Effects of Various Steroids on Nidation and Fetal Survival in Ovariectomized Rats

Abstract

The number of implantation sites in ovariectomized rats, following a period of delayed implantation, was used as a measure of the blastocyst-maintaining ability of various test compounds administered to animals during the delay period. Groups of 8–15 rats were ovariectomized on day 3 postcoitus, injected daily with progesterone or other steroid compounds from days 3 to 8, and injected daily with 4000 μg progesterone and 1 μg estrone from days 9 to 24 postcoitus. Progesterone was used as the standard. The relative potencies of 17α-ethyl-19-nortestosterone and 17α-acetoxy-21-fluoro-6αa-methylprogesterone were estimated as 6.35 and 47.5 times progesterone, respectively, in their ability to maintain the viability of blastocysts during the period of retardation of development. Other compounds with known relative potencies in the Clauberg assay, ranging from 0.05 to 2 times progesterone, were tested for maintenance of blastocyst viability, using daily doses of 1000 and 4000 μg. Testosterone propionate, 17α-ethynyl-17βdiacetate were inactive. 17α-Ethynyl-19- nortestosterone was inactive at 4000 μg but showed weak activity with the 1000 μg dose. In these studies, treatment with progesterone resulted in fewer sites with 8000 μg than with 4000 μg amounts. 17α-Acetoxy-21-fluoro-6α-methylprogesterone resulted in more sites than obtained with 4000 μg progesterone. Postimplantation embryonal survival was consistently higher for all compounds with the lower dose of steroid than with the higher dose of the same compound. The method appears to be applicable to studies of the relationship between the blastocyst and its environment, including uterine fluids, uterine tissue and circulating hormones. (Endocrinology74: 573,1964)