Robert Castro

All Publications

• Role of Oral Mucosal Fluid and Electrolyte Absorption and Secretion in Dry Mouth. The Chinese journal of dental research : the official journal of the Scientific Section of the Chinese Stomatological Association (CSA) Zhang, G. H., Castro, R. 2015; 18 (3): 135-154

  Abstract

  Dry mouth is induced by dehydration of the oral mucosa, resulting from an imbalance of fluid supply and clearance within the oral cavity. Saliva is the major source of oral mucosal fluid, whereas oral fluid clearance includes evaporation and swallowing. Oral mucosal fluid absorption has been suggested to play a critical role in oral fluid clearance; over-absorption of water and ions across the oral mucosa under certain conditions may be a major component for oral fluid imbalance, leading to mucosal dehydration. While numerous studies have confirmed that the oral mucosa absorbs fluid and electrolytes, the pathways and mechanisms mediating the absorption remain undefined. The transcellular pathway regulating oral mucosal epithelial absorption includes aquaporins, epithelial Na+ channel and/or Na+/H+ exchanger, whereas the paracellular transport is likely to be mediated by tight junctions. The regulatory mechanisms of these pathways require further elucidation. It remains unclear whether the oral mucosa also secretes fluid and ions into the oral cavity. Although intercellular lipids secreted by epithelial cells form the major barrier to paracellular water and ion transport, the role and regulation of these lipids in oral mucosal hydration in physiological and pathological conditions need further investigation. Delineation of these mechanisms will be conducive to the development of preventive and therapeutic interventions for dry mouth.

  View details for PubMedID 26485506

• The Joint Admission Medical Program: A Statewide Approach to Expanding Medical Education and Career Opportunities for Disadvantaged Students ACADEMIC MEDICINE Dalley, B., Podawiltz, A., Castro, R., Fallon, K., Kott, M., Rabek, J., Richardson, J., Thomson, W., Ferry, P., Mabry, B., Hermesmeyer, P., Smith, Q. 2009; 84 (10): 1373-1382

  Abstract

  In 2003, Texas initiated an experiment to address enrollment disparities in its medical schools. With bipartisan support from key Texas legislators, funding was allocated in 2002 to establish the Joint Admission Medical Program (JAMP). Texas' then eight medical schools created, through JAMP, a partnership with the state's 31 public and 34 private undergraduate colleges and universities. Cognizant of legal prohibitions against reliance solely on race or ethnicity in promoting diversity, JAMP is designed to enhance opportunities for economically disadvantaged students from across the state, including those from (1) rural and remote areas of the state, and (2) institutions that have historically sent few students to medical school. Now in its seventh year of operation, JAMP is overseen by a council with representatives from all nine Texas medical schools. For the six years-2003 to 2008-for which data are available, indicators of JAMP performance can be seen in (1) the numbers of applicants to JAMP (1,230 applicants in the first six years), (2) levels of JAMP participation (480 participants), and (3) matriculation of JAMP participants into medical schools (164 of 288 of those accepted into the program in the years 2003-2006).The authors provide a brief history of JAMP, describe its structure and operation, summarize objective performance data, and identify some of the challenges still faced. These include increasing the participation of students from underrepresented minority groups within the legal structure for the program, and fostering substantive participation in JAMP by all of Texas' undergraduate institutions. A focused effort is under way to strengthen the evaluative aspects of JAMP so that more comprehensive data, including subjective evaluation data from participants, can be shared with colleagues in the future.

  View details for DOI 10.1097/ACM.0b013e3181b6c76b

  View details for Web of Science ID 000207786100018

  View details for PubMedID 19881424

• Regulation of Epithelial Na+ Channel (ENaC) in the Salivary Cell Line SMG-C6 EXPERIMENTAL BIOLOGY AND MEDICINE Vasquez, M. M., Mustafa, S. B., Choudary, A., Seidner, S. R., Castro, R. 2009; 234 (5): 522-531

  Abstract

  Glucocorticoids and mineralocorticoids modulate Na+ transport via epithelial Na+ channels (ENaC). The rat submandibular epithelial cell line, SMG-C6, expresses alpha-ENaC mRNA and protein and exhibits amiloride-sensitive Na+ transport when grown in low-serum (2.5%) defined medium, therefore, we examined the effects of altering the composition of the SMG-C6 cell growth medium on ENaC expression and function. No differences in basal or amiloride-sensitive short-circuit current (Isc) were measured across SMG-C6 monolayers grown in the absence of thyroid hormone, insulin, transferrin, or EGF. In the absence of hydrocortisone, basal and amiloride-sensitive Isc significantly decreased. Similarly, monolayers grown in 10% serum-supplemented medium had lower basal Isc and no response to amiloride. Adding hydrocortisone (1.1 microM) to either the low or 10% serum medium increased basal and amiloride-sensitive Isc, which was blocked by RU486, the glucocorticoid and progesterone receptor antagonist. Aldosterone also induced an increase in alpha-ENaC expression and Na+ transport, which was also blocked by RU486 but not by the mineralocorticoid receptor antagonist spironolactone. Thus, in the SMG-C6 cell line, hydrocortisone and aldosterone increased ENaC expression and basal epithelial Na+ transport. The absence of endogenous ENaC expression in culture conditions devoid of steroids makes the properties of this cell line an excellent model for investigating pathways regulating ENaC expression and Na+ transport.

