insulin/IGF-I regulate expression of alpha1 receptors in VSMCs and potentially enhance the effects of catecholamines in settings of hyperinsulinemia.
View details for Web of Science ID A1996VN97300019
View details for PubMedID 8878434
The capacity of various growth factors to induce c-fos expression is diminished with senescence. Because adenosine 3',5'-cyclic monophosphate (cAMP)-mediated responses are also blunted with aging, we wondered whether cAMP-induced c-fos gene expression might be impaired with senescence. Using IMR fibroblasts, we found that prostaglandin E1 (PGE1) and forskolin, stimulators of cAMP accumulation in young and senescent cells, increased abundance of c-fos and junB mRNA more in young than senescent cells. The abundance of the cAMP response element binding protein (CREB), a transcription factor which enhances gene expression when phosphorylated by protein kinase A, was markedly decreased in both whole cell and nuclear extracts of senescent cells, in both Western blotting and in gel retardation assays. Also, PGE1-induced phosphorylation of CREB by protein kinase A was markedly attenuated in senescent cells. There is a marked decrement in expression of CREB with senescence, and the results suggest the possibility that the diminished expression of CREB may contribute to altered cAMP-mediated regulation of gene expression with senescence.
View details for Web of Science ID A1996UX53400041
View details for PubMedID 8760066
Alpha 1 adrenoreceptors mediate inotropic and chronotropic responses in the heart and vaso-constriction in blood vessels. Pharmacological studies using selective antagonists for subtypes of alpha 1 receptor suggest that different receptor subtypes may mediate different physiological effects. Prior studies have demonstrated that alpha 1-mediated cardiac responses are altered in aging and that alpha 1 receptor number declines with age in the rat heart. The distribution of alpha 1 receptor subtypes in cardiac tissue and subtype-specific changes with aging, however, have not been established. Using R Nase protection assays and in situ hybridization techniques, we have detected message for alpha 1B, alpha 1A, and alpha 1D in all four chambers of the rat heart and in multiple blood vessels. We found no significant changes in alpha 1 receptor subtype mRNA levels in hearts from young (4 months) and old (25 months) Sprague-Dawley rats. Also, there was expression of these three subtypes in all blood vessels assayed. We conclude that transcriptional regulation of alpha 1 adrenoreceptor subtypes does not account for age-related changes in cardiac alpha-adrenergic responsiveness.
View details for Web of Science ID A1996UN98900002
View details for PubMedID 8783191
Induction of heat shock proteins (hsp) most likely is a homeostatic mechanism in response to metabolic and environmental insults. We have investigated signal transduction mechanisms involved in alpha1, adrenergic receptor stimulation of hsp7O gene expression in isolated aortas with age. We found that alpha1 adrenergic agonists directly induced hsp70 mRNA in rat aorta in vitro; the alpha1, selective antagonist prazosin blocked this effect whereas chloroethylclonidine, an antagonist which has some selectivity for alpha1B receptors, was ineffective. This response was insensitive to pertussis toxin and was partially blocked by the protein kinase C inhibitor H7. Removal of extracellular calcium attenuated induction of hsp70 mRNA but not the induction of c-fos or c-myc. The induction of hsp70 mRNA by either norepinephrine or by phorbol dibutyrate was blunted in aortas from old (24-27 mo) rats whereas c-fos responses were not diminished in the older vessels. The hsp70 response to elevated temperature (42 degrees C) was not changed with age. Activation of hsp70 expression most likely involves a pertussis toxin insensitive G protein which activates protein kinase C, and requires extracellular calcium. With age, hsp70 gene expression induced by stimulation of alpha1 adrenergic receptors is markedly attenuated, which could modify responses to stress or vascular injury with aging.
View details for Web of Science ID A1996UM57400021
View details for PubMedID 8636412
View details for PubMedCentralID PMC507312
Many different types of cells develop increased adenylyl cyclase activity (sensitization) on prior treatment with drugs such as opiates that acutely inhibit the enzyme. We found that human embryonic kidney (HEK) 293 m2 cells, which express the inhibitory m2 muscarinic cholinergic receptor, exhibit a large increase in forskolin-stimulated cAMP synthesis when the cells are preincubated with the muscarinic agonist carbachol for > or = 5 min and forskolin stimulation is performed in the presence of the muscarinic antagonist atropine. To determine whether a specific isoform of adenylyl cyclase is susceptible to the adaptation induced by prior activation of inhibitory receptors, cells were transfected with expression vectors encoding adenylyl cyclase types I, II, and VI, representing three major groups of the adenylyl cyclase family. Preincubation of the cells with carbachol for 30 min resulted in a significant increase in prostaglandin E1-stimulated cAMP accumulation in cells expressing type VI, but not type I or type II, adenylyl cyclase. A similar selective increase in activity from type VI adenylyl cyclase was observed for prior treatment with the D2 dopamine agonist quinpirole and stimulation of cAMP synthesis with human chorionic gonadotropin in cells transfected with expression vectors coding for the cognate receptors. We next investigated whether beta gamma subunits play a role in the sensitization of type VI adenylyl cyclase activity; using expression of alpha tau to inhibit beta gamma-mediated effects, we found that the quinpirole-induced sensitization of type VI adenylyl cyclase was abolished. However, beta gamma subunits do not seem to directly activate type VI adenylyl cyclase, in contrast with their ability to directly activate the type II enzyme. Therefore, beta gamma subunits liberated after activation of inhibitory receptors seem to indirectly cause an increase in activity of type VI adenylyl cyclase. Indirect activation of the type VI enzyme by beta gamma subunits is a novel mechanism contributing to the sensitization of adenylyl cyclase.
View details for PubMedID 8622641
Activation of alpha1 adrenergic receptors stimulates mitogenesis in human vascular smooth muscle cells (HVSMCs). To examine signaling pathways by which activation of alpha1 receptors may induce mitogenesis in HVSMCs, we have found that alpha1 receptor stimulated-DNA synthesis and activation of mitogen-activated protein (MAP) kinase are blocked by wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI 3-kinase). To determine directly if activation of alpha1 receptors stimulated PI 3-kinase, in vitro assays of kinase activity were performed in immunocomplexes precipitated by an antibody against the p85 alpha subunit of PI 3-kinase. Noradrenaline stimulated a time- and concentration-dependent activation of PI 3-kinase in the presence of a beta adrenergic receptor antagonist. Noradrenaline-stimulated PI 3-kinase activation was blocked by antagonists of alpha1 receptors and by pertussis toxin, suggesting that alpha1 receptors activate PI 3-kinase via a pertussis toxin-sensitive G protein. Direct activation of protein kinase C by a phorbol ester did not stimulate PI 3-kinase; also, a Ca2+ L-channel blocker did not inhibit noradrenaline-stimulated PI 3-kinase activity. Increased PI 3-kinase activity was detected in both anti-Ras and anti-phosphotyrosine immunoprecipitates from noradrenaline-stimulated HVSMCs. Moreover, noradrenaline stimulated formation of active Ras-GTP complexes. Because blockade of PI 3-kinase by wortmannin inhibited formation of this complex, this result suggests that Ras might be a target of PI 3-kinase. Noradrenaline stimulated tyrosine phosphorylation of the p85 subunit of PI 3-kinase, and a phosphorylated tyrosine protein could be co-immunoprecipitated with anti-p85 of PI 3-kinase. These results demonstrate that stimulation of alpha1 receptors activates PI 3-kinase in HVSMCs and that alpha1 receptor-activated PI 3-kinase is associated with an increase in active Ras-GTP and activation of tyrosine protein phosphorylation. These pathways may contribute to alpha1 receptor-stimulated mitogenic responses including activation of MAP kinase and DNA synthesis in HVSMCs.
View details for Web of Science ID A1996UE73000074
View details for PubMedID 8621543
Are the anti-sexual effects of propranolol and pindolol due to actions within the brain? To answer this, these agents were administered directly into the brain ventricular system (ICV). Additionally, atenolol and metoprolol were evaluated to see whether differential delivery to the brain contributed to the observed lack of effect of systemically administered beta 1-adrenoceptor antagonists. ICV administration of pindolol (45 or 90 micrograms) was followed by a suppression of copulation. At 45 micrograms, inhibition was limited to performance aspects of copulation, whereas at 90 micrograms, decrements in motivational and performance aspects of copulation were evident. ICV administration of propranolol also suppressed copulatory behavior. At 45 micrograms, no significant effects were observed, whereas at 90 micrograms decrements in motivational and performance aspects of copulation were evident. In contrast, ICV administration of the beta 1-adrenoceptor antagonists, atenolol and metoprolol, was not associated with any major modifications in copulatory behavior. We suggest that the inhibitory effects of propranolol and pindolol may involve interactions with 5-HT1A receptors in the CNS. Alternatively, it may be that the adverse effects of pindolol and propranolol are due to the simultaneous blockade of both beta 1- and beta 2-adrenoceptors.
View details for Web of Science ID A1996VG96200005
View details for PubMedID 8838601
Blunted cAMP responses to beta-adrenergic agonists play a major role in diminished smooth muscle relaxation in blood vessels from older animals, although the mechanisms remain uncertain. A diminished cAMP response could potentially arise from changes in the expression of adenylyl cyclase-coupled G proteins, such as a diminished expression of Gs or an increased expression of Gi. We tested the hypothesis that a loss in Gs or increased expression of Gi could occur in tissues such as the aorta, heart and kidney with aging, which would provide a unifying explanation for blunted cAMP responses to many hormones with aging in a variety of cells. Using Western blotting with specific antibodies, we found no generalized changes in G protein expression with aging. Also, injection of pertussis toxin (which functionally inactivates Gi) into older animals did not restore vascular relaxation mediated by beta-adrenergic receptors. We previously found an elevated ratio of regulatory to catalytic subunits of protein kinase A in the aorta of older rats, which would tend to impair activation of the catalytic unit; this alteration was not generalized to other organs such as the heart and kidney. Old rats fed a low salt diet did not show the restored beta-adrenergic agonist-induced vasodilation previously found in elderly humans, suggesting that there are species differences in the development of this deficit. Altogether, these results suggest that altered G protein expression does not provide a general explanation for blunted activation of adenylyl cyclase with aging.
View details for Web of Science ID A1996TX12900002
View details for PubMedID 8866733
The role of the endothelium in modulating smooth muscle cell growth is unclear. alpha 1 adrenergic receptors activate proto-oncogene expression in smooth muscle. We have now found in rat aorta that carbachol, a muscarinic cholinergic agonist that promotes release of nitric oxide (NO), inhibits expression of c-fos and c-jun mRNA induced by alpha 1 receptors. NO synthase inhibitors blocked the effects of carbachol on c-fos mRNA and a cGMP analog mimicked carbachol. After balloon injury in rat aorta using in situ hybridization, the catecholamine-induced increase in c-fos mRNA expression in the medial layer was inhibited by the alpha 1 receptor antagonists, prazosin and chloroethylclonidine. In the neointima, this response was fully blocked by prazosin; however, chloroethylclonidine only partially inhibited it. These results suggest that NO, acting through a cGMP-dependent mechanism, inhibits expression of the c-fos and c-jun genes in arteries, which may contribute to the growth-inhibiting effects of the endothelium. After endothelial damage, the activation of c-fos in neointima by adrenergic stimulation may involve a subtype of alpha 1 receptor different from that utilized in medial smooth muscle.
View details for Web of Science ID A1996XP14400005
View details for PubMedID 9259051
We have previously reported that propranolol adversely affects sexual behavior in male rats. To elucidate whether the effects of propranolol might involve decrements in ability, we examined two components of sexual function ex copula--ejaculatory reflex capacity and erectile reflexes. In the first study, we examined the effects of various doses of (+/-)-propranolol (1.25-10 mg/kg) administered subcutaneously. Marked inhibition was observed, evidenced by increases in the latency to ex copula ejaculation and to initial erection and decrements in the number of seminal emissions and in the number of erectile reflexes. Analyses of dose-response relationships indicated that the degree of inhibition increased with increasing dose. In the second study, we evaluated the stereo-selectivity of the responses. Both (+)- and (-)-propranolol (1.25 mg/kg) significantly inhibited ejaculatory reflex potential, and although (+)- and (-)-propranolol significantly inhibited erectile reflexes, (-)-propranolol had a greater effect. The data are interpreted to indicate that a) propranolol-induced sexual dysfunction involves both motivational and ability aspects; and b) propranolol-induced inhibition of genital reflexes may be due, at least in part, to mechanisms other than beta-adrenoceptor blockade.
View details for PubMedID 8545471
We recently reported that alpha1-adrenoceptor agonists, administered at the beginning of neurulation (Stage 11a) in rat embryos grown in culture, interfere with normal development of the left/right body axis leading to situs inversus. Despite these pharmacological findings, expression of alpha1-adrenoceptor genes at such an early stage of development has not been demonstrated. In the present study, we examined the expression of mRNAs for cloned alpha1-adrenoceptor subtypes in rat embryos at Stage 11a. Timed-pregnant Sprague-Dawley rats were killed in the morning of gestational day 9 (vaginal plug day = day 0), and the implantation sites were removed. The implantation sites were separated into embryo, ectoplacental cone and decidua, only those at Stage 11a were selected, and these were immediately frozen on dry ice, and subsequently their total RNA was isolated. RNase protection assays were then performed for cloned alpha1a-, alpha 1b- and alpha1d-adrenocepter subtypes using 20-30 mug of total RNA for each hybridization. In all tissues, strong and weak signals were detected for alpha1b- and alpha1a-adrenoceptor subtype mRNAs, respectively. In contrast, a signal for alpha1d mRNA was not detected in any tissues. These results, together with previous pharmacological findings, suggest the existence of alpha1a- and alpha1b-adrenoceptor subtypes in rat embryos at Stage 11a.
View details for Web of Science ID A1995TC68900005
View details for PubMedID 20650135
Alterations in adenylyl cyclase activity in cultured cells after prolonged exposure to drugs such as morphine have been extensively studied as models for drug tolerance and withdrawal. NG108-15 cells develop increased intracellular cAMP concentrations after abrupt withdrawal from chronic treatment with the muscarinic cholinergic agonist carbachol. To determine whether this withdrawal-induced increase in cAMP modifies gene expression, we studied phosphorylation of the cAMP response element-binding protein (CREB) and expression of the c-fos gene, known to contain a cAMP response element, in NG108-15 cells after abrupt withdrawal from chronic treatment with carbachol. Prostaglandin E1, which activates adenylyl cyclase, caused concentration-dependent increases in the phosphorylation of CREB and in the abundance of c-fos mRNA. These changes occurred with small increments in cAMP accumulation. In cells treated with carbachol for 48 hr, induction of withdrawal with the muscarinic antagonist atropine led to a small increase in intracellular cAMP concentration but an 11.6-fold increase in the phosphorylation of CREB and a 3.4-fold increase in accumulation of c-fos mRNA. The adenylyl cyclase inhibitor 2',5'-dideoxyadenosine, which attenuated the chronic carbachol-induced increase in cAMP concentration, prevented the increased phosphorylation of CREB and the enhanced accumulation of c-fos mRNA during atropine-induced withdrawal. These results indicate that expression of the c-fos gene is induced by the small increments in cAMP concentration that can occur in cells on withdrawal from chronic treatment with drugs such as muscarinic agonists.
View details for PubMedID 7476883
Aging is associated with alterations in the responses to several important vasoactive drugs. We have investigated histamine-mediated venodilation across the adult age range using the human hand vein compliance technique. Histamine produces dilation in human veins by activating both H1- and H2-receptors.Full dose-response curves to histamine were constructed in 16 healthy volunteers (mean age, 47 +/- 20 years; age range, 21 to 80 years) by infusing histamine (2 to 136 ng/min) into dorsal hand veins preconstricted with the alpha-adrenergic selective agonist phenylephrine.Histamine was an efficacious venodilator across the age range; the average maximal response (Emax) was 122 +/- 45% and the geometric mean ED50 (the dose producing half-maximal response) was 16.6 ng/min for all subjects. Dose-response curves to histamine were repeated after infusion of the H2-selective antagonist cimetidine at a dose sufficient to completely block the H2-mediated response (49 micrograms/min). Cimetidine did not inhibit the Emax in the elderly as much as it did in the young subjects. The Emax to histamine in the presence of cimetidine plotted against age showed a significant relationship (r = 0.62, p = 0.02).These results suggest that, although the overall histamine-induced venodilation is conserved in aging, there is a loss of the signal transduction pathway activated by way of H2-receptors but no loss in function of H1-receptors. Consequently, these results suggest differential changes in function of H1- versus H2-histamine receptors with aging. Because H1-receptors are coupled to endothelial-derived relaxing factor release and because H2-receptors activate cyclic adenosine monophosphate in smooth muscle, the results are compatible with hypothesis that there are specific changes in these signal transduction pathways with aging.
View details for Web of Science ID A1995RL59000009
View details for PubMedID 7628185
We have previously reported that administration of racemic mixtures of propranolol was associated with a marked inhibition of mating behavior in male rats. To compare the effects of (+)-propranolol, (-)-propranolol, and (+/-)-propranolol in sexually experienced males, rats ejaculating in four or more mating tests were divided into three groups (N = 16 per group) such that no differences in parameters of copulatory behavior were evidence in preexperimental tests. No major effect of propranolol on parameters of behavior associated with initiation of sexual behavior was evident. In contrast, other measures of behavior were profoundly modified. The ejaculatory threshold, indicated by the number of intromissions preceding ejaculation, was increased after (+)- and (+/-)-propranolol, but not (-)-propranolol. The number of mounts without intromission preceding ejaculation was increased only after (+/-)-propranolol. A decrease in copulatory efficacy was evident after (-)- or (+/-)-propranolol, but not after (+)-propranolol. Increases in ejaculation latency, intercopulatory interval, and postejaculatory interval were observed after (-)- and (+/-)-propranolol, but not after (+)-propranolol. In summary, the present data indicate that the (-) isomer of propranolol is the active form necessary for the inhibitory effects of propranolol on male sexual function. We suggest that this inhibition is due to specific receptor-mediated mechanisms, involving beta-adrenoceptors and 5-HT1A receptor interactions.
