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 in itiating luteolysis. Ewes received ovarian arterial infusions of 4 alp ha-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 progester one 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 i n PMA-treated ewes had returned to control values; but in PGF(2 alpha) -treated ewes they remained low for the duration of the experiment. Lu teal weights and progesterone contents at 48 h were similar in 4 alpha -phorbol- and PMA-treated ewes but were decreased in PGF(2 alpha)-trea ted ewes (P < 0.05). Experiment III was designed to determine whether PGF(2 alpha) or PKC activation induced oligonucleosome formation or in fluenced 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 o ligonucleosome formation was increased (p < 0.05) in PGF(2 alpha)-trea ted ewes compared to controls or to PMA-treated ewes by 12 h. Concentr ations of mRNA encoding for cytochrome P450(scc) were reduced (P < 0.0 5) at 3 and 12 h after the PMA infusion compared to the value in 4 alp ha-phorbol-treated controls, but were not different in PGF(2 alpha)-tr eated ewes compared to controls. Infusion of PMA or PGF(2 alpha) decre ased concentrations of mRNA encoding 3 beta-HSD at 3 and 12 h (p < 0.0 5), 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 b y 24 h. Thus, PKC activation decreased progesterone production without initiating luteolysis. Treatment with PGF(2 alpha) increased oligonuc leosome formation while PKC activation did not, and PGF(2 alpha) decre ased levels of mRNA for 3 beta-HSD, probably through activation of PKC .