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Biomedical subjects

J E Robillard

Publications and source records attributed to J E Robillard.

At least 37 records · Page 2Linked to original sources
PubMed1995

Role of glucocorticoids in the maturation of renal cortical Na+/H+ exchanger activity during fetal life in sheep.

We have studied the role of glucocorticoids in inducing the maturation in activity of the proximal tubule Na+/H+ exchanger that follows birth. Renal cortical microvillus membrane vesicles were prepared from 132-day gestation sheep fetuses (n = 8) that had received intraperitoneal cortisol (13 micrograms.kg-1.h-1) for the previous 48 h. Membrane vesicles were also obtained from sham-operated twin controls (n = 8). Amiloride-sensitive uptake of 22Na+ by these vesicles was measured, and Woolf-Augustinsson-Hofstee plots were used to determine the Michaelis constant (Km) and maximal velocity (Vmax). There was no significant difference in Km; however, the Vmax was 61% higher in cortisol-treated fetuses. Posttreatment circulating cortisol levels were significantly higher in the treated fetuses. Total RNA was collected from renal cortex of the eight pairs of twins when killed. Renal cortex Na+/H+ exchanger 3 (NHE3) mRNA levels were approximately fourfold higher in cortisol-treated than in control fetuses. Although proximal tubule Na+/H+ exchanger activity and renal cortex NHE3 mRNA levels increased significantly in cortisol-treated fetuses, cortisol infusion did not stimulate renal sodium reabsorption in the fetus but rather produced a natriuresis. These results demonstrate that glucocorticoids can induce an increase in both Na+/H+ exchanger activity and NHE3 mRNA levels during the last trimester of gestation in sheep. However, these changes are not associated with an increased ability of the fetal kidney to reabsorb sodium.

Animals↗
PubMed1995

Adenoviral-mediated gene transfer to fetal pulmonary epithelia in vitro and in vivo.

Vector-mediated gene transfer offers a direct method of correcting genetic pulmonary diseases and might also be used to correct temporary abnormalities associated with acquired, nongenetic disorders. Because the fetus or newborn may be a more immune tolerant host for gene transfer using viral vectors, we used replication defective recombinant adenoviral vectors to test the feasibility of gene transfer to the fetal pulmonary epithelium in vitro and in vivo. Both proximal and distal epithelial cells in cultured fetal lung tissues from rodents and humans diffusely expressed the lacZ transgene 3 d after viral infection. In vivo gene delivery experiments were performed in fetal mice and lambs. Delivery of Ad2/CMV-beta Gal to the amniotic fluid in mice produced intense transgene expression in the fetal epidermis and amniotic membranes, some gastrointestinal expression, but no significant airway epithelial expression. When we introduced the adenoviral vector directly into the trachea of fetal lambs, the lacZ gene was expressed in the tracheal, bronchial, and distal pulmonary epithelial cells 3 d after viral infection. Unexpectedly, reactive hyperplasia and squamous metaplasia were noted in epithelia expressing lacZ in the trachea, but not in the distal lung of fetal lambs. 1 wk after infection, adenovirus-treated fetuses developed inflammatory cell infiltrates in the lung tissue with CD4, CD8, IgM, and granulocyte/macrophage positive immune effector cells. Transgene expression faded coincident with inflammation and serologic evidence of antiadenoviral antibody production. While these studies document the feasibility of viral-mediated gene transfer in the prenatal lung, they indicate that immunologic responses to E1-deleted recombinant adenoviruses limit the duration of transgene expression.

Adenoviruses, Human↗
PubMed1995

Effect of cortisol on gene expression of the renin-angiotensin system in fetal sheep.