View details for Web of Science ID A1995RB49100043
View details for PubMedID 7667366
Fatty acid synthase is a key enzyme in thede novo synthesis of fatty acids. Expression of fatty acid synthase mRNA in adipocytes is inhibited by beta adrenergic agonists. We wondered if prolonged exposure to high concentrations of catecholamines might inhibit expression of the fatty acid synthase gene in fat cells. In this study we investigated the effects of adrenergic stimulation on the regulation of fatty acid synthase in fat cells. Rats were infused continuously with epinephrine (60 μg/kg/hr) or vehicle for 48 h and fat pads were isolated. The infusion of epinephrine down-regulated expression of the fatty acid synthase mRNA as well as decreasing enzyme activity. Both epinephrine and isoproterenol inhibited fatty acid synthase mRNA expression when adipocytes were activatedin vitro. These effects were blocked by the β adrenergic antagonist propranolol. In contrast, incubation with the adenosine receptor agonist phenylisopropyl-adenosine which decreases cAMP accumulation in fat cells, caused an increase in accumulation of fatty acid synthase mRNA. These results indicate that prolonged exposure to catecholamines, acting via β adrenergic receptors, inhibit expression of the fatty acid synthase gene possibly by increasing intracellular concentrations of cAMP.
View details for Web of Science ID A1995RF37300009
View details for PubMedID 21153248
Angiotensin II (ANG II) induces vascular smooth muscle contraction and functions as a growth factor stimulating vascular smooth muscle cell (VSMC) hypertrophy. We wondered whether ANG II might induce expression of alpha 1-adrenergic receptors (ARs) in cultured VSMCs, which would then potentially accentuate the effects of catecholamines in the cells. Rat VSMCs were preincubated with phenoxybenzamine to inactivate alpha 1-ARs; the cells were then treated with ANG II for 24 h. ANG II-treated cells expressed an increased number of alpha 1-ARs compared with controls, suggesting that ANG II increased the rate of alpha 1-AR synthesis. ANG II markedly induced accumulation of alpha 1A/D- and alpha 1B-AR mRNAs in a concentration- and time-dependent manner. This effect of ANG II was blocked by the specific ANG II-receptor agonist [Sar1-Ile8]ANG II. ANG II-induced accumulation of alpha 1A/D-AR mRNAs was completely abolished by transcriptional inhibitor actinomycin D. ANG II markedly increased the transcriptional rate of the alpha 1A/D-AR gene without changing stability of alpha 1A/D-AR mRNAs. Protein kinase C (PKC) activator 4 beta-phorbol 12-myristate 13-acetate also induced accumulation of alpha 1A/D-AR mRNAs, and PKC inhibitor H-7 completely blocked ANG II-induced accumulation of the alpha 1A/D-AR mRNAs. Neither the biologically inactive ANG II analogue des-Phe8-ANG II nor the calcium ionophores A-23187 and BAY K-8466 induced alpha 1A/D-AR mRNAs. Finally, ANG II preincubation increased alpha 1-AR agonist phenylephrine-stimulated expression of the c-fos gene.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for Web of Science ID A1995QL35800011
View details for PubMedID 7900855
In mouse and rat embryos, the embryonic disc develops within a cup-shaped "egg cylinder" and consists of an inner layer of ectoderm and an outer layer of endoderm. Because of this configuration, the embryo first develops in a dorsally flexed position and then undergoes "axial rotation" to a ventrally flexed position. In the present study, we first analyzed the morphological process of axial rotation in rat embryos using novel reference axes set in the egg cylinder that remained invariant during the process. Our new perspective allowed us to demonstrate that the process consists of three movements which start at different stages of development: twisting of the upper body at stage 12/s7-8, twisting of the middle body at stage 13/s11-12, and twisting of the lower body (so called "tail") at stage 14/s15-16. Axial rotation is an interesting developmental event not only because it is such a dynamic process but also because it is one of the earliest morphological signs of body asymmetry. This asymmetry is strongly biased in that the tail almost always finishes up on the right side of the embryo for reasons that are still unknown. In the second part of the study, we performed microsurgical experiments to extend our previous finding that removal of the allantois results in random determination of tail sidedness. We demonstrated that an allantois transplanted from another embryo can prevent this abnormal sidedness in an embryos whose allantois had been removed and that transecting the allantois did not lead to abnormal tail sidedness. A possible explanation is that the allantois produces a chemical factor that controls tail sidedness.
View details for Web of Science ID A1995QZ36200007
View details for PubMedID 7660327
beta-Adrenergic responses have been shown to decline with aging, particularly in the cardiovascular system. We infused terbutaline, a selective beta 2-adrenoceptor agonist, into the brachial artery of 10 young (mean age 25 yr, range 22-31 yr) and 9 elderly (mean age 73 yr, range 68-81 yr) healthy subjects to examine its effects on nutrient flux. Forearm K+, PO4, free fatty acid (FFA), and glycerol uptake were determined by measurement of forearm blood flow (using dye dilution) and brachial arterial and deep venous plasma substrate concentrations. Elderly subjects were less sensitive to terbutaline-mediated increases in forearm blood flow, net fluxes of K+, and glycerol but not net fluxes of FFA or PO4. The mean fitted slopes of each parameter vs. the log of the terbutaline concentration, a measure of forearm beta-adrenergic sensitivity, for young and elderly groups were 4.9 +/- 1.7 (SD) vs. 2.4 +/- 2.3 for forearm blood flow (P < 0.05), 0.84 +/- 0.46 vs. 0.43 +/- 0.37 for K+ net flux (P < 0.05), -157 +/- 113 vs. -26 +/- 26 for glycerol net flux (P < 0.01), -336 +/- 429 vs. -44 +/- 457 for FFA net flux (P = 0.11), and 0.31 +/- 0.24 vs. 0.18 +/- 0.16 for PO4 net flux (P = 0.14). Terbutaline promoted net uptake of K+ into skeletal muscle less well in the elderly, although net PO4 flux was similar in the two groups. Terbutaline-stimulated vasodilation and net glycerol efflux but not FFA efflux were impaired with aging. These data demonstrate that heterogeneous changes in beta-adrenergic responses occur with aging.
View details for Web of Science ID A1995QC30100025
View details for PubMedID 7713808
While growth of blood vessels is important in hypertension, relatively little is known about the contribution of catecholamines. Using isolated rat aorta and cultured smooth muscle cells, we examined adrenergic stimulation of gene expression. Phenylephrine, a selective alpha 1 adrenergic receptor agonist, caused a rapid and transient increase in c-fos mRNA accumulation which was inhibited by prazosin, an alpha 1 receptor antagonist. Similarly, phenylephrine stimulated c-jun and c-myc mRNA accumulation. Chloroethyl-clonidine, a compound which irreversibly blocks alpha 1B receptors, completely blocked the phenylephrine-induced increase in c-fos mRNA. RNase protection experiments demonstrated that rat aorta prominently expressed mRNA for alpha 1B and alpha 1A/D receptors. Phenylephrine-induced c-fos mRNA was partially inhibited by H-7, a protein kinase C inhibitor, and by nifedipine, a Ca2+ channel blocker; these two compounds together had additive effects. In situ hybridization showed that expression of c-fos mRNA induced by phenylephrine was localized to aorta's medial layer. These results suggest that alpha 1 receptor-induced increase in c-fos mRNA in aorta is mediated by a chloroethyl-clonidine-sensitive receptor subtype signaling via increasing intracellular Ca2+ concentrations and activating protein kinase C.
View details for Web of Science ID A1994NW49600028
View details for PubMedID 8040263
With aging, in many cells there is a blunted capacity of beta-adrenergic agonists to increase adenosine 3',5'-cyclic monophosphate (cAMP) accumulation. We wondered if blunted cAMP responses led to impaired regulation of genes in which expression is modified by cAMP. To test this hypothesis, adipocytes were isolated from 2- and 12- to 16-mo-old Sprague-Dawley rats that were stimulated with isoproterenol, and the inhibitory effect on expression of genes for lipoprotein lipase (LPL) and fatty acid synthase (FAS) were examined. Isoproterenol-stimulated cAMP accumulation and glycerol release were impaired in adipocytes from the older rats. Isoproterenol inhibited expression of LPL and FAS mRNAs in cells from the younger but not older rats. Removal of endogenous adenosine partially restored isoproterenol-mediated inhibition of expression of these genes in the cells. These results demonstrate that blunted cAMP responses associated with aging in obese Sprague-Dawley rats led to altered regulation of LPL and FAS genes. These findings extend the possible physiological implications of impaired hormone-induced cAMP responses with aging.
View details for Web of Science ID A1994NJ99400048
View details for PubMedID 8178988
In previous studies, we have demonstrated that stimulation of alpha 1 but not alpha 2 or beta adrenergic receptors in rat embryos grown in culture interferes with normal development of the left/right body axis leading to situs inversus. In the present study, we aimed to determine the alpha 1 adrenergic receptor subtype and signal transduction pathway involved in this phenomenon. Rat embryos at Stage 11a by a modified Theiler's staging system were cultured for 50 hr in medium containing various compounds which are known to activate or inhibit different sites of the signal transduction pathways associated with alpha 1 adrenergic receptors. They were then examined to determine the sidedness of asymmetric body structures. WB4101, a selective antagonist of alpha 1A adrenergic receptor subtype, but not chlorethylclonidine, a selective antagonist of alpha 1B adrenergic receptor subtype, inhibited phenylephrine (an alpha 1 adrenergic agonist)-induced situs inversus. Neither the protein kinase C (PKC) activators phorbol 12-myristate 13-acetate and SC-9 nor the PKC inhibitor calphostin C caused situs inversus. Furthermore, calphostin C did not block phenylephrine-induced situs inversus. A23187, a Ca2+ ionophore, induced situs inversus; nifedipine, a L-type Ca2+ channel blocker, partially blocked phenylephrine-induced situs inversus. The calmodulin antagonists trifluoperazine, W-7, and W-13 blocked phenylephrine-induced situs inversus, although they did not cause situs inversus by themselves. KN-62, a Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) inhibitor, dose-dependently blocked phenylephrine-induced situs inversus. However, higher concentrations of this compound produced no block in the presence of phenylephrine and in its absence produced a 50% incidence of situs inversus. These results indicate that alpha 1 adrenergic stimulation-induced situs inversus is mediated by the alpha 1A adrenergic receptor subtype and that activation of CaM kinase II but not PKC may be involved.
View details for Web of Science ID A1994ND48700020
View details for PubMedID 8150214
Histamine is a potent vasodilatory substance released during anaphylaxis. The purpose of this study was to investigate the mechanism by which histamine produces venodilation in humans in vivo with the use of the dorsal hand-vein compliance technique. In healthy volunteers full dose-response curves were constructed by infusing histamine, before and after administration of an H1 or H2 antagonist or both antagonists, into dorsal hand veins preconstricted with the alpha-adrenergic agonist phenylephrine. In the presence of the H1 antagonist brompheniramine (530 ng/min), the maximal venodilatory response to histamine decreased from 128% +/- 57% to 78% +/- 15% (p < 0.05). In the presence of H2 antagonist cimetidine (49 micrograms/min), the maximal venodilatory response to histamine decreased from 120% +/- 33% to 48% +/- 26% (p < 0.01). Concurrent infusion of histamine with the combination of cimetidine and diphenhydramine resulted in almost complete abolishment of histamine-induced venodilation. Methylene blue (6.8 micrograms/min), an inhibitor of the action of endothelium-derived relaxing factor, decreased the vasodilatory response to histamine from 131% +/- 23% to 73% +/- 24% (p = 0.01). The results suggest that the venodilatory response of histamine is mediated through both H1 and H2 receptor subtypes and that this response is mediated in part by endothelium-derived relaxing factor.
View details for Web of Science ID A1994ND14000007
View details for PubMedID 8151062
Desensitization of alpha 1-adrenergic receptor-mediated contraction occurs in rat aorta after in vitro exposure to alpha-adrenergic agonists; we previously showed that a component of the desensitization is endothelial cell dependent. Our primary purpose was to examine possible alterations in either the release or action of endothelium-derived relaxing factor (EDRF) in desensitized blood vessels. Rings of rat aorta were desensitized in vitro by exposure to phenylephrine (PE) for 6 h with impaired subsequent ability of PE to induce smooth muscle contraction. PE also induced heterologous desensitization of serotonin-induced contraction, which was blocked by the alpha 1-adrenergic selective antagonist prazosin. Using a "sandwich" bioassay technique, we noted enhanced release of EDRF from the aortic rings that had been previously exposed to PE as compared with controls. The capacity of PE to activate accumulation of inositol monophosphate was impaired in the desensitized blood vessels, both with and without endothelium. Our results suggest that prolonged exposure to alpha-adrenergic agonists leads to several adaptations in vascular smooth muscle (VSM), including enhanced release of EDRF. Although impaired action of EDRF has been suggested to play a role in diseases such as diabetes and atherosclerosis, our results indicate that release and action of EDRF may be enhanced with prolonged exposure to alpha-agonists.
View details for Web of Science ID A1994MR52900024
View details for PubMedID 7511767
View details for Web of Science ID A1994MY42100252
The enzyme nitric oxide synthase mediates synthesis of nitric oxide (NO) from 1-arginine in endothelial cells. NO, also known as endothelium-dependent relaxing factor (EDRF), diffuses to smooth muscle cells where it leads to cGMP production and dilation. We characterized the potency, efficacy and time course of NG-monomethyl-l-arginine (l-NMMA) as an inhibitor of bradykinin-mediated, endothelium-dependent dilation using the human hand-vein compliance technique. We also compared the efficacy of l-NMMA with methylene blue, an inhibitor of guanylate cyclase, in blocking bradykinin-mediated vasodilation. l-NMMA potently inhibited bradykinin-induced venodilation with a log ED50 of 3.74 +/- 0.52 (geometric mean of 5.5 micrograms/min). Responses to bradykinin (0.27-555 ng/min) were tested in veins pre-constricted with the alpha-adrenergic agonist phenylephrine. l-NMMA (25 micrograms/min) decreased bradykinin's maximal venodilatory response from 90 +/- 22% to 39 +/- 15% (p < 0.05). Complete recovery of bradykinin venodilation was obtained within 155 minutes after stopping l-NMMA infusion, indicating that its effects were reversible. In another set of experiments we compared the efficacy of methylene blue to l-NMMA; methylene blue decreased bradykinin-mediated venodilatory response to 53 +/- 17%; when l-NMMA was added, the response was further decreased to 32 +/- 9% (p < 0.002). We conclude that l-NMMA is a very efficacious NO synthase inhibitor in human veins and it is likely functionally reversible.
View details for Web of Science ID A1994MY29500008
View details for PubMedID 7515369
We have examined the relationship between cell density and alpha 2A adrenergic receptor number and mRNA in HT-29 cells. alpha 2A receptors increased with increasing cell density from 75 +/- 25 to 400 +/- 73 fmol/mg protein; alpha 2A receptor mRNA also increased about 4 fold with no change in abundance of beta-actin mRNA. We prepared serum-free conditioned medium (SFCM) from confluent dishes of HT-29 cells and applied this SFCM to cells seeded at low density. A 4.7-fold increase in receptor number was observed in HT-29 cells cultured in SFCM for 3 days and alpha 2A receptor mRNA level increased about 3-fold after 24 h. Dialysis of SFCM against fresh growth medium did not abolish these effects. These results suggest that a substance secreted from HT-29 cells regulates expression of alpha 2A receptors.
View details for Web of Science ID A1994NJ35000005
View details for PubMedID 8196492
Expression of the human alpha 2A-adrenergic receptor gene is induced by cAMP. The present studies were designed to define potential cAMP-responsive enhancer elements (CREs) in the promoter region of this gene. Regions from the 5'-flanking sequences of the gene were placed in a promoterless vector with a chloramphenicol acetyltransferase (CAT) reporter gene, and cAMP-stimulated CAT activity was assayed in transfected JEG-3 placental carcinoma cells. Enhancer activity responsive to cAMP was located in DNA sequences both upstream and downstream from the endogenous promoter region. Within the upstream sequences there is a putative "core sequence" homologous to the eight base CRE consensus palindrome, but this region did not function independently as a CRE enhancer; additional upstream sequences were required to provide significant enhancer activity in response to cAMP. Regulation of expression of the alpha 2A-adrenergic gene by cAMP is complex and involves multiple and likely novel DNA sequences.
View details for PubMedID 8011430
The pathogenesis of Raynaud's disease is unclear; an enhanced response to catecholamines has been hypothesised to contribute to this vasospastic disorder. Impaired endothelium-dependent dilation occurs in other diseases associated with vasospasm, such as coronary atherosclerosis. We investigated both endothelium-dependent and endothelium-independent venodilatory function in Raynaud's disease using the hand-vein compliance technique. Full dose-response curves to noradrenaline were constructed in 10 subjects with primary Raynaud's disease and 10 age and sex matched control subjects. The two groups did not have a different response to noradrenaline. Mean (SD) log values of ED50s (the dose producing half maximum response) were 1.00 (0.59) (geometric mean 10 ng/min) in Raynaud's disease compared with 1.29 (0.66) (20 ng/min) in control subjects (p = 0.16). The efficacy of noradrenaline as a venoconstrictor was similar in the two groups: mean maximum dilation (Emax) to noradrenaline was 81 (14)% in the Raynaud's group and 89 (8)% in the control group (p = 0.08). Full dose-response curves to the endothelium-dependent dilator bradykinin were constructed. Emax to bradykinin was significantly lower in the Raynaud's group than in the control group (65  vs 91 [29%], p = 0.02). ED50 values (doses producing half maximum response) for bradykinin were similar in the two groups. Maximum dilation with nitroprusside, a direct releaser of the vasodilator nitric oxide, was not diminished in the Raynaud's group (94  vs 102 % in controls, p = 0.26). These results suggest that endothelium-dependent venodilation is impaired in peripheral vessels in Raynaud's disease, possibly due to diminished release of nitric oxide, and may contribute to the pathogenesis of the disorder.
View details for Web of Science ID A1993ML21700008
View details for PubMedID 7902481
alpha 1-Adrenergic receptors play important roles in mediating a wide range of important cellular responses; regulation of expression of these receptors may have pathophysiological significance in diseases such as hypertension. In order to pursue understanding of mechanisms involved in the regulation of expression of alpha 1 receptors, the effects of protein synthesis inhibitor cycloheximide on alpha 1B receptor gene expression were examined in DDT1 MF-2 smooth muscle cells. Cycloheximide markedly induced accumulation of the alpha 1B receptor mRNAs in a concentration- and time-dependent manner as detected by Northern blotting assays. The increased accumulation of alpha 1B receptor mRNA could be detected at 1 hr (1.7 +/- 0.2-fold) and the maximal accumulation occurred at 6 hr (5.4 +/- 0.3-fold, p < 0.01). Nuclear runoff assays reveal that cycloheximide markedly increased the transcriptional rate of the alpha 1B receptor gene. The stability of alpha 1B receptor mRNAs measured by RNase protection assays was essentially unchanged by cycloheximide. Incubation of DDT1 MF-2 cells with two additional protein synthesis inhibitors, anisomycin and emetine, had similar effects to those of cycloheximide. However, a further inhibitor, puromycin, did not induce alpha 1B receptor mRNAs when protein synthesis was almost completely inhibited. Furthermore, puromycin did not inhibit the capacity of cycloheximide to induce transcription of the alpha 1B receptor gene. These observations suggest that cycloheximide induces alpha 1B receptor gene expression through direct activation of gene transcription rather than inhibition of protein synthesis.
