FUNCTIONAL MATURATION OF THE PRIMATE FETAL ADRENAL IN-VIVO .2. ONTOGENY OF CORTICOSTEROID SYNTHESIS IS DEPENDENT UPON SPECIFIC ZONAL EXPRESSION OF 3-BETA-HYDROXYSTEROID DEHYDROGENASE ISOMERASE/

Cortisol, produced by the primate fetal adrenal, regulates the mat mat uration of organ systems necessary for extrauterine life. During most of primate pregnancy, however, the fetal adrenal lacks the enzyme 3 be ta-hydroxysteroid dehydrogenase/isomerase (3 beta HSD), which is essen tial for cortisol synthesis. Therefore, we used immunohistochemistry a nd in situ hybridization techniques to investigate the developmental e xpression of 3 beta HSD in the fetal rhesus monkey adrenal from 109 da ys' gestation until term (165 +/- 5 days) and assessed the role of ACT H in the induction of its expression and localization. We also examine d whether ACTH regulates the expression of two other steroidogenic enz ymes, cytochrome P450 cholesterol side-chain cleavage (P450scc) and P4 50 17 alpha-hydroxylase, 17/20-lyase (P450c17), in the fetal rhesus mo nkey adrenal. To stimulate ACTH secretion from the fetal pituitary in vivo, we administered metyrapone to late gestation fetal rhesus monkey s for 3-7 days. Adrenals were collected from untreated fetuses at 109- 125 days (n = 5), 130-148 days (n = 7), 155-172 days (n = 4), and afte r metyrapone treatment at 135-137 days (n = 4). The cortical width and total amount of 3 beta HSD staining were measured using an image anal ysis system. 3 beta HSD was localized primarily in the definitive zone cells of the adrenal from fetuses between 109-148 days, whereas at te rm (155-172 days), 3 beta HSD was localized in both definitive and tra nsitional zone cells. The cortical width and total amount of 3 beta HS D staining in the adrenal increased significantly (P < 0.05) between 1 48 days (137 +/- 14 pm and 3,689 +/- 522 grains) and 155 days (315 +/- 61 mu m and 7,321 +/- 2,008 grains). Interestingly, in metyrapone-tre ated fetuses at 135-137 days, 3 beta HSD messenger RNA (mRNA) and prot ein were localized extensively in both the definitive and transitional zones, a pattern seen only in term fetal adrenals in untreated animal s. In addition, metyrapone treatment significantly (P < 0.05) increase d cortical width (386 +/- 95 mu m) and total 3 beta HSD immunostaining (29,063 +/- 13,692 grains) compared with age-matched controls. In con trast to 3 beta HSD, P450scc mRNA was detected in the definitive, tran sitional, and fetal zones, and its expression was not altered after me tyrapone treatment. P450c17 mRNA was detected in the transitional and fetal zones, and the relative abundance was greater in the transitiona l zone. The relative abundance of P450c17 mRNA was increased in the fe tal zone after metyrapone treatment. In summary, at term or after mety rapone treatment, expression of 3 beta HSD is induced in the transitio nal zone of the fetal rhesus monkey adrenal gland, an indication of fu nctional maturation of the primate adrenal cortex. These data suggest that the ontogenetic increase in fetal pituitary ACTH secretion plays an important role in the induction of 3 beta HSD expression in the tra nsitional zone.