Differential ontogeny of in vitro vascular responses to three categories of calcium channel antagonists in rats

We examined the ontogeny of relaxation responses to three categories of calcium channel antagonists, represented by verapamil, diltiazem, and nifedipine, for both potential-operated (KCl-mediated) and receptor-operated channels [norepinephrine (NE)-mediated] in rat thoracic aorta. Aortic rings from 2- to 3-d, 1-wk, and 12-wk-old Sprague Dawley rats were mounted in an organ bath, bathed in Krebs' solution, and connected to a force-displacement transducer to measure isometric tension. Endothelium intact vessels at optimal passive force were exposed to a single ED50 of isotonic KCl or NE, equilibrium contraction was measured, then vessels were washed and exposed for 30 min to 1 microM verapamil, 1 microM diltiazem, or 0.1 microM nifedipine, followed by another dose of KCl or NE. Verapamil and diltiazem demonstrated significant (p less than 0.05) age-related increases in effectiveness for blocking KCl-mediated contraction [(% reduction of control contraction +/- SEM) (Verapamil: 2-3 d, 67.7 +/- 4.2; 1 wk, 72.5 +/- 1.8; 12 wk, 89.5 +/- 1.0. Diltiazem: 2-3 d, 64.6 +/- 2.9; 1 wk, 73.5 +/- 3.0; 12 wk, 83.1 +/- 1.8]. Nifedipine was equally effective at all ages: 2-3 d, 85.6 +/- 1.3; 1 wk, 90.0 +/- 1.6; and 12 wk, 91.3 +/- 1.4. Verapamil and diltiazem also showed significant age-related increases in effectiveness for blocking NE-mediated contraction (Verapamil: 2-3 d, 6.2 +/- 3.9; 1 wk, 28.0 +/- 4.8; 12 wk, 44.1 +/- 6.0. Diltiazem: 2-3 d, 8.0 +/- 3.1; 1 wk, 20.5 +/- 3.9; 12 wk, 46.5 +/- 4.8).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intrauterine growth retardation on renal function on day one of life

We measured inulin clearance per kilogram, fractional sodium excretion per kilogram, osmolality, and urinary prostaglandin concentration in seven growth-retarded neonates and six appropriately grown neonates matched for gestational age during the first 24 hours of life to determine the effect of fetal growth retardation on renal function. There was a nonsignificant reduction in inulin clearance per kilogram in the growth-retarded neonates (p = 0.11). Inulin clearance correlated with gestational age in both groups. It was significantly correlated with birthweight in the growth-retarded group (p less than 0.05) but did not reach significance in the control group (p less than 0.06). Fractional sodium excretion was significantly higher in the growth-retarded fetuses (p less than 0.05). This increase was not explainable by differences in mean blood pressure and intravenous fluid intake, although differences in urinary prostaglandin concentrations during the study interval may be involved. In conclusion, we have demonstrated that growth retardation is associated with impaired renal maturation, which during the first 24 hours of life is manifest as decreased glomerular filtration rate and increased sodium excretion.

Neural control of renal hemodynamics and function during development

This review summarizes our current understanding of the role of the renal sympathetic nervous system during development. Recent evidence suggests that renal innervation appears early during fetal life and may play an important role in promoting cellular development. It has also been observed that renal nerve stimulation decreases renal blood flow and increases renal vascular resistance in fetal sheep, but to a lesser extent than in newborn and adult sheep. Moreover, it has been shown that, contrary to previous findings in adult animals, renal nerve stimulation during alpha-adrenoceptor blockade induces renal vasodilation in fetal and newborn sheep, but not in adult sheep. Recent studies have also demonstrated that renal nerves modulate the natriuretic response to a saline load in newborn lambs and influence sodium reabsorption in near-term fetal sheep. The role of renal nerves and neuronally released norepinephrine on renin secretion in the developing kidney is discussed. Finally, it is suggested that efferent renal sympathetic nerve activity might influence fetal renal hemodynamics during stressful conditions.

Evaluation of a percutaneously placed 27-gauge central venous catheter in neonates weighing less than 1200 grams

A percutaneous 27-gauge OD central venous catheter was inserted at 4 +/- 3 (SD) days of age and left in place for up to 2 weeks in 20 neonates with birth weights less than 1200 g and greater than 24 h of age. Parenteral nutritional solutions and medications were administered through these catheters. Twenty neonates matched for birth weight and gestational age served as paired controls. In vitro studies demonstrate that the maximum infusion rate for parenteral nutrition solutions is about 20 ml/hr. Packed red blood cells could not be infused through these catheters. In vivo results demonstrate a significant (p less than 0.05) reduction in number of peripheral iv catheters inserted during study (2 +/- 1 vs 7 +/- 4, SD) with no difference in cost per day of iv access ($79.42 +/- 113.51 vs $43.91 +/- 15.99, SD). Two-dimensional ultrasound assessment of catheter thrombosis was unsuccessful. Moreover, there was no correlation between angiographic and electron microscopic evaluation of catheter tip thrombosis. Electron microscopy of catheter tips revealed 33% with complete, partial and no occlusion, respectively, and 39% with sheath thrombosis. In summary, percutaneous insertion of a 27-gauge OD Vialon central venous catheter is a feasible alternative in providing venous access in very low birth weight infants.