View details for Web of Science ID A1993MN46600003
View details for PubMedID 8264546
Hypercholesterolemia impairs endothelium-dependent dilation in arteries. We tested the hypothesis that hypercholesterolemia impairs endothelium-dependent vasodilation by an interaction between elevated plasma lipoproteins and a presumably normal endothelium using human veins in vivo; veins do not generally develop atherosclerosis and are appropriate for testing functional alterations.Full dose-response curves were constructed in 13 hypercholesterolemic and 12 normocholesterolemic subjects by infusing bradykinin (0.25 to 508 ng/min) into hand veins preconstricted with the alpha-adrenergic agonist phenylephrine. The maximal relaxation induced by bradykinin was 80 +/- 38% in the controls and 103 +/- 40% in subjects with hypercholesterolemia (P = .08). Responsiveness to bradykinin was also determined after infusion of indomethacin (5.4 micrograms/min), a cyclooxygenase inhibitor, to block the contribution of prostaglandins; maximal responsiveness was greater in hypercholesterolemic subjects (112 +/- 41%) than in controls (81 +/- 31%) (P = .03). Hypercholesterolemic subjects were more sensitive to bradykinin, with an ED50 of 4.2 ng/min versus 10.9 ng/min in controls (P = .05); a similarly increased sensitivity was found in the presence of indomethacin. The response to a maximally effective dose of nitroglycerin was greater in hypercholesterolemic subjects (142 +/- 31%) versus 106 +/- 28% in controls (P = .007). In five hypercholesterolemic subjects, treated with lovastatin to normalize serum cholesterol concentrations, maximal responsiveness to bradykinin decreased from 103 +/- 52% to 80 +/- 28%.These results demonstrate that hypercholesterolemia in humans does not impair endothelium-derived relaxing factor-mediated venodilation.
View details for Web of Science ID A1993ML69900034
View details for PubMedID 8252688
View details for Web of Science ID A1993MA68201776
Exercising skeletal muscle releases large amounts of potassium into plasma. beta-adrenergic receptors enhance reuptake of potassium into muscle. Since beta-adrenergic responses decline with aging in many tissues, the elderly might be predisposed to hyperkalemia during exercise.Venous plasma potassium (K+) was measured during graded bicycle exercise (30 W initial workload with 3-minute 30 W increments) in 18 healthy young men (24.0 +/- 2.9 yrs; mean +/- SD), 18 healthy untrained elderly men (70.0 +/- 3.6 yrs), and 7 elderly master athletes (70.0 +/- 4.6 yrs). Subjects exercised to exhaustion.Exercise times and maximal oxygen uptake were: young (N = 14; 19.6 +/- 4.4 min, 42.1 +/- 3.8 ml/kg/min), elderly (N = 13; 11.7 +/- 1.9 min, 26.6 +/- 8.0 ml/kg/min), elderly master athletes (N = 6; 16.8 +/- 2.4 min, 40.2 +/- 10.2 ml/kg/min). The rate of increase in K+ was greater in both elderly (89 +/- 59 mumol/l/min) and elderly master athletes (88 +/- 26) compared with healthy young men (60 +/- 30), p < .05. Despite this greater rate of increase, the elderly group did not achieve higher maximal K+ concentrations than the young because of the much shorter duration of exercise in the elderly group. For subjects performing a maximal exercise test, the maximal increase in K+ was similar in the elderly (1.15 +/- 0.91), but significantly greater in elderly master athletes (1.70 +/- 0.31), compared with healthy young men (1.31 +/- 0.45).Changes in K+ during short-lasting exercise are similar in untrained healthy elderly men compared with healthy young men, but elderly master athletes have greater changes in K+ during exercise. The greater rate of increase in potassium in healthy and athletic subjects supports the hypothesis of an age-related impairment of the beta 2-adrenergic process that mediates potassium flux into skeletal muscle.
View details for Web of Science ID A1993LL26100029
View details for PubMedID 8315226
We investigated the effects of clentiazem, a 1,5-benzothiazepine calcium antagonist, on epinephrine-induced cardiomyopathy in rats. With 2-week chronic epinephrine infusion, 16 of 30 rats died within 4 days, and severe ischemic lesions and fibrosis of the left ventricles were observed. In epinephrine-treated rats, left atrial and left ventricular papillary muscle contractile responses to isoproterenol were reduced, but responses to calcium were normal or enhanced compared to controls. Left ventricular alpha and beta adrenoceptor densities were also reduced compared to controls. Treatment with clentiazem prevented epinephrine-induced death (P < .05), and attenuated the ventricular ischemic lesions and fibrosis, in a dose-dependent manner. Left atrial and left ventricular papillary muscle contractile responses to isoproterenol were reduced compared to controls in groups treated with clentiazem alone, but combined with epinephrine, clentiazem restored left atrial responses and enhanced left ventricular papillary responses to isoproterenol. On the other hand clentiazem did not prevent epinephrine-induced down-regulation of alpha and beta adrenoceptors. Interestingly, clentiazem, infused alone, resulted in decreased adrenergic receptor densities in the left ventricle. Clentiazem also did not prevent the enhanced responses to calcium seen in the epinephrine-treated animals, although the high dose of clentiazem partially attenuated the maximal response to calcium compared to epinephrine-treated animals. In conclusion, clentiazem attenuated epinephrine-induced cardiac injury, possibly through its effect on the adrenergic pathway.
View details for Web of Science ID A1993LN29300037
View details for PubMedID 8392553
Investigated the adverse sexual effects of two antihypertensive drugs, atenolol and slow-release nifedipine, in a placebo-controlled, randomized, crossover study. Subjects were 16 older men (mean age = 66.6 years, SEM = 1.4) with mild to moderate hypertension. Subjects completed daily self-reports on 13 measures of sexuality: frequency of desire, coitus, noncoital partner sex, masturbation, morning erections, spontaneous erections, orgasms in coitus and masturbation, firmness of morning, masturbatory and coital erections, and subjective pleasure in coitus and masturbation. Except for a significant decrease in masturbatory erectile firmness with nifedipine therapy, variables did not differ between the two drug treatments or between either drug and placebo. Although the sample was relatively small, small differences between treatment means suggest that these antihypertensive agents are fairly benign relative to sexual function in men.
View details for Web of Science ID A1993KX37900002
View details for PubMedID 8476337
To determine whether the considerable interindividual variability in nitroglycerin-induced venodilation in humans is related to the polymorphic expression of the mu class of glutathione S-transferase (GST mu). Recently vascular glutathione S-transferase (EC 126.96.36.199) of the mu-class (GST mu), a polymorphic group of enzymes present in only about 60% of the population, have been identified and shown in vitro to possess high metabolic activity toward nitroglycerin. Their clinical relevance is unknown.Dose-response relationships to nitroglycerin were constructed in vivo measuring changes in compliance of dorsal hand veins in 26 healthy volunteers during local infusion of small amounts of nitroglycerin. Polymerase chain reaction was applied to detect the deoxyribonucleic acid sequence that codes GST mu in whole blood samples.The GST mu isozyme was present in 15 subjects (58%) and deficient in 11 subjects. Values for mean maximum venodilation (Emax) and dose rates producing 50% of Emax (ED50) were not significantly different between the groups with or without GST mu. The respective values were 98% and 103% dilation for Emax and 9 and 16 ng/min for ED50. There was no gender difference in the venodilatory response to nitroglycerin.Subjects lacking GST mu can clearly respond normally to nitroglycerin, and the large interindividual variability in nitroglycerin potency is not related to the expression of this polymorphic enzyme. Intersubject variability is therefore more likely to be the result of differences in the presence or activity of other vascular enzymes or in steps further distal in the venodilatory cascade.
View details for Web of Science ID A1993KY91100011
View details for PubMedID 8477563
Protein kinase C (PKC) regulates many cellular functions; we have examined the role of PKC in the regulation of the alpha 1B adrenergic receptor gene. Exposure of DDT1 MF-2 cells to phorbol 12-myristate 13-acetate (PMA) (10 nM) increased values of alpha 1B receptor mRNA with peak changes found at 4 h (3.2-fold increase). Increased values of alpha 1B receptor mRNA occurred at PMA concentrations as low as 10 pM with a maximal response at 100 nM. Also, PMA induced a time-dependent increase in the number of alpha 1B receptors. Stimulation of cells with phenylephrine led to an increase in IP3 production after 3, 6, and 12 h of treatment with PMA. Induction of the alpha 1B receptor mRNA was suppressed by the PKC inhibitors H7 (1-(5-isoquinolinylsulsulfonyl)2-methylpiperazine) and saurosporine; the inactive phorbol ester 4 alpha-phorbol didecanoate and calcium ionophores A23187 and Bay K8644 did not increase alpha 1B receptor mRNA. The half-life of the alpha 1B receptor mRNA was unchanged by PMA. Nuclear runoff assays demonstrated that PMA produced a marked increase in the transcription rate of alpha 1B adrenergic receptor expression is mediated by a PKC-dependent mechanism that occurs at the level of transcription.
View details for Web of Science ID A1993KM16100089
View details for PubMedID 8381435
Bradykinin, a nonapeptide, dilates vascular smooth muscle at least in part via endothelial cell-dependent mechanisms. The aim of this study was to examine the action of bradykinin in human veins in vivo. Utilizing the dorsal hand vein technique, dose-response curves to bradykinin (maximum dose = 513 ng/min) were constructed in veins preconstricted with the alpha-adrenergic agonist phenylephrine in healthy young volunteers. Bradykinin almost fully dilated the veins back to their baseline diameter. To determine if desensitization of bradykinin-mediated vasodilation occurs, two bradykinin dose-response curves were constructed with a short (10 min) interval between studies. The second dose-response curve showed a diminished response. The EMAX of the first curve was 97.8 +/- 47.4% dilation and the EMAX of the second curve was 64.3 +/- 28.0% dilation (p < 0.05). However, when the two curves were separated by 40 min, there was no loss of responsiveness. To investigate the mechanism by which bradykinin caused vasodilation, we used methylene blue to antagonize endothelium-derived relaxing factor, and indomethacin to block prostaglandin-dependent effects. Methylene blue partially antagonized the vasodilatory response to bradykinin, decreasing the EMAX by 50%. Indomethacin also partially antagonized the vasodilatory response, but to a lesser extent than did methylene blue. The vasodilatory response to bradykinin was not fully antagonized with concurrent infusion of both methylene blue and indomethacin. The mechanism of bradykinin-induced vasodilation involves both EDRF and prostacyclin, and possibly another, as yet unidentified, mediator as well.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for Web of Science ID A1993KH73600009
View details for PubMedID 7679158
Insulin resistance may contribute to non-insulin-dependent diabetes mellitus, hypertension, and dyslipidemia; increased free fatty acid concentrations could both promote and maintain this state of insulin resistance. Therefore, agents that inhibit lipolysis and decrease plasma concentrations of free fatty acids could be of therapeutic interest. We have measured metabolic effects of clonidine, an alpha 2 adrenergic agonist, and adenosine in healthy human subjects since human fat cells have alpha 2 and adenosine A1 receptors, which inhibit lipolysis in vitro. Clonidine, as expected, significantly lowered systolic and diastolic blood pressure; clonidine also decreased the plasma concentration of free fatty acids. Although clonidine caused a transient mild increase in plasma glucose, insulin and triglyceride concentrations were unchanged. The metabolic effects of adenosine were examined with two protocols. In the first study, volunteers received a graded infusion of adenosine (at 0, 10, 20, 50 and 100 micrograms/kg.min for 30 min/dose), and glucose, insulin, free fatty acids, as well as respiratory rate, systolic and diastolic blood pressures, and heart rate were measured. There was no change in glucose, insulin, or free fatty acid concentrations. In the second study a graded infusion was used and was maintained at 100 micrograms/kg/min for 120 minutes. Heart rate and respiratory rate significantly increased. Glucose and free fatty acid concentrations were unchanged, while insulin concentrations were significantly increased. All subjects had significant symptomatic complaints (dyspnea, chest pressure) during the adenosine infusion.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for Web of Science ID A1993KR38100005
View details for PubMedID 8458615
Administration of interleukin-1 beta (IL-1 beta) to humans initiates a cascade of metabolic, hematologic, and cardiovascular events. To investigate the role of the sympathetic nervous system in the early cardiovascular response to IL-1 beta in humans, we recorded the heart rate, blood pressure, and changes in hand vein compliance in five patients with malignant melanoma treated with a 30-min infusion of 10,000-20,000 U/kg of human recombinant IL-1 beta. All patients developed fever, chills, and marked hemodynamic changes. During or shortly after the infusion, a dramatic decrease in hand vein compliance occurred (vasoconstriction). At the time of maximum venoconstriction (35 min after the start of the IL-1 beta infusion), the mean heart rate and systolic blood pressure were significantly increased by 30 mm Hg and 31 beats/min, respectively. Venoconstriction always preceded the onset of chills by several minutes (mean of 7 min), was closely correlated with the heart rate, and could be reversed by local administration of the alpha-antagonist phentolamine, indicating involvement of catecholamines. Our study shows that cardiovascular responses that occur early after IL-1 beta administration in humans are most likely the result of adrenergic stimulation possibly through its effect on the central nervous system.
View details for Web of Science ID A1993KJ60300009
View details for PubMedID 8318499
In some blood vessels, the alpha 2-adrenergic agonist clonidine simultaneously activates vasoconstrictive alpha-adrenoceptors on smooth muscle cells and endothelial alpha 2-adrenoceptors mediating release of endothelium-derived relaxing factor (EDRF), with the net vascular response representing a balance between these two counteracting pathways. To investigate whether clonidine's modest constrictor effect in human veins is due to simultaneous release of EDRF, the dorsal hand vein compliance technique was used to measure vascular responses in healthy volunteers. Clonidine-induced venoconstriction was not potentiated by methylene blue, an inhibitor of EDRF-mediated relaxation. After preconstriction with angiotensin II, clonidine did not cause venodilation but rather promoted further constriction, which could be reversed by the alpha 1-antagonist labetalol. However, in veins preconstricted with the full alpha 1-agonist phenylephrine, clonidine induced venodilation, suggesting that clonidine is a partial agonist at venous alpha 1-adrenoceptors. In conclusion, we found no evidence for endothelial alpha 2-adrenoceptor-mediated release of EDRF in human hand veins. The results further suggest that postjunctional alpha 1-adrenoceptors participate in clonidine-induced venoconstriction in humans.
View details for Web of Science ID A1993KN68100011
View details for PubMedID 8095374
Buprenorphine is an opiate drug with a mixed agonist-antagonist profile and has therapeutic efficacy in attenuating drug craving and addiction. Because the adenylyl cyclase system has been implicated in the biochemical basis of opiate withdrawal phenomena, we have compared the acute and chronic effects of buprenorphine with the full opiate agonist etorphine on cyclic AMP (cAMP) synthesis in the human neuroblastoma cell SK-N-SH. Both drugs acutely inhibited prostaglandin (PG)E1-stimulated cAMP accumulation; the inhibition caused by either drug was prevented by pretreatment with the opiate antagonist naltrexone or with pertussis toxin. Chronic treatment of the cells with etorphine induced an increase in PGE1-stimulated cAMP synthesis which was observed after withdrawal of the inhibitory drug. Chronic treatment with buprenorphine appeared to have the opposite effect, resulting in an attenuated PGE1 stimulation; additionally, buprenorphine prevented the etorphine-induced enhancement in cAMP synthesis, whether administered before or after prolonged incubation of the cells with etorphine. The attenuating effect of buprenorphine occurred within 5 min and was prevented by a prior application of naltrexone, but could not be reversed by a subsequent treatment with antagonist. These findings suggest that buprenorphine was binding (pseudo)irreversibly to the opiate receptor, resulting in a persistent inhibition of cAMP synthesis which masks the etorphine-induced enhancement of adenylyl cyclase activity. This hypothesis was confirmed by experiments demonstrating that treatment of the cells with buprenorphine significantly reduced available opiate receptor binding sites despite extensive washing of the cells to remove unbound buprenorphine. These pharmacodynamic actions of buprenorphine may be relevant to its therapeutic efficacy in treating drug abuse and addiction.
View details for PubMedID 8380866
Independent of the route of nitroglycerin administration, substantial amounts of 1,2-glyceryl dinitrate (1,2-GDN) and 1,3-glyceryl dinitrate (1,3-GDN) metabolites accumulate in humans. Thus far their pharmacologic activity in comparison to nitroglycerin in humans is unknown. To compare the venodilatory potency of nitroglycerin and of 1,2-GDN and 1,3-GDN in vivo, cumulative dose-response curves were established in nine healthy volunteers by use of the dorsal hand vein compliance technique. Separated by a washout period, two of the three venodilators were infused in randomized order after preconstriction with phenylephrine. Values for maximum vasodilation were similar for all compounds: nitroglycerin, 109%; 1,2-GDN, 100%; and 1,3-GDN, 106%. The respective values for the dose rate exerting 50% of maximum vasodilation were 5.1, 43, and 60 ng/min, indicating that the dinitrates were about 10 times less potent than nitroglycerin (p < 0.001) but not significantly different from each other. The findings support the hypothesis that activity of nitroglycerin metabolites is related to the number of nitrate groups in the molecule and are in agreement with lower dinitrate potencies found in animal experiments.
View details for Web of Science ID A1992KD48100003
View details for PubMedID 1458768
Chronic administration of alpha 1-receptor antagonists is associated with loss of clinical efficacy, especially in congestive heart failure, although the mechanism is uncertain. To evaluate changes in venous alpha 1-adrenoceptor responsiveness during chronic alpha 1-adrenoceptor blockade, dose-response curves to phenylephrine and angiotensin II were constructed in 10 healthy subjects before, during, and after administration of terazosin 1 mg orally for 28 d. Terazosin initially shifted the dose-response curve of phenylephrine to the right, with a significant increase in ED50 for phenylephrine from a control value of 102 to 759 ng/min on day 1 of terazosin (P < 0.001). However, by day 28, the dose-response curve had shifted back towards baseline with an ED50 of 112 ng/min. After discontinuing terazosin, the ED50 for phenylephrine remained near the baseline value, indicating no evidence of supersensitivity to phenylephrine. There was no change in responsiveness to angiotensin II during the course of treatment with terazosin. Plasma terazosin concentrations were stable throughout the period of drug administration. The mean Kd of terazosin was estimated as 11 +/- 15 nM in the first few days of treatment. This study demonstrates that pharmacological tolerance to the alpha 1-adrenoceptor blocking action of terazosin occurs in man and may be responsible for loss in efficacy with chronic therapy.
