EFFECTS OF THE ANTIPROGESTIN AND ANTI-GLUCOCORTICOID STEROID RU486 ON CELL-PROLIFERATION IN OVIDUCTAL EMBRYOS OF LACTATING MICE

The effects of the progestin and glucocorticoid antagonist RU486 on cleavage rate of oviductal embryos from lactating mice was studied. Preliminary experiments suggested that, owing to suppression of follicular activity by lactation, the effects of RU486 during early embryo development could be studied independently of overt oestrogen dominance in mice mated at postpartum oestrus. After treatment with RU486 on days 1-3 of pregnancy in lactating mice, embryos recovered on day 4, but not on day 3, had significantly fewer cells than did those from control animals. However, neither exogenous progestins nor dexamethasone could reverse this effect of RU486. Nevertheless, embryos recovered from lactating mice treated with progestins alone had significantly more cells on day 4 than did those from control animals. In contrast, embryos recovered from mice treated with dexamethasone alone had significantly fewer cells per embryo on day 4 than did those from control mice. These results provide further evidence that the growth rate of oviductal embryos in mice is influenced by the maternal hormone milieu.