Developmental changes in sodium nitroprusside and atrial natriuretic factor mediated relaxation in the guinea pig aorta

Sodium nitroprusside (SNP), a nonreceptor mediated stimulant of soluble guanylate cyclase, and atrial natriuretic factor, a receptor-dependent stimulator of particulate guanylate cyclase, mediate relaxation responses by increasing intracellular cGMP. This in vitro study was designed to compare the ontogeny of relaxation responses to SNP and atrial natriuretic factor in the guinea pig thoracic aorta. Aortic rings from fetuses at 55-60 d gestation (term = 68 d), 1- to 3-d-old newborn, and 12-wk-old adult Hartley guinea pigs were mounted in an organ bath, bathed in Kreb's solution, and connected to a force-displacement transducer to measure isometric tension. Relaxation responses to SNP and atriopeptin III were studied with the vessels at optimal resting tension and after preconstriction with an EC85 concentration of norepinephrine. SNP-mediated relaxation showed a significant increase in sensitivity with development among the three age groups (p less than 0.05). Methylene blue, an inhibitor of soluble guanylate cyclase, produced no inhibition of relaxation to SNP in fetal aortae, significantly decreased responses along the straight portion of the concentration-response curve in newborn aortae (p less than 0.05), and significantly shifted the concentration-response curve to the right (p less than 0.05) in adult aortae; but did not prevent vessels from relaxing almost 100% in any age group. However, atriopeptin III-mediated responses were similar in the three age groups and were unaffected by methylene blue. These results suggest that 1) sensitivity to SNP increases with age from fetal through adult life; 2) relaxation mediated by atriopeptin III is similar during development; 3) methylene blue does not affect SNP mediated relaxation in fetuses but progressively decreases sensitivity to SNP in newborns and adults; and 4) methylene blue does not affect atriopeptin III-mediated relaxation in any age group.

Ontogeny of vasoconstrictor neurohypophysial hormone function in rats

This in vitro study examined the ontogeny of arginine vasopressin (AVP) and arginine vasotocin (AVT) compared with norepinephrine (NE)-mediated contraction in rat thoracic aortas. Aortas from three age groups (2-3 days, 6-7 days, and 12 wk) of Sprague-Dawley rats were used. Ring segment resting length was adjusted to optimize tension developed to a dose that produces half-maximal tension of NE in Krebs solution (pH 7.4, 37 degrees C) and gassed with 95% O2-5% CO2. Cumulative dose-response curves were generated for KCl (5-100 mM), NE (10(-10)-10(-5) M), AVP, and AVT (both 10(-10)-10(-6) M) in the presence and absence of a selective V1 vasopressinergic inhibitor, [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine]arginine vasopressin ([d(CH2)5Tyr(Me)]AVP). A progressive increase in sensitivity among all age groups was found for KCl and NE. There was a slight decrease in sensitivity to both AVP and AVT in the 1st wk. Maximum contractile response to NE increased between 2-3 and 6-7 days, whereas no change was observed for KCl, AVP, or AVT. AVP- and AVT-mediated contractions were selectively inhibited by [d(CH2)5Tyr(Me)]-AVP. These results suggest 1) receptor-mediated contractility is present from 2 days of age for NE, AVP, and AVT; 2) sensitivity to KCl and NE increases progressively during postnatal development, whereas sensitivity to AVP and AVT slightly decreases in the 1st wk with no progressive age-related increase by 12 wk; 3) AVP and AVT mediate contraction via a similar V1-like receptor.

Ontogeny of neuronally released norepinephrine on renin secretion in sheep

The role of renal nerves and norepinephrine release on renin secretion during fetal and postnatal maturation has not been studied. Experiments were performed to determine the effect of veratridine, a substance known to promote norepinephrine release from nerve terminals, on active and inactive renin secretion from renal cortical slices of fetal (134-138 days gestation; term is 145 days), newborn (4-9 days of age), and adult nonpregnant sheep. Veratridine (10-300 microM) significantly increased active renin secretion and produced a small but nonsignificant rise in inactive renin secretion in all three groups of animals (P less than 0.05). The percent rise in active renin secretion during veratridine stimulation was similar among all groups. Veratridine-stimulated (300 microM) active renin secretion was antagonized by tetrodotoxin (0.5 and 5.0 microM) and DL-propranolol (1 microM) in fetal renal cortical slices. However, neither tetrodotoxin nor propranolol completely inhibited the stimulatory effect of veratridine on active renin secretion. These results suggest that 1) norepinephrine released from nerve terminals may regulate active renin secretion early during development; 2) the effect of veratridine on active renin secretion was similar in fetal, newborn, and adult sheep; 3) veratridine had no significant effect on inactive renin secretion; and 4) active renin secretion due to depolarization of nerve terminals in fetal sheep is dependent on activation of beta-adrenoceptors as it is in adults.

Crystallization of a complex between ribonuclease Ms and 3'-guanylic acid

The crystals of a complex between ribonuclease Ms, the extracellular ribonuclease from Aspergillus saitoi, and 3'-guanylic acid were obtained from 2-methyl-2,4-pentanediol solution by vapor diffusion technique in the hanging drop mode. The crystals belong to orthorhombic space group P2(1)2(1)2(1) with dimensions a = 47.0 A, b = 62.8 A, c = 37.9 A. The crystals diffract strongly up to at least 2.0 A resolution.

