PROTEIN-KINASE-C 2ND MESSENGER SYSTEM MEDIATES THE ANTISTEROIDOGENIC EFFECTS OF PROSTAGLANDIN-F2-ALPHA IN THE OVINE CORPUS-LUTEUM IN-VIVO

Experiment I was designed to determine the optimal dose of phorbol 12-myristate 13-acetate (PMA) that inhibited progesterone production when infused into the ovarian artery. The most efficacious dose of PMA was 2 mu mol. Experiment II was designed to determine whether activation of protein kinase C (PKC) inhibited progesterone production without initiating luteolysis. Ewes received ovarian arterial infusions of 4 alpha-phorbol (2 mu mol, n = 4), PMA (2 mu mol, n = 8), or prostaglandin F-2 alpha (PGF(2 alpha); 1 mu mol, n = 5). Concentrations of progesterone in serum decreased by 3 h in PMA-treated ewes and by 5 h in PGF(2 alpha)-treated ewes (p < 0.05) By 48 h, serum levels of progesterone in PMA-treated ewes had returned to control values; but in PGF(2 alpha)-treated ewes they remained low for the duration of the experiment. Luteal weights and progesterone contents at 48 h were similar in 4 alpha-phorbol- and PMA-treated ewes but were decreased in PGF(2 alpha)-treated ewes (P < 0.05). Experiment III was designed to determine whether PGF(2 alpha) or PKC activation induced oligonucleosome formation or influenced mRNA levels for cytochrome P450(scc) or 3 beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase (3 beta-HSD). Ewes received treatments as in experiment II, and CL were collected at 3, 12, or 24 h (n = 3-4 per group). Luteal weights were decreased (P < 0.05) and oligonucleosome formation was increased (p < 0.05) in PGF(2 alpha)-treated ewes compared to controls or to PMA-treated ewes by 12 h. Concentrations of mRNA encoding for cytochrome P450(scc) were reduced (P < 0.05) at 3 and 12 h after the PMA infusion compared to the value in 4 alpha-phorbol-treated controls, but were not different in PGF(2 alpha)-treated ewes compared to controls. Infusion of PMA or PGF(2 alpha) decreased concentrations of mRNA encoding 3 beta-HSD at 3 and 12 h (p < 0.05), and these values remained low at 24 h in the PGF(2 alpha)-treated ewes. In the PMA-treated ewes, levels of mRNA encoding 3 beta-HSD were intermediate between those in control and PGF(2 alpha)-treated ewes by 24 h. Thus, PKC activation decreased progesterone production without initiating luteolysis. Treatment with PGF(2 alpha) increased oligonucleosome formation while PKC activation did not, and PGF(2 alpha) decreased levels of mRNA for 3 beta-HSD, probably through activation of PKC.