  View details for DOI 10.3181/0806-RM-209

  View details for Web of Science ID 000265626800006

  View details for PubMedID 19234051

• Induction of Serum- and Glucocorticoid-Induced Kinase-1 (SGK1) by cAMP Regulates Increases in alpha-ENaC JOURNAL OF CELLULAR PHYSIOLOGY Vasquez, M. M., Castro, R., Seidner, S. R., Henson, B. M., Ashton, D. J., Mustafa, S. B. 2008; 217 (3): 632-642

  Abstract

  Alpha-ENaC expression and activity is regulated by a variety of hormones including beta-adrenergic agonists via the second messenger cAMP. We evaluated the early intermediate pathways involved in the up-regulation of SGK1 by DbcAMP and whether SGK1 is a prerequisite for induction of alpha-ENaC expression. Submandibular gland epithelial (SMG-C6) cells treated with DbcAMP (1 mM) induced both SGK1 mRNA and protein expression. DbcAMP-stimulated SGK1 mRNA expression was decreased by actinomycin D and mRNA and protein expressions were attenuated by PKA inhibitors (H-89 and KT5720). Inhibition of PI3-K with either LY294002 or dominant negative PI3-K reduced DbcAMP-stimulated SGK1 protein and mRNA levels, attenuated the phosphorylation of CREB (a cAMP-activated transcription factor) and decreased alpha-ENaC protein levels and Na(+) transport. In addition, the combination of PKA inhibitors with dominant negative PI3-K synergistically inhibited DbcAMP-induced Na(+) transport. Inhibition of SGK1 expression by siRNA decreased but did not obliterate DbcAMP-induced alpha-ENaC expression. Thus, in a cell line which endogenously exhibits minimal alpha-ENaC expression, induction of SGK1 by DbcAMP occurs via the PI3-K and PKA pathways. Increased alpha-ENaC levels and function are partly dependent upon the early induction of SGK1 expression.

  View details for DOI 10.1002/jcp.21534

  View details for Web of Science ID 000260981300009

  View details for PubMedID 18615584

• Inhibition of Ca2+ influx by surfactant in NR8383 alveolar macrophages INFLAMMATION RESEARCH Castro, R., Sun, X. H., Liu, X., Martinez, J. R., Zhang, G. H. 2008; 57 (10): 489-496

  Abstract

  Pulmonary surfactants reduce alveolar surface tension and alter inflammatory cell function. We studied the effects of surfactant preparations on Ca2+ influx regulated by protein kinase C (PKC) and mitogen-activated protein kinases (MAPK) and cytokine secretion in the alveolar macrophage (AM) cell line NR8383.Fura-2-loaded AMs were stimulated with zymosan (200 microg/ml), 1,2-dioctanoyl-sn-glycerol (DOG, 20 microM) or C6-ceramide (C6C, 10 microM) in the presence of exogenous surfactants (beractant, calfactant or colfosceril) or surfactant phospholipid (dipalmitoyl phosphatidylcholine, DPPC), at 250 microg/ml phospholipid and changes in cytosolic free Ca2+ (Delta[Ca2+]i) and cytokines were measured.Zymosan-induced Delta[Ca2+]i (117 +/- 5 nM) at 3 min was reduced (p <0.001) by beractant (50 +/- 6 nM), colfosceril (61 +/- 2 nM), calfactant (46 +/- 5 nM), and DPPC (52 +/- 5 nM). Beractant inhibited the Delta[Ca2+]i by PKC stimulation with DOG and all preparations reduced the MAPK-induced Ca2+ influx by C6C. Beractant and Ca2+ channel blocker SKF 96365 (10 microM) together abolished the zymosan-stimulated Delta[Ca2+]i. Zymosan-stimulated TNF-alpha and IL-1beta secretion was also inhibited by surfactant pretreatment.These results indicate that exogenous surfactant inhibits Ca2+ influx and cytokine secretion in zymosan-stimulated AMs. This anti-inflammatory activity may be through an interaction with downstream signaling elements or Ca2+ channels.

  View details for DOI 10.1007/s00011-008-6214-y

  View details for Web of Science ID 000261984800008

  View details for PubMedID 18827971

• Protein kinase A and mitogen-activated protein kinase pathways mediate cAMP induction of alpha-epithelial Na+ channels (alpha-ENaC) JOURNAL OF CELLULAR PHYSIOLOGY Mustafa, S. B., Castro, R., Falck, A. J., Petershack, J. A., Henson, B. M., Mendoza, Y. M., Choudary, A., Seidner, S. R. 2008; 215 (1): 101-110

