Comparison of the Adrenal and Renal Responses to Angiotensin II Fetal Lambs and Adult Sheep

The adrenal and renal responses to similar increases in plasma angiotensin II (AII) were studied in chronically catheterized fetal lambs (112-131 days gestation: term 145 days) and adult nonpregnant sheep. The rate of AII infusion was adjusted to compare the effect of similar rises in plasma AII concentration between fetuses and adult ewes. Increases in plasma AII were associated with a decrease in plasma renin activity (PRA) in both fetuses (5.55 +/- 1.53 to 2.11 +/- 0.59 ng/ml per hr, P less than 0.05) and adult ewes (1.28 +/- 0.34 to 0.62 +/- 0.16 ng/ml per hr, P less than 0.05), but the percent changes in PRA for similar increases in plasma AII were not different when fetuses were compared to adult ewes. Contrary to the effect of AII on PRA, the increase in plasma AII did not produce parallel changes in plasma aldosterone concentration when fetuses were compared to adult ewes. The percent changes in plasma aldosterone concentration for similar increases in AII concentration were significantly higher in adult ewes (+165 +/- 37%) than in fetuses (+58 +/- 15%)(P less than 0.01). Finally, there were no significant changes in fetal urinary excretion of PGE and PGF2alpha when a significant rise (P less than 0.05) was observed in adult ewes at the highest level of plasma AII concentration. In summary, the present results tend to suggest that there are differences between fetuses and adult ewes in the response to AII, the response being smaller in fetuses.