Novel studies on influence of gonadotropins and insulin-like growth factor-I on growth of cumulus oophorus in the rat.

In the final developmental stage of a Graafian follicle, there are two functionally distinct types of granulosa cells: the cumulus cells (CCs) and the mural granulosa cells (MGCs). Previous studies focused on follicle-stimulating hormone (FSH) and insulin-like growth factor I (IGF-I) interactions in MGCs. Our goal was to study these interactions in CC proliferation. Immature rats received in vivo treatments of either saline, equine chorionic gonadotropin (eCG) with high FSH activity, an IGF-I analog (LR3-IGF-I) with poor binding to IGF-I binding proteins, or a combination of both hormones. CCs from each in vivo treatment were then cultured and treated in vitro with either saline, FSH, or IGF-I. CCs proliferation were assessed by measurement of 3H-thymidine incorporation. Prior in vivo treatment with eCG resulted in the highest proliferative activity of CCs when combined with FSH in vitro treatment. In vivo treatment with LR3-IGF-I had no effect on CC replication. CC replication was higher in FSH in vitro treatment than of IGF-I. The combination of eCG and LR3-IGF-I was the only in vivo treatment to stimulate higher CC proliferation with IGF-I in vitro treatment. This study suggests that FSH does not act through IGF-I, a mechanism previously proposed.