Are fetal adrenocorticotropic hormone and renin secretion suppressed by maternal cortisol secretion?

Previous studies from this laboratory have demonstrated that intravenous infusions of hydrocortisone (cortisol) into fetal sheep at rates that produce plasma concentrations achieved during fetal stress inhibit fetal adrenocorticotropic hormone (ACTH) and renin secretion. The present study was designed to test for inhibition of fetal renin and ACTH after maternal adrenal secretion of cortisol. ACTH-(1-24) or saline infusion into 12 pregnant ewes (120-132 days gestation) at rates of 0, 1, 5, or 20 ng ACTH.kg-1.min-1 for 5 h produced dose-related increases in maternal plasma ACTH and cortisol concentrations and fetal plasma cortisol concentration. In the 20-ng.kg-1.min-1 group, increases in fetal plasma cortisol of 8.0 ng/ml (to 24.3 +/- 3.7 ng/ml) did not suppress basal fetal plasma renin activity. One hour after the end of the maternal vehicle or ACTH infusion, fetal ACTH secretion was stimulated by fetal intravenous infusion of sodium nitroprusside. In the 0-, 1-, and 5-ng.kg-1.min-1 groups, fetal ACTH responses to nitroprusside were suppressed in animals infused with ACTH. Together, these results indicate that the maternal adrenal secretion of cortisol inhibits stimulated secretion of ACTH but not renin in 120- to 132-day-gestation fetal sheep.