Kenneth T Nakamura

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.

Renal Hemodynamics and Functional Changes during the Transition from Fetal to Newborn Life in Sheep

ABSTRACT: 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 μEq/min) and fractional excretion of sodium (FENa) (from 7.6 ± 0.9 to 1.1 ± 0.3%). In summary, present results demonstrate that transition from fetal to newborn life is associated with a rapid rise in glomerular filtration rate and an important decrease in urinary sodium excretion and fractional excretion of sodium. These changes seem to be independent of changes in renal blood flow velocity, renal vascular resistance, and blood pressure.

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.

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

ABSTRACT.: 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 <115 days gestation (n=6) and >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 >125 days and in the majority of fetuses <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 Hemodynamic Response to Atrial Natriuretic Factor in Fetal and Newborn Sheep

ABSTRACT: 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 µg/kg of body wt in fetuses and 0.25 to 8.0 µg/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< 0.001) and a decrease in renal vascular resistance (F=38.3, p< 0.001) in both groups. The magnitude of changes in renal blood flow velocity and renal vascular resistance expressed as percentage of changes (%δ) from control values, were similar (p> 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.

Loop diuretics and in vitro relaxation of human fetal and newborn mouse airways.

This study was designed to test the hypotheses that furosemide directly causes relaxation in human fetal airway and that delivery of loop diuretics to either the adventitial or epithelial surface of newborn mouse airway results in equivalent relaxation. Isometric tension changes were measured in human fetal (11–16 wk) trachea and mainstem bronchus rings exposed to furosemide (300 μM) or saline after acetylcholine or leukotriene D4 constriction. Significant decreases in isometric tension to furosemide were demonstrated after constriction with acetylcholine or leukotriene D4. To examine the site of effect and mimic aerosolized and systemic administration, furosemide (3–300 μM) and bumetanide (0.3–30 μM) were applied separately to epithelial and adventitial surfaces of newborn mouse airways. No differences in airway diameter changes to epithelial or adventitial furosemide or bumetanide were observed, but a 10-fold difference in potency was found. In summary, human fetal airway relaxed to furosemide when constricted with either neurotransmitter or inflammatory mediator in vitro. Further, no differences in relaxation to equimolar epithelial and adventitial furosemide were observed in isolated newborn mouse airway. Taken together, this provides evidence that furosemide has a direct, nonepithelial-dependent effect on airway smooth muscle tone.

Ontogeny of Renal β-Adrenoceptor-Mediated Vasodilation in Sheep: Comparison between Endogenous Catecholamines

ABSTRACT. The renal hemodynamic response to renal arterial infusions of norepinephrine was compared to epinephrine infusions during renal a-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 < 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 < 0.001). Increases in renal blood flow velocity produced by both norepinephrine and epinephrine infusions were completely inhibited by intrarenal infusion of ICI118,551, a fo-adrenoceptor antagonist. Taken together, these results suggest that the renal vascular fo-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/32-adrenoceptor mediated renal vasodilatory capacity is observed during fetal life.

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.

Effects of Epinephrine on the Renal Vascular Bed of Fetal, Newborn, and Adult Sheep

ABSTRACT: 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 jug/ml. Epinephrine infusions during renal α-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 < 0.001). This vasodilation produced by epinephrine during a-adrenoceptor blockade was completely inhibited by ICI 118, 551, a β2-adrenoceptor antagonist. Inhibition of renal vascular β-adrenoceptors with propranolol in fetal sheep did not enhance α-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 a-adrenoceptor blockade were greater in fetal compared to newborn and adult sheep. However, epinephrine-mediated renal vasoconstriction was not enhanced by blockade of β-adrenoceptors in fetal sheep.

Developmental Changes in Sodium Nitroprusside and Atrial Natriuretic Factor Mediated Relaxation in the Guinea Pig Aorta

ABSTRACT: 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 Krebs 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 < 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 < 0.05), and significantly shifted the concentration-response curve to the right (p < 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; and4) methylene blue does not affect atriopeptin III-mediated relaxation in any age group.