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

The adrenal and renal responses to similar increases in plasma angiotensin II (All) were studied in chronically catheterized fetal lambs (112-131 days gestation; term 145 days) and adult nonpregnant sheep. The rate of All infusion was adjusted to compare the effect of similar rises in plasma AH concentration between fetuses and adult ewes. Increases in plasma All 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 < 0.05) and adult ewes (1.28 ± 0.34 to 0.62 ± 0.16 ng/ml per hr, P< 0.05), but the percent changes in PRA for similar increases in plasma All were not different when fetuses were compared to adult ewes. Contrary to the effect of All on PRA, the increase in plasma All 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 All concentration were significantly higher in adult ewes (+165 ± 37%) than in fetuses (+58 ± 15%) (P < 0.01). Finally, there were no significant changes in fetal urinary excretion of PGE and PGF2a when a significant rise (P < 0.05) was observed in adult ewes at the highest level of plasma All concentration. In summary, the present results tend to suggest that there are differences between fetuses and adult ewes in the response to All, the response being smaller in fetuses. Circ Res 50:140-147, 1982