Effect of antiprogestagen RU486 on both natural and prolactin-induced morphological luteolysis in rat

Adult female cyclic rats were hypophysectomized and their pituitary glands autotransplanted beneath the left kidney capsule (Aptr) on day 1 (metestrus). To induce the luteolytic effect of prolactin (PRL) the rats were injected s.c. with 0.4 mg of 2-bromo-alpha-ergocryptine (CB154) on cycle days 12, 13 and 14. Other groups of Aptr rats were injected daily with CB154 or ethanol vehicle from day 12 to day 23. To study the role of progesterone (P) on the luteotrophic effect of PRL as well as on the natural and on the PRL-induced luteolysis, rats without CB154 treatment or with long or short CB154 treatment were injected s. c. with 2 mg of the antiprogestagen RU486 or 0.1 ml oil from day 1 to day 23. From each rat the mean weight of the corpus luteum (CL) was noted on day 24. The serum PRL level rose from day 1 to day 12 and fell thereafter by day 15 in CB154-treated rats. The serum level of PRL rose again in short term CB154-treated rats, and remained low in long term CB154-treated rats. No effect of RU486 on serum PRL levels was noted in any group. The serum P level fell rapidly as the treatment with CB154 began after day 12. Neither the rise in serum PRL after day 15 in short term CB154-treated rats nor RU486 treatment affected the P level. Treatment with RU486 did not affect the CL weight on day 24 in ethanol vehicle injected rats.(ABSTRACT TRUNCATED AT 250 WORDS)