Developmental changes in marmoset granulosa cell responsiveness to insulin-like growth factor-I: interactions with...

The biological actions of insulin-like growth factor-I (IGF-I) on granulosa cell steroidogenesis at defined stages of preovulatory follicular development in the marmoset monkey were examined. Studies were carried out by primary cell culture of granulosa cells derived from small antral (0.5-1.mm diameter) and large preovulatory (2-3.mm diameter) follicles collected during the mid-late follicular phase of the ovarian cycle. IGF-I (0.3-100 ng/ml) had no effect on progesterone accumulation or aromatase activity during 48-h culture of granulosa cells from small follicles. Progesterone accumulation by cells from large follicles was also unaffected by IGF-I over the same time period, although aromatase activity was stimulated in a dose-dependent manner (18-fold increase over basal levels with a maximally stimulatory dose of 30 ng IGF-I/ml). In contrast, granulosa cells from small and large follicles responded to IGF-I in terms of both progesterone accumulation and aromatase activity after longer periods of culture (4 days for progesterone; 6 days for aromatase). Concurrent treatment of granulosa cells from small follicles with estradiol (10(-7) M) enhanced the dose-dependent actions of IGF-I on both indices of steroidogenesis and advanced the time at which IGF-I stimulated activity was first detectable. The effects of estradiol on granulosa cell IGF-I responsiveness were independent of cell number. A synergistic action of IGF-I on FSH-stimulated granulosa cell steroidogenesis was not apparent.(ABSTRACT TRUNCATED AT 250 WORDS)