Components of the renin-angiotensin system have been found in a variety of tissues during fetal and postnatal life and appear to be developmentally regulated. We postulated that hormonal changes associated with parturition participate in the regulation of renin, angiotensinogen (Ao) and angiotensin type 1 receptor (AT1) gene expression. Cortisol, which increases rapidly in fetal blood before delivery, has been shown to influence the maturation of various systems in the developing fetus. To test the hypothesis that an increase in cortisol regulates fetal renin. Ao, and AT1 mRNA gene expression, we used Northern blot analysis to study the effects of an intraperitoneal infusion of cortisol (3 mg/h, 1 mL/h) for 48 h on the expression of these genes in twin ovine fetuses (n = 10 pairs) at 130-d gestation (term 145 d); one twin in each pair served as a saline-treated control (0.9% NaCl, 1 mL/h). Plasma cortisol levels were significantly higher in cortisol-treated fetuses (113 +/- 23 nmol/dL) than in twin controls (4.6 +/- 0.8 nmol/dL). Cortisol infusion significantly decreased AT1 receptor mRNA levels in kidney and liver by 24 +/- 7% and 27 +/- 8%, respectively, when compared with controls (p < 0.05), whereas in contrast, increased mRNA levels (p < 0.05) in heart right atrium (91 +/- 23%) and ventricle (59 +/- 20%). Renin mRNA levels decreased in renal cortex by 77 +/- 13% (p < 0.05) in cortisol-treated animals compared with controls. Hepatic Ao mRNA levels decreased by 15 +/- 5% in response to cortisol (p < 0.05), whereas no significant effect was seen on renal Ao gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensinogen↗
PubMed1995

Differential gene expression and regulation of renal angiotensin II receptor subtypes (AT1 and AT2) during fetal life in sheep.

Previous studies have shown that angiotensin II subtype 2 (AT2) receptors appear early during renal embryonic development. Factors involved in the regulation of AT2 receptors during renal development, however, have not been investigated. The present study was designed 1) to characterize the ontogeny of renal AT2 gene expression during the last half of gestation in fetal sheep and newborn lambs, 2) to compare changes in AT1 and AT2 gene expression during renal development, 3) to determine the influence of AII in modulating renal AT1 and AT2 gene expression during fetal life, and 4) to characterize the role of cortisol in modulating renal AT2 gene expression during the last trimester of gestation in fetal sheep. To perform these studies, we first isolated and cloned a polymerase chain reaction product that has 92 and 90% homology with the cDNA encoding the human and rat AT2 receptors, respectively. Using this sheep AT2 cDNA probe, we demonstrated that the sheep AT2 gene was encoded in a single locus. In addition, we showed that renal AT2 mRNA expression was high early during fetal life (60-90-d gestation) and decreased rapidly thereafter. In contrast, the expression of renal AT1 receptor gene was low at 60-d gestation and increased during the last trimester of gestation. We found that a continuous i.v. infusion (1 mL/h) of AII (9.5 mM/n) for 24 h, which raised plasma AII levels from 84 +/- 9 pg/mL to 210 +/- 21 pg/mL, decreased the expression of both renal AT1 and AT2 genes in third trimester fetal sheep. On the other hand, we observed that cortisol, known to decrease AT1 gene expression in the fetus, had no effect on AT2 gene expression. In summary, this study demonstrates that AII, but not glucocorticoids, contributes to the regulation of renal AT2 gene expression during development and that there is differential regulation of AT1 and AT2 receptors.

Angiotensin II↗
PubMed1994

Functional expression of the human angiotensinogen gene in transgenic mice.

The renin-angiotensin system is a major determinant of arterial pressure and volume homeostasis in mammals through the actions of angiotensin II, the proteolytic digestion product of angiotensinogen. Molecular genetic studies in several human populations have revealed genetic linkage between the angiotensinogen gene and both hypertension and increased plasma angiotensinogen. Transgenic mice were generated with a human angiotensinogen genomic clone to develop an animal model to examine tissue- and cell-specific expression of the gene and to determine if overexpression of angiotensinogen results in hypertension. Human angiotensinogen mRNA was expressed in transgenic mouse liver, kidney, heart, adrenal gland, ovary, brain, and white and brown adipose tissue and, in kidney, was exclusively localized to epithelial cells of the proximal convoluted tubules. Plasma levels of human angiotensinogen were approximately 150-fold higher in transgenic mice than that found normally in human plasma. The blood pressure of mice bearing the human angiotensinogen gene was normal but infusion of a single bolus dose of purified human renin resulted in a transient increase in blood pressure of approximately 30 mm Hg within 2 min. These results suggest that abnormalities in the angiotensinogen gene resulting in increased circulating levels of angiotensinogen could potentially contribute in part to the pathogenesis of essential hypertension.