Ontogeny of isoproterenol-stimulated renin secretion from sheep renal cortical slices

The ontogeny of renin secretion from renal cortical slices was studied in two groups of fetal (107-109 days of gestation and 131-136 days of gestation; term is 145 days), newborn (3-9 days old), and adult nonpregnant sheep. Isoproterenol (ISO; 10(-8)-10(-5) M) significantly increased active renin secretion in all age groups (P less than 0.05), with newborns having the highest values at all concentrations. However, the percent changes in active renin secretion were similar among all ages. Inactive renin secretion also increased with ISO stimulation, with newborns having the highest rate of inactive renin secretion. The percent of total renin in the active form differed among ages, ranging at base line from 60 +/- 10% in fetuses at greater than 130 days of gestation to 88 +/- 6% in fetuses at less than 110 days of gestation (P less than 0.05). Propranolol (1 microM) inhibited ISO (10(-6) M)-stimulated active renin secretion at all ages. On the other hand, the prostaglandin (PG) synthase inhibitor aspirin (1.6 x 10(-5) M) did not inhibit ISO (10(-6) M)-mediated increases in active renin secretion in fetal (greater than 130 days of gestation) kidney slices and produced values intermediate between base line and ISO alone in newborns and adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional variation of postjunctional alpha-adrenoceptor responses in the developing renal vascular bed of sheep

Postjunctional alpha 1- and alpha 2-adrenoceptor vasoconstrictor responses were evaluated in isolated segments of main renal artery, segmental renal artery, and renal vein from fetal (130-138 d of gestation; term 145 d), newborn (3-15 d age), and nonpregnant adult sheep. Vascular rings were mounted at their optimal resting tension and responses to phenylephrine (alpha 1-adrenoceptor agonist) and guanabenz and UK14304 (both alpha 2-adrenoceptor agonists) were determined. Optimal resting tension increases with development in the main renal artery, segmental renal artery, and renal vein of sheep. Arterial vessels develop more isometric tension to alpha 1-adrenoceptor stimulation than to alpha 2-adrenoceptor stimulation, whereas venous segments develop similar isometric tension to alpha 1- and alpha 2-adrenoceptor stimulation. The segmental renal artery develops more isometric tension to alpha 2-adrenoceptor stimulation than the main renal artery. No large developmental differences exist among vessels in the sensitivity (concentration required for half maximal response, ED50) to alpha-adrenoceptor stimulation except for the renal vein with alpha 2-adrenoceptor stimulation. Maximum isometric tension corrected for vessel cross-sectional area decreases with age for all vessels with both alpha 1- and alpha 2-adrenoceptor stimulation. These findings may reflect developmental differences in receptor number and affinity or differences in vascular smooth muscle function. In addition, these data suggest that whereas both alpha 1- and alpha 2-adrenoceptors mediate vasoconstriction in the renal circulation, they may do so at different sites.

Crystallization of a new class of microbial ribonuclease from Rhizopus niveus

Crystals of ribonuclease Rh, a new class of microbial ribonuclease from Rhizopus niveus, were obtained from polyethylene glycol 8000 solution by a vapour diffusion technique in the hanging drop mode. Two crystal forms, type I and type II, were obtained from the same droplet solution. Both forms belong to the space group P2(1)2(1)2(1), but their cell dimensions are markedly different: a = 68.3 A, b = 73.0 A, c = 50.0 A for type I and a = 67.5 A, b = 72.3 A, c = 44.2 A for type II. The type I crystals diffract beyond 2.0 A resolution and are suitable for X-ray structure analysis at high resolution.

Renal hemodynamic response to atrial natriuretic factor in fetal and newborn sheep

We have previously demonstrated that systemic atrial natriuretic factor (ANF) infusion induced a renal vasoconstrictor response in fetal and newborn sheep. The present study was designed to test the hypothesis that the fetal and neonatal renal vasculatures do, in fact, vasodilate in response to ANF but that this effect is negated by vasoconstrictor compensatory mechanisms when ANF is infused systemically. To test this hypothesis, the renal hemodynamic response to intrarenal infusion of ANF was studied in chronically instrumented fetal (125-135 d of gestation; term 145 d) and newborn (8-15 d) sheep. Intrarenal infusion of ANF (0.125 to 4.0 micrograms/kg of body wt in fetuses and 0.25 to 8.0 micrograms/kg in newborns) had no significant effect on mean arterial blood pressure and heart rate. However, ANF produced a concentration-dependent increase in renal blood flow velocity (F = 40.9, p less than 0.001) and a decrease in renal vascular resistance (F = 38.3, p less than 0.001) in both groups. The magnitude of changes in renal blood flow velocity and renal vascular resistance expressed as percentage of changes (% delta) from control values, were similar (p greater than 0.05) in both fetal and newborn sheep during intrarenal infusion of ANF. These results demonstrate that ANF exerts direct vasodilator action on the fetal and neonatal renal vasculature and that the renal vasoconstriction previously observed during systemic infusion of ANF was probably secondary to activation of compensatory mechanisms.

