The intracellular mechanism that mediates the stimulatory effect of prostaglandin F2α (PGF2α) on progesterone secretion by bovine luteal cells is not well understood. In the present study, we investigated to test the hypothesis that PGF2α stimulates progesterone secretion through activation of protein kinase C (PKC) by using a cell culture system. Bovine mid-luteal cells (Days 8-12 of the estrous cycle) were cultured for 24 h and then exposed to varying concentrations of PGF2α (10 -8 , 10 -7 ,

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... 0 -6 M) or luteinizing hormone (LH; 100 ng/ml) for 4, 6, or 16 h. Treatment of the cells with the highest dose of PGF2α (10 -6 M) or LH resulted in increases in progesterone secretion for all three exposure times. Following down-regulation of PKC with a tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA; 10 -6 M), the stimulatory effect of PGF2α was no longer evident, whereas the response to LH was unaffected. These results support the hypothesis that the luteotropic action of PGF2α is mediated by the activation of intracellular PKC.