View details for Web of Science ID A1992JZ47500017
View details for PubMedID 1358918
Many cells develop enhanced adenylate cyclase activity after prolonged exposure to drugs that acutely inhibit the enzyme and it has been suggested that this adaptation may be due to an increase in Gs alpha. We have treated wild-type and Gs alpha-deficient cyc- S49 mouse lymphoma cells with a stable analogue (SMS 201-995) of the inhibitory agonist somatostatin. After incubation with SMS for 24 h, the forskolin-stimulated cAMP synthetic rate in intact cyc- cells was increased by 76%, similar to the increase found in the wild-type cells. Forskolin-stimulated adenylate cyclase activity in the presence of Mn2+ was also increased in membranes prepared from SMS-treated cyc- cells; however, guanine nucleotide-mediated inhibition of adenylate cyclase activity was not changed despite a small decrease in inhibitory Gi alpha subunits detected by immunoblotting. Pretreatment of cyc- cells with pertussis toxin prevented SMS from inducing the enhancement of forskolin-stimulated cAMP accumulation in intact cells. After chronic incubation of cyc- cells with SMS, exposure to N-ethylmaleimide, which abolished receptor-mediated inhibition of cAMP accumulation, did not attenuate the enhanced rate of forskolin-stimulated cAMP synthesis compared to N-ethylmaleimide-treated controls. These results with cyc- cells demonstrate that an adaptive increase in adenylate cyclase activity induced by chronic treatment with an inhibitory drug can occur in the absence of expression of Gs alpha.
View details for PubMedID 1329904
The aim of this study was to determine whether there is an age-related decline in vascular responsiveness to bradykinin, whose vasodilatory action is mediated chiefly through endothelium-derived relaxing factor (EDRF). Dose-response curves for bradykinin were constructed using the dorsal hand vein compliance technique in veins preconstricted with phenylephrine in 27 volunteers (16 male, 11 female) aged 18 to 81 years. At the end of the bradykinin study, 12 subjects had a single infusion of a high dose of isoproterenol. There was no correlation between age and the EMAX or the log ED50 for bradykinin, although the same subjects showed a correlation between age and EMAX for isoproterenol, as previously found. There was no significant difference in either the EMAX or the log ED50 between male and female subjects. The results suggest that bradykinin-induced vasodilation is independent of age or gender.
View details for Web of Science ID A1992JM62400016
View details for PubMedID 1512432
NG108-15 neuroblastoma x glioma hybrid cells and S49 lymphoma cells exhibit an enhancement in adenylyl cyclase activity after chronic treatment with receptor agonists that acutely inhibit the enzyme. Using agonists that activate five distinct inhibitory receptors in NG108-15 cells, we have found that there is a correlation between the extent of acute inhibition of prostaglandin E1 (PGE1)-stimulated cAMP accumulation and efficacy for induction of enhanced PGE1 stimulation of cAMP accumulation after chronic treatment and withdrawal. Chronic treatment with dideoxyadenosine, which acutely inhibits adenylyl cyclase activity by a mechanism independent or cell surface receptors or pertussis toxin-sensitive G proteins, did not induce enhanced PGE1 stimulation of cAMP accumulation in NG108-15 cells or forskolin stimulation of cAMP accumulation in S49 cells. While control basal cAMP concentrations were acutely decreased by carbachol in NG108-15 cells and by somatostatin in S49 cells, when the cAMP concentrations were maintained above the control basal values with a phosphodiesterase inhibitor, chronic treatment with these inhibitory drugs nonetheless resulted in enhanced cAMP responses in both NG108-15 and S49 cells. These results provide evidence that the initial decrement in cAMP concentrations caused by inhibitory drug is not the requisite signal for inducing the subsequent sensitization of adenylyl cyclase in NG108-15 and S49 cells but that activation of a pertussis toxin-sensitive G protein is involved in the development of this important adaptation.
View details for PubMedID 1329899
To compare the effects of atenolol and nifedipine on mood and cognitive function in elderly hypertensive patients.Randomized, double-blind, crossover trial.Thirty-one elderly volunteers (7 women and 4 men) 60 to 81 years of age with mild to moderate hypertension were recruited from the general community and a Veterans Affairs hospital hypertension clinic. Six volunteers withdrew at early phases of the study for reasons unrelated to adverse drug effects.Participants had 2 weeks of placebo, to 6 weeks of titration with atenolol or nifedipine, and weeks of treatment followed by similar periods with the other drug.Psychometric tests designed to assess mood and cognitive function.In the group first treated with nifedipine, the summed recall score on the Buschke selective reminding test (a test of verbal learning and memory) decreased by 9.3 words (95% CI, 2.8 to 15.6 words), or 0%, during nifedipine treatment compared with placebo (P = 0.031). The group first treated with atenolol showed no improvement in summed recall scores when results seen during atenolol therapy and placebo administration were compared (P = 0.10); however, this group had an improvement of 16.1 words (CI, 5.6 to 26.5 words), or of 16%, when the atenolol score was compared with the nifedipine score (P = 0.026). In the group first treated with nifedipine, 6 of 11 patients 55%) showed a decrease of 5 words or more during nifedipine therapy compared with placebo, whereas only 1 of the 14 patients (7%) in the group first treated with atenolol showed a similar decrease (P less than 0.01). On the digit symbol test (a psychomotor test), patients treated first with atenolol tended to improve, whereas patients treated first with nifedipine tended to decline. The difference between nifedipine and atenolol, in terms of the change from the score seen during placebo, was 4.3 codings (CI, 0.7 to 7.9 codings) or 10% (P = 0.043). No statistically significant differences were seen between nifedipine and atenolol therapy regarding the other measures of psychomotor ability, sustained attention, motor performance, verbal fluency, or abstract reasoning, and no effects of either drug on mood or psychopathologic symptoms were noted.Although atenolol and nifedipine are generally free of gross effects on cognition or mood, nifedipine may subtly impair learning and memory in some elderly hypertensive patients.
View details for Web of Science ID A1992HN84400002
View details for PubMedID 1546860
Presomite stage rat embryos were cultured for 45-49 hr with medium containing various adrenergic agonists and antagonists. L-Norepinephrine but not D-norepinephrine (several orders of magnitude less potent than the L-isomer at alpha-1 adrenergic receptors) resulted in a dose-dependent increase of situs inversus similar to that found for phenylephrine, an alpha-1 adrenergic agonist. Prazosin, an alpha-1 adrenergic antagonist, inhibited phenylephrine-induced situs inversus in a dose-dependent manner. Neither dexmedetomidine, an alpha-2 adrenergic agonist, nor isoproterenol, a beta adrenergic agonist, caused situs inversus. These results provide pharmacological evidence that stimulation of alpha-1 but not of alpha-2 and beta adrenergic receptors modulates the control of left/right sidedness in rat embryos.
View details for Web of Science ID A1992HK69600017
View details for PubMedID 1348038
This study was designed to investigate the relative ability of a series of cyclic opioid peptides to initiate the first activation steps following their binding of delta-opioid receptors. The extent of stimulation of low Km guanosine-triphosphatase (GTPase activity) and inhibition of hormonally-stimulated cAMP accumulation in the NG108-15 (neuroblastoma-glioma) hybrid cell line were determined and compared for six closely related peptides. In addition, their binding affinity was assessed by competition with 3H-[D-Pen2D-Pen5]-enkephalin (3H-DPDPE) in membranes from these cells. All peptides tested elicited comparable maximal effects for both functional responses. Different potencies in stimulating the low Km GTPase was observed at sub-maximal agonist concentrations, although the shallow dose-response behavior did not allow accurate determination of ED50s. Estimation of ED50s for inhibition of cAMP accumulation could be made by curve fitting and were similar for four of these peptides, while DCDPE and 3R-methylDCDPE, the highest affinity analogs, were considerably more potent. In general, the observed differences in hormonal activity somewhat parallel the rank order of binding affinities, but no strict relationship was found between receptor binding and activation.
View details for Web of Science ID A1992HT91000010
View details for PubMedID 1328097
Regulation of beta-adrenoceptors in animal tissues and human cell cultures has been extensively described; on the other hand, relatively little is known about regulation of beta-adrenoceptors in human tissues in vivo. Both beta-adrenoceptors and the prostaglandin E1 (PGE1) receptors stimulate vasodilation. We wondered if prolonged infusion of isoproterenol or PGE1 would cause desensitization of smooth muscle relaxation and used the dorsal hand-vein compliance technique to investigate this question. After constructing a dose-response curve to either the beta-agonist isoproterenol or to PGE1 in a phenylephrine preconstricted vein, isoproterenol (271 ng/min), PGE1 (956 pg/min), or saline was infused for 4 h in separate experiments. There was no change in the ED50 or Emax for either isoproterenol or PGE1 after saline infusion. After a 4-h infusion of isoproterenol, the maximal vasodilator response to isoproterenol was significantly (p less than 0.01) attenuated from 61 +/- 33% to 19 +/- 10%, while the ED50 significantly increased (p less than 0.01) from a geometric mean of 37 to 197 ng/min. After infusion of isoproterenol, the mean maximum PGE1-induced venorelaxation of 129 +/- 29% was modestly but significantly (p less than 0.05) blunted to 96 +/- 35%, while the ED50 of PGE1 increased significantly (p less than 0.01) from a geometric mean of 81 to 398 pg/min. A 4-h infusion of PGE1 significantly (p less than 0.01) attenuated the maximum response to PGE1 from 73 +/- 35 to 28 +/- 16%. The maximal vasodilatory response to isoproterenol was also significantly blunted (p less than 0.05) from 62 +/- 35 to 42 +/- 41%, with no change in ED50.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for Web of Science ID A1992HE96000023
View details for PubMedID 1378128
1. Diabetic autonomic neuropathy causes loss of sympathetic cardiovascular control and is associated with increased vascular sensitivity to catecholamines. Supersensitivity to catecholamines could be due to either a postsynaptic increase in vascular sensitivity or to decreased catecholamine uptake into peripheral sympathetic nerve endings. 2. To differentiate between these possible mechanisms we have measured the responsiveness in vivo to noradrenaline and phenylephrine with local infusions into peripheral veins of diabetic patients with and without symptomatic autonomic neuropathy and of healthy control subjects. The dorsal hand vein compliance technique was used. 3. Symptomatic diabetic patients required significantly lower doses of noradrenaline for half-maximal venoconstriction (ED50) (geometric mean 2.14 ng/min) than control subjects (geometric mean 6.61 ng/min, P = 0.032), but there was no difference in the results from the phenylephrine dose-response curves between the groups. There were no differences in venous responsiveness to noradrenaline or phenylephrine between the asymptomatic diabetic group and the control group. However, in the asymptomatic diabetic group, postural blood pressure change (an index of loss of sympathetic control) was correlated with the ED50 for noradrenaline (r = 0.74, P = 0.014), but not with the ED50 for phenylephrine. In the control group the ED50 values for noradrenaline and phenylephrine were correlated with each other (r = 0.81, P = 0.0005). 4. Both vasopressor drugs act on vascular alpha-adrenoceptors, but only noradrenaline is taken up into peripheral sympathetic nerve endings. Our results suggest that, in diabetic patients, vascular supersensitivity to catecholamines is primarily determined by decreased neuronal catecholamine uptake. A postsynaptic increase in vascular alpha-adrenoceptor stimulation does not appear to be prominent in diabetic autonomic neuropathy.
View details for Web of Science ID A1992HD88500007
View details for PubMedID 1347259
View details for Web of Science ID A1992HE70300217
Desensitization of alpha-1 adrenergic receptor-mediated contraction occurs in aortic smooth muscle from rats after in vitro exposure to norepinephrine (NE). The purpose of this study was to examine effects of pretreatment of blood vessels with catecholamines on relaxant responses of the vessels to sodium nitroprusside (SNP) and atriopeptin III (ANF). Vessels preincubated with NE for 4 hr had a markedly increased sensitivity to relaxation induced by SNP as compared to controls. The concentration of SNP giving half-maximal relaxation (log EC50) was -8.78 +/- 0.09 in the vessels pretreated with NE and -7.40 +/- 0.18 in controls (P less than .001). NE-treated vessels also had an increased sensitivity to ANF (EC50 -8.23 +/- 0.11 vs. -7.03 +/- 0.31, respectively; P less than .01). However, both desensitized and control vessels had similar sensitivity to relaxation induced by 8-bromo-cyclic GMP. The capacity of SNP to stimulate intracellular cyclic GMP accumulation in vessels pretreated with NE was greater than controls at a high concentration of SNP (10(-5) M.). However, there was no correlation between vasodilation induced by lower concentrations of SNP and stimulation of cyclic GMP accumulation in these blood vessels. Activity of soluble and particulate guanylate cyclase in NE-treated vessels was increased compared to controls. Changes in sensitivity of smooth muscle relaxation to SNP and ANF after prolonged exposure to catecholamines may relate to changes in capacity of the cyclic GMP system.
View details for Web of Science ID A1992HD21700048
View details for PubMedID 1346644
1. Ageing is associated with a decline in beta-adrenergic responsiveness in several tissues. Reduced beta-adrenoceptor mediated smooth muscle relaxation in aged man has been demonstrated using the dorsal hand vein technique. Isoprenaline and adenosine activate adenylate cyclase through separate membrane bound receptors to induce vasodilatation. 2. To determine the specificity of reduced beta-adrenergic responsiveness in smooth muscle of aged man, and possible sites of the defect responsible, venodilatory responses to isoprenaline, a beta-adrenoceptor agonist and adenosine were determined in nine young (age 26 +/- 3 years: mean +/- s.d.) and eight elderly (age 70 +/- 5 years), healthy male volunteers. Veins were partially constricted with the alpha 1-adrenoceptor agonist phenylephrine and increasing doses of adenosine (5 to 1220 micrograms min-1) or isoprenaline (271 ng min-1) were infused. 3. Maximal dilatation induced by isoprenaline was 83 +/- 26% in the young and 51 +/- 34% in the elderly, P = 0.02. Maximal dilatation induced at the highest dose of adenosine (1220 micrograms min-1) was similar in young and elderly: 79 +/- 25% vs 88 +/- 28%, P = 0.26. 4. Adenosine venodilatation was measured before and after infusions of theophylline (6.8 to 135 micrograms min-1) for 30 min in six subjects. Adenosine responsiveness was unchanged following theophylline: 48 +/- 16% to 49 +/- 40%, P = 0.44. 5. The results suggest that the age-associated reduced responsiveness of the beta-adrenergic system in human vascular smooth muscle is not shared by venodilatation mediated by adenosine.
View details for Web of Science ID A1992GZ12700013
View details for PubMedID 1311596
Aging is associated with diminished beta-adrenergic responsiveness in a variety of tissues. Desensitization of tissues secondary to the age-associated increase in sympathetic nervous system activity has been proposed as a potential explanation for diminished beta-adrenergic responsiveness. If this hypothesis is correct, then beta-blockade in older people might be expected to reverse the blunted beta-adrenergic responses of tissues having diminished responsiveness. Cardiac chronotropic responses to bolus isoproterenol (ISO) doses and ISO-induced venous smooth muscle dilatation in superficial hand veins were examined in 8 young (26.2 +/- 2.6 yrs) and 9 elderly (68.0 +/- 2.2 yrs) healthy subjects before, during, and 3 and 7 days following 2 weeks of treatment with propranolol. Baseline cardiac chronotropic responsiveness, CD25, was 1.55 +/- 0.77 mcg in the young and 5.97 +/- 2.77 mcg in the elderly subjects (p less than .01), increasing to 84 +/- 56 mcg and 194 +/- 172 mcg during treatment with propranolol. At 3 and 7 days following withdrawal of propranolol, CD25s were respectively 1.24 +/- 0.79 (p = .14) and 1.10 +/- 0.42 (p = .04) in the young and 5.63 +/- 2.34 (p = .31) and 4.85 +/- 2.37 (p = .05) in the elderly subjects. In contrast, there was no decrease in the ED50 or increase in Emax for ISO-induced venodilation of hand veins following propranolol withdrawal. These results demonstrate that both young and elderly subjects have similar increases in cardiac chronotropic responsiveness following discontinuation of beta-blockade and do not support the concept that desensitization is responsible for the diminished beta-adrenergic responsiveness seen with aging.
View details for Web of Science ID A1992GY68000014
View details for PubMedID 1730849
Sustained exposure of vascular smooth muscle to catecholamines results in desensitization of alpha 1-adrenoreceptor-mediated vascular smooth muscle contraction. The present study was designed to determine the effects of prolonged exposure of blood vessels to catecholamines on protein kinase C (PKC) activity. Incubation of rat aortic smooth muscle with 10 microM norepinephrine (NE) for 4 h resulted in a threefold decrease in sensitivity of the contractile response of rat aortic smooth muscle to the phorbol ester 4 beta-phorbol 12,13-dibutyrate (PDBu); this loss in sensitivity was dependent on the presence of endothelium. NE induced a 45% decrease in enzymatic activity of the soluble and particulate forms of PKC. With [3H]PDBu used to label phorbol ester receptor binding sites in the aorta, there was a 34% decrease in [3H]PDBu binding sites in NE-treated blood vessels without change in binding affinity for the ligand. To determine whether this loss in enzymatic activity and [3H]PDBu binding resulted from a decrease in the quantity of the enzyme, Western blot analyses were performed using a monoclonal antibody (MoAb) against PKC. This approach confirmed the presence of an 80-Kd immunoreactive PKC in the soluble fraction of rat aortic smooth muscle and demonstrated a 44% decrease in the amount of PKC in blood vessels after sustained exposure to catecholamines. Our results demonstrate that prolonged activation of alpha-adrenoceptors in blood vessels leads to down-regulation of PKC which may contribute to desensitization of contraction mediated by vasoconstrictors.
