17-Hydroxyprogesterone metabolism in the monkey fetal adrenal: C 17–20Lyase and 21-hydroxylase activities

Abstract

C 17–20Lyase and 21-hydroxylase activities were measured during late gestation In the rhesus monkey ( Macaca mulatta ) fetal adrenal. Activities were assessed in 10,000 × g supernatants with 17-hydroxyprogesterone and NADPH as substrates. Although conversion of [ 14C]17-hydroxyprogesterone to [ 14C]androstenedione was noted, activity was often nonlinear and far less than the rate of hydroxylation which together prevented an accurate estimation of lyase rate, K m and V max. 21-Hydroxylase activity was characterized; the mean reaction rate was 1.6 × 10 −3 μmoles NADPH oxidized/min. × mg −1 protein with an apparent K m of 3.6 × 10 −7 M and a V max of 2.2 × 10 −3 μmoles/min. × mg −1 protein. These values were similar to data obtained In adrenals from adult monkeys. A relatively high level of hydroxylase activity in the fetal gland might lead to an Inadequate supply of precursors for the synthesis of dehydroepiandrosterone sulfate (DHEAS) in the adrenal if it also contained 3β-hydroxysteroid dehydrogenase (3β-hsdh). However, the fact that the fetal adrenal reportedly is deficient in 3β-hsdh may serve to protect both DHEAS and corticoid synthesis.