Hormonal regulation of the growth and steroidogenic function of human granulosa cells.
The aim of this study was to assess development-related interactions between gonadotropins and insulin-like growth factor (IGF-I) on DNA synthesis and steroidogenesis in human granulosa cells. "Immature" granulosa cells were obtained from follicles during the late luteal phase or first half of the follicular phase; "mature" granulosa cells came from follicles during the second half of the follicular phase but before the midcycle LH surge; and granulosa-lutein cells were obtained as a by-product of in vitro fertilization. Granulosa cells were cultured for 96 h in serum-free medium 199 with and without LH or FSH, and in the presence and absence of IGF-I. The cell monolayers were then incubated with [3H]methyl thymidine to assess DNA synthesis. Spent culture medium was assayed for progesterone and estradiol content. Immature granulosa cells: Tritiated thymidine uptake in granulosa cell cultures from immature follicles were significantly increased by IGF-I. FSH was able to maintain or increase basal and IGF-I stimulated growth whereas LH had no effect. Basal progesterone production was low and not increased by either FSH or LH. However, treatment with FSH, but not LH, increased aromatase activity. Mature granulosa cells: IGF-I also stimulated thymidine uptake. However, whereas FSH either maintained or increased thymidine uptake by these cells, LH dose dependently suppressed thymidine uptake. This inhibitory action of LH was accentuated by the presence of IGF-I. Despite the inhibitory effect of LH on thymidine uptake, the gonadotropin markedly stimulated steroid production and the maximal steroidogenic response to LH was equivalent to 3-fold greater than that to FSH. Granulosa-lutein cells: Patterns of basal and IGF-I- and gonadotropin-stimulated steroid synthesis were similar to those observed for mature granulosa cells but steroid production rates were higher. Suppression of basal and IGF-I-stimulated thymidine uptake by LH was even more pronounced. These results suggest that the granulosa cell LH receptor, once expressed, negatively regulates cell growth and, simultaneously, positively regulates steroid synthesis. This development related event could be crucial to the mechanism whereby granulosa cells cease to divide and commence maximal rates of steroid synthesis in response to the LH surge.