Angiotensinogen↗
PubMed1994

Neonatal renal function and physiology.

Birth rapidly changes the demands placed on the kidneys with respect to infant homeostasis. Conceptional age (gestational plus postnatal), general health, and medical management may independently, or, in concert, give rise to important metabolic abnormalities marked by apparent renal functional inadequacies. The chronology of the renal functional changes occurring with maturation in infants born before or at term is now well described. The confounding effects of treatment on the development of renal function in very low birth weight infants are also becoming more apparent. However, the mechanisms responsible for these changes are just becoming to be understood with the use of molecular biologic techniques.

Age Factors↗
PubMed1994

Role of endogenous ANG II on resetting arterial baroreflex during development.

Angiotensin II (ANG II) has been shown in adults to modulate baroreflex responses in heart rate (HR) and sympathetic outflow. To test the hypothesis that high circulating levels of ANG II in the newborn period contribute to the resetting of the arterial baroreflex observed postnatally, we studied baroreflex-mediated changes in HR and renal sympathetic nerve activity (RSNA) before and after angiotensin-converting enzyme (ACE) inhibition in fetal and newborn sheep. In the newborn, administration of the ACE inhibitor enalaprilat produced significant (P < 0.05) decreases in baseline RSNA (69 +/- 5 vs. 47 +/- 7% maximum) and HR (81 +/- 3 vs. 59 +/- 4% max), as well as in the baroreflex curve midpoints for RSNA (93 +/- 4 vs. 87 +/- 3 mmHg) and HR (95 +/- 4 vs. 81 +/- 5 mmHg); no change in the sensitivities (gains) of the baroreflex responses were seen. In contrast, no significant changes in baseline RSNA, HR, baroreflex curve midpoint, or sensitivity were demonstrated in the fetus. Infusion of ANG II in newborn lambs reversed the effects of ACE inhibition on the baroreflex responses. Additional experiments evaluating the effects of ACE inhibition in vagotomized newborns again showed resetting of the baroreflex, demonstrating that vagally mediated mechanisms are not involved in regulating the changes in sympathetic outflow during the neonatal period. These results suggest that endogenous ANG II contributes to the resetting of the baroreflex observed postnatally.

Angiotensin II↗
PubMed1994

Cardiopulmonary and arterial baroreflex responses to acute volume expansion during fetal and postnatal development.

Recent studies demonstrated that renal denervation had no effect on the natriuretic response to volume expansion (VE) in fetal sheep, suggesting that the sensitivity of the cardiopulmonary reflex in response to VE is impaired in the fetus. To test this hypothesis, we investigated the renal sympathetic nerve activity (RSNA) and heart rate (HR) responses to 20 and 50% intravascular VE in fetal (130-135 days gestation; term 145 days) (n = 7), newborn (n = 8), and 6- to 8-wk-old sheep (n = 9). Despite similar increases in right atrial pressure (RAP) in the three groups, 20% VE had no significant effect on RSNA and HR in fetal sheep but significantly decreased RSNA in newborn (-22.8 +/- 7.3%) and 6- to 8-wk-old sheep (-32.1 +/- 11.7%). Bradycardic responses to VE were also observed in both newborn (from 237 +/- 6 to 200 +/- 12 beats/min) and 6- to 8-wk-old sheep (from 170 +/- 9 to 140 +/- 9 beats/min). A 50% VE had no significant effect on fetal RSNA and HR, whereas it increased RAP by 6.8 +/- 0.9 mmHg. In addition, we tested the hypothesis that interactions between cardiopulmonary and arterial baroreflexes in response to VE change during development. We found that 20 and 50% VE shifted the RSNA and HR arterial baroreflex response curves to the right in the fetus but had no significant effects on the gain of the arterial baroreflex curves in either fetal, newborn, or 6- to 8-wk-old sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1994

Changes in ovine renal sympathetic nerve activity and baroreflex function at birth.