  Abstract

  A major mechanism for Na+ transport across epithelia occurs through epithelial Na+ channels (ENaC). ENaC is a multimeric channel consisting of three subunits (alpha, beta, and gamma). The alpha-subunit is critical for ENaC function. In specific culture conditions, the rat submandibular gland epithelial cell line (SMG-C6) demonstrates minimal Na+ transport properties and exposure to dibutyryl cAMP (DbcAMP) for up to 48 h caused an elevation of alpha-ENaC mRNA and protein expression and amiloride-sensitive short-circuit current (I(SC)). Here we examined the early signaling pathways evoked by DbcAMP which contribute to the eventual increase in Na+ transport is present. Treatment with either of the protein kinase A (PKA) inhibitors KT5720 or H-89 followed by exposure to 1 mM DbcAMP for 24 h markedly attenuated DbcAMP-induced alpha-ENaC protein formation and I(SC). Exposure of SMG-C6 cells to 1 mM DbcAMP induced a rapid, transient phosphorylation of the cAMP response element binding protein (CREB). This response was attenuated in the presence of either KT5720 or H-89. Dominant-negative CREB decreased DbcAMP-induced alpha-ENaC expression. Suppression of the extracellular signal-regulated protein kinase (ERK 1,2) with PD98059 or the p38 mitogen-activated protein kinase (MAPK) pathway with SB203580 reduced DbcAMP-induced alpha-ENaC protein levels in SMG-C6 cells. DbcAMP-induced phosphorylation of CREB was markedly attenuated by PD98059 or SB203580. DbcAMP-induced activation of the either the p38 or the ERK 1,2 MAPK pathways was abolished by either of the PKA inhibitors, H-89 or KT5720. Cross talk between these signaling pathways induced by DbcAMP via the activation of CREB appears to contribute to increased levels of alpha-ENaC observed after 24 h of treatment in SMG-C6 epithelial cells.

  View details for DOI 10.1002/jcp.21291

  View details for Web of Science ID 000254427900011

  View details for PubMedID 17960568

• Immunosuppressive properties of surfactant in alveolar macrophage NR8383 INFLAMMATION RESEARCH Kerecman, J., Mustafa, S. B., Vasquez, M. M., Dixon, P. S., Castro, R. 2008; 57 (3): 118-125

  Abstract

  To evaluate the anti-inflammatory effects of exogenous surfactants and surfactant phospholipid without surfactant proteins (SP-A and SP-D) on the lipopolysaccharide- (LPS) stimulated rat alveolar macrophage (AM) cell line NR8383.Exogenous surfactants (beractant, calfactant or colfosceril) and surfactant phospholipid (dipalmitoyl phosphatidylcholine, DPPC), standardized to phospholipid content of 25-1,000 microg/ml were incubated with LPS- (1 microg/ml) stimulated NR8383 AMs.TNF-alpha and IL-1beta secretion and nitric oxide (NO) formation following LPS stimulation were inhibited by treatment with surfactants or DPPC. Furthermore, LPS-dependent NO production and iNOS protein levels were significantly suppressed in cells pretreated for one hour with beractant compared to beractant added simultaneously with or following LPS. Additionally, LPS-stimulated oxidative burst, measured by flow cytometry, was significantly decreased by beractant. Finally, beractant inhibited the translocation of NF-kappaB from cytoplasmic into nuclear extract in LPS-stimulated NR8383 AMs.Exogenous surfactants and surfactant phospholipid inhibit secretion of proinflammatory cytokines and NO in NR8383 AMs. The inhibitory effects of beractant on oxygen radical and LPS-induced NO formation may result from unique mechanisms of decreasing cell signaling. The anti-inflammatory activity of surfactant products used in the treatment of neonatal respiratory distress syndrome (RDS) may depend upon the specific preparation or dose used.

  View details for DOI 10.1007/s00011-007-7212-1

  View details for Web of Science ID 000254436500005

  View details for PubMedID 18369576

• Regulation of Ca2+ signals in a parotid cell line Par-C5 ARCHIVES OF ORAL BIOLOGY Liu, X. B., Mork, A. C., Sun, X. H., Castro, R., Martinez, J. R., Zhang, G. H. 2001; 46 (12): 1141-1149

  Abstract

  The Ca(2+) signaling system in an established immortalized rat parotid acinar cell line, Par-C5, was examined using the Ca(2+)-sensitive fluorescent indicator fura-2 and by measuring inositol 1,4,5-trisphosphate (IP(3)) formation. Agonist-induced increase in intracellular Ca(2+) ([Ca(2+)](i)) by mobilization of intracellular stores and influx across the cell membrane was stimulated by acetylcholine (ACh) and ATP, whereas noradrenaline-(NA)-induced a small [Ca(2+)](i) increase mediated primarily by release from intracellular Ca(2+) stores. [Ca(2+)](i) increase by ACh and ATP was mediated through the phosphoinositide signal pathway since both agonists significantly increased 1,4,5-IP(3) formation and Ca(2+) mobilization was abolished by the phospholipase C inhibitor U73122. In Ca(2+)-free medium, ACh or ATP discharged the IP(3)-sensitive Ca(2+) store and essentially abolished subsequent [Ca(2+)](i) response to thapsigargin (TG). Exposure to ionomycin and monensin after TG induced a further mobilization of Ca(2+), suggesting IP(3)-insensitive stores are present. Furthermore, depletion of IP(3)-sensitive Ca(2+) stores by TG, ACh and ATP enhanced plasmalemmal Ca(2+)-entry pathways. Exposure to tumor necrosis factor-alpha (TNF-alpha), a cytokine associated with lymphocyte invasion of salivary epithelial cells in autoimmune disorders, significantly reduced ACh-stimulated Ca(2+) mobilization. TNF-alpha inhibitory effect on Ca(2+) mobilization was not directly due to an interaction on muscarinic receptors since ACh-induced 1,4,5-IP(3) formation was not altered. These results in the Par-C5 cell line indicate 1) [Ca(2+)](i) is regulated by muscarinic and P2Y-nucleotide receptors and partly by alpha(1)-adrenergic receptors; 2) IP(3)-sensitive and -insensitive Ca(2+) stores exist; 3) Ca(2+) influx activated by ACh, ATP or TG is mediated by the store-operated Ca(2+) entry pathway; and 4) muscarinic agonist-stimulated Ca(2+) mobilization is altered by the cytokine TNF-alpha.