Ontogeny of renal hemodynamic response to terbutaline and forskolin in sheep

The renal hemodynamic response to renal arterial infusions of terbutaline and forskolin were compared in chronically instrumented fetal (129-139 days gestation; term 145 days), newborn (7-14 days old) and nonpregnant adult sheep. Infusions of terbutaline produced renal vasodilation in all age groups with maximal increases being higher in fetal (47 +/- 7%) than in newborn (30 +/- 8%) or adult sheep (24 +/- 5%). Terbutaline-mediated renal vasodilation was inhibited by the selective beta 2 adrenoceptor antagonist, ICI 118,551, whereas infusion of selective beta 1 adrenoceptor antagonist, ICI 89,406, had no effect. Moreover, terbutaline effects were unchanged after phentolamine infusion to inhibit potential antagonistic effects of neuronal norepinephrine release by presynaptic beta 2 adrenoceptor stimulation. Renal arterial infusion of forskolin produced renal vasodilation of similar magnitude in all age groups, with maximal increases of 46 +/- 5, 38 +/- 3 and 38 +/- 5% in fetal, newborn and adult sheep, respectively. Taken together, these results suggest that renal vasodilatory mechanisms stimulated by selective activation of beta 2 adrenoceptors (terbutaline) are greater during fetal life. However, direct activation of adenylate cyclase with forskolin produces essentially similar renal vasodilatory responses during development in sheep. Thus, reasons to explain age-dependent differences in renal vasodilation observed previously with endogenous catecholamines may be at the receptor-hormone level.

Plasma and urinary clearance rates of atrial natriuretic factor during ontogeny in sheep

The present study was designed to determine the plasma clearance rate of atrial natriuretic factor (ANF) during development in chronically-instrumented fetal, newborn and adult non-pregnant sheep. To determine the contribution of the kidney in the metabolism of ANF, urinary clearance of ANF was also measured. Intravenous infusion of ANF (0.025 and 0.1 microgram.min-1.kg-1) produced a significant decrease in mean arterial blood pressure in newborn lambs and in adult non-pregnant sheep. Estimated plasma ANF clearance rate for the 0.025 and 0.1 microgram.min-1.kg-1 ANF infusion rate were respectively 177 +/- 55 and 155 +/- 34 ml.min-1.kg-1 in fetuses, 138 +/- 26 and 97 +/- 13 ml.min-1.kg-1 in newborn lambs and, 148 +/- 33 and 103 +/- 25 ml.min-1.kg-1 in adult nonpregnant ewes. Fetal, newborn and adult ANF plasma clearance rates during high ANF infusion rate (0.1 microgram.min-1.kg-1) were not significantly different. Low or high ANF infusion rate was not associated with significant changes in urinary ANF concentration or urinary ANF excretion rate. Taken together, the present study demonstrates that ANF plasma clearance rate is similar in fetal, newborn and adult non-pregnant sheep and that the excretory function of the kidney contributes only minimally to ANF plasma clearance rate.

Neurohormonal regulation of renal function during development

This review summarizes current understanding of fetal renal physiology and considers the role of the neuroadrenergic system and renin-angiotensin system in controlling renal hemodynamics and function during development. Recent evidence suggests that renal innervation appears early during fetal life but is not an important modulator of renal hemodynamics and function during resting conditions in immature animals. It has also been observed that the renal hemodynamic response to renal nerve stimulation (RNS) is less in fetal and newborn animals than in adults. But contrary to previous findings in adult animals, RNS during alpha-adrenoceptor antagonism produces renal vasodilation in fetal and newborn sheep, but not in adult ewes. The role of the renin-angiotensin system (RAS) in modulating renal hemodynamics and function during prenatal and postnatal maturation is discussed. It is suggested that the RAS plays an important role in regulating blood pressure early during fetal life, whereas its influence on renal hemodynamics and function appears later during development.

Ontogeny of the renal response to natriuretic peptide in sheep

The ontogeny of the renal response to continuous systemic infusion of atrial natriuretic peptide (ANP) was studied in chronically instrumented fetal, newborn, and adult nonpregnant sheep. Plasma immunoreactive ANP (ANPir) concentrations during low (0.025 microgram.kg-1.min-1) and high rate (0.1 microgram.kg-1.min-1) ANP infusion were similar between each group of animals. Decrease in renal blood flow velocity (RBFV) and rise in renal vascular resistance (RVR) were observed in fetal and newborn lambs during ANP infusion. The percent changes in RBFV and RVR were of significantly (P less than 0.05) greater magnitude during high ANP infusion rate in fetuses (-28.5 +/- 8.5 and 93 +/- 6.4%) than in adult sheep (-6.6 +/- 3.2 and -4.4 +/- 4.9%). ANP produced no changes in urine flow (V) in fetuses but increased V significantly in newborn lambs and adult sheep. Glomerular filtration rate increased significantly during ANP infusion in adult sheep but not in fetal and newborn lambs. Percentage changes in urinary excretion rate of Na (UNaV) during high ANP infusion rate were significantly higher in adult sheep (3,520 +/- 2,414%) than in newborn (157 +/- 106%) and fetal lambs (198 +/- 84%). These results suggest that the cardiovascular, renal hemodynamic, and possibly renal function responses to continuous ANP infusion increase during maturation, the overall response being larger in adult animals.