View details for Web of Science ID A1992KC72200020
View details for PubMedID 1282603
The objective of this study was to determine whether the dorsal hand vein could be used as a model to study tolerance to oral nitrates, and whether oral N-acetylcysteine (NAC) could reverse tolerance if present. Dose-response curves to nitroglycerin were constructed for 11 normotensive volunteers before and during treatment with a sustained-release formulation of isosorbide dinitrate, 80 mg, three times daily for 7 days and followed by concurrent treatment with NAC at a mean dose of 150 mg/kg/day, in divided doses, for 2 days. In separate studies, dose-response curves were constructed for seven normotensive volunteers before and after treatment with oral NAC at the same dose for 2 days. Nitroglycerin's Emax was significantly attenuated from 115 +/- 36 to 77 +/- 22% after treatment with isosorbide dinitrate alone (p < 0.009). Concurrent treatment with NAC reversed this decrease, as nitroglycerin's Emax of 108 +/- 26% during coadministration of isosorbide dinitrate and NAC was not different from its Emax in the control period. There was also no difference in the dose of phenylephrine required to cause 80% of maximal venoconstriction throughout the study. These studies demonstrate that smooth muscle tolerance to nitrates can be demonstrated in medium-sized veins in humans. In addition, high-dose oral NAC can reverse existing tolerance to oral nitrates in human veins. These results indicate that the dorsal hand vein compliance technique is a good model for the clinical investigation of tolerance to nitrates in humans.
View details for Web of Science ID A1992KC72200010
View details for PubMedID 1282593
Endothelial cell derived relaxing factor (EDRF) mediated relaxation of blood vessels is impaired in vessels exposed to lipoproteins in vitro and in arteries of hyperlipidemic humans and animals. To investigate the mechanism by which lipoproteins impair the effects of EDRF, which is likely nitric oxide (NO) or a related molecule, we have bioassayed EDRF/NO activity by measuring its ability to increase cGMP accumulation in rat fetal lung cultured fibroblasts (RFL-6 cells). Low density lipoprotein modified by oxidation (ox-LDL) induced a concentration-dependent inhibition of EDRF activity that had been released from bovine aortic endothelial cells (BAEC) stimulated with bradykinin or the calcium ionophore A23187. In addition, lipoproteins directly impaired authentic NO-induced stimulation of cGMP accumulation in the detector cells; stimulation by sodium nitroprusside was unaffected. Ox-LDL or oxidized HDL3 were highly potent in blocking NO-stimulated cGMP accumulation with EC50's of approximately 1 microgram/ml. Lipid extracted from ox-LDL blocked NO-stimulated cGMP accumulation to about the same extent as intact ox-LDL, while the protein component of ox-LDL did not inhibit the cGMP response. These results suggest that the lipid component of oxidized lipoproteins inactivate EDRF after its release from endothelial cells.
View details for Web of Science ID A1992GY56100002
View details for PubMedID 1309534
The objective of this study was to determine the relationship between peripheral venous responsiveness (use of the dorsal hand vein compliance technique) and systemic vascular responsiveness (measurement of blood pressure changes) to phenylephrine and angiotensin II in humans. There was a significant correlation (r = 0.70, p less than 0.02) between the dose causing a 20 mm increase in mean arterial pressure and the dose producing half-maximal response in the hand vein (log ED50) for phenylephrine but not for angiotensin II. There was no correlation between the systemic responses to angiotensin II and phenylephrine, but there was a significant correlation (r = 0.70, p less than 0.02) between the log ED50 measurements for phenylephrine and angiotensin II in the hand vein experiments. These findings suggest that systemic and hand vein responsiveness to phenylephrine are similar. Consequently, in evaluating alpha-adrenergic receptor mediated responses, the dorsal hand vein compliance approach offers a satisfactory alternative to the use of systemic hemodynamic changes.
View details for Web of Science ID A1992HA81700009
View details for PubMedID 1732078
Hypertension and cardiomyopathy are prominent findings in both humans and rats harboring pheochromocytomas, tumors that secrete enormous quantities of catecholamines in an unregulated fashion. We used New England Deaconess Hospital rats harboring pheochromocytomas to investigate the effects of chronic exposure to high concentrations of catecholamines on desensitization of alpha- and beta-adrenergic receptor-mediated responses activated by catecholamines. In addition, rats harboring pheochromocytomas provide a useful model to investigate catecholamine-induced hypertension and cardiomyopathy.
View details for PubMedID 1657774
Vasodilators have varying hemodynamic properties that may be important in determining their efficacy for different disorders. We used the dorsal hand vein technique to measure the effects of several vasodilators infused locally and to measure the action of systemically administered nifedipine. The venodilatory effects of hydralazine, verapamil, diazoxide, and nitroglycerin were determined in peripheral veins of healthy subjects. The potency (ED50, the dose producing half-maximal response) was as follows: nitroglycerin (0.0007 micrograms/min) greater than verapamil (6.5 micrograms/min) greater than diazoxide (75 micrograms/min) greater than hydralazine (660 micrograms/min). The effect of oral nifedipine on alpha-adrenergic responsiveness of hand veins was determined. Nifedipine given in therapeutic doses for the treatment of hypertension was associated with a threefold increase in the ED50 for phenylephrine (92 to 277 ng/min; p less than 0.05) and norepinephrine (2.9 to 11.5 ng/min; p less than 0.05). Therapeutic doses of nifedipine are associated with measurable shifts in the dose-response curves to these two alpha-adrenergic agonists in the hand vein. The hand vein technique can be used not only to compare the potency of locally infused drugs but also to measure venous effects of vasoactive drugs at therapeutic concentrations achieved after systemic administration.
View details for Web of Science ID A1991GC70500011
View details for PubMedID 1651200
Steroid hormones modulate physiological processes by a number of mechanisms including regulation of gene expression. We wondered if glucocorticoids might induce expression of alpha 1 adrenergic receptors, which could contribute to the increased sensitivity of vascular smooth muscle to catecholamines that may occur with glucocorticoid excess. We examined the effects of dexamethasone on the expression of the alpha 1B adrenergic receptor gene in DDT1 MF-2 smooth muscle cells. Dexamethasone (10(-6) M) produced a 1.8 +/- 0.2-fold increase in expression of alpha 1B receptors determined with [3H]prazosin. Steady-state values of alpha 1B adrenergic receptor mRNA, analyzed by Northern blotting, increased 2.8 +/- 0.7-fold after 48 h exposure to dexamethasone. This effect of dexamethasone occurred in the presence of the protein synthesis inhibitor cycloheximide. alpha 1B receptor mRNA abundance was also increased by testosterone and aldosterone, whereas beta estradiol and progesterone had no effect. The alpha 1B receptor gene transcription rate, determined in nuclear run-off assays, increased 2.6 +/- 0.6-fold in cells treated with dexamethasone for 24 h. The half-life of the alpha 1B receptor mRNA was unchanged by dexamethasone. These data indicate that glucocorticoids regulate expression of alpha 1B receptors by increasing the rate of transcription of this gene.
View details for Web of Science ID A1991GA27600005
View details for PubMedID 1650792
We compared the ability of adipocytes isolated from the epididymal fat pads of Sprague-Dawley and Fischer 344 rats of different ages and weights to release glycerol in response to beta-adrenergic stimulation. Twelve-month-old Sprague-Dawley rats weighed approximately three times more than did 2-month-old rats of the same strain (761 +/- 61 g vs 223 +/- 8 g, p less than .001). Basal glycerol release was increased in the adipocytes of the 12-month-old rats (128 +/- 8 nmol/10(5) cells/L compared to the 2-month-old rats 51 +/- 3 nmol/10(5) cells/L). However, the ability of isoproterenol to stimulate glycerol release above basal was markedly decreased in the older and fatter Sprague-Dawley rats (178 +/- 15 nmol/10(5) cells/L vs 482 +/- 20 nmol/10(5) cells/L, p less than .001), and significant correlation coefficients between isoproterenol-stimulated glycerol release and both total body (r = .76, p less than .001) and fat pad (r = .83, p less than .001) weight were seen in Sprague-Dawley rats. Total body weights of 2-month (188 +/- 16 g), 12-month (393 +/- 15 g), and 27-month-old (402 +/- 36 g) Fischer 344 rats were less disparate. Isoproterenol-stimulated glycerol release was similar in the three groups of Fischer 344 rats, and there was no correlation between either total body or fat pad weight and lipolysis in these rats.
View details for Web of Science ID A1991FW03300016
View details for PubMedID 2071826
Desensitization of alpha-adrenergic receptor-mediated smooth muscle contraction occur in aortas from New England Deaconess Hospital (NEDH) rats harboring pheochromocytoma (PHEO) and following chronic exposure to the alpha-adrenergic agonist phenylephrine in vitro. Endothelium is known to release an endothelial cell-derived relaxing factor that promotes smooth muscle relaxation. We wondered if the endothelium might contribute to the desensitization of contraction. The role of the endothelium in desensitization was studied using aortic rings with endothelium [E(+)] and with endothelium removed [E(-)]. Maximal phenylephrine (PE)-induced contraction (Emax) for E(+) was 1.7 +/- 0.3 g in controls and 0.4 +/- 0.1 g in PHEO (p less than 0.001), demonstrating desensitization; however, for E(-), Emax was 2.4 +/- 0.2 g in PHEO vs. 2.5 +/- 0.2 g in controls, demonstrating restoration of maximal contraction when the endothelium was removed. However, sensitivity [-log EC50(M)] to PE in E(-) remained significantly lower in PHEO compared to controls (6.94 +/- 0.12 vs. 7.51 +/- 0.14, respectively, p less than 0.001). Similarly, in aortic ring segments desensitized in vitro with phenylephrine, the maximal contraction in phenylephrine-exposed aortas was 60% of that seen in controls. Removal of the endothelium from the vessels pretreated with phenylephrine fully restored the maximal response and sensitivity of these vessels. Treatment of desensitized vessels with hemoglobin (5 x 10(-5) M) restored the maximal contraction and sensitivity to phenylephrine. When the endothelium was removed prior to chronic exposure to phenylephrine, the sensitivity to phenylephrine decreased while the Emax remained similar to controls.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for Web of Science ID A1991FU13800020
View details for PubMedID 1719284
Since cAMP has a number of important effects regulating activity of adrenergic receptor pathways, we wondered if expression of the alpha 2A adrenergic receptor gene is regulated by this second messenger. We have examined the effects of a cAMP analog (Bt2cAMP) on the expression of alpha 2A adrenergic receptors in HT-29 cells. Bt2cAMP induced a 5.3 +/- 0.8-fold increase in alpha 2A receptor mRNA abundance as did forskolin and vasoactive intestinal polypeptide which both increase cAMP accumulation in these cells. Bt2cAMP increased alpha 2A receptor number up to 2.4 +/- 0.3-fold. The rate of alpha 2A receptor gene transcription increased 7.8 +/- 3.2-fold in cells treated with Bt2cAMP for 2 h; after 24 h, the transcription rate was 3.7 +/- 1.7-fold higher than in controls. The increased rate of transcription occurred in the presence of the protein synthesis inhibitor cycloheximide. The half life of the alpha 2A receptor mRNA in cells incubated with Bt2cAMP for 2 h increased by 1.5-fold but returned to the original value after exposure to Bt2cAMP for 24 h. The increased expression of alpha 2A receptors was associated with an increased efficacy of inhibition of cAMP accumulation mediated by the alpha 2 adrenergic agonist UK14304. Using a chloramphenicol acetyltransferase (CAT) reporter plasmid containing 5'-flanking sequences of the alpha 2A receptor gene, we found that co-transfection of JEG-3 cells with expression vectors containing cAMP-dependent protein kinase regulatory subunit cDNA with mutations at both cAMP binding sites inhibited basal and Bt2cAMP-stimulated expression of CAT activity. These results demonstrate that an alpha 2A adrenergic receptor gene is regulated by the second messenger cAMP via cAMP-dependent protein kinase, mainly by controlling the rate of transcription, which leads to an increased expression of these receptors.
View details for Web of Science ID A1991FD37000060
View details for PubMedID 1848558
beta-Adrenergic agonists stimulate cyclic 3',5'-adenosine monophosphate (cAMP) accumulation and relaxation in vascular smooth muscle; both of these responses decline in rat aorta with increasing age. To ascertain whether the deficit in beta-receptor stimulated cAMP accumulation persists in isolated aortic smooth muscle cells, the effect of isoproterenol on cAMP accumulation was measured in cultured vascular smooth muscle cells (VSMC) and vascular fibroblasts taken from young (4-6 weeks) and older (8-12 months) Fischer 344 male rats. Immunofluorescent staining confirmed the identity of VSMC as distinct from fibroblasts. Isoproterenol stimulated cAMP accumulation in a time- and concentration-dependent manner in both cell types; maximal cAMP accumulation induced by beta-adrenergic stimulation in cultured cells was much higher than those seen in the intact aorta. While there was a blunting of cAMP response to isoproterenol in fibroblasts cultured from the older rats, the response in VSMC cultured from the older rats was actually increased compared to the VSMC cultured from the younger rats. In contrast, activation of cAMP accumulation in the cultured cells by forskolin was similar in cells from older and young animals. The results suggest that the blunting in isoproterenol-stimulated cAMP accumulation found in aortas from older animals is not seen in VSMC cultured from these animals; whether this change in the culture reflects removal of some extrinsic factor in the older rats or is a consequence of intrinsic changes in the cells in culture requires further investigation.
View details for Web of Science ID A1991EZ03800005
View details for PubMedID 1647473
Various aspects of carbohydrate and lipid metabolism have been studied in two groups of patients with mild hypertension before and after four months of treatment with either nifedipine (n = 12) or atenolol (n = 12). Mean (+/- SEM) blood pressure fell to the same degree following treatment with either nifedipine (147 +/- 3/98 +/- 2 to 134 +/- 2/85 +/- 2 mm Hg) or atenolol (149 +/- 3/99 +/- 2 to 135 +/- 2/86 +/- 3 mm Hg). Circulating plasma glucose, insulin, and triglyceride concentrations were measured at hourly intervals from 8:00 AM to 4:00 PM, before and after breakfast (8:00 AM), and at lunch time (noon). The response to treatment was different in the two groups. Specifically, plasma glucose concentration were unchanged and insulin concentrations were higher in association with atenolol treatment. In contrast, nifedipine-treated patients had similar plasma insulin, but lower plasma glucose and triglyceride concentrations after four months of therapy. The changes in day-long plasma glucose and insulin responses suggested that resistance to insulin-stimulated glucose uptake had increased in association with atenolol treatment and decreased following nifedipine. This conclusion was supported in that measurement of insulin-stimulated glucose disposal showed a decrease in atenolol-treated patients and an increase in nifedipine-treated patients. Finally, plasma lipoprotein cholesterol concentrations did not change following atenolol therapy, whereas plasma high density lipoprotein cholesterol increased in association with nifedipine administration. These data show that changes in carbohydrate and lipid metabolism observed with treatment of mild hypertension can vary significantly as a function of the drug used, despite similar beneficial effects on blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for Web of Science ID A1991FC49300001
View details for PubMedID 2043298
The effect of prazosin treatment on blood pressure, plasma HDL-cholesterol concentration, and apoprotein-AI/HDL (apoAI/HDL) kinetics was studied in 11 patients with mild hypertension. Blood pressure (mean +/- SEM) fell from 143 +/- 1/96 +/- 1 to 134 +/- 1/86 +/- 1 mm Hg after 4 to 5 months of prazosin treatment (P less than .001), associated with an increase in plasma HDL-cholesterol concentration from 38 +/- 2 to 46 +/- 2 mg/dL (P less than .001). Both the fractional catabolic rate (FCR) and total synthetic rate of apoAI/HDL, which were higher than previous reported values for normal individuals, decreased from 0.36 +/- 0.02 to 0.30 +/- 0.02 L/day and 17.4 +/- 1.1 to 13.8 +/- 1.1 mg/kg/min, respectively. These changes were statistically significant, and the post-treatment values for both variables were now within the normal range. When the decay curve was further analyzed by nonlinear curve fitting, it was shown that the return to normal of the FCR of apoAI/HDL in patients treated with prazosin was accounted for by the decrease of the decay constants of the second [p(2)] and third [p(3)] components of the 125I-AI/HDL disappearance curve. In conclusion, abnormalities in HDL concentration and HDL kinetics exist in patients with very mild hypertension. These defects were significantly improved with prazosin treatment, and this may render the compound of particular clinical benefit in the treatment of patients with mild hypertension.
View details for Web of Science ID A1990ED20500005
View details for PubMedID 2121164
Essential hypertension is more prevalent among blacks than whites although the explanation is unknown. It is possible that an altered vascular adrenoceptor responsiveness in blacks may play a role in the etiology of this racial difference. To test this hypothesis, we have compared the diameter changes in superficial veins in response to phenylephrine, an alpha-adrenergic agonist, and to isoproterenol, a beta-adrenergic agonist, in black and white young normotensive males using the dorsal hand vein compliance technique. The maximal venoconstriction after phenylephrine (Emax) was 92 +/- 9% (mean +/- SD) in the whites but only 74 +/- 12% in the blacks (p = 0.00046). The ED50 of phenylephrine was 342 ng/min (geometric mean) in whites and 245 ng/min in blacks (p = 0.50). The Emax and ED50 for isoproterenol-mediated venodilation was not significantly different between the racial groups. These results indicate a decreased maximal responsiveness to alpha-adrenergic stimulation in normotensive blacks. How these changes relate to cardiovascular alterations in hypertensive blacks requires further study.
View details for Web of Science ID A1990DP61900001
View details for PubMedID 1697371
Significant increases (P less than 0.001) in plasma insulin and triglyceride concentrations and in blood pressure were seen when SHR and WKY rats ate a fructose-enriched diet for 14 days. However, all of the changes were significantly accentuated (P less than 0.02-0.001) in SHR rats. Specifically the increment in plasma insulin concentration following the fructose-enriched diet was 42 +/- 4 microU/ml in SHR as compared to 25 +/- 4 microU/ml in WKY rats (P less than 0.001). Plasma triglyceride concentrations also increased to a greater degree in response to fructose in SHR rats (260 +/- 24 vs. 136 +/- 20 mg/dl, P less than 0.001). Finally, the fructose-induced increase in blood pressure of 29 +/- 4 mm of Hg in SHR rats was greater (P less than 0.02) than that seen in WKY rats (19 +/- 2 mm of Hg). There was no change in plasma glucose concentration in response to the fructose diet. WKY rats gained more weight than did the SHR rats. Thus, although plasma triglyceride and insulin concentration and blood pressure increased when either WKY or SHR rats consumed a fructose enriched diet, the magnitude of these changes was greater in SHR rats.