  View details for Web of Science ID 000172499700007

  View details for PubMedID 11684033

• Echovirus 7 infection and necrotizing enterocolitis-like symptoms in a premature infant. Journal of perinatology Castro, R. 2000; 20 (8): 558-561

  Abstract

  Echovirus type 7 has been previously recognized as a virulent serotype in the premature neonate. However, reports of fatal disseminated infections have often been perinatally acquired from symptomatic mothers at the time of delivery. Nosocomial outbreaks in full-term and premature infants have been reported from newborn intensive care units; however, deaths attributed to Echovirus 7 in convalescing prematures are rare in the literature. We report the case of a growing premature neonate presenting with an overwhelming sepsis-like syndrome, including symptoms consistent with necrotizing enterocolitis. Despite intensive supportive care including ventilatory support, cardiovascular pharmacotherapy, and blood product administration, the infant succumbed to overwhelming Echovirus 7 infection.

  View details for PubMedID 11190599

• Ion transport in an immortalized rat submandibular cell line SMG-C6 PROCEEDINGS OF THE SOCIETY FOR EXPERIMENTAL BIOLOGY AND MEDICINE Castro, R., Barlow-Walden, L., Woodson, T., Kerecman, J. D., Zhang, G. H., Martinez, J. R. 2000; 225 (1): 39-48

  Abstract

  The immortalized rat submandibular epithelial cell line, SMG-C6, cultured on porous tissue culture supports, forms polarized, tight-junction epithelia facilitating bioelectric characterization in Ussing chambers. The SMG-C6 epithelia generated transepithelial resistances of 956+/-84Omega.cm2 and potential differences (PD) of -16.9 +/- 1.5mV (apical surface negative) with a basal short-circuit current (Isc) of 23.9 +/- 1.7 microA/cm2 (n = 69). P2 nucleotide receptor agonists, ATP or UTP, applied apically or basolaterally induced a transient increase in Isc, followed by a sustained decreased below baseline value. The peak DeltaIsc increase was partly sensitive to Cl- and K+ channel inhibitors, DPC, glibenclamide, and tetraethylammonium (TEA) and was completely abolished following Ca2+ chelation with BAPTA or bilateral substitution of gluconate for Cl-. The major component of basal Isc was sensitive to apical Na+ replacement or amiloride (half-maximal inhibitory concentration 392 nM). Following pretreatment with amiloride, ATP induced a significantly greater Isc; however, the poststimulatory decline was abolished, suggesting an ATP-induced inhibition of amiloride-sensitive Na+ transport. Consistent with the ion transport properties found in Ussing chambers, SMG-C6 cells express the rat epithelial Na+ channel alpha-subunit (alpha-rENaC). Thus, cultured SMG-C6 cells produce tight polarized epithelia on permeable support with stimulated Cl- secretory conductance and an inward Isc accounted for by amiloride-sensitive Na+ absorption.

  View details for Web of Science ID 000089590100005

  View details for PubMedID 10998197

• Regulation of (1-3)-beta-glucan-stimulated Ca2+ influx by protein kinase C in NR8383 alveolar macrophages JOURNAL OF CELLULAR BIOCHEMISTRY Mork, A. C., Sun, X. H., Liu, X. B., Rodriguez, D., Martinez, J. R., Castro, R., Zhang, G. H. 2000; 78 (1): 131-140

  Abstract

  Stimulation of (1-3)-beta-glucan receptors results in Ca(2+) influx through receptor-operated channels in alveolar macrophages (AMs), but the mechanism(s) regulating Ca(2+) influx is still undefined. In this study we investigated the role of protein kinase C (PKC) regulation of Ca(2+) influx in the NR8383 AM cell line using the particulate (1-3)-beta-glucan receptor agonist zymosan. PKC inhibition with calphostin C (CC) or bisindolymaleimide I (BSM) significantly reduced zymosan-induced Ca(2+) influx, whereas activation of PKC with phorbol-12-myristate 13-acetate (PMA) or 1, 2-dioctanoyl-sn-glycerol (DOG) mimicked zymosan, inducing a concentration-dependent Ca(2+) influx. This influx was dependent on extracellular Ca(2+) and inhibited by the receptor-operated Ca(2+) channel blocker SK&F96365, indicating that zymosan and PKC activate Ca(2+) influx through a similar pathway. NR8383 AMs expressed one new PKC isoform (delta) and two atypical PKC isoforms (iota and lambda), but conventional PKC isoforms were not present. Stimulation with zymosan resulted in a translocation of PKC-delta from the cytosol to the membrane fraction. Furthermore, inhibition of protein tyrosine kinases (PTKs) with genistein prevented zymosan-stimulated Ca(2+) influx and PKC-delta translocation. These results suggest that PKC-delta plays a critical role in regulating (1-3)-beta-glucan receptor activated Ca(2+) influx in NR8383 AMs and PKC-delta translocation is possibly dependent on PTK activity.

