Comparison between the progestin secretion responsiveness to gonadotrophins of rat cumulus and mural granulosa cells in vitro

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Abstract
Several studies showed differences in gonadotropin receptor content between different granulosa cell (gc) populations within the ovarian follicle, but little is known about the gonadotropin sensitivity in gc from different parts of the follicle. This study is an investigation of progestin synthesis and responsiveness to highly purified human and partly purified rat gonadotropins. It involves short-term culture of rat cumulus and mural gc obtained from preovulatory follicles of PMSG[pregnant mare serum gonadotropin]-treated immature rats. The responsiveness to FSH in terms of progestin accumulation was similar in the 2 gc populations, while the responsiveness to LH [luteinizing hormone] was greater in the mural gc than in the cumulus. The morphological response in the cumulus cells (mucification) correlated with the steroidogenic response. The pattern of progestin synthesis differed between the 2 gc populations. In the cumulus gc progesterone was dominant, while 20.alpha.-dihydroprogesterone was the main progestin secreted in the mural gc. The difference in responsiveness to gonadotropins correlates well with the reported differences in receptor content in the 2 gc populations.