View details for Web of Science ID A1990DP87800001
View details for PubMedID 2205554
Both vascular relaxation and cAMP accumulation mediated by beta adrenergic agonists declines with increasing age. We have developed a method to measure the biologically relevant cAMP bound to the regulatory subunits of cAMP-dependent protein kinase in rat aorta. In homogenates of rat aorta, binding of [3H]cAMP was saturable with a Kd of 8.0 +/- 1.5 nM; the dissociation of [3H]cAMP from the binding sites was comprised of fast and slow components at 4 degrees C. Endogenous cAMP binding in aortas stimulated with isoproterenol (10(-5) M) or forskolin (10(-5) M) was quantitated by radioimmunoassay. Compared to basal values, isoproterenol increased cAMP binding by 37% (P less than 0.05) in aortas from young animals (5-6 weeks) but had essentially no effect on binding in older animals (9-11 months). In contrast, forskolin, which causes full relaxation in aortas from older rats, equally elevated bound cAMP values in aortas in the two age groups. In addition, the ratio of total cAMP binding sites to cAMP-dependent protein kinase catalytic activity was 45% higher in aortas from the older rats, suggesting that there were proportionately more regulatory subunits in those vessels. The deficit in isoproterenol-stimulated cAMP binding in vascular smooth muscle in older animals may in part explain the loss in relaxation mediated by beta adrenergic agonists.
View details for Web of Science ID A1990CY55200001
View details for PubMedID 2160570
The increase in hormone-stimulated cyclic AMP accumulation observed in a variety of intact cells after chronic pretreatment with drugs that inhibit adenylate cyclase activity has been attributed to an increase in adenylate cyclase activity following withdrawal of the inhibitory drug. In NG 108-15 mouse neuroblastoma X rat glioma hybrid cells (NG cells) chronically treated with the muscarinic cholinergic agonist carbachol, we have found a significant decrease in the apparent degradation rate constant for cyclic AMP, in addition to an increase in the prostaglandin E1 (PGE1)-stimulated cyclic AMP synthesis rate in intact cells. In carbachol-pretreated NG cells that were stimulated with a maximally effective dose of PGE1, and that accumulated steady-state cyclic AMP concentrations fourfold or more higher than in control cells, the apparent rate constant for degradation was about 53% lower than the value for control cells. In carbachol-pretreated cells stimulated with a submaximal dose of PGE1 to yield a steady-state cyclic AMP concentration comparable to control cells, the apparent rate constant was 31% lower than the value for control cells. In S49 mouse lymphoma cells (S49 cells) chronically treated with an analog of the inhibitory agonist somatostatin, the first-order rate constant for cyclic AMP degradation in intact cells following isoproterenol stimulation was 29% lower than the value for control cells. Despite these changes in the kinetics of cyclic AMP degradation in intact NG cells and S49 cells, there was either no change or a minimal change (less than 10%) in phosphodiesterase activities assayed in extracts of cells chronically exposed to inhibitory drugs.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for PubMedID 1688917
Hypertension and cardiomyopathy are prominent findings in humans and rats harboring pheochromocytomas, tumors that can secrete enormous quantities of catecholamines. We have previously found that alpha- and beta-adrenergic receptor antagonists may ameliorate the hypertension and cardiomyopathy found in New England Deaconess Hospital rats implanted with pheochromocytoma. The present studies were designed to determine the possible action of the angiotensin converting enzyme inhibitor captopril on these changes in rats harboring pheochromocytomas. Rats were implanted with transplantable pheochromocytomas and treated with captopril dissolved in the drinking water (1 mg/ml) for 4-6 weeks. Systolic blood pressure was monitored by using the tail-cuff technique. In the rats with pheochromocytoma, blood pressure progressively increased to 184 +/- 3 mm Hg after the tumor was implanted. However, in rats with pheochromocytoma treated with captopril in the drinking water before the development of hypertension, blood pressure did not increase (137 +/- 3 mm Hg). In rats with pheochromocytoma with established hypertension, captopril normalized the systolic blood pressure. Plasma norepinephrine was markedly elevated to a similar extent in both groups compared with unimplanted control rats. Plasma renin activities were slightly lower in rats with pheochromocytoma compared with unimplanted control rats. Treatment with captopril of rats with pheochromocytoma did not modify contraction of isolated rings of thoracic aorta exposed in vitro to either phenylephrine or angiotensin II. Treatment with captopril markedly attenuated the cardiomyopathy induced by pheochromocytoma. These results demonstrate that captopril prevents the development of hypertension despite markedly elevated concentrations of catecholamines. In addition, captopril attenuates catecholamine-induced cardiomyopathy in pheochromocytoma.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for Web of Science ID A1990CM99200014
View details for PubMedID 2154406
Many cells develop an adaptive increase in the capacity of adenylate cyclase to synthesize cyclic AMP (cAMP) after prolonged (hours or days) exposure to drugs which initially inhibit enzyme activity. Recent evidence suggests that adaptive increases in cAMP responses can be induced within minutes by inhibitory drugs. We have investigated the kinetics for induction and decay of this phenomenon in mouse neuroblastoma x rat glioma hybrid cells. The muscarinic cholinergic agonist carbachol induced an increase in prostaglandin E1-stimulated cAMP accumulation within 2 min of pretreatment with carbachol; the increase was 70 to 100% above control values after exposure to carbachol for 30 min. Enhanced cAMP responsiveness decayed with a half-life of about 8 min after removal of carbachol. Pretreatment with carbachol for 30 hr led to an enhanced cAMP response which decayed in two components, a rapid component and an additional, more stable component which persisted for at least 2 hr after withdrawal of carbachol. Pertussis toxin prevented these effects of carbachol. Prevention of carbachol-induced inhibition of cAMP accumulation below basal concentrations with a phosphodiesterase inhibitor did not prevent the ability of carbachol to acutely induce augmented prostaglandin E1-stimulated cAMP accumulation. Mouse neuroblastoma x rat glioma hybrid cells exhibit an enhanced cAMP response after both acute and chronic exposure to a muscarinic cholinergic agonist although these processes decay with different time courses. The signal for this acutely induced adaptation does not appear to be the decrease in cellular cAMP concentration resulting from inhibition of adenylate cyclase but does require a pertussis toxin-sensitive substrate.
View details for PubMedID 2156056
1. Blood pressure regulation was studied in 12 healthy elderly subjects after double-blind randomised administration of placebo, 15 mg and 30 mg temazepam at 10.00 h and 22.00 h. 2. Supine and standing heart rate and blood pressure were measured after daytime administration and supine measurements were obtained during sleep. 3. Temazepam caused a fall in systolic blood pressure and an increase in heart rate after morning administration. These changes were greater in the standing position and were dose-dependent; for standing blood pressure and heart rate 1 h after administration there was a 7 mm Hg fall and 6 beats min-1 increase after 15 mg temazepam and a 10 mm Hg fall and 8 beats min-1 increase after 30 mg temazepam. Temazepam magnified the fall in systolic blood pressure and increase in heart rate that occurred with standing. Temazepam enhanced the fall in systolic blood pressure that occurred during sleep (mean +/- s.d.; placebo: -23 +/- 10 mm Hg, 15 mg temazepam: -31 +/- 13 mm Hg, 30 mg temazepam: -36 +/- 14 mm Hg). 4. These changes in blood pressure regulation caused by temazepam may have clinical importance in some elderly individuals.
View details for Web of Science ID A1990CG78400009
View details for PubMedID 1967533
Patients with untreated hypertension have been shown to be resistant to insulin-stimulated glucose uptake and both hyperinsulinemic and hypertriglyceridemic when compared with matched control groups with normal blood pressure. In addition, insulin resistance, hyperinsulinemia, and hypertriglyceridemia have been demonstrated in rat models of hypertension, including spontaneously hypertensive rats and Sprague-Dawley rats fed a fructose-enriched diet, and the defect in insulin-stimulated glucose uptake in these experimental models can also be shown at the cellular level. Furthermore, experimental interventions that prevent insulin resistance and/or hyperinsulinemia from developing in fructose-fed rats also greatly attenuate the increase in blood pressure. Finally, endogenous hyperinsulinemia and hypertriglyceridemia have been identified as factors that increase the risk of coronary artery disease, and may contribute to the increased prevalence of ischemic heart disease in patients with high blood pressure. The fact that past antihypertensive treatment has not focused on these metabolic abnormalities, and, indeed, may have exacerbated them, could help explain why it has been difficult to show that lowering blood pressure decreases risk of coronary artery disease. These observations raise the possibility that abnormalities of carbohydrate and lipoprotein metabolism may play a role in both the etiology and the clinical course of hypertension.
View details for PubMedID 2688409
View details for Web of Science ID A1989CE25900002
Nitroglycerin (NTG) is a potent vascular smooth muscle relaxant. With the widespread use of transdermal NTG patches for the prophylaxis of angina, two important issues have arisen: (a) the relative efficacy of transdermal NTG patches compared to other formulations of NTG, and (b) the possibility of development of tolerance to transdermal NTG. We have investigated these two issues by studying the effect of systemically administered NTG (transdermal patches, ointment, and sublingual tablets) on alpha-adrenergic receptor agonist-mediated constriction of human dorsal hand veins. Nitroglycerin patches and ointment (15-60 mg/24 h) applied for 1-4 h did not modify the sensitivity (ED50) to the alpha-adrenergic agonist, phenylephrine. However, sublingual NTG (0.15-0.60 mg) administration caused significant relaxation of partially constricted veins. Following exposure for 24 h to a NTG patch (15 mg/24 h), NTG dose-response curves were not altered suggesting there was no development of tolerance to transdermal NTG. We conclude from our observations that tolerance to transdermal NTG does not appear in veins, possibly due to the low plasma NTG concentrations produced by this preparation. Our results also indicate that high doses of transdermal NTG do not modify phenylephrine-mediated constriction of peripheral veins in humans.
View details for Web of Science ID A1989AQ65100004
View details for PubMedID 2478766
The ability of insulin to stimulate glucose uptake and inhibit catecholamine-induced lipolysis was measured in adipocytes of similar size isolated from SHR and WKY rats. The results indicate that glucose transport was decreased in adipocytes from SHR rats; both basal (19 +/- 2 vs. 32 +/- 2 fmol.cell-1.s-1, P less than .001) and maximal (207 +/- 30 vs. 373 +/- 20 fmol.cell-1.s-1, P less than .01) insulin-stimulated glucose transport were lower in SHR than in WKY rats. In addition, the EC50 of insulin-stimulated glucose uptake was higher (921 +/- 82 vs. 557 +/- 69 pM insulin, P less than .05) in adipocytes from SHR rats than from WKY rats. The ability of phenylisopropyladenosine (PIA) to modulate basal and maximal insulin-stimulated glucose uptake was compared in adipocytes from SHR and WKY rats. These results also demonstrated that glucose uptake was decreased in adipocytes from SHR rats and that PIA similarly enhanced both basal and maximal insulin-stimulated glucose uptake in adipocytes from both groups. Although maximal isoproterenol-stimulated lipolysis was decreased in adipocytes from SHR rats, the ability of insulin to inhibit catecholamine-stimulated lipolysis was at least as great in adipocytes from SHR as from WKY rats. Despite the decrease in insulin-stimulated glucose transport in isolated adipocytes from SHR rats, total number of insulin receptors, their affinity for insulin, and the ability of insulin to stimulate receptor-associated tyrosine kinase activity were similar in adipocytes from SHR and WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for PubMedID 2670644
Desensitization of alpha 1-adrenoceptor-mediated activation of glycogen phosphorylase was investigated in rabbit aorta. Activation of glycogen phosphorylase by epinephrine was antagonized by the alpha 1-receptor selective antagonist prazosin but not by yohimbine (alpha 2-receptor selective) or by propranolol (beta-receptor antagonist). Preincubation of rabbit aortic ring segments for 5 h with norepinephrine (NE, 10(-5) M) led to a 30-fold loss in sensitivity and a 55% decrease in maximal activation of the enzyme by alpha agonists. Preincubation of aortic ring segments with phenylephrine (10(-5) M) in the presence of propranolol (10(-6) M) also caused desensitization of glycogen phosphorylase activation. The desensitization was heterologous since maximal activation of the enzyme by histamine or KCl was also markedly diminished in segments preincubated with NE. In contrast to these results, catecholamine-induced desensitization to alpha 1-adrenoceptor-mediated smooth muscle contraction in aortic ring segments resulted in loss in sensitivity but not maximal force of contraction on subsequent stimulation by alpha 1 agonists. These results suggest that the mechanism responsible for desensitization of glycogen phosphorylase is distal to receptor activation and may involve attenuation of responses to intracellular Ca2+-dependent enzymes which have limited reserve.
View details for Web of Science ID A1989AG42700014
View details for PubMedID 2476602
Beta adrenergic receptor-mediated relaxation of blood vessels declines with age although the mechanism is unknown. We have utilized the mesenteric artery and aorta of young and older rats to investigate this problem. In vessels from 12-month-old rats there was a marked loss in relaxation mediated by beta adrenergic and adenosine receptors compared to younger rats whereas relaxation induced by muscarinic cholinergic receptors, [cyclic AMP (cAMP) independent], was not impaired. Maximal relaxation to forskolin and dibutyryl cAMP were intact in the vessels from older rats. Isoproterenol-stimulated cAMP accumulation and cAMP-dependent protein kinase activation were attenuated markedly in the vessels from the older rats. Maximal forskolin-stimulated cAMP accumulation and cAMP-dependent protein kinase activation were similar in older and young animals. There was an excellent correlation between cAMP-dependent protein kinase activity and relaxation and the relationship was similar in the two age groups. Continuous infusion of the beta adrenergic antagonist timolol for 1 week into older animals partially restored relaxation to beta adrenergic and adenosine receptor agonists in the aorta. These results suggest that the age-related loss of response to beta adrenergic receptor agonist-induced relaxation may be due in part to attenuated activation of cAMP dependent protein kinase and this change may be partially dependent on endogenous catecholamines.
View details for Web of Science ID A1989AB67300022
View details for PubMedID 2543812
Plasma glucose and insulin responses to an oral glucose challenge and insulin-stimulated glucose uptake were measured in 47 age-, weight-, and sex-matched lean white men (16 with normal blood pressure, 14 with untreated hypertension, nine treated with a thiazide diuretic only, and eight treated with combined diuretic and beta-adrenergic antagonist drugs). Following a 75-g glucose dose, plasma glucose and insulin were measured for a three-hour period. In separate studies, insulin-stimulated glucose uptake was estimated by measuring the steady-state plasma glucose (SSPG) and insulin (SSPI) concentrations achieved during the last 30 minutes of a 180-minute continuous infusion of somatostatin, insulin, and glucose (insulin suppression test). Under these conditions endogenous insulin secretion was suppressed, and differences in SSPG concentration allowed comparisons of the ability of exogenous insulin to stimulate disposal of an identical glucose load in different individuals. The results indicated that men with untreated hypertension had significantly elevated plasma glucose (P less than .001) and insulin concentrations (P less than .001) after an oral challenge compared to normal volunteers. Mean SSPG concentrations were also higher (P less than .05) than normal in patients with untreated hypertension.2+ Furthermore, plasma glucose and insulin concentrations after the oral glucose challenge and SSPG concentration during the insulin suppression test were higher in treated than in treated patients than in untreated patients with hypertension. These results confirm earlier observations that untreated patients with hypertension are insulin resistant, hyperglycemic, and hyperinsulinemic compared to a well-matched normotensive control group, and suggest that conventional treatment programs for lowering blood pressure many exaggerated these metabolic defects.
View details for Web of Science ID A1989AD20000001
View details for PubMedID 2667570
Prolonged exposure of many types of cells to drugs or hormones that inhibit the activity of the enzyme adenylate cyclase, such as narcotics and alpha 2-adrenergic agonists, leads to enhanced accumulation of cAMP upon removal of the inhibitory drug. We have found previously that chronic infusion of the adenosine A1 receptor agonist phenylisopropyladenosine (PIA), an inhibitor of adenylate cyclase, into rats leads to enhanced isoproterenol-stimulated cAMP accumulation in adipocytes isolated from these animals. The enhanced cAMP accumulation was associated with an impaired ability of PIA to inhibit lipolysis in these cells. In the present study we have investigated the mechanism of the enhanced cAMP accumulation in adipocytes from PIA-infused rats and the relationship of these changes to the impaired antilipolytic action of the drug. The enhanced isoproterenol-stimulated cAMP accumulation in adipocytes prepared from PIA-infused rats was due to both an increased rate of cAMP synthesis and a decreased rate of cAMP metabolism at high concentrations of cAMP without a change in phosphodiesterase activity. There was heterologous desensitization of the ability of PIA, prostaglandin E1, and nicotinic acid to inhibit cAMP accumulation in the adipocytes from PIA-infused rats; there was an increase in the EC50 of each of these agonists, although maximal inhibition of cAMP accumulation was similar. The relationship between the activation of cAMP-dependent kinase and extent of lipolysis was similar in the two groups of cells. We demonstrated that the explanation for the impaired ability of PIA to decrease the rate of isoproterenol (10(-7) M)-stimulated lipolysis in the cells from the PIA-infused rats was due to the markedly increased concentrations of cAMP in these cells, which led to sufficient activation of the kinase to maintain a high rate of lipolysis even in the presence of PIA. In addition, we found that the changes induced by the PIA infusion were largely reversible over a 2-day period after discontinuing the PIA infusion. These results demonstrate that adipocytes from PIA-infused rats provide an interesting model to investigate the mechanisms of tolerance to inhibitory drugs.
View details for PubMedID 2539980
Regulation of hormone action with aging has been extensively studied; adipocytes provide an interesting model for some of these questions. We have compared the ability of insulin to stimulate glucose uptake and suppress lipolysis in adipocytes isolated from two month and twelve month-old rats. The ability of insulin to stimulate maximal glucose transport was decreased in adipocytes from the older rats (P less than 0.001); as well, insulin's EC50 was also higher (P less than 0.01) in these cells. Furthermore, these defects were present when insulin-stimulated glucose transport was measured in the presence or absence of adenosine deaminase which metabolizes endogenously released adenosine. Endogenously released adenosine is a stimulator of glucose transport and an inhibitor of lipolysis. Maximal suppression of isoproterenol-induced lipolysis by insulin was similar when adipocytes isolated from the two age groups were incubated in the absence of adenosine deaminase. However, maximal insulin-mediated suppression of lipolysis was found to be significantly decreased (P less than 0.001) in adipocytes isolated from older rats when the experiments were done in the presence of adenosine deaminase; also, insulin's EC50 was increased in these cells under these conditions (P less than 0.001). These results emphasize the importance of the adenosine receptor in modulating the response of isolated adipocytes to insulin, particularly for lipolysis, and document the presence of age-associated defects in insulin regulation of both glucose transport and lipolysis.
