INHIBIN, ACTIVIN, FOLLISTATIN AND TRANSFORMING GROWTH-FACTOR-BETA (TGF-BETA) - OVARIAN PRODUCTION AND POSSIBLE ROLE IN THE REGULATION OF FOLLICULOGENESIS IN PRIMATES

The aim of this review is to provide recent data concerning the ovarian production of the inhibin-related peptides and their possible role in the regulation of ovarian folliculogenesis in primates. Activin is mainly produced by recruitable follicles, whereas inhibin, FSP and TGF-beta are mainly produced by preovulatory follicles. Activin could play a key role in the selection of the follicle destined to ovulate by enhancing the responsiveness of granulosa cells to FSH. Activin inhibits production of aromatizable androgens by theca interna cells but, by stimulating the FSH-induced aromatase at the level of granulosa cells, it prepares the early selected follicle to play its further endocrine function. The full endocrine function of the preovulatory follicle is triggered, among others, by inhibin which strongly stimulates the production of aromatizable androgens by theca interna cells, by TGF-beta which may favour cytodifferentiation of granulosa cells, and by FSP which, by binding activin, suppresses the negative actions of activin on preovulatory maturation.