Ontogeny of alpha-adrenoceptor responses in renal vascular bed of sheep

The renal hemodynamic response to renal arterial infusions of guanabenz (alpha 2-adrenoceptor agonist) and phenylephrine (alpha 1-adrenoceptor agonist) were compared in conscious and chronically instrumented fetal (132-140 days gestation; term 145 days), newborn (6-15 days postnatal), and nonpregnant adult sheep. Phenylephrine produced similar dose-related decreases in renal blood flow velocity in all three groups at low concentrations (less than 1.8 X 10(-7) M) of drug in renal blood, whereas at the highest concentration adults demonstrated the most vasoconstriction and newborns the least (P less than 0.05 ANOVA). Responses to phenylephrine infusion during renal alpha 1-adrenoceptor blockade with prazosin were completely inhibited. Guanabenz produced greater renal vasoconstriction in adult sheep (P less than 0.05 ANOVA) at all concentrations (0.6 X 10(-6) to 8 X 10(-6) M) when compared with fetal and newborn sheep. Guanabenz-mediated vasoconstriction was not affected by alpha 1-adrenoceptor blockade with prazosin but was completely inhibited by the addition of an alpha 2-adrenoceptor antagonist idazoxan. Results of the present study demonstrate that renal vasoconstriction is mediated by both alpha 1- and alpha 2-adrenoceptors in fetal, newborn, and adult sheep. Moreover, these results suggest that renal alpha 1- and alpha 2-adrenoceptor-mediated vasoconstrictor responses mature at different rates.

Effects of epinephrine on the renal vascular bed of fetal, newborn, and adult sheep

The renal hemodynamic response to renal artery infusions of epinephrine were compared in conscious and chronically instrumented fetal (125-139 days gestation; term 145 days), newborn (5-13 days postnatal), and nonpregnant adult sheep. Epinephrine produced similar dose related decreases in renal blood flow velocity in all three groups. The mean estimated concentration of epinephrine in renal blood producing a 50% decrease in renal blood flow velocity, ED50, was 0.008 microgram/ml. Epinephrine infusions during renal alpha-adrenoceptor blockade with phentolamine produced increases in renal blood flow velocity that were of greater magnitude in fetal compared to newborn and adult sheep. The maximal increase in renal blood flow velocity observed were 57 +/- 11%, 22 +/- 3%, and 18 +/- 3% in fetal, newborn, and adult sheep, respectively (p less than 0.001). This vasodilation produced by epinephrine during alpha-adrenoceptor blockade was completely inhibited by ICI 118,551, a beta 2-adrenoceptor antagonist. Inhibition of renal vascular beta-adrenoceptors with propranolol in fetal sheep did not enhance alpha-adrenoceptor-mediated renal vasoconstriction with epinephrine infusions. Results of the present study demonstrate similar renal vasoconstrictor responses to renal artery infusion of epinephrine in fetal, newborn, and adult sheep. In contrast, the renal vasodilator responses observed with epinephrine infusions during renal alpha-adrenoceptor blockade were greater in fetal compared to newborn and adult sheep. However, epinephrine-mediated renal vasoconstriction was not enhanced by blockade of beta-adrenoceptors in fetal sheep.

Dopamine receptors in the developing sheep kidney

These studies were designed to characterize dopamine receptor density and affinity in kidneys removed from sheep of varying ages (fetal, newborn, and adult) using radioligand binding methods. Three different radioligands were used: the specific dopamine-1 antagonist 3H-SCH 23390, the dopamine-1/dopamine-2 antagonist 3H-haloperidol, and the dopamine-2 antagonist 3H-spiroperidol. The specific binding of 3H-haloperidol and 3H-spiroperidol was saturable with time and ligand concentration, being indicative of dopamine receptors. The specific binding of the dopamine-1 selective radioligand 3H-SCH 23390 was also saturable with time but displayed several points of saturation with increasing ligand concentration. The specific binding of 3H-haloperidol, which had a low affinity and is indicative of dopamine-1 receptors, showed no age-related changes in maximum receptor density or affinity. On the other hand, the maximum receptor density of dopamine-2 receptors measured by 3H-spiroperidol decreased with age. The observations that renal dopamine-1 receptor density or affinity do not change with maturation are in agreement with our previous studies that showed no age-related changes in dopamine-receptor-mediated renal vasodilatation in sheep. The significance of the decrease in renal dopamine-2 receptor density with age remains to be determined.

Hormonal regulation of renal function during development

The present review summarizes current and new knowledge concerning the major hormonal systems that directly or indirectly affect renal function during development. The role of the renin-angiotensin-aldosterone system in regulating renal function during fetal and postnatal life is reviewed. A summary of the role of this system during fetal and postnatal stresses is also provided. The physiological role of the renal kallikrein-kinin system in the control of renal blood flow, renin release and sodium excretion during development is examined. Possible influences of the prostaglandin system on regulation of renal function and renin secretion during fetal and postnatal maturation are explored. The effect of vasopressin on the ability of the fetal and postnatal kidney to concentrate urine and regulate body fluid homeostasis is reviewed in detail. The physiologic action of vasotocin on renal sodium and water homeostasis is described. New information regarding the role of the sympathetic system in the regulation of renal hemodynamics and in the control of renal function during development is presented. Finally, recent studies demonstrating the effect of atrial natriuretic factor and corticosteroids on the developing kidney are discussed.

