Mifepristone And Pgf(2)Alpha Activate Phosphatidylinositol Hydrolysis In The Ovine Corpus Luteum

Two experiments were conducted to determine whether mifepristone (RU486) and PGF(2)alpha activate the phos-phatidylinositol hydrolysis pathway during the midluteal phase of the ovine estrous cycle. In experiment 1, ewes on day 8 of the cycle were given 10 mu g RU486 or vehicle into the ovarian artery with removal of the corpus luteum (CL) after 10 min. Blood collected prior to and after treatment was analyzed for progesterone. Aliquots of CL were incubated with 10 mu Ci of H-3-inositol and in the presence and absence of PGF(2)alpha (10 nM) for 15 min. Exposure of CL to RU486 and PGF(2)alpha increased phosphatidylinositol hydrolysis (p < 0.05). Serum progesterone was reduced in both control and RU486-treated ewes (p < 0.05) compared to concentrations before treatments. In experiment 2, aliquots of CL collected from ewes on day 8 of the cycle were incubated with 3H-inositol and exposed to RU486 (2 mu M) in the presence and absence of PGF(2)alpha (1 mu M) for 15 min. Treatments stimulated phosphatidylinositol hydrolysis as in Exp 1 (p < 0.05). Progesterone concentrations in incubation medium were increased in response to RU486 and PGF(2)alpha (p < 0.05). Collectively, these data suggest that RU486 and PGF(2)alpha act to stimulate phosphatidylinositol hydrolysis in the mature ovine CL.