[Effect of different estro-progesterone sequences on nidation of dormant blastocysts administered in diapause in ovariectomized rats].

The hormonal condition permitting delayed nidation in rats ovarectomized on day 4 or 5 of pregnancy was studied by administering progesterone and estradiol in differents sequences between days 9 and 14. The best result was obtained when progesterone was given 3 days before an estrogen-progesterone association. The same treatment induced delayed nidation in rats receiving Reserpine and ovariectomized day 5, but not when progesterone and estradiol were present day 4.