ROLE OF THE IGF SYSTEM IN THE OVARY

The stimulating effect of Insulin-like Growth Factors (IGFs) on ovaria n folliculogenesis is modulated by binding proteins (IGFBPs). During f ollicular growth, levels of IGFBP-2, -4 and -5 decrease in follicular fluid. These changes are a consequence of a decrease in synthesis and of a degradation by gonadotropin-stimulated specific proteases. They l ead to an increase in the bioavailability of IGFs and their action on granulosa cells. By contrast, follicular atresia is characterized by a high increase in the synthesis and levels of IGFBPs < 40kDa, and by a dramatic decrease in IGFs bioavailability. Finally, at least part of intrafollicular IGFs and IGFBP-3 may be derived from the circulatory p ool. Their levels only change slightly during follicular growth and at resia.