  View details for Web of Science ID 000087216100012

  View details for PubMedID 10797572

• DECREASED SURFACTANT DOSE-RESPONSE AFTER DELAYED ADMINISTRATION TO PRETERM RABBITS AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE Seidner, S. R., Ikegami, M., Yamada, T., Rider, E. D., Castro, R., Jobe, A. H. 1995; 152 (1): 113-120

  Abstract

  Preterm rabbits from 14 litters were delivered at 27 d gestation, anesthetized, and treated with surfactant at birth, 15 min, or 30 min after the onset of mechanical ventilation. Doses of surfactant ranging from 0 to 100 mg/kg body weight were given intratracheally and the rabbits were ventilated for 45 min after birth. Pressure-volume curves and dynamic compliances demonstrated that the dose response to surfactant progressively decreased with delayed treatment. Following surfactant treatments of 50 mg/kg at birth, 15 min, and 30 min, peak lung volumes at 35 cm H2O were increased by 49, 30, and 8.4%, respectively over those of untreated controls. Lung lavages from rabbits receiving surfactant at 30 min had significantly higher protein contents and minimum surface tensions on the Wilhelmy balance than those from rabbits treated at birth (23.1 +/- 1.1 versus 16.0 +/- 2.7 dynes/cm), and lung sections from rabbits treated at 30 min had a significantly less uniform distribution of surfactant than those from rabbits treated at birth. While increasing phospholipid concentrations may reverse the inhibition of surfactant by serum proteins in vitro, there was a progressive inability of exogenous surfactant to overcome this inhibition in vivo following delayed administration to very immature rabbits. This inability to overcome inhibition with increasing surfactant dose was associated with a less uniform distribution of surfactant following its delayed administration.

  View details for Web of Science ID A1995RH67800021

  View details for PubMedID 7599809

• VASCULAR EFFECTS ALTER EARLY-GESTATION FETAL RENAL RESPONSES TO VASOPRESSIN AMERICAN JOURNAL OF PHYSIOLOGY Ervin, M. G., Terry, K. A., Calvario, G. C., Castro, R., Ross, M. G., LEAKE, R. D., Fisher, D. A. 1994; 266 (3): R722-R729

  Abstract

  Distinct receptors mediate the vascular (V1) and renal (V2) effects of arginine vasopressin (AVP). Although ovine fetal AVP-induced antidiuresis can be demonstrated in early gestation (< 120 days; term 150 days), the early-gestation fetal renal responses to AVP are variable, including increases in urine flow and glomerular filtration rate (GFR). AVP V1 receptor predominance and/or V2 receptor system immaturity may contribute to variable early-gestation renal responses to AVP. To differentiate these possibilities, we assessed early-gestation fetal V2 receptor function in the presence and absence of V1 receptor-mediated effects by comparing the responses to AVP (a combined V1-V2 receptor agonist; n = 10; 112 +/- 2 days) with the selective V2-receptor agonist 1-desamino-8-D-arginine vasopressin (DDAVP) (n = 5; 111 +/- 2 days). AVP infusion increased fetal mean arterial pressure (MAP; 36 +/- 1 to 44 +/- 2 mmHg) and decreased heart rate (197 +/- 2 to 171 +/- 3 beats/min); DDAVP infusion had no effect on MAP or heart rate. Free water clearance decreased in response to AVP (0.13 +/- 0.02 to 0.02 +/- 0.01 ml.min-1.kg-1) and DDAVP (0.21 +/- 0.04 to 0.04 +/- 0.02 ml.min-1.kg-1), and urine osmolality increased in response to both analogues (AVP: 145 +/- 4 to 283 +/- 15 mosmol/kgH2O; DDAVP: 146 +/- 5 to 244 +/- 32 mosmol/kgH2O).(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for Web of Science ID A1994NF86100064

  View details for PubMedID 8160865

• OVINE MATERNAL AND FETAL GLOMERULAR ATRIAL-NATRIURETIC-FACTOR RECEPTORS - RESPONSE TO DEHYDRATION BIOLOGY OF THE NEONATE Fujino, Y., Ross, M. G., Ervin, M. G., Castro, R., LEAKE, R. D., Fisher, D. A. 1992; 62 (2-3): 120-126