View details for PubMedID 2666294
1. The basic biochemical defect of cystic fibrosis (CF) remains undetermined, but impaired function of the beta-adrenoceptor-mediated adenosine 3':5'-cyclic monophosphate (cyclic AMP)-dependent regulatory pathway in secretory cells is likely to be involved in the pathophysiology of the disease. 2. We have compared responsiveness to beta-adrenergic stimulation in vivo by infusing isoprenaline locally into peripheral veins of CF patients and control subjects; the dorsal hand vein technique was used to measure the vascular response to isoprenaline. 3. CF patients required significantly higher doses of isoprenaline for half-maximal dilatation of the preconstricted veins (ED50) than controls (geometric mean: 44.5 ng/min in CF patients compared with 14.8 ng/min in controls; P less than 0.05). Maximal venodilatation was 74 +/- 30% of baseline in CF patients compared with 94 +/- 50% in controls (NS between groups). 4. The clinical score of CF patients was uncorrelated with the ED50 of isoprenaline. Thus the decreased beta-adrenergic responsiveness does not seem to be related to the severity of the disease. 5. Our results indicate a defect in the cyclic-AMP-dependent pathway in vascular smooth muscle cells of CF patients. Whether this is associated with the CF gene defect itself requires further study.
View details for Web of Science ID A1989T589700010
View details for PubMedID 2924520
This study evaluated the effect of prazosin in controlled mild hypertension and evaluated select metabolic changes that occurred with prazosin monotherapy. Various aspects of glucose, insulin, and lipid metabolism were studied before and after approximately 10 weeks of prazosin treatment in 12 patients with mild hypertension. Prazosin was well tolerated and induced a significant decrease (p less than 0.001) in both systolic and diastolic blood pressures, without any change in body weight. Plasma concentrations of glucose, free fatty acid, and lactate, which were measured hourly from 8 A.M. to 4 P.M. following meals consumed at 8 A.M. and noon, did not change with prazosin treatment. However, the plasma insulin response from 8 A.M. to 4 P.M. decreased significantly (p less than 0.001) following prazosin treatment. In addition, fasting plasma triglyceride and cholesterol concentrations were significantly lower (p less than 0.05) in prazosin-treated persons, as were postprandial triglyceride concentrations (p less than 0.001). Lower total plasma triglyceride and cholesterol concentrations were accounted for by decreases in very low-density lipoprotein cholesterol and triglyceride and low-density lipoprotein cholesterol and triglyceride, whereas both high-density lipoprotein triglyceride and high-density lipoprotein cholesterol concentrations increased following prazosin treatment. Finally, although both apolipoprotein A1 and apolipoprotein B concentrations decreased in association with prazosin treatment, the decrease in apolipoprotein B was much greater in magnitude, leading to an increase in the ratio of apolipoprotein A1 to apolipoprotein B. In this study, treatment of mild hypertension with prazosin led to lower blood pressures and changes in insulin and lipoprotein metabolism that are important in this patient population.
View details for Web of Science ID A1989T105000004
View details for PubMedID 2643861
Many different types of cells exhibit a supersensitivity of adenylate cyclase after chronic treatment with inhibitory drugs; this phenomenon is manifested by enhanced cAMP accumulation upon removal of the inhibitory drug. Acute treatment of wild-type S49 cells with the somatostatin analog SMS 201-995 (SMS) results in inhibition of cAMP accumulation. We have found that chronic SMS treatment of S49 cells results in enhanced isoproterenol- and forskolin-stimulated cAMP accumulation after removal of the SMS. The forskolin-stimulated cAMP synthetic rate was about 57% higher in SMS-pretreated cells (14.22 +/- 1.02 pmol of cAMP/10(6) cells/min) than in untreated control cells (9.08 +/- 0.84 pmol of cAMP/10(6) cells/min). The time course of forskolin-stimulated intracellular cAMP accumulation is complex, with desensitization of cAMP synthesis and marked egress of cAMP from the cells. We have modeled the forskolin-stimulated cAMP time course to a simple function incorporating the initial synthetic rate and rate constants for desensitization and elimination (degradation plus egress). The mathematical modeling suggests that the difference in forskolin-stimulated cAMP time courses between control and SMS-pretreated cells can be explained on the basis of a difference in initial synthetic rates. We tested the hypothesis that the SMS-induced change in forskolin-stimulated cAMP accumulation is triggered by the decrement in the concentration of intracellular cAMP caused by SMS. We studied two independently isolated mutants of S49 cells that are devoid of cAMP-dependent protein kinase activity (kin-). Although SMS acutely inhibits cAMP accumulation in both kin- mutants, neither mutant exhibited an enhanced forskolin-stimulated cAMP synthetic rate after chronic SMS treatment. These results suggest that cAMP-dependent protein kinase is important in the induction of adenylate cyclase supersensitivity in wild-type S49 cells. The mechanistic signal for induction of supersensitivity may be the decreased cAMP accumulation that occurs in response to stimulation of inhibitory receptors, although other hypothetical mechanisms may be invoked.
View details for PubMedID 2563303
Patients with essential hypertension show an increase in vascular resistance. It is unclear whether this is caused by structural changes in the arterial wall or by hyperresponsiveness of vascular smooth muscle to endogenous alpha adrenergic agonists. Using the dorsal hand vein compliance technique we compared the changes in diameter of superficial veins in response to phenylephrine, an alpha 1 adrenergic receptor agonist, and to nitroglycerin, a venorelaxant, in patients with essential hypertension and in normotensive subjects. The dose of phenylephrine that produced 50% of maximal venoconstriction (ED50) in the hypertensive subjects was 257 ng/min (geometric mean; log mean +/- SD was 2.41 +/- 0.54). In the control subjects the ED50 was 269 ng/min (geometric mean; log mean was 2.43 +/- 0.43). Maximal response (Emax) for phenylephrine was 84 +/- 13% in the hypertensive subjects and 90 +/- 6% in the control subjects. Differences in the group means of the ED50 (P = 0.92) or the Emax (P = 0.27) were not significant. There were no significant differences in the ED50 (P = 0.54) or the Emax (P = 0.08) for nitroglycerin between the two groups. These results show no evidence for a generalized change in alpha adrenergic responsiveness in hypertension and support the concept that increased blood pressure responses to alpha adrenergic stimulation in hypertensives are due to structural and geometric changes in the arterial wall rather than to an increased responsiveness of postsynaptic alpha adrenergic receptors. The phenylephrine studies were repeated in seven hypertensive patients during treatment with prazosin, an alpha 1 adrenergic antagonist. The mean dose ratio of the shift in phenylephrine ED50 (ED50 during prazosin therapy/ED50 before prazosin therapy) was 6.1. This indicates that small doses of prazosin (1-2 mg) cause significant in vivo shifts in the dose-response relationship of alpha adrenergic agonists. The dorsal hand vein compliance technique is useful in detecting systemic effects of alpha adrenergic antagonists.
View details for Web of Science ID A1989R755100016
View details for PubMedID 2562959
Aging in humans is associated with a general decline in beta-adrenergic receptor responsiveness. Whether this is a consequence of a defect at the receptor level or along the adenylate cyclase pathway is not known. Using a technique to measure compliance of dorsal hand veins, we investigated the venodilatory response to isoproterenol and prostaglandin E1 (PGE1), which interact with distinct membrane-bound receptors but activate the same adenylate cyclase system. Studies were conducted in 7 young (Y, less than 30 years) and 7 elderly (E, greater than 60 years) healthy male volunteers. Dilatation induced by isoproterenol (mean +/- SD) was 43 +/- 8% in E vs 97 +/- 17% in Y, p = .003. However, PGE, produced complete relaxation in both Y and E subjects (122 +/- 17% vs 97 +/- 19% respectively, p = .270). The sensitivity to PGE1 was not significantly different between the Y and E. Our results demonstrate that PGE1 is a potent venodilator in humans and that the age-related decline in vascular response is specific to beta-adrenoceptor agonists and does not reflect a generalized loss in responsiveness to adenylate cyclase coupled receptors.
View details for Web of Science ID A1989R841500004
View details for PubMedID 2536054
The venorelaxant effect of atrial natriuretic factor in man was studied using the dorsal hand vein technique. Infusion of met-ANF to preconstricted veins at doses up to 240 ng min-1 in 11 healthy male subjects caused only minimal venorelaxation. Atrial natriuretic factor is unlikely to have a significant venorelaxant effect at physiological doses in man.
View details for Web of Science ID A1988R422100018
View details for PubMedID 2977285
This study was initiated to see if the insulin resistance, hyperinsulinemia, and hypertension that follow feeding normotensive Sprague-Dawley rats a fructose-rich diet could be prevented by letting rats run spontaneously in exercise wheel cages. Blood pressure in sedentary rats increased from (mean +/- SEM) 125 +/- 2 to 148 +/- 3 mm Hg in response to 2 weeks of a high fructose diet, and this increment was significantly (p less than 0.001) attenuated in exercising rats (from 121 +/- 1 to 131 +/- 2 mm Hg). In addition, mean (+/- SEM) plasma insulin concentration was lower in fructose-fed rats allowed to run spontaneously (44 +/- 2 vs 62 +/- 5 microU/ml; p less than 0.01). Finally, resistance to insulin-stimulated glucose uptake was assessed by determining the steady state plasma glucose response to a continuous glucose and exogenous insulin infusion during a period in which endogenous insulin secretion was suppressed. The results of these studies indicated that the mean (+/- SEM) steady state plasma glucose concentration was significantly lower in the exercise-trained rats (127 +/- 5 vs 168 +/- 6 mg/dl; p less than 0.001), despite the fact that the steady state plasma insulin levels were also lower in rats allowed to run spontaneously (75 +/- 4 vs 90 +/- 5 microU/ml; p less than 0.05). Thus, the ability of exercise-trained rats to stimulate glucose disposal was enhanced as compared with that of sedentary rats fed the same fructose-rich diet. These data demonstrate that the insulin resistance, hyperinsulinemia, and hypertension produced in normotensive rats by feeding them a high fructose diet can be attenuated if rats are allowed to run spontaneously.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for Web of Science ID A1988P816100007
View details for PubMedID 3410522
Prolonged stimulation of beta-adrenergic receptors with catecholamines leads to desensitization of their ability to activate cAMP accumulation. However, little is known about the relationship between these changes and possible alterations in physiological responses. We have used isolated adipocytes prepared from NEDH rats harboring pheochromocytomas, a norepinephrine-secreting tumor, to address this question. As expected, there was a decrease in the ability of isoproterenol to maximally activate cAMP accumulation in adipocytes from rat harboring pheochromocytoma [323 +/- 107 vs. 707 +/- 145 pmol/10(5) cells.min (mean +/- SD) in controls]. This change was associated with an increase in the EC50 of isoproterenol for activation of cAMP-dependent protein kinase (5.8 X 10(-8) vs. 2.4 X 10(-8) M in controls) and a decrease in maximal activation of the kinase (38 +/- 16% vs. 77 +/- 14% in controls). For lipolysis there was a loss in sensitivity to isoproterenol but no change in maximal lipolytic rate in the adipocytes from rats harboring pheochromocytoma. For both groups there was a similar relationship between kinase activation and lipolysis; maximal lipolysis had already occurred for protein kinase-A activity ratios less than 30%. Therefore, the blunted cAMP response in adipocytes from rats harboring pheochromocytoma did not impair the maximal lipolytic rate. These results demonstrate that adipocytes can efficiently maintain maximal lipolysis in a desensitized state because of considerable reserve in the biochemical cascade leading to the lipolytic response. In addition, our findings demonstrate that there are no regulatory changes induced by prolonged exposure to catecholamines that are distal to cAMP accumulation.
View details for Web of Science ID A1988P042000067
View details for PubMedID 2838264
View details for Web of Science ID A1988M818001893
The effect of halothane on isoproterenol-stimulated lipolysis was determined in isolated rat epididymal fat cells. The maximal lipolytic response (Emax) activated by isoproterenol was 350 +/- 61 nmol of glycerol/10(5) cells/hr with an EC50 of 5.1 X 10(-9) M. When the adipocytes were simultaneously bubbled with 2.5% halothane, the Emax decreased to 158 +/- 43 nmol of glycerol/10(5) cells/hr and the dose response curve for isoproterenol was shifted to the right (EC50 3.5 X 10(-8) M, p less than 0.05). When lipolysis was maximally stimulated with (-)-isoproterenol (10(-6)M), the inhibitory effect of halothane was found to be both dose dependent (IC50 approximately 2.5%, v/v) and reversible following washout. Neither the nonhydrolyzable cAMP analog, 8-(4-chlorophenylthio) adenosine 3',5'-cyclic monophosphate (2 X 10(-3)M), nor forskolin (10(-6) M) was able to normalize lipolysis in the presence of halothane. The activation of cAMP-dependent protein kinase (EC 188.8.131.52) activity by isoproterenol was not different in halothane-exposed cells when compared to unexposed cells. When control adipocytes were exposed to isoproterenol (10(-6) M), there was a 2.5-fold increase in the activity of hormone-sensitive lipase (EC 184.108.40.206) from 0.64 +/- 0.13 to 1.53 +/- 0.32 pkat (pmol/sec) per mg (p less than 0.005, n = 10). However, in the presence of halothane (2.5%, v/v) isoproterenol stimulation of hormone-sensitive lipase was attenuated by 50% to values of 1.06 +/- 0.23 pkat/mg (p less than 0.01, n = 10). Halothane had no direct inhibitory effect on hormone-sensitive lipase since this enzyme's activity was unaffected when homogenates of isoproterenol-stimulated control cells were incubated with halothane. These studies suggest that halothane impairs the activation of hormone-sensitive lipase by cAMP-dependent protein kinase and in this manner inhibits beta-adrenergic-stimulated lipolysis.
View details for Web of Science ID A1988M717900014
View details for PubMedID 3352597
To investigate the cardiac muscle damage observed in pheochromocytoma, New England Deaconness Hospital rats were implanted subcutaneously with a transplantable pheochromocytoma. The tumor was evident 4 weeks after transplantation. Approximately 5-6 weeks after transplant, systolic blood pressure was significantly increased in tumor-bearing animals (183 +/- 13 vs 119 +/- 7 in controls). At this time a cardiomyopathy with the following features was apparent in the tumor-bearing animals: multifocal lesions of enhanced interstitial and replacement fibrosis; granularity of the cytoplasm and contraction band necrosis; and mixed inflammatory infiltrates. Using a morphological scoring system from 0 (no cardiac damage) to 3 (complete involvement of the ventricular cross section studied), the pheochromocytoma animals had a cardiomyopathy score of 1.8 +/- 0.1, which is significantly greater than that found in age- and sex-matched controls: 0.4 +/- 0.1, p less than .001. A significant increase in the wet heart weights (1.28 +/- 0.07 vs. 1.12 +/- 0.04 in controls) was also observed in these animals, indicating the possibility of cardiac hypertrophy in the pheochromocytoma rats. There was a marked decrease in sensitivity to isoproterenol in isolated, electrically driven left atrial strips from pheochromocytoma rats. Isoproterenol's EC50 increased eightfold from 1.5 +/- 0.6 x 10(-8) M in controls to 1.3 +/- 0.4 x 10(-7) M in left atrial strips from the pheochromocytoma rats. However, there was no difference in maximal contractile response to isoproterenol in either the left atrial strips or in right or left ventricular papillary muscle strips. Also, there was no change in responsiveness of either left atrial or right ventricular muscle strips from pheochromocytoma hearts to contraction induced by 3.75 mM calcium chloride. However, the contractile response to calcium was enhanced in left ventricular papillary muscle from tumor-bearing animals (808 +/- 195 vs 372 +/- 101 mg tension in controls, p less than 0.05). These results demonstrate a catecholamine-induced cardiomyopathy in hearts from pheochromocytoma-bearing rats. Furthermore, the results demonstrate a functional beta-adrenergic receptor desensitization in isolated left atrial strips from tumor-bearing rats, whereas maximal contraction of heart muscle, induced by either isoproterenol or calcium chloride, remains intact.
View details for PubMedID 3207483
In this study the effect of two drugs [etomoxir and nicotinic acid (NA)] on plasma glucose, free-fatty acid (FFA), and triglyceride (TG) concentrations was determined in rats with streptozocin (STZ)-induced diabetes. The two compounds modify FFA metabolism by different mechanisms, etomoxir (ethyl-2-[6-(4-cholorophenoxyl)-hexyl]oxirane-2-carboxylate) by inhibiting hepatic fatty acid oxidation, and NA by inhibiting lipolysis in adipose tissue. Diabetes was induced in male Sprague-Dawley rats, weighing approximately 400 g, by STZ injection (30 mg/kg i.v.), and the metabolic effects of the two drugs were studied 7-10 days later. The acute administration of either etomoxir or NA lowered plasma glucose concentrations in diabetic rats by approximately 150 mg/dl (P less than .001) in 4 h. However, the two drugs differed dramatically in their effects on plasma FFA and TG concentrations. Specifically, etomoxir produced striking increases in plasma FFA and TG concentrations, whereas NA administration caused a marked decrease. However, when NA was given in conjunction with etomoxir, NA prevented the increase in plasma FFA and TG concentration seen with etomoxir; the combination of NA and etomoxir approximately doubled the decrease in plasma glucose concentration produced by NA or etomoxir when given alone. Because plasma insulin concentrations did not change in response to either drug, whether administered singly or in combination, these metabolic effects do not result from a change in insulin secretion. These results suggest that modulation of FFA metabolism at the level of the adipocyte or the liver can have dramatic effects on carbohydrate and lipid metabolism.
