Progesterone stimulation by prostaglandin f_2α involves the protein kinase c pathway in cultured bovine luteal cells

The intracellular mechanism that mediates the stimulatory effect of prostaglandin F_2α (PGF_2α) on progesterone secretion by bovine luteal cells is not well understood. In the present study, we investigated to test the hypothesis that PGF_2α 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 PGF_2α (10^-8, 10^-7, 10^-6 M) or luteinizing hormone (LH; 100 ng/ml) for 4, 6, or 16 h. Treatment of the cells with the highest dose of PGF_2α (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 PGP_2α was no longer evident, whereas the response to LH was unaffected. These results support the hypothesis that the luteotropic action of PGF_2α is mediated by the activation of intracellular PKC.