Growth hormone and insulin-like growth factor-I accelerate PMSG-induced differentiation of granulosa cells

To investigate the nature of the interactions between growth hormone (GH), insulin-like growth factor-I (IGF-I) and follicle stimulating hormone (FSH), their temporal and dose-related effects on steroidogenesis were studied in granulosa cells from stilboestrol-treated immature rats, stimulated in vitro with pregnant mare's serum gonadotropin (PMSG) or FSH. GH in the presence of PMSG enhanced aromatase activity and progesterone synthesis above that induced by maximally stimulating doses of PMSG alone, and accelerated PMSG-induced peak levels for both progesterone and aromatase activity. IGF-I also enhanced PMSG-induced aromatase activity and progesterone production, and accelerated their peak responses in a similar fashion to the effects observed for GH. The stimulatory actions of IGF-I could still be observed after the removal of FSH from the cultures, and appeared to be partly independent of cAMP. It is concluded that both GH and IGF-I act on FSH-induced granulosa cells to accelerate the differentiation of the follicular cell to a lutein cell.