View details for PubMedID 3275556
Both nicotinic acid (NA) and the adenosine receptor agonist phenylisopropyladenosine (PIA) are potent antilipolytic agents. We have evaluated the ability of these compounds to lower plasma glucose concentration in 450-g male diabetic rats. Diabetes was induced by intravenous streptozotocin, and the rats were studied 7-10 days later. Mean (+/- SE) fasting glucose decreased 4 h after subcutaneous injections of PIA at 0 and 2 h. A similar change in plasma glucose level was also seen in rats injected with NA. The decrease in the concentration of plasma glucose in both instances was preceded by marked sustained reductions in plasma free fatty acid (FFA) concentrations; FFA decreased in PIA-injected rats and in response to NA. With injection of normal saline, neither plasma glucose nor FFA concentrations decreased in diabetic rats. There was no change in the plasma insulin concentration of rats that had hypoglycemic responses to PIA or NA. In vitro glucose uptake was determined in isolated adipocytes, and both PIA and NA were shown to increase basal and maximal insulin-stimulated glucose uptake. The stimulating effect of the two compounds was similar, and the magnitude of the effect was comparable in adipocytes from either normal or diabetic rats. As a result, neither NA nor PIA could restore the defects in glucose transport to normal in adipocytes from diabetic rats. Insulin-stimulated glucose uptake was assessed in vivo by determining the steady-state glucose response of diabetic rats to a continuous infusion of insulin and glucose and was found to be significantly enhanced in response to NA compared with NaCl.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for PubMedID 2962514
The DDT1-MF2 cell line is a transformed smooth muscle cell line which is known to possess both alpha 1 and beta 2 adrenergic receptors. We have utilized these cells to compare the effects of epinephrine pretreatment on the functional capabilities of these two different adrenergic receptors. Pretreatment of the cells grown in suspension with 10(-7) M epinephrine for 6 hr resulted in desensitization of beta receptor stimulated cyclic AMP accumulation. The maximal response to isoproterenol was decreased to 46 +/- 6% of the value in controls (P less than 0.05); there was also a decrease in the sensitivity of the cells to isoproterenol (log EC50 = -6.65 +/- 0.22 vs -7.26 +/- 0.11 in controls, P less than 0.05). Also, there was a decrease in the number of beta receptors from 257 +/- 29 to 163 +/- 22 fmol/mg protein. In contrast, pretreatment with 10(-6) M epinephrine for 6 hr failed to induce a loss of sensitivity in the ability of the alpha 1 receptor agonist phenylephrine to stimulate inositol triphosphate accumulation (log EC50 = -5.59 +/- 0.18 vs -5.42 +/- 0.44 in control cells). A 2-fold increase in basal inositol monophosphate accumulation was observed after epinephrine pretreatment (P less than 0.05); however, there was no change in maximal phenylephrine-stimulated inositol monophosphate accumulation in these cells. There was a small decrease in the alpha 1 receptor number after epinephrine pretreatment (Bmax = 457 +/- 89 fmol/mg protein vs 540 +/- 94 in control cells, P less than 0.05). In contrast to epinephrine pretreatment, pretreatment of cells in suspension with 10(-7) M 12-O-tetradecanoylphorbol-13-acetate (TPA) for 15 min resulted in a nearly complete blunting in the ability of both norepinephrine and phenylephrine to stimulate inositol phosphate accumulation: after norepinephrine stimulation, 774 +/- 34 dpm in TPA-pretreated cells vs 2590 +/- 10 in control cells; inositol monophosphate accumulation after phenylephrine stimulation 576 +/- 25 dpm in TPA-pretreated cells vs 1660 +/- 27 in control cells. Basal levels of inositol monophosphate remained unchanged at 544 +/- 28 dpm vs 505 +/- 31 in TPA-pretreated cells compared to control cells. These data indicate that protein kinase C may exert a negative feedback control on the alpha 1 receptor in these cells and that direct activation of protein kinase C by phorbol esters may have a different effect on the alpha 1 adrenergic receptor system in DDT1-MF2 cells than does prolonged exposure to epinephrine.
View details for Web of Science ID A1987L357700024
View details for PubMedID 2825723
Pheochromocytomas are rare tumors, typically found in the adrenal medulla, which may secrete large quantities of catecholamines such as dopamine, norepinephrine, and epinephrine. Pheochromocytomas are usually associated with hypertension, which may be severe. Relatively little is known about the cardiovascular manifestations of pheochromocytoma because of the rarity of the disease and the difficulty of ethically studying patients with this explosive and potentially lethal disease. New England Deaconess rats (a Wistar-derived strain) harbor a transplantable pheochromocytoma which has many features reminiscent of the human disease. These rats develop markedly elevated concentrations of norepinephrine that are associated with severe hypertension, desensitization of alpha and beta adrenergically mediated responses, and catecholamine-induced cardiomyopathy. This paper briefly reviews work undertaken in the author's laboratory on the mechanisms of these alterations in the cardiovascular system of rats harboring pheochromocytoma.
View details for Web of Science ID A1987L576600009
View details for PubMedID 2831003
To determine if hypertension could be produced in normal rats by feeding them a fructose-enriched diet, Sprague-Dawley rats were fed either normal chow or a diet containing 66% fructose as a percentage of total calories for approximately 2 weeks. At the end of this period systolic blood pressure had increased from 124 +/- 2 to 145 +/- 2 (SEM) mm Hg in the fructose-fed rats, whereas no change occurred in the control group. In addition, hyperinsulinemia and hypertriglyceridemia were associated with hypertension in fructose-fed rats. The addition of clonidine to the drinking water inhibited fructose-induced hypertension, but not the increase in plasma insulin or triglyceride concentration seen in fructose-fed rats. Thus, the metabolic changes associated with fructose-induced hypertension are unlikely to be secondary to an increase in sympathetic activity. Whether or not this is also true of the hypertension remains to be clarified.
View details for Web of Science ID A1987M462800008
View details for PubMedID 3311990
We have previously demonstrated a progressive loss in the ability of the beta-receptor agonist isoproterenol to relax veins with increasing age. In this study the influence of age on the responsiveness of medium-sized veins to local infusions of nitroglycerin was studied in two groups of 15 healthy male volunteers using the dorsal hand vein compliance technique. A dorsal hand vein was preconstricted with submaximally effective doses of phenylephrine and a dose-response curve with nitroglycerin was established. The nitroglycerin dose that caused a 50% venodilation ranged from 0.7 to 22.4 ng/min (geometric mean 3.6 ng/min) in the younger group (aged 19 to 29 years; mean +/- SD 23 +/- 3 years) and from 0.2 to 17.9 ng/min (geometric mean 3.6 ng/min) in the older subjects (aged 50 to 74 years; mean +/- SD 63 +/- 7 years) (P = 0.49 between geometric means). The mean (+/- SD) maximal venodilation, based on the pretreatment baseline, was 103% +/- 65% in the younger and 125% +/- 64% in the older subjects (P = 0.18). These results indicate that there is no age-related change in venous responsiveness to nitroglycerin.
View details for Web of Science ID A1987K962200008
View details for PubMedID 3119271
It is proposed that abnormalities of glucose and insulin metabolism have a role in both the aetiology and the clinical course of hypertension. There is resistance to insulin-stimulated glucose uptake in patients with hypertension, which is associated with glucose intolerance and hyperinsulinaemia. Hyperinsulinaemia could contribute to hypertension by stimulating the activity of the sympathetic nervous system and kidney sodium and volume reabsorption. Glucose intolerance and hyperinsulinaemia have been identified as risk factors for coronary artery disease, and their presence may help explain why the frequency of this disease has not been reduced by treatment of hypertension. The fact that several antihypertensive drugs deleteriously affect glucose, insulin, and lipid metabolism makes it even more important to consider these factors in the treatment of high blood pressure.
View details for Web of Science ID A1987J690800013
View details for PubMedID 2887735
The ability of a number of hormones to activate cellular responses in a variety of cells declines with age. The mechanisms responsible for these alterations are complex and incompletely understood. Rat adipocytes have served as an important model to study blunted responses to stimulatory hormones which function by activating cAMP accumulation. We have previously found that the blunted lipolytic response of adipocytes from older rats to the beta adrenergic receptor agonist isoproterenol appeared to be due to a lessened ability of isoproterenol to activate cAMP accumulation. Further, the blunted response to isoproterenol was apparently caused by an accentuated inhibition of lipolysis, mediated by adenosine receptors activated by endogenously released adenosine. The present studies were designed to test and extend those conclusions. We have utilized forskolin to augment the cAMP accumulation that occurs in the presence of isoproterenol. Isoproterenol-activated lipolysis was greater in adipocytes from 2 month old rats compared with those from 12 month old rats (603 +/- 32 vs 450 +/- 29 nmol/10(5) cells/hr, P less than 0.01). However, in the presence of forskolin (10(-6) M), there was no significant difference in the response to isoproterenol between the two groups (646 +/- 23 vs 615 +/- 29 nmoles/10(5) cells/hr). As we had seen previously, the adenosine receptor agonist phenylisopropyladenosine more effectively inhibited lipolysis in the adipocytes from older rats. We now also find that PGE1 more efficaciously inhibits lipolysis in the cells from older rats. These data confirm that diminished cAMP accumulation in adipocytes from older rats appears to be a rate-limiting alteration in the regulation of lipolysis.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for PubMedID 2822560
Hypertension due to pheochromocytoma is generally considered to be a straightforward, direct consequence of the elevated concentrations of circulating catecholamines. However, clonidine, a centrally acting antihypertensive drug, has been reported to lower blood pressure in patients with pheochromocytoma, suggesting the possibility that the sympathetic nervous system is involved in the maintenance of hypertension in this disease. We have investigated this possibility in New England Deaconess Hospital rats harboring a transplantable pheochromocytoma that secretes norepinephrine and dopamine. Both clonidine and chlorisondamine, a ganglionic blocker, markedly decreased blood pressure in tumor-bearing rats. However, in other rats made acutely hypertensive with a norepinephrine infusion, neither clonidine nor chlorisondamine decreased blood pressure. This result indicates that in an acute model of hypertension, where baroreflex mechanisms have likely withdrawn sympathetic tone, neither clonidine nor chlorisondamine had nonspecific antihypertensive effects. A central nervous system site of action for the antihypertensive effect of clonidine in the rats harboring pheochromocytoma was suggested by the observation that the opiate antagonist naloxone both reversed and prevented clonidine's effect on blood pressure. Prazosin and yohimbine were utilized to determine the respective contributions of alpha-1 and alpha-2 adrenergic receptors in the maintenance of hypertension in rats harboring pheochromocytoma. Both drugs markedly lowered blood pressure in these rats. Our data suggest that both the sympathetic nervous system and circulating catecholamines are involved in the maintenance of hypertension due to pheochromocytoma.
View details for Web of Science ID A1987H936900018
View details for PubMedID 3598906
New England Deaconness Hospital rats harboring a transplantable pheochromocytoma exhibit plasma norepinephrine concentrations 20-fold higher than controls. A cardiomyopathy (CM) characterized by multifocal areas of interstitial and replacement fibrosis, mixed inflammatory infiltrates and contraction band necrosis is evident 35 to 45 days after tumor implantation. Using a morphological scoring system of 0 (no cardiac damage) to 3 (involvement of almost the complete ventricular cross-section sampled), a CM score of 1.8 +/- 0.1 was found in rats harboring pheochromocytoma, a significant increase over that in age- and sex-matched controls (0.4 +/- 0.1, P less than .001). The pheochromocytoma rats also had hypertension (systolic blood pressure = 182 +/- 4 vs. 131 +/- 2 mm Hg in controls, P less than .001). In an effort to prevent the CM, rats harboring pheochromocytoma were treated with either the beta receptor antagonist timolol, the alpha receptor antagonists phentolamine or phenoxybenzamine or the nonspecific vasodilator hydralazine. Hydralazine normalized systolic blood pressure (135 +/- 6 mm Hg), whereas timolol (144 +/- 5 mm Hg), phenoxybenzamine (166 +/- 5 mm Hg) or phentolamine (154 +/- 10 mm Hg) only moderately decreased blood pressure in rats harboring pheochromocytoma. Hydralazine had no effect on CM score (1.8 +/- 0.1). Timolol markedly attenuated the CM score (0.6 +/- 0.1), whereas the alpha adrenergic antagonists were not as effective (phenoxybenzamine CM score = 1.3 +/- 0.2; phentolamine CM score = 1.7 +/- 0.2). Furthermore, timolol prevented desensitization of beta adrenergic receptor-mediated contraction in the hearts of rats harboring pheochromocytoma.(ABSTRACT TRUNCATED AT 250 WORDS)
View details for Web of Science ID A1987G903800052
View details for PubMedID 2883296
Beta adrenergic relaxation of vascular smooth muscle, mediated by cyclic AMP, is blunted with age in a variety of experimental animals. The applicability of these observations to man is uncertain. The dorsal hand vein technique provides an excellent method to examine the direct effects of aging on vascular responsiveness. Thirty-nine healthy male volunteers over the age range of 19 to 79 were studied. No differences in vascular responsiveness to phenylephrine, an alpha adrenergic agonist, were found for either the ED50 (dose producing 50% vasoconstriction) or Emax (maximum vasoconstriction attained). In marked contrast, vascular relaxation induced by isoproterenol, a beta adrenergic agonist, was significantly different in both the ED50 (dose producing 50% of maximum relaxation from a preconstricted state) and Emax (maximum relaxation attained). ED50 +/- S.E.M. for the youngest and oldest deciles were 8.9 +/- 2.3 and 60 +/- 17.0 ng/min, respectively (P less than .05); Emax +/- S.E.M. were 96.7 +/- 3.3 and 37.7 +/- 8.7%, respectively (P less than .001). Nitroglycerin, a smooth muscle relaxant whose effects are not mediated through the cyclic AMP system, was also used to examine the specificity of this blunted response to isoproterenol. Almost complete relaxation was achieved with the infusion of nitroglycerin in the older group. These results suggest that aging is associated with a specific decrease in beta adrenoreceptor-mediated vascular relaxation.
View details for Web of Science ID A1986F424700028
View details for PubMedID 3025419
Desensitization of smooth muscle contraction was studied in aortic ring segments obtained from New England Deaconness Hospital rats harboring pheochromocytomas, a norepinephrine-secreting tumor. Rats were studied 5 to 6 weeks after implantation of the pheochromocytoma, by which time severe hypertension had developed. Aortic ring segments from the pheochromocytoma rats were significantly less sensitive to the alpha-1 adrenergic agonist phenylephrine [log10 (ED50) = -7.21 +/- 0.09 vs. -7.63 +/- 0.11 in controls). In addition, the maximal force of contraction induced by phenylephrine was decreased in the aortas from pheochromocytoma rats (1.31 +/- 0.15 g) compared to controls (2.17 +/- 0.23 g). The potency of the thromboxane A2 receptor agonist U-46,619 was decreased in the aortic ring segments from pheochromocytoma rats compared to controls, although it elicited a similar maximal force of contraction. Desensitization of alpha receptor-mediated contraction was prevented by treating the pheochromocytoma-bearing rats with the reversible alpha adrenergic antagonist phentolamine (200 micrograms/kg/hr) via osmotic minipumps for 2 weeks. However, phentolamine did not decrease the hypertension in these rats. Also, large doses of the irreversible alpha adrenergic antagonist phenoxybenzamine (4 mg/kg/day i.p.) did not decrease blood pressure in rats harboring pheochromocytoma or did the drug completely block aortic alpha receptors in these rats as it did in controls. The results indicate that pheochromocytoma induces heterologous desensitization of smooth muscle contraction in rat aorta. The desensitization is due to direct effects of catecholamines unrelated to hypertension. The New England Deaconess Hospital rat harboring pheochromocytoma is an interesting model to study the effects of high concentrations of plasma catecholamines on smooth muscle contraction.
View details for Web of Science ID A1986D601100002
View details for PubMedID 3016236
View details for Web of Science ID A1986A294901978
The effects of development on adrenergic regulation of glycogenolysis were studied in rat liver. In isolated hepatocytes, the activation of glycogen phosphorylase by alpha-adrenergic stimulation decreased moderately with advancing age. However, activation by beta-adrenergic receptors more markedly declined and almost disappeared in isolated hepatocytes from 6-month-old rats. Furthermore, the ability to glucagon to stimulate phosphorylase activity and cAMP generation was found to decrease with increasing age. The age-related changes in the pattern of stimulation of glycogen phosphorylase by catecholamines in isolated hepatocytes were accompanied by parallels changes in the numbers of alpha 1- and beta-adrenoceptors in membranes prepared from the isolated hepatocytes. A progressive decrease in the total number of alpha 1-receptors measured with [3H]-prazosin and beta-receptors measured with [125I]cyanopindolol (CYP) was found with increasing age. The loss of beta-adrenergic receptors was much more dramatic. Our results suggest that age-related alterations of hepatic glycogen phosphorylase activation by catecholamines may in part be explained by the changes in the expression adrenergic receptors.
View details for Web of Science ID A1986A418800005
View details for PubMedID 3007877
Desensitization of alpha-1 receptor-mediated smooth muscle contraction was studied in rabbit aorta. Incubation of rabbit aorta ring segments with epinephrine (10(-6) M) for 7 hr resulted in a 10-fold loss in sensitivity of the tissue to alpha-1 adrenergic receptor-mediated contraction with no change in maximal force of contraction. This loss in sensitivity was specific for alpha-1 receptor-mediated contraction because responses to histamine and serotonin were unchanged in these aortas. Conversely, prolonged exposure of vessels to histamine (10(-5) M) led to desensitization of histamine-mediated contraction without altering responses to alpha-1 receptor stimulation. Using [125I] BE2254, a potent alpha-1 receptor antagonist, the loss in sensitivity to catecholamines was found not to be mediated by down-regulation of alpha-1 receptors nor by a loss in their affinity for epinephrine. However, desensitization was associated with a blunting of alpha-1 receptor stimulation of phosphatidylinositol turnover. These results suggest that desensitization of alpha-1 receptor-mediated contraction in rabbit aorta does not appear to be mediated by changes in receptor number or affinity but may involve alterations in receptor coupling.
View details for Web of Science ID A1985AMB6300021
View details for PubMedID 2989501
View details for Web of Science ID A1984SF05400260
Alpha-adrenergic receptors may play an important role in regulating vascular tone and reactivity. To study alpha-adrenergic receptors in blood vessels, we have developed a method to characterize and quantitate alpha-adrenergic receptors in a particulate fraction of individual rabbit aortas using the high specific activity alpha antagonist [125I] BE2254. [125I] BE2254 specifically labels a single class of binding sites with a dissociation constant of 286 pM and a maximal binding capacity of 16.7 fmoles/mg protein. Catecholamines compete for [125I] BE2254 binding stereospecifically and with the characteristic alpha-adrenergic potency series of (-)epinephrine greater than or equal to (-)norepinephrine much greater than (-)isoproterenol. The alpha 1-selective antagonist prazosin (KD = 0.7 nM) is much more potent in competing for [125I] BE2254 binding than is the alpha 2-selective antagonist yohimbine (KD = 1000 nM), which suggests that the alpha adrenergic receptor identified is predominantly of the alpha 1 subtype. Also, the dissociation constants from these binding studies were in good agreement with those reported in rabbit aorta from classical pharmacological experiments where contraction was found to be mediated via alpha 1 receptors. This extension of radioligand binding techniques to individual rabbit aortas should simplify the study of vascular alpha adrenergic receptor regulation, and provide a basis for broadening the understanding of vascular alpha adrenergic receptors.
View details for Web of Science ID A1984RZ09800005
View details for PubMedID 6321870
View details for Web of Science ID A1983QM89400097
View details for Web of Science ID A1983QD23402091
View details for Web of Science ID A1982PH11400834
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