The secretion of prolactin in intact and lutectomized pregnant ewes. Effect of the anti-progesterone steroid RU 486

Abstract To study the role, if any, of luteal factors in the control of prolactin secretion during the last two thirds of pregnancy in the ewe, we examined: a) the effect of RU 486 administration on prolactin secretion on days 97, 112 and 131 of pregnancy in five intact ewes and in five ewes from which the corpus luteum (CL) was removed on day 78 of pregnancy; and b) the secretory patterns of prolactin on days 60, 80, 100 and 120 of pregnancy in five intact ewes and in five ewes from which the CL was removed on day 70 of pregnancy. In a pilot experiment, we showed that daily i.v. injections (from day 91 to day 105 of pregnancy) of RU 486 at a dose of 50 mg caused a marked release of prolactin, without any effect on the secretion of progesterone and progression of pregnancy. In experiment 1, a single i.v. injection of 50 mg of RU 486 resulted in a significant ( P