  Abstract

  In pregnancy, dehydration produces marked effects on maternal and fetal body water homeostasis including an increase in fetal urinary sodium concentration and excretion. To examine the role of fetal plasma atrial natriuretic factor (ANF) and glomerular ANF receptors in dehydration-induced natriuresis, we compared plasma ANF levels and glomerular ANF binding characteristics in dehydrated and control maternal and fetal sheep. Mean (+/- SEM) maternal and fetal plasma ANF levels in control animals (n = 9) at 132-136 days gestation were 37 +/- 3 pg/ml and 138 +/- 20 pg/ml, respectively. Although mean ANF receptor maximum binding capacities (Bmax) were significantly higher in maternal than in fetal glomeruli (83 +/- 11 vs 34 +/- 12 fmol/mg protein, respectively), the dissociation constants (Kd) for ANF binding were not different (2.7 +/- 0.6 and 3.7 +/- 1.7 x 10(-10) M, respectively). In an additional 9 animals studied after 63 +/- 4 h of water deprivation, maternal plasma ANF levels were significantly lower than in the control group (14 +/- 4 vs. 37 +/- 3 pg/ml), maternal glomerular ANF receptor Bmax values were significantly higher (732 +/- 203 vs. 83 +/- 11 fmol/mg protein), and Kd values were six-fold higher (17.0 +/- 7.1 vs. 2.7 +/- 0.6 x 10(-10) M), although this difference was only marginally significant (p = 0.06). In contrast to the adult, there was a small, nonsignificant decrease in plasma ANF levels and no difference in Bmax or Kd values between the dehydrated and euhydrated fetal animals.(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for Web of Science ID A1992JQ05400009

  View details for PubMedID 1420611

• ONTOGENY OF ATRIAL-NATRIURETIC-FACTOR RECEPTORS AND CYCLIC-GMP RESPONSE IN RABBIT RENAL GLOMERULI PEDIATRIC RESEARCH Castro, R., LEAKE, R. D., Ervin, M. G., Ross, M. G., Fisher, D. A. 1991; 30 (1): 45-49

  Abstract

  Atrial natriuretic factor (ANF) has been identified in fetal and newborn mammals, and considerable data regarding fetal ANF metabolism are available. However, there is limited information concerning ANF receptors or receptor ontogenesis in developing mammals. We measured ANF receptor binding capacity, affinity, and ANF-induced cyclic GMP (cGMP) generation in isolated renal glomeruli from fetal (29 d gestation, term = 31 d), newborn (3 d), juvenile (28 d), and adult rabbits. The (mean +/- SEM) glomerular receptor binding capacity values for ANF in fetal and newborn animals (10 +/- 1 and 12 +/- 3 fmol/mg protein) were similar and significantly lower than the values for juvenile and adult animals (30 +/- 8 and 74 +/- 15 fmol/mg protein, respectively). In contrast, there were no significant differences in ANF receptor affinity values or dose-dependent increases in ANF-stimulated cGMP generation among the age groups studied. In competition studies, we observed effective displacement of 125I-ANF by C-ANF4-23, a ring-deleted ANF analogue, in adult, juvenile, and newborn glomeruli; however, C-ANF displaced only about 50% of the 125I-ANF in fetal tissue. The addition of C-ANF did not elicit cGMP generation, nor did C-ANF affect ANF-induced cGMP generation in fetal, newborn, or adult glomeruli. These results indicate that 1) the ANF receptor-guanylate cyclase system is intact in 29-d fetal rabbit glomeruli, and 2) the ANF-induced cGMP formation is similar in fetal and adult animals, whereas receptor binding capacity is relatively higher in adult glomeruli. These results suggest a higher proportion of nonguanylate cyclase-coupled ANF receptors in the mature rabbit.

  View details for Web of Science ID A1991FT78800009

  View details for PubMedID 1653934

• EFFECT OF A RING-DELETED ATRIAL-NATRIURETIC-FACTOR ANALOG ON OVINE FETAL RENAL AND CARDIOVASCULAR FUNCTION PEDIATRIC RESEARCH Castro, R., Ervin, M. G., LEAKE, R. D., Ross, M. G., Fisher, D. A. 1991; 29 (4): 342-346

  Abstract

  The proposed actions of atrial natriuretic factor (ANF) are mediated through specific plasma membrane (R1) receptors coupled to guanylate cyclase. A second receptor, R2, has been characterized by its ability to bind to an acyclic, truncated ANF analog (C-ANF4-23). The ANF-R2 receptor has not been identified in the fetus. Our study was conducted to determine the effects of C-ANF on fetal renal and cardiovascular function and plasma ANF clearance rates. Chronically catheterized ovine fetuses (n = 6) at 111 to 117 d gestation (term 145 d) received a C-ANF infusion (1 microgram/min/kg) for 30 min followed by a combined infusion of C-ANF and ANF (C-ANF, 1 microgram/min/kg; ANF, 100 ng/min/kg) for an additional 30 min. C-ANF infusion significantly increased (mean +/- SEM) plasma ANF concentration (437 +/- 45 to 1067 +/- 297 pg/mL), urinary flow rate (0.26 +/- 0.04 to 0.38 +/- 0.07 mL/min/kg), sodium excretion (12.9 +/- 3.5 to 21.7 +/- 6.1 mumol/min/kg), and osmolar clearance (0.14 +/- 0.02 to 0.21 +/- 0.04 mL/min/kg) (p less than 0.05). The combined C-ANF/ANF infusion further increased plasma ANF concentration to 2394 +/- 532 pg/mL and resulted in significant increases in urinary flow rate, sodium excretion, osmolar clearance, GFR, and free water clearance compared with C-ANF infusion alone (p less than 0.05). These renal responses, however, were not significantly different from the responses to ANF infusion alone (100 ng/min/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for Web of Science ID A1991FE03600005

