INFLUENCE OF ESTRADIOL AND ANDROSTENEDIONE ON ACTH AND CORTISOL SECRETION IN THE OVINE FETUS

OBJECTIVE: To test the hypothesis that physiologic increases in fetal plasma 17 beta-estradiol and androstenedione modulate the activity of the fetal hypothalamic-pituitary-adrenal (HPA) axis. METHODS: Seventee n pregnant ewes and their fetuses were chronically catheterized. At th e time of surgery, the fetuses received implants that released 17 beta -estradiol (n = 5) alone or 17 beta-estradiol and androstenedione (n = 6), each at a rate of approximately 250 mu g/day for each steroid. Th e control group (n = 6) received either no pellet (n = 2) or a ''place bo'' pellet, which contained no steroid (n = 4). Fetal blood samples w ere drawn for hormone and blood gas analysis at 1-3 day intervals unti l the time of spontaneous parturition. Fetal plasma ACTH and cortisol concentrations were fit to semilogarithmic equations and analyzed by s tepwise multiple linear regression analysis for statistically signific ant effects of 17 beta-estradiol and androstenedione. RESULTS: Estradi ol significantly increased and androstenedione significantly decreased the ACTH and cortisol concentrations. Treatment with both 17 beta-est radiol and androstenedione resulted in parturition approximately 4 day s earlier than in the other groups (P < .05). CONCLUSIONS: Physiologic increases in fetal plasma estradiol and androstenedione modify the ac tivity of the HPA axis. Copyright (C) 1997 by the Society for Gynecolo gic Investigation.