Pregnenolone metabolism in developing follicles of the frog Rana Pipiens.

Abstract

To investigate ovarian steroid metabolism in th¥ frog Rana pipiens, follicles at different stages of development were incubated with 3H-pregnenolone, and the metabolites were analyzed by thin layer chromatography. A decrease in the percentage of unmetabolized 3H-pregnenolone in the medium and in the follicles suggested that total steroidogenesis increased in later stage follicles. The main metabolites formed were estradiol by early stage follicles and testosterone by later stage follicles. Besides these two main metabolites, androstenedione, estrone, and progesterone were also identified, suggesting the presence of the 64 pathway of steroid metabolism in Rana follicles. The change in the main metabolite from estradiol to testosterone might be due to inhibition of aromatase activity. The possibility that a steroidal aromatase inhibitor might be synthesized during follicular development was investigated but none was identified. Stage 3 follicle incubation in the presence of a known aromatase inhibitor, 4-hydroxy-androstenedione (4-0HA), resulted in a large increase in androstenedione as well as a smaller increase in testosterone. Such an increase in androstenedione did not occur in untreated late stage follicles. Therefore, synthesis of a steroidal aromatase inhibitor seems unlikely. Follicles also metabolized 3Hpregnenolone to several polar metabolites. However, the polar metabolites synthesized by stage 3 follicles preincubated with or without 4-0H-A were similar. Therefore, it is suggested that the polar metabolites are not derived from either estradiol or testosterone, but are probably progesterone metabolites.