ACTIVATION OF THE BABOON FETAL PITUITARY-ADRENOCORTICAL AXIS AT MIDGESTATION BY ESTROGEN - ADRENAL DELTA-5-3-BETA-HYDROXYSTEROID DEHYDROGENASE AND 17-ALPHA-HYDROXYLASE-17,20-LYASE ACTIVITY

We have recently demonstrated that treatment of pregnant baboons with androstenedione (DELTA-4A) at midgestation to increase estrogen production induced a pattern of placental cortisol (F) metabolism which was similar to that at term and resulted in de novo F production by the fetus, presumably by activation of the fetal hypothalamic-pituitary-adrenocortical axis. The present study was designed to examine the subcellular events in the fetal adrenal that were apparently stimulated by estrogen-induced alterations in transplacental corticosteroid metabolism. Therefore, we determined the effects of estrogen treatment at midgestation and removal of estrogen action near term on the specific activity of the rate-limiting enzymes DELTA-5-3-beta-hydroxysteroid dehydrogenase (3-beta-HSD) and 17-hydroxylase-17,20-lyase (17-alpha-OHase). Fetal adrenals were obtained on day 100 (n = 11) or day 165 (n = 11) of gestation (term = day 184) from untreated animals, on day 100 from animals receiving DELTA-4-A daily between days 70-100 (n = 9) to increase placental estrogen production, and on day 165 from baboons treated daily between days 130-164 with antiestrogen ethamoxytriphetol (MER-25; n = 7). The activity of 17-alpha-OHase was determined by incubating adrenal microsomes (105,000 x g) with [H-3]progesterone, NAD+, and NADH in phosphate buffer. The radiolabeled products 17-hydroxyprogesterone, DELTA-4A, and testosterone were purified, and enzyme activity expressed as picograms of product per min/mg tissue. The activity of 3-beta-HSD was determined by incubating adrenal microsomes with [H-3]pregnenolone and NAD+ in phosphate buffer. The radiolabeled progesterone product was purified, and enzyme activity was expressed as nanograms per min/mg tissue. Treatment with DELTA-4A increased estrogen concentrations at midgestation 3-fold to levels comparable to those measured near term. Although fetal adrenal weight was greater at term than at midgestation (P < 0.05), weight was not increased by DELTA-4A treatment. The specific activity (mean +/- SE) of fetal adrenal 17-alpha-OHase at midgestation (181 +/- 29) was increased (P < 0.05) 3-fold by treatment with DELTA-4A to levels (591 +/- 105) comparable to those in adrenal microsomes prepared from untreated animals near term (816 +/- 130). Enzyme activity in adrenals of MER-25-treated baboons was 40%, but not significantly lower than that in term controls. The specific activity of 3-beta-HSD at term (41 +/- 11) was 100-fold greater (P < 0.05) than that at midgestation and was reduced (P < 0.05) by more than 60% by treatment in vivo with MER-25. Enzyme activity at midgestation (0.4 +/- 0.1) was increased 4-fold, but not significantly, by treatment with DELTA-4A. These findings indicate that the specific activities of 3-beta-HSD and 17-alpha-OHase in fetal adrenals were significantly increased with advancing gestation, enhanced prematurely at midgestation by treatment with DELTA-4A, and reduced at term after treatment with MER-25. We propose that the ontogenesis of de novo F synthesis at term and in DELTA-4A-treated animals at midgestation is the result of an increase in specific activities of adrenal 3-beta-HSD and 17-alpha-OHase.