Role of angiotensin II on the adrenal and vascular responses to hemorrhage during development in fetal lambs.

Developmental aspects of fetal adrenal and vascular responses to endogenous increase in plasma angiotensin II (All) following sequential reductions of fetoplacental blood volume were studied in two groups of chronically catheterized fetal lambs (seven were <120 days and seven were >130 days of gestation, term being 145 days). At similar levels of hemorrhage, the rise in plasma renin activity (PRA) was found to be greater in fetuses >130 days than in those <120 days (P < 0.025). Similarly, the effect of hemorrhage on plasma All was more pronounced in fetuses >130 days than in those <120 days (P < 0.05). No changes in plasma aldosterone were seen during hemorrhage in fetuses <120 days, whereas plasma aldosterone increased (P < 0.001) in those >130 days. This increase correlated with the rise in plasma All (r = 0.70, P < 0.001). In order to determine whether factors other than the rise in plasma All were responsible for the increase in plasma aldosterone in fetuses >130 days, these results were compared to results obtained in four nephrectomized fetuses >130 days submitted to similar degrees of hemorrhage. No changes in PRA or plasma All were observed. However, a small increase in plasma aldosterone (from 31 ± 13 to 47 ± 11 pg/ml, P < 0.01) was found, and this correlated with changes in plasma potassium concentration (r = 0.50, P < 0.05). Finally, mean arterial blood pressure decreased during hemorrhage in fetuses <120 days (P < 0.05), whereas no changes were observed in those >130 days unless their kidneys were removed. This suggests that the renin-angiotensin system is an important modulator of fetal blood pressure during hemorrhagic stress. (Circ Res 50: 645-650, 1982)