The purposes of this study were to characterize the changes in renal sympathetic nerve activity (RSNA) and baroreflex function at birth in conscious sheep. One hour after delivery by cesarean section, RSNA increased by 239 +/- 24% compared with fetuses. The upper and lower plateau values of the baroreflex function curves for RSNA, expressed as the percent maximum achieved in the fetus, were greater (P < 0.05) at 1 h (260 +/- 41 and 142 +/- 40%) and 5 h of age (254 +/- 34 and 100 +/- 19%) than in fetuses (100 and 10 +/- 3%), respectively. Curve midpoint pressures also were higher (P < 0.05) at 1 h (62 +/- 3 mmHg) and 5 h (66 +/- 4 mmHg) than in fetuses (51 +/- 2 mmHg). No changes in the sensitivity (gain) of the RSNA response to baroreceptor stimulation were seen. The baroreflex response curves for heart rate showed similar increases in the curve midpoint pressures, while gain did not change. To determine whether the high circulating levels of angiotensin II (ANG II) in the newborn period contribute to the rise in RSNA or the resetting of the baroreflex toward higher pressures, the angiotensin-converting-enzyme inhibitor, enalaprilat, was administered to five lambs before delivery. No differences in the increase in RSNA after birth were detected between control and treated animals. The curve midpoint pressures of both the RSNA and heart rate baroreflex response curves were significantly less (P < 0.05) in the treated compared with control lambs.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1994

Ontogenic changes in renal response to alpha 1-adrenoceptor stimulation in sheep.

The present study was designed to examine the effect of direct intrarenal infusion of the alpha 1-adrenoceptor agonist, phenylephrine, on urinary flow rate (UFR) and on renal Na and Cl excretion in conscious and chronically instrumented fetal (128-133 days gestation, term 145 days), newborn (6-12 days), and adult sheep. Five different renal concentrations of phenylephrine, varying from 5 +/- 1 to 72 +/- 2 ng/ml, were studied. Low renal phenylephrine concentration (< or = 12 +/- 1 ng/ml) induced a significant renal vasoconstrictor response in fetuses but not in newborn and adult sheep. The effects of intrarenal phenylephrine infusion on UFR and fractional excretion of Na (FENa) was greater (P < 0.05) in newborn lambs than in fetal and adult sheep. At a renal concentration of phenylephrine between 9 +/- 1 and 12 +/- 1 ng/ml, the percent decrease in UFR was greater (P < 0.05) in newborn lambs (-19.1 +/- 4.7%) than in fetal (9.8 +/- 8.9%) and adult sheep (-3.3 +/- 3.9). The percent decrease in FENa at renal concentration of phenylephrine between 18 +/- 1 and 24 +/- 1 ng/ml was also significantly (P < 0.05) larger in newborn lambs (-20.2 +/- 2.8%) than in fetal (-8.0 +/- 3.1%) and adult sheep (-11.2 +/- 2.6%). In summary, the present results indicate that the fetal kidney has a limited ability to increase sodium reabsorption in response to stimulation of alpha-adrenoceptors and that the effect of renal alpha-adrenoceptor stimulation on urinary volume and urinary sodium excretion increases during the newborn period.

Aging↗
PubMed1994

Maturation of proximal tubule Na+/H+ antiporter activity in sheep during transition from fetus to newborn.

We have studied maturational changes in the kinetics of the proximal tubule Na+/H+ antiporter. Microvillus membrane vesicles were prepared from renal cortex of fetal and newborn lambs. Amiloride-sensitive uptake of 22Na+ by these vesicles was measured and Woolf-Augustinsson-Hofstee plots were used to determine the Michaelis constant (Km) and rate of maximal uptake (Vmax). Initial studies of fetal lambs at 130-132 days gestation (n = 5; term is 145 days) and 3- to 4-day-old lambs (n = 5) revealed no maturational change in Km (7.27 +/- 1.25 for fetuses and 9.01 +/- 1.03 mM for lambs); however, there was a 242% increase in Vmax (from 1.28 +/- 0.33 in the fetuses to 4.37 +/- 0.85 nmol.s-1.mg protein-1 in the lambs, P = 0.005). Further definition of the developmental change in Na+/H+ antiporter Vmax was obtained when 144-day-gestation fetuses (n = 5) were compared with 24-h-old sibling lambs (n = 5) that had been delivered by cesarean section at 144 days gestation. Again, no significant difference was seen in Na+/H+ antiporter Km (14.9 +/- 6.5 for fetuses and 12.5 +/- 3.4 mM for lambs); however, a significant increase in Na+/H+ antiporter Vmax occurred (from 1.41 +/- 0.51 in the fetuses to 3.32 +/- 0.37 nmol.s-1.mg protein-1 in the lambs, P < 0.01). This study shows that there is a maturational increase in renal cortical Na+/H+ antiporter Vmax during the transition from fetal to newborn life. This increase parallels the increase in renal tubular Na+ reabsorption that occurs at this time.

