IMMUNOHISTOCHEMICAL LOCALIZATION OF 3-BETA-HYDROXYSTEROID DEHYDROGENASE IN THE RAT OVARY DURING FOLLICULAR DEVELOPMENT AND ATRESIA

In the adult ovary, cohorts of growing follicles are continuously generated, from which dominant follicles are selected during each estrous cycle. To compensate for the rapid proliferation of follicular cells in the growing pool of follicles, follicles are eliminated by atresia, thereby maintaining ovarian tissue mass. Estrogens and androgens have been implicated as intraovarian regulators of follicular growth and atresia, suggesting that the fate of an individual follicle to develop to the preovulatory stage or to undergo atresia is associated with distinct profiles of steroid production. We therefore have localized 3beta-hydroxysteroid dehydrogenase (3beta-HSD), an enzyme required for the biosynthesis of all major steroid hormones, in ovaries of immature and adult rats during follicular development, atresia, and corpus luteum formation. The pattern of immunostaining for 3beta-HSD remained constant in the interstitial cell compartment and was not affected by the age of the rats nor the stage of the estrous cycle. As thecal cells differentiated from the surrounding stroma and restructured around the secondary follicle, they expressed intense staining for 3beta-HSD. This staining persisted in preantral, antral, and preovulatory follicles. Granulosa cells in primary, secondary, and antral follicles did not contain detectable levels of 3beta-HSD and did not stain positively until the follicle reached the preovulatory stage of development. A novel finding presented in this paper is that 3beta-HSD persisted in the thecal cells of follicles throughout the entire process of atresia, suggesting that during atresia the potential for the synthesis of androgens is retained. These observations, together with the previous reports that anti-androgens rescue follicles from atresia induced by hCG, indicate that thecal cell-derived androgens may be involved in the regulation of follicular dynamics.