Inhibitory and stimulatory action of porcine follicular fluid on FSH-induced 125I-hCG specific binding in rat granulosa cells.

: In previous studies, follicular fluid (FF) of large antral follicles (LFF) manifested a stimulatory effect on granulosa cell (GC) luteinization in domestic livestock, but was found to have an inhibitory effect on rodent GC. In the present study, the type of LFF effect on the luteinizing of rat GC was reevaluated in two different models. GC obtained from immature hypophysectomized rats treated with diethylstilbestrol were cultured with increasing concentrations of FSH alone or FSH + estradiol-17 beta (E2), either for 3 or 4 successive days of culture (model 1) or for 4 days of culture with medium change after 2 days of culture (model 2). The addition of FSH increased 125I-hCG specific binding in a dose-dependent manner to a maximum of approximately 110-fold (model 1) or 45-fold (model 2) compared with GC culture in medium alone. At the maximal effective dose of FSH, addition of E2 increased the 125I-hCG binding 2-fold (model 1) and 3.5-fold (model 2). 125I-hCG specific binding induced by FSH or FSH + E2 in model 1 was decreased by concurrent treatment (added on the day of cell inoculation) with porcine LFF (approximately 3-fold) or porcine serum (approximately 4.5-fold). In model 2, however, porcine LFF increased FSH-induced 125I-hCG specific binding 3-fold, provided LFF was added only after GC were primed with FSH alone for 2 days. When porcine serum was added instead of porcine LFF, only a permissive action was observed. These data may suggest that an initial GC differentiation is indispensible for obtaining the FF stimulatory effect on FSH-induced 125I-hCG specific binding in rat GC.