A MECHANISM FOR THE ACTION OF PREGNANT MARE SERUM GONADOTROPIN ON AROMATASE-ACTIVITY IN THE OVARIAN FOLLICLE OF THE MEDAKA, ORYZIAS-LATIPES

Our recent studies (Sakai et al., '88) have shown that there is a progressive increase in aromatase activity, assessed indirectly by the conversion of exogenous testosterone to estradiol-17-beta, in medaka (Oryzias latipes) vitellogenic follicles isolated between 28 and 20 hr before spawning. The present study was designed to determine if pregnant mare serum gonadotropin (PMS) and cAMP are able to induce aromatase activity in early vitellogenic follicles isolated at 32 hr before spawning. Both 100 IU/ml PMS and 100 ng/ml testosterone alone significantly stimulated estradiol-17-beta production by follicles at this stage. PMS also enhanced testosterone-induced estradiol-17-beta production. This enhancing effect of PMS on aromatization of exogenous testosterone to estradiol-17-beta was completely inhibited by 10-mu-g/ml actinomycin D and 10-mu-g/ml cycloheximide. Both 5 mM dibutyryl cAMP (dbcAMP) and 10-mu-M forskolin, an adenylate cyclase activator, alone significantly stimulated estradiol-17-beta production. A 1-mu-g/ml dose of cyanoketone, a potent inhibitor of 3-beta-hydroxysteroid dehydrogenase, completely suppressed PMS- and forskolin-induced estradiol-17-beta production in the absence of testosterone, but did not influence the enhancing effect of either PMS or forskolin on the conversion of exogenous testosterone to estradiol-17-beta. These results indicate that PMS induces aromatase activity in medaka vitellogenic follicles via an adenylate cyclase-cAMP system, and further suggest that this action of PMS is dependent upon both transcriptional and translational processes.