Ontogeny of renal beta-adrenoceptor-mediated vasodilation in sheep: comparison between endogenous catecholamines

The renal hemodynamic response to renal arterial infusions of norepinephrine was compared to epinephrine infusions during renal alpha-adrenoceptor blockade in chronically instrumented and unanesthetized fetal (127-141 days gestation; term 145 days), newborn (6-10 days old), and nonpregnant adult sheep. Infusions of either catecholamines produced renal vasodilation which was of greater magnitude in fetal compared to newborn and adult sheep. Maximal increases in renal blood flow velocity during norepinephrine infusion were 64 +/- 5% in fetal, 23 +/- 4% in newborn, and 24 +/- 7% in adult sheep (p less than 0.001). Similar age-dependent increases in renal blood flow velocity were observed during epinephrine infusion, with maximal changes being 74 +/- 10% in fetal, 23 +/- 4% in newborn, and 19 +/- 4% in adult sheep (p less than 0.001). Increases in renal blood flow velocity produced by both norepinephrine and epinephrine infusions were completely inhibited by intrarenal infusion of ICI 118,551, a beta 2-adrenoceptor antagonist. Taken together, these results suggest that the renal vascular beta 2-adrenergic receptor that mediates vasodilation may be stimulated by both norepinephrine and epinephrine with equal potency. In addition, results of this study demonstrate that enhanced beta 2-adrenoceptor mediated renal vasodilatory capacity is observed during fetal life.

Changes in arterial blood gases following cardiac asystole during fetal life

A case of suspected fetal cardiac asystole with normal umbilical cord blood gas values is reported. Possible explanations of this apparent discrepancy were examined by measuring sequential changes in fetal arterial acid-base and blood gas values after induced cardiac asystole in chronically instrumented fetal lambs at 132-141 days' gestation. Arterial pH values did not decrease from baseline for at least ten minutes. Elevation of pCO2 values were observed at 30 minutes. Arterial pO2 and HCO3 values remained unchanged for at least 30 minutes. Therefore, we conclude that sudden fetal cardiac asystole occurring within ten minutes of delivery may be one reason why umbilical cord acid-base and blood gas values do not correlate with Apgar scores.

Ontogeny of renal hemodynamic response to renal nerve stimulation in sheep

The renal hemodynamic response to direct electrical stimulation of renal nerves was studied in conscious and chronically instrumented fetal (130-142 days gestation; term 145 days), newborn (7-12 days postnatal), and adult nonpregnant sheep. Renal nerve stimulation (RNS) produced a significant decrease in renal blood flow (RBF) velocity and a significant increase in renal vascular resistance (RVR) in all three groups of animals. The overall decline in RBF velocity and the overall rise in RVR was less pronounced in fetal than in adult sheep (P less than 0.05). Changes in RBF velocity and RVR using an RNS frequency of 16 Hz were -35 +/- 4 and 81 +/- 19% in fetal sheep, -61 +/- 10 and 374 +/- 128% in newborn lambs, and -84 +/- 12 and 540 +/- 94% in adult sheep, respectively. RNS during intrarenal infusion of the alpha-adrenoceptor antagonist phentolamine was associated with a significant increase in RBF velocity and decrease in RVR in both fetal sheep and newborn lambs, but not in adult sheep. Moreover, it was found that the rise in RBF velocity and the decrease in RVR associated with RNS during alpha-adrenoceptor antagonism were completely inhibited by intrarenal infusion of ICI 118,551, a beta 2-adrenoceptor antagonist and unaffected by either cholinergic or dopaminergic antagonists. Taken together, these results suggest that the overall renal vasoconstrictor response to RNS is age dependent. Furthermore, the present results demonstrate that, contrary to observations made in adult animals, RNS can produce renal vasodilation in immature animals that is mediated by beta 2-adrenoceptors.

Renal hemodynamics and functional changes during the transition from fetal to newborn life in sheep

The effects of delivery on renal function and renal hemodynamics were studied in conscious and chronically instrumented fetal sheep. Each fetus was studied 1 h before delivery and 1, 4, and 24 h following delivery by cesarean section. Delivery was not associated with significant changes in plasma renin activity, plasma angiotensin II, plasma aldosterone, and plasma arginine vasopressin concentrations when determined 1 h after birth. On the other hand, the transition from fetal to newborn life was accompanied by significant increases in plasma epinephrine and norepinephrine concentrations. No significant changes in renal blood flow velocity or in renal vascular resistance were observed during the transition from fetal to newborn life; percent changes in renal blood flow velocity and renal vascular resistance values were respectively 15.4 +/- 11 and -2.4 +/- 1.0% at 1 h, 4.0 +/- 8.0 and 5.8 +/- 9.1% at 4 h, and 3.2 +/- 8.0 and 9.7 +/- 13% at 24 h. No significant changes in urinary flow rate, urine osmolality, free water clearance, and osmolar clearance were observed in the first 24 h following delivery. On the other hand, glomerular filtration rate increased 3-fold from 3.3 +/- 0.4 ml/min in fetuses to 10.1 +/- 1.2 ml/min in newborn lambs at 24 h of age. This rise in glomerular filtration rate was associated with significant decreases in urinary sodium excretion (UNaV) (from 36 +/- 7 to 13 +/- 3 microEq/min) and fractional excretion of sodium (FENa) (from 7.6 +/- 0.9 to 1.1 +/- 0.3%).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dopamine in the renal vascular bed of fetal, newborn, and adult sheep

