INFLUENCE OF 19-NORTESTOSTERONE AND ANDROGENS ON PROGESTERONE BIOSYNTHETIC-ENZYMES IN EARLY HUMAN PLACENTAL EXPLANTS

We recently showed that the production of progesterone (P4) in human placental explant culture from early gestation is enhanced by treatment with 19-nortestosterone (19-NT) or with certain androgens, namely androstenedione (A-dione), 5-alpha-androstane-3-alpha,17-beta diol (3-alpha-diol) and 5-alpha-androstane-3-beta,17-beta diol (3-beta-diol). This stimulation of P4 was explored further in this study. There was little metabolism of radioactive P4 when incubated for 24 h in the presence or absence of these steroids. The role of different steroids in the regulation of P450 cholesterol side-chain cleavage enzyme (P450scc) and 3-beta-hydroxysteroid dehydrogenase (3-beta-HSD) was evaluated by measuring the conversion of P4 derived from unlabelled 25-hydroxycholesterol and from labelled pregnenolone, respectively. The results showed that 19-NT, A-dione and 3-alpha-diol stimulated P450scc activity; however, 3-beta-diol was ineffective. While 19-NT and 3-beta-diol enhanced the bioconversion of pregnenolone to P4, A-dione and 3-alpha-diol were without effect. The initial rapid stimulation of P4 by 19-NT within 2 h of incubation was not blocked by concurrent treatment with cycloheximide (CH). However, after incubation for 24 h, 70% of the 19-NT-stimulated P4 was abolished by CH. During the same incubation period, P4 stimulation by A-dione, 3-alpha- and 3-beta-diol were completely blocked by treatment with CH. Thus our observations suggest that 19-NT-stimulated P4 accumulation is due to the combined effects on P450scc and 3-beta-HSD enzyme activities. A-dione and 3-alpha-diol increase biosynthesis of P4 by acting selectively on P450scc enzyme. However, the stimulatory action of 3-beta-diol on P4 is only at the level of 3-beta-HSD. Since CH blocks the stimulatory actions, the mechanism(s) by which androgens (A-dione, 3-alpha-diol and 3-beta-diol) and norandrogen (19-NT) augment the biosynthetic enzyme activities appears to be mediated by a process inhibited by CH. Since CH interference was absent during the initial rapid P4-stimulation by 19-NT, there may be a direct action of this steroid at the cellular level which is not dependent on new protein synthesis.