Patterns of 3 beta-hydroxysteroid dehydrogenase/delta 5-4isomerase activity in the rhesus monkey placenta and fetal adrenal.

3 beta-Hydroxysteroid dehydrogenase/delta 5-4isomerase activity (3 beta-HSDH) was examined in the rhesus monkey (Macaca mulatta) placenta and fetal adrenal at 135 and 155-162 days of gestation. Activity was evaluated in microsomes by the conversion of [3H]pregnenolone to [3H]progesterone. There was a 7-fold increase in enzyme activity in the whole adrenal (minus medulla) between the two stages of development. Combining data from both periods, enzyme activity was greater in the outer than in the inner region of the adrenal. No stage-dependent change in placental activity was evident. The temporal patterns in 3 beta-HSDH activity are consistent with corticoid and progesterone patterns in the circulation. Thus, the level of 3 beta-HSDH activity may be rate limiting in both the fetal adrenal and placenta. Enzyme activity was assessed in incubations which included unextracted, heat-treated, 100,000 g tissue supernatants. In both placental and adrenal incubations, competitive inhibition was noted. Ethyl ether extracts of 100,000 g tissue supernatants also inhibited 3 beta-HSDH in the respective tissues. GLC analysis of these extracts revealed the presence of putative dehydroepiandrosterone. Hormone levels and the nature of the inhibition that were observed are compatible with the conclusion that dehydroepiandrosterone can inhibit the conversion of pregnenolone to progesterone in vivo. The physiological importance of this remains to be determined.