The renal hemodynamic response to renal arterial dopamine infusions was compared in unanesthetized fetal (129-137 days gestation, full term 145 days), newborn, and adult sheep. Mean arterial blood pressure and heart rate remained unchanged during intrarenal dopamine infusions. Dopamine produced dose-related decreases in mean renal blood flow velocity in all three groups. When compared with adult sheep fetal sheep were slightly more sensitive to the vasoconstrictive effects of dopamine ED50 (mean effective dose ratio: fetus/ED50 adult = 0.368 +/- 0.047, P less than 0.05). Increases in mean renal blood flow velocity were not seen at any dose given (1-16 micrograms/kg body wt in fetuses, 2-32 micrograms/kg body wt in newborns and adults) until dopamine was infused during alpha- and beta-adrenoceptor blockade. The largest mean increase in renal flow velocity was 13 +/- 3, 16 +/- 3, and 17 +/- 4% in fetal, newborn, and adult sheep, respectively. cis-Flupentixol inhibited the vasodilation. This study demonstrates the presence of renal vasodilation following renal arterial dopamine infusions in fetal, newborn, and adult sheep when renal alpha- and beta-adrenoceptors are blocked. Vasodilator responses are similar in all three groups, and increases in renal blood flow velocity are small compared with that of other experimental models.

Effects of renal denervation on renal responses to hypoxemia in fetal lambs

The role of renal nerves in mediating renal hemodynamics and renal function during normal physiological conditions and following moderate hypoxemia was studied in chronically catheterized fetal lambs (125-141 days of gestation) following unilateral renal denervation. Base-line values for renal blood flow (RBF), renal vascular resistance (RVR), glomerular filtration rate (GFR), urinary flow rate (UFR), urinary electrolyte (Na+, K+, and Cl-) excretion rate, and urine osmolality (Uosm) were similar in both intact and denervated kidneys. Hypoxemia was associated with a significant rise in mean arterial blood pressure and a significant decrease in heart rate. Hypoxemia produced a similar decrease in GFR and similar increases in urinary Na+ and Cl- excretion rates in both intact and denervated kidneys. However, the effect of hypoxemia on renal hemodynamics differed between intact and denervated kidneys. Hypoxemia produced a continuous and progressive decrease in RBF and increase in RVR in the intact kidney. On the other hand, renal denervation was associated with an early renal vasodilation and attenuated the reduction in RBF and the rise in RVR during hypoxemia; this early renal vasodilation was blunted following prostaglandin synthesis inhibition. Taken together, these results suggest that fetal renal denervation is not associated with significant changes in renal hemodynamics or renal function during normal physiological conditions but that renal denervation partially inhibited the renal vasoconstriction associated with fetal hypoxemia. Finally, it was found that endogenous prostaglandins counteract the renal vasoconstriction associated with fetal hypoxemia.

Effects of aldosterone on urinary kallikrein and sodium excretion during fetal life

The present study was designed to investigate the effect of acute (2 h) and chronic aldosterone (4 days) infusion on urinary kallikrein excretion rate and on renal handling of Na+ and K+ in chronically catheterized fetal lambs less than 115 days gestation (n = 6) and greater than 125 days gestation (n = 7). Chronic aldosterone infusion decreased plasma renin activity in both groups of fetuses. Both acute and chronic aldosterone infusion produced significant decreases in UNa + V in fetuses greater than 125 days and in the majority of fetuses less than 115 days gestation (five of six). Aldosterone infusion did not increase K+ excretion in either group of fetuses. It is also demonstrated that chronic aldosterone infusion induced an increase in urinary kallikrein excretion rate in both groups of fetuses. Taken together, these results demonstrate that aldosterone has antinatriuretic but no kaliuretic effects during fetal life, but produces a rise in urinary kallikrein excretion rate during the last trimester of gestation in fetal lambs.

Renal responses to hypoxemia during renin-angiotensin system inhibition in fetal lambs

The role of the renin-angiotensin system (RAS) in modulating the renal hemodynamic and functional responses to hypoxemia was studied in chronically catheterized fetal lambs (132-143 days gestation; term 145 days) before and during administration of either captopril or [Sar1-Gly8]ANG II. Base-line mean arterial blood pressure decreased significantly after administration of either captopril or [Sar1-Gly8]ANG II. This decrease was associated with a significant decline in renal vascular resistance (RVR) in captopril-treated fetuses, whereas no changes in RVR were observed in [Sar1-Gly8]ANG II-treated fetuses. However, the decline in renal blood flow (RBF) and the rise in RVR associated with hypoxemia in control fetuses were not attenuated significantly during inhibition of the RAS using either captopril or [Sar1-Gly8]ANG II. Moreover neither captopril nor [Sar1-Gly8]ANG II blunted the hypertensive response associated with fetal hypoxemia. The renal functional response to captopril was different from the response observed during infusion of [Sar1-Gly8]ANG II. Administration of [Sar1-Gly8]ANG II produced significant decreases in urinary flow rate (UFR), glomerular filtration rate (GFR), and urinary electrolyte (Na+, K+, Cl-) excretion rates, whereas no changes were observed during captopril infusion. The effects of hypoxemia on renal function were not modified after captopril. However, [Sar1-Gly8]ANG II tended to increase UFR and GFR, but these changes were pressure-dependent and not directly related to inhibition of the RAS. This study suggests that the RAS is not an important mediator of the fetal renal hemodynamic and functional responses to hypoxemia.

