Cortisol-induced inhibition of ovine renin and aldosterone responses to hypotension.

Previous studies from this laboratory have demonstrated that in preterm fetal sheep increases in plasma cortisol (F) concentration equal in amplitude to fetal F stress responses suppress plasma renin activity (PRA). The purpose of this study was to investigate the possibility that this negative interaction exists in adult sheep. Five conscious ewes with chronically prepared carotid arterial loops were infused intravenously with F (6 micrograms X kg-1 X min-1) or vehicle (5% ethanol in 0.9% saline) for 5 h. One hour after the end of F or vehicle infusion, renin secretion was stimulated by hypotension produced by infusion of sodium nitroprusside (20 micrograms X kg-1 X min-1, iv). F infusion increased plasma F from 26 +/- 3 to 46 +/- 8 ng/ml; during vehicle infusion plasma F did not change from 20 +/- 4 ng/ml. F infusion decreased hematocrit from 29 +/- 2 to 26 +/- 1%. Basal PRA in vehicle- and F-infused groups were 0.4 +/- 0 and 0.2 +/- 0.1 ng angiotensin I X ml-1 X h-1 and did not change. In vehicle-infused ewes, PRA increased from 0.4 +/- 0 and 0.2 +/- 0.1 ng angiotensin I X ml-1 X h-1 and did not change. In vehicle-infused ewes, PRA increased from 0.4 +/- 0 to 4.6 +/- 0.4 and plasma aldosterone from 26.0 +/- 1.0 to 173.1 +/- 21.8 pg/ml, while, in F-infused ewes, PRA increased from 0.2 +/- 1 to 3.3 +/- 0.4 ng angiotensin I X ml-1 X h-1 and aldosterone from 25.0 +/- 0 to 48.2 +/- 23.2 pg/ml, significantly smaller responses.(ABSTRACT TRUNCATED AT 250 WORDS)