  View details for PubMedID 1649430

• FETAL RENAL RESPONSE TO ATRIAL-NATRIURETIC-FACTOR DECREASES WITH MATURATION AMERICAN JOURNAL OF PHYSIOLOGY Castro, R., Ervin, M. G., LEAKE, R. D., Ross, M. G., Sherman, D. J., Fisher, D. A. 1991; 260 (2): R346-R352

  Abstract

  The presence of atrial natriuretic factor (ANF) in fetal tissues and plasma early in gestation suggests that ANF may have a physiological role in cardiocirculatory homeostasis in utero. However, reported responsiveness of the fetal kidney to ANF varies markedly. To characterize the ontogeny of fetal renal responsiveness to ANF, chronically catheterized ovine fetuses at 114 +/- 1 days (n = 6) and 131 +/- 1 days (n = 6) received successive (30 min each) intravenous infusions of ANF at rates of 5, 25, and 100 ng.min-1.kg-1. Mean (+/- SE) fetal plasma ANF levels increased from 328 +/- 54 to 1,866 +/- 482 and 521 +/- 135 to 1,579 +/- 295 pg/ml in the younger and more mature fetuses, respectively. Mean urine volume (0.17 +/- 0.03 to 0.37 +/- 0.09 ml.min-1.kg-1) and GFR (0.9 +/- 0.2 to 1.8 +/- 0.4 ml.min-1.kg-1) increased in the early gestation fetuses but did not change in the older fetuses. Mean urine sodium excretion and osmolar clearance increased by 352 and 155% in the early gestation fetal lambs and 118 and 50% in the older animals. The fetal plasma ANF clearance rates (PCANF) were lower in the early vs. the late gestation fetuses (68 +/- 15 vs. 116 +/- 28 ml.min-1.kg-1, respectively). These results demonstrate a decrease in fetal renal responsiveness to ANF with advancing fetal age. Multiple factors appear to contribute, including changes in PCANF and maturational changes in glomerular filtration rate, renal tubular function and ANF receptor metabolism.

  View details for Web of Science ID A1991EY85600056

  View details for PubMedID 1825457

• OVINE FETAL RENAL AND HORMONAL RESPONSES TO CHANGES IN PLASMA EPINEPHRINE AMERICAN JOURNAL OF PHYSIOLOGY Ervin, M. G., Castro, R., Sherman, D. J., Ross, M. G., Padbury, J. F., LEAKE, R. D., Fisher, D. A. 1991; 260 (1): R82-R89

  Abstract

  Circulating epinephrine alters atrial natriuretic factor (ANF) and arginine vasopressin (AVP) secretion, and all three hormones influence renal function. To quantify the relationships among fetal plasma epinephrine levels, fetal ANF and AVP secretion, and fetal renal function, six chronically catheterized fetal lambs (132 +/- 1 days gestation) received successive 40-min epinephrine infusions (0.1, 0.4, and 1.8 micrograms.min-1.kg-1). The second epinephrine infusion dose evoked significant increases in urine flow (V; 0.7 +/- 0.2 to 1.2 +/- 0.2 ml/min), free water clearance (CH2O; 0.3 +/- 0.1 to 0.7 +/- 0.1 ml/min), glomerular filtration rate (GFR; 3.9 +/- 0.7 to 5.4 +/- 0.8 ml/min), fractional water excretion (V/CH2O; 19 +/- 3 to 25 +/- 2%), mean arterial pressure (MAP; 45 +/- 3 to 51 +/- 4 mmHg), and a 94% increase in plasma ANF levels. A fourfold increase in the infusion dose significantly increased osmolar clearance (0.3 +/- 0.1 to 0.6 +/- 0.1 ml/min), sodium excretion (28 +/- 8 to 53 +/- 13 mueq/min), and plasma AVP levels (2.4 +/- 0.5 to 6.4 +/- 2.4 pg/ml) with no additional effect on V, CH2O, GFR, V/GFR, MAP, or plasma ANF levels. Urine osmolality and fractional sodium excretion did not change in response to epinephrine infusion. Our results demonstrate that epinephrine infusion stimulates fetal ANF secretion and to a lesser extent AVP secretion and significantly influences fetal renal function.