Amiloride↗
PubMed1994

Role of sympathetic activity in the generation of heart rate and arterial pressure variability in fetal sheep.

Significant fluctuation in heart rate (HR) and arterial pressure occur during fetal life. However, the mechanisms regulating this normal variability are not completely understood. To test the hypothesis that the normal variability in fetal HR and blood pressure are produced by intrinsic fluctuations in sympathetic outflow, we recorded HR, mean arterial blood pressure (MABP), and renal sympathetic nerve activity (RSNA) in conscious, chronically instrumented, near-term fetal sheep (n = 5; 132-137 d of gestation, term being 145 d) and correlated the relationships between RSNA and MABP, and RSNA and HR. RSNA, HR, and MABP were sampled at a frequency of 4 Hz and the values averaged by 5-min blocks over a 4-h period. Linear regression analysis demonstrated a positive correlation between RSNA and both HR and MABP in all five fetuses (p < 0.02). In a second group of fetuses (n = 5), ganglionic blockade with trimethaphan (150-250 mg/kg/min) significantly attenuated (p < 0.05) the coefficients of variation of HR (12.3 +/- 1.9% versus 1.7 +/- 0.6%) and MABP (5.8 +/- 0.6% versus 3.6 +/- 0.5%). These results demonstrate that, in the fetus, fluctuations in HR and MABP are mediated by changes in sympathetic outflow and suggest an important role for the autonomic nervous system in fetal cardiovascular regulation.

Animals↗
PubMed1994

Ontogenic changes and regulation of renal angiotensin II type 1 receptor gene expression during fetal and newborn life.

Factors regulating the expression of the angiotensin II subtype 1 (AT1) receptor during fetal life have not been investigated previously. The present study was designed 1) to characterize the ontogeny of AT1 receptor gene expression in the kidney of fetal and newborn sheep and 2) to determine the influence of both glucocorticoids and renal nerves in modulating AT1 gene expression during fetal life and during the transition from fetal to newborn life. We first isolated and cloned a PCR product that has 98 and 94% homology with the cDNA encoding the bovine and pig AT1 receptors, respectively, and 99 and 98% homology with the corresponding deduced protein sequences. Probing with this cDNA, we demonstrated that renal AT1 mRNA expression did not change significantly during the last trimester of gestation in fetal sheep or immediately after birth but decreased significantly 10 d after birth. We also demonstrated that renal denervation in the fetus had no effect on renal AT1 gene expression in 24-h-old newborn lambs. On the other hand, we observed in 130-d twin fetuses that a continuous intraperitoneal infusion (1 mL/h) of cortisol (3 mg/h or 6.2 mumol/h) for 48 h in one of the twins increased the fetal plasma cortisol concentration from 32.0 +/- 7.1 to 1126 +/- 231 nmol/L and produced a significant decrease (p < 0.005) in renal AT1 gene expression compared with the control twin receiving an intraperitoneal infusion of 0.9% NaCl. In summary, this study demonstrates that renal AT1 gene expression is elevated during fetal life and decreases after birth. It is also shown that glucocorticoids, but not renal nerves, contribute to the regulation of renal AT1 gene expression during development.

Amino Acid Sequence↗
PubMed1993

Influence of renal nerves on renal function during development.

