EFFECT OF OESTRONE ON THE DELAY OF NIDATION, IMPLANTATION AND FOETAL SURVIVAL IN OVARIECTOMIZED RATS

Abstract

SUMMARY Eighty-six female rats were ovariectomized 3 days after coitus and treated daily with 4000 μg. progesterone either alone, or in combination with 0·01–10 μg. oestrone from day 3 to day 8 after coitus. Ten additional animals with intact ovaries were treated daily with corn oil. Ovariectomized rats were treated with 4000 μg. progesterone and 1 μg. oestrone from day 9 to day 19, if nidation occurred by day 8, and from day 9 to 24, if implantation sites were absent 8 days after coitus. A delay of implantation usually occurred in animals treated with progesterone alone or in combination with 0·01, 0·03 or 0·1 μg. oestrone ('delay' class). Implantation occurred at about the normal time during treatment with progesterone combined with 0·3, 1 or 3 μg. oestrone and in non-ovariectomized animals treated with corn oil ('non-delay' class). Nidation was usually prevented permanently by 10 μg. oestrone in combination with progesterone. In the 'delay' class the addition of 0·01–0·1 μg. oestrone to progesterone did not alter the ability of blastocysts to undergo nidation or affect embryonic survival. In animals in the 'non-delay' class, nidation was induced with equal success when 0·3, 1, or 3 μg. oestrone were administered. Embryonic survival, however, was maximal in animals treated with 0·3 μg. oestrone and progressively less in rats treated with 1 and 3 μg. The number of implantation sites was larger in non-ovariectomized 'non-delay' animals than in ovariectomized 'non-delay' rats. The number of sites in the 'non-delay' class was consistently larger than the number of sites in the 'delay' class.