  View details for Web of Science ID A1991EU07100052

  View details for PubMedID 1825160

• OVINE FETAL LUNG FLUID RESPONSE TO ATRIAL NATRIURETIC FACTOR AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY Castro, R., Ervin, M. G., Ross, M. G., Sherman, D. J., LEAKE, R. D., Fisher, D. A. 1989; 161 (5): 1337-1343

  Abstract

  The fetal lung is an important site of fluid production and is postulated to serve a regulatory role in fetal fluid balance. To assess the role of atrial natriuretic factor on fetal lung liquid production, we studied the effect of intravenous atrial natriuretic factor infusion on tracheal fluid production in fetal sheep with chronic vascular and tracheal catheters. Ovine fetuses (mean gestation = 130 days +/- 1 day) received successive 40-minute intravenous infusions of increasing doses of synthetic fragment 1-28 atrial natriuretic factor (5, 25, and 100 ng/min.kg-1). In response to the 25 ng/min.kg-1 infusion, fetal tracheal fluid production decreased from 1.2 +/- 0.3 ml/10 min to 0.6 +/- 0.2 ml/10 min (p less than 0.05), and remained suppressed during the 100 ng/min.kg-1 infusion (0.5 +/- 0.2 ml/10 min). There was a significant inverse correlation between tracheal fluid production and fetal plasma atrial natriuretic factor levels (r = -0.61, p less than 0.001). Basal tracheal fluid sodium and potassium concentrations (147 +/- 1 mEq/L and 5 +/- 1 mEq/L) and osmolality (291 +/- 3 mOsm) did not change during the atrial natriuretic factor infusion periods. The observation that atrial natriuretic factor acts to decrease fetal lung fluid production suggests that atrial natriuretic factor may be important in the fetal adaptive response to extrauterine life.

  View details for Web of Science ID A1989CA61800055

  View details for PubMedID 2531548

• OVINE FETAL LUNG FLUID RESPONSE TO INTRAVENOUS SALINE SOLUTION INFUSION - FETAL ATRIAL NATRIURETIC FACTOR EFFECT AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY Sherman, D. J., Ross, M. G., Ervin, M. G., Castro, R., Hobel, C. J., Fisher, D. A. 1988; 159 (6): 1347-1352

  Abstract

  The fetal lung, a significant source of in utero fluid production, has been postulated to serve a regulatory role in maintenance of fetal body fluid homeostasis. Whereas the fetus responds to intravascular saline solution infusions with increased urine output, the fetal lung fluid response to this stimulus is unclear. Tracheal fluid output was measured in four chronically catheterized ovine fetuses (mean gestation, 129 +/- 1 days) subjected to successive 40-minute intravenous 0.9% saline solution infusions at rates of 0.5 and 1 ml/min/per kilogram of body weight. Tracheal fluid output decreased significantly (1.7 +/- 0.1 to 1.1 +/- 0.1 ml/10 min, p less than 0.01) during the infusion and returned to basal levels during the recovery period. Lung fluid osmolality and electrolyte concentration did not change. Fetal plasma atrial natriuretic factor increased significantly in response to the saline solution infusion (364 +/- 90 to 790 +/- 286 pg/ml, p less than 0.05) and returned to basal levels during the recovery period. There was a significant inverse correlation between plasma atrial natriuretic factor levels and tracheal fluid output. These results suggest that increased fetal plasma atrial natriuretic factor decreases lung fluid production. Lung fluid does not appear to compensate for fetal body water excess. Rather, lung fluid production appears to promote intrauterine pulmonary growth and to facilitate the transition to the extrauterine environment.

  View details for Web of Science ID A1988R550700006

  View details for PubMedID 2974683

• OVINE FETAL AND ADULT ATRIAL NATRIURETIC FACTOR METABOLISM AMERICAN JOURNAL OF PHYSIOLOGY Ervin, M. G., Ross, M. G., Castro, R., Sherman, D., Lam, R. W., Castro, L., LEAKE, R. D., Fisher, D. A. 1988; 254 (1): R40-R46

  Abstract

  Studies were conducted to quantify ovine fetal and adult atrial natriuretic factor (ANF) metabolism. A total of 14 pregnant ewes with singleton fetuses were prepared with vascular catheters. In protocol 1, six fetuses (mean gestation, 131 +/- 1 days) received intravenous infusions of synthetic human ANF (hANF, 100 ng.min-1.kg-1) for 60 min. Mean basal fetal plasma ANF levels increased from 180 +/- 44 pg/ml to a steady-state level of 1,233 +/- 192 pg/ml. In protocol 2, five fetuses (mean gestation, 130 +/- 1 days) received successive 40-min infusions of hANF at 5, 25, and 100 ng.min-1.kg-1. Although basal fetal plasma ANF levels (522 +/- 135 pg/ml) were greater than those observed in protocol 1, fetal plasma ANF levels increased to 1,580 +/- 295 pg/ml at the highest infusion rate. In both protocols 1 and 2, basal fetal plasma ANF levels were three- to fourfold greater than maternal levels. The fetal plasma ANF clearance rates calculated from protocol 1 and from the 25- and 100-ng.min-1.kg-1 infusions from protocol 2 were similar (89 +/- 10, 120 +/- 31, and 116 +/- 38 ml.min-1.kg-1, respectively) and were combined to yield a mean estimated fetal plasma ANF clearance rate of 102 +/- 11 ml.min-1.kg-1. In protocol 3, adult plasma ANF levels increased from 137 +/- 36 to 4,142 +/- 776 pg/ml in response to ANF infusion at 200 ng.min-1.kg-1. The mean plasma ANF clearance rate calculated for the adult animals was 59 +/- 12 ml.min-1.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for Web of Science ID A1988L825600032

  View details for PubMedID 2962518