LH-Stimulated cAMP Formation in Rat Granulosa Cells During Follicular Maturation — A Non-Refractory Response
In early experiments on isolated granulosa cells from porcine ovaries Kolena and Channing (1,2) reported that the in vitro administration of either FSH or LH caused an acute stimulation of cAMP formation by these cells. The same group (3) also found that there was an induction of LH receptors on the surface of granulosa cells that parallelled with follicular maturation. Both FSH and estradiol are believed to be essential for the development of LH receptors in rat granulosa cells (4, 5, 6). In recent studies on granulosa cells from immature rat ovaries (7, 8) and on granulosa cells from small follicles isolated from sheep ovaries (9), LH was found to have a lack of effect in vitro on cyclic AMP formation. With increasing maturation of follicles from which the granulosa cells were derived, LH was not, in the case of the rat, able to stimulate cyclic AMP formation until the preovulatory stage. Exposure to LH in vitro of intact preovulatory follicles from this species caused acute stimulation of cAMP formation (10) but in addition refractoriness to a new stimulation by the same hormone is induced for several hours (11). A similar mechanism seems to be active in vivo with a decreased sensitivity to LH after the endogenous LH-FSH surge (12, 13). In general, the mechanism(s) for hormonal refractoriness is poorly understood and has in the above-mentioned context not been investigated in detail (14). The present study was intended to explore if a similar refractoriness to LH is present in granulosa cells separated and isolated from preovulatory rat follicles obtained from a PMSG rat model.
KeywordsGranulosa Cell Preovulatory Follicle cAMP Formation Follicular Maturation Acute Stimulation
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