Delayed Nidation in the Rat Induced by Progesterone.

Abstract
Embryo nidation in rats was delayed 1 to 45 days by ovariectomizing on the 3d day after mating and injecting 4 mg of progesterone/day. Unimplanted blastocysts were recovered from 1 horn of the uterus during this period and subsequently implantation was induced in the remaining horn by adding 1ug of estrone/day to the progesterone.