Factors controlling aldosterone secretion during hypoxemia in fetal lambs

Factors modulating the fetal aldosterone response to hypoxemia were studied in three groups of chronically catheterized fetal lambs between 131 and 143 days of gestation (term, 145 days). One group (control group) received an infusion of 5% dextrose in water; the second group (captopril-treated group) was given captopril, an inhibitor of angiotensin-converting enzyme; the third group (captopril plus dexamethasone-treated group) received dexamethasone in addition to captopril. In all groups of fetuses, hypoxemia was associated with a significant increase in plasma K+ concentration (+0.7 +/- 0.1 meq/liter). In control fetuses, changes in plasma aldosterone concentration during hypoxemia correlated closely with changes in plasma K+ concentration r = 0.79; P less than 0.001) and with changes in plasma angiotensin II concentration (r = 0.77; P less than 0.001). In the captopril-treated fetuses, the rise in plasma aldosterone concentration during hypoxemia correlated closely with plasma K+ (r = 0.79; P less than 0.001) but not with plasma angiotensin II values (r = 0.17). No significant correlation was found between percent changes in maternal aldosterone and percent changes in fetal aldosterone during hypoxemia and following recovery (r = 0.36; P greater than 0.1) in captopril-treated fetuses. Administration of dexamethasone to fetuses receiving captopril completely inhibited the rise in plasma aldosterone associated with hypoxemia. Taken together, the present results suggest that the rise in plasma aldosterone during hypoxemia is not related to the level of activity of the renin-angiotensin system but depends probably on the increased secretion of adrenocorticotrophin by the fetus.(ABSTRACT TRUNCATED AT 250 WORDS)

Tympanic membrane temperature of term and preterm neonates

Deep body temperatures of 70 term and 24 preterm newborn infants were measured at two sites: deep rectum (5 cm beyond the anus) and tympanic membrane. A significant correlation was found between deep rectal and tympanic membrane temperatures in both term and preterm infants. Mean deep rectal and tympanic membrane temperatures in term infants were 37.01 degrees C and 36.83 degrees C, respectively. Mean deep rectal and tympanic membrane temperatures in preterm infants were both 36.69 degrees C.

Fulminant neonatal septicemia due to Hemophilus parainfluenzae

A woman with premature rupture of membranes and chorioamnionitis gave birth to a 0.73-kg infant at 28 weeks' gestation. The infant died of fulminant septicemia caused by Hemophilus parainfluenzae. This organism should be recognized as a potential cause of chorioamnionitis and neonatal septicemia.

Temperature measurement in term and preterm neonates

Body temperatures of 99 term and 44 preterm infants were measured at four sites: core (5 cm beyond the anus, with an electronic telethermometer), rectum (2 cm, with a mercury-in-glass thermometer), axilla, and between the skin and mattress. Temperatures measured at the four sites agreed closely in this group of largely normothermic infants. However, five of seven term infants with abnormal core temperature (greater than 1.5 SD below or above the mean) would have been judged to be normothermic by each of the three other measurements. The temperatures in preterm infants were lower and varied less with the site of measurement, indicating a smaller core-surface temperature gradient because of their relative lack of thermal insulation by body fat. Axillary temperature was as reliable as rectal temperature measured in the usual way with a mercury-in-glass thermometer. Measurement of the temperature between the skin and mattress was nearly as accurate as the other more frequently used methods. Ninety percent of temperatures were within 0.1 degree C of their final stabilization readings by 5 minutes for each type of thermometer and measurement site.

Preliminary crystal structure analysis of a microbial, guanine-specific ribonuclease St at 2.5 A resolution

The three-dimensional structure of Ribonuclease St (RNase St), the extracellular ribonuclease from Streptomyces erythreus, has been deduced based on a preliminary electron density map at 2.5 A resolution. RNase St has a substrate specificity similar to ribonuclease T1 which catalyzes the splitting of the phosphodiester bond of guanylic acid. Crystals grown as diamond plates have space group C2 with unit cell parameters a=88.4, b=33.0, c=69.0 A, beta = 98.4 degrees having two enzyme molecules per asymmetric unit. Phases were obtained by use of KAu(CN)4, phenylmercuric acetate and UO2 (CH3COO)2. The overall dimensions of the molecule are 40 X 30 X 25 A. The most prominent secondary structural features are two turns of alpha-helix and a three strand stretch of antiparallel beta-sheet. The alpha-carbon backbone of RNase St seems to have no apparent correlation with that of ribonuclease A.