Delayed nidation in the rat induced by progesterone.

Abstract

SummaryNidation of embryos was delayed from 1 to 45 days in rats ovariectomized on the 3rd day after mating, by subcutaneous injection of 4 mg of progesterone per day. Implantation was delayed until such time as 1 μg of estrone per day was given in addition to the progesterone. Recovery of blastocysts from one horn of the uterus during progesterone treatment and subsequent implantation of the embryos in the other horn induced by the progesterone-estrogen indicates that the embryos are maintained in the uterus in a viable, but resting condition during progesterone treatment. If rats were ovariectomized on the 3rd day and untreated for 8 days, nidation of embryos was not observed when progesterone and estrogen was initiated on the 9th day and given for the next 5 to 12 days. Rats ovariectomized on the 4th day after mating were variable in their response to 4 mg of progesterone, some exhibited delay others implanted at the normal time. Delayed nidation up to at least 3 days was obtained in hypophysectomized ...