Fetal adrenocorticotropin (ACTH) and renin secretion are increased by a variety of stimuli and decreased by cortisol negative feedback inhibition. However, the time courses of these interactions are unknown. The present studies were designed to test for rapid feedback negative suppression of ACTH and renin secretion in fetal and adult sheep. In chronically catheterized fetal sheep, ACTH and renin secretion were stimulated by intravenous infusion of sodium nitroprusside, a vasodilator drug. Vehicle or cortisol, infused at rates of 1, 2, or 4 micrograms/min for 2 min before and during the infusion of nitroprusside did not significantly alter the fetal ACTH or renin responses to nitroprusside. In five nonpregnant ewes, chronically prepared with skin loops containing the carotid arteries, nitroprusside (20 micrograms X kg-1 X min-1) was infused beginning 2 min after infusion of vehicle or cortisol (3.5 or 7 micrograms X kg-1 X min-1). Cortisol infusion produced a rising plasma cortisol concentration similar to that after stress but did not alter the magnitude of the ACTH response to nitroprusside. The results indicate that cortisol-induced suppression of ACTH secretion does not occur rapidly in the fetal or adult sheep and that the cortisol-induced suppression of fetal plasma renin activity is a slow process.
- Copyright © 1986 the American Physiological Society