Effect of Luteinizing Hormone and Follicle-Stimulating Hormone on Progesterone Synthesis by Cultured Rat Cumulus Cells*

This study examined the responsiveness of the rat cumulus oophorus to gonadotropin in terms of progesterone (P) secretion. Immature female rats pretreated with a single injection of PMS gonadotropin were used. Oocyte-cumulus complexes were isolated aseptically from large preovulatory follicles or from the oviduct shortly after ovulation and cultured in modified Eagle's medium. Ten cumuli from each rat were cultured for 24 or 48 h, with change of medium after 12 and 24 h. P accumulation in the culture medium was determined by RIA, and cell morphology was examined. Cumuli isolated from rats killed before the endogenous LH/FSH surge and cultured in hormone-free medium secreted low amounts of P (<10 pg/cumulus/ day) throughout the culture period. By contrast, cumuli isolated 3–5 h after the surge secreted high amounts of P (300–400 pg/day). This increment in P secretion was abolished by pentobarbital treatment of the rats during the critical period. Postovulatory cumuli isolated from the oviduct 5–9 h after ovulation also secreted high amounts of P. Cumuli isolated before the LH/FSH surge and cultured in the presence of ovine FSH (0.1–10 μg/ml) or ovine LH (10 μg/ml) showed increased P secretion, with a more potent stimulation obtained with FSH. When maximal concentrations of LH and FSH were combined, there was no additivity. (Bu)2cAMP significantly enhanced P secretion. Morphological examination revealed that cumuli which were not exposed to gonadotropins attached to the dish forming monolayers within 24 h of culture, whereas those exposed to significant amounts of gonadotropin in vivo or in vitro did not form monolayers until the second day of culture. The outgrowing cells were similar for all groups and were fibroblastlike. The study shows that rat cumulus granulosa cells respond to direct gonadotropin stimulation with increased P synthesis and morphological changes in vitro. Whether this steroidogenic response plays a role in developmental changes within the oocyte is not presently known.