In vitro inhibition of trophoblast maturation and expansion of early rat blastocysts by an oestrogen antagonist

Abstract

Rat blastocyst development and expansion were studied in an in vitro culture system. Early blastocysts collected from rats on the morning of day 5 developed normally and underwent expansion when placed in bovine serum albumin supplemented culture medium for 12 h at 37.degree. C. Nafoxidine, an estrogen antagonist, prevented embryo expansion when added to the culture medium, and if estradiol-17.beta. was added to this medium this inhibitory effect was removed and the embryos again expanded. Ethanol, used as a solvent for steroids, and cholesterol were added to the medium containing nafoxidine but the blastocysts still remained unexpanded after 12 h in culture. These results suggest a need for estrogen action during blastocyst expansion in vitro. Cultured rat blastocysts were subjected to histochemical study for acid phosphatase (ACPase) and leucylnaphthylamidase (LNAse). In unexpanded blastocysts ACPase was low while LNAse activity was higher when compared with enzyme distribution patterns in expanded blastocysts.