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Increasing evidence suggests that local ovarian agents play a central role in the regulation of follicular maturation and corpus luteum formation. In previous studies, we have shown that porcine follicular fluid induces granulosa cell luteinization in sow, human and rat. In the present study, the effect was investigated of either human follicular fluid (FF) alone, human follicle-stimulating hormone (FSH) alone, or both upon progesterone secretion of human granulosa-luteal cells. Granulosa-luteal cells were cultured in the presence of either FSH (5, 50 and 250 ng/ml), lyophilized FF (50 and 250 μg/ml) or both. Secretion of progesterone increased from a minimum of 2.5-fold to a maximum of 23-fold in the presence of FSH alone and, significantly less (∼2-fold) in the presence of FF alone, compared to cells cultured in medium alone. The co-administration of FSH and FF was significantly more effective than either alone, while addition of both FSH (250 ng/ml) and FF (250 μg/ml) gave maximal progesterone secretion. In granulosa-luteal cells pre-cultured with both FSH and FF, subsequent exposure to human chorionic gonadotrophin (HCG) alone increased progesterone secretion 1.6-fold to 11-fold, compared to cells pre-cultured with FSH alone. The effect of FF from individual follicles was also studied. FF from follicles yielding mature cumulus—oocyte complexes was 4.2-fold more effective, than FF obtained from follicles yielding immature cumulus—oocyte complexes in enhancing the FSH stimulation of progesterone secretion. A pre-culture of granulosa-luteal cells in FSH plus FF from mature follicles was 1.8-fold more effective in enhancing HCG-induced progesterone secretion, compared to FF from immature follicles. This study suggests that progesterone secretion by granulosa-luteal cells is regulated by gonadotrophins and other factors accumulating in FF. [ABSTRACT FROM PUBLISHER]