Renal hemodynamic responses to hypoxemia during development: Relationships to circulating vasoactive substances

Abstract

Chronically catheterized fetal lambs (n = 11, gestational age 111-139 days) and neonatal lambs (n = 20, postnatal age 4-30 days) were studied to explore during development the relationship of renal hemodynamic responses during hypoxemia to plasma epinephrine con­centration (E), plasma norepinephrine concentration (NE), plasma arginine vasopressin concentration (AVP), and plasma renin activity (PRA). A low oxygen gas mixture (11.1 ± 0.1% 02) was administered for 30 min to the pregnant ewe or neonatal lamb to induce hypoxemia with maintenance of normal arterial pC02 and pH. Arterial blood pressure was recorded continuously and renal blood flow (RBF) was determined by the radiolabeled micro­sphere technique. Moderate hypoxemia (p02 16 ± 2 torr and 33 ± 6 torr in fetus and neonate, respectively) induced increases in E, NE (measured by radioenzymatic assay), and AVP (measured by radioimmunoassay) in both fetus and neonate. PRA (measured by radioimmunoassay) also increased in response to hypoxemia in neonatal lambs. The change in mean arterial pressure with hypoxemia (ΔMAP) was significant in fetuses (ΔMAP 8 ± 14%, p < 0.05) but not in lambs (ΔMAP 1 ± 10%, p > 0.5). Similarly, the change in renal blood flow with hypoxemia (ΔRBF) was significant (ΔRBF -51 ± 24%, p < 0.001) in fetuses but not in neonatal lambs (ΔRBF -9 ± 38%, p > 0.1). These results reflected a change in renal vascular resistance with hypoxemia (ΔRVR) that was significant in fetal lambs (ΔRVR 169 ± 168%,/p < 0.01) but not in neonatal lambs (ΔRVR 51 ± 180%, p > 0.2). The relationships of these renal hemodynamic responses to the measured vasoactive substances, and the influence of their interactions to pro­duce these responses, were assessed by response surface regression analysis. The response surface regression model of responses to hypoxemia of E (ΔE), NE (ΔNE), AVP (ΔAVP), and PRA (ΔPRA) to ΔMAP and ΔRVR over the entire development period fit the data well (adjusted R20.8427 and 0.8274, respectively). AE was the most predic­tive of the components for both ΔMAP and ΔRVR (F ratio 7.89 and 7.25, respectively). Contour plots of the interac­tion of ΔE with postconceptional age and ΔNE demon­strated considerable age dependence of the relationship of ΔE and ΔNE to ΔMAP and ΔRVR during development. The results are consistent with the hypothesis that asyn­chronous maturation of vascular β-adrenergic (vasodila-tory) and α-adrenergic (vasoconstrictor) effector mecha­nisms occurs throughout the fetal/neonatal period. © 1988 International Pediatric Research Foundation, Inc.