The present review summarizes recent studies describing the role of renal sympathetic innervation in the regulation of renal function during development. The afferent renal innervation appears early during fetal life and probably precedes the development of efferent renal nerves. There is suggestive evidence that renal nerves are required for the proper development of the kidney and that neurotrophic growth factors play an important role in renal embryogenesis and in renal tubular differentiation. Renal sympathetic innervation modulates renal hemodynamics early during development. Renal nerve stimulation during alpha-adrenoceptor blockade produces renal vasodilation in fetal and newborn animals but not in adults. Unlike the effect of renal nerves on fetal renal hemodynamics which is observed in the young fetus, the role of renal sympathetic nerves in modulating fluid and electrolyte homeostasis seems to develop during late gestation. Recent studies have also shown that renal nerves play an important role in regulating renin secretion during the transition from fetal to newborn life. For example, renal denervation during fetal life suppressed the physiological rise in plasma renin activity associated with delivery and decreased renal renin mRNA levels after birth. Taken together, these studies suggest that renal nerves influence fetal renal development and that the influence of renal sympathetic innervation on renal hemodynamics and function changes with maturation.

Animals↗
PubMed1993

The renin-angiotensin system and blood pressure regulation during infancy and childhood.

The renin-angiotensin system plays multiple roles in the maintenance of normal blood pressure and renal function. The balance and integration of these roles change during development in ways that we do not yet fully understand. This article reviews the ways in which the renin-angiotensin system maintains normal cardiovascular homeostasis during development and its participation in physiologic and biochemical events.

Aging↗
PubMed1993

Indomethacin compromises hemodynamics during positive-pressure ventilation, independently of prostanoids.

We examined whether prostanoids contribute to the impaired cardiac function and decrease in regional blood flow induced by increasing mean airway pressure. Using microspheres, we measured cardiac output and major organ blood flow and assayed prostaglandin E2, 6-ketoprostaglandin F1 alpha, and thromboxane B2 in blood at mean airway pressures of 5-25 cmH2O in mechanically ventilated newborn piglets treated with ibuprofen (40 mg/kg, n = 6), indomethacin (0.3 mg/kg, n = 6), or vehicle (n = 6). Blood gases and pH were stable throughout the experiments. Prostanoid levels remained constant with increasing mean airway pressure in vehicle-treated pigs and were unchanged by indomethacin. However, ibuprofen decreased the prostanoid levels at all mean airway pressures studied (P < 0.01). As ventilatory pressure was progressively increased, cardiac output decreased gradually and similarly by 42-45% (P < 0.05) in all groups. At the highest mean airway pressure, blood flow decreased to the kidneys by 37-57%, to the ileum by 58-74%, and to the colon by 53-71% (P < 0.05) in all groups. Cerebral blood flow remained constant at all ventilatory pressures regardless of the treatment. There was no difference in cardiac output and regional hemodynamics between ibuprofen- and vehicle-treated animals. However, after indomethacin, ileal blood flow at the higher ventilatory pressures was 41-46% lower and cerebral blood flow at all mean airway pressures was 14-25% lower than after the other treatments (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Hemodynamic changes during endotracheal suctioning are mediated by increased autonomic activity.

Endotracheal suctioning of intubated infants produces profound changes in cardiovascular and cerebral hemodynamics, but the mechanisms regulating these changes are not fully understood. To determine the role of the autonomic nervous system in regulating these physiologic changes, we investigated the effects of endotracheal suctioning on heart rate (HR), mean arterial blood pressure (MABP), and renal sympathetic nerve activity (RSNA) in nine ventilated newborn lambs. In the first part of the study (n = 6), ventilation was interrupted for suctioning. With suctioning (15 s), HR decreased by 39 +/- 6% (p < 0.05), whereas MABP and RSNA increased significantly (p < 0.05) by 36 +/- 5% and 68 +/- 8%, respectively. These changes were significantly (p < 0.05) larger than changes observed during disconnection from the ventilator (15 s) without suctioning. Administration of atropine (0.02 mg/kg) blocked the HR response to suctioning without altering MABP or RSNA changes. After bilateral vagotomy, suctioning produced no changes in any parameter. When a closed tracheal suction system was used and ventilation was maintained, suctioning again resulted in significant (p < 0.05) increases in MABP (+10 +/- 3%) and RSNA (+34 +/- 5%) and a decrease in HR (-15 +/- 4%). These data suggest that suctioning stimulates sympathoexcitatory receptors localized in large airways whose afferent fibers course within the vagus, resulting in increased sympathetic activity, which induces peripheral vasoconstriction and elevates MABP. In contrast, the HR response appears to be mediated by increased parasympathetic activity as this is abolished by atropine.

Animals↗