Evidence that "embryonic estrogen" is a factor which controls the development of the mouse preimplantation embryo.

The hypothesis that mouse preimplantation embryos (PIEs) can synthesize estrogens and that PIE estrogen is a controlling factor during preimplantation embryogenesis was tested. Pregnant female mice of the Carworth strain (CFW1) were used. They were killed on the morning of either Day 3 or 4 of pregnancy. Mouse PIEs of 4-8 cells were exposed to an antiestrogen, CI-628, for 48 hours in media containing several concentrations of the antiestrogen. The concentration of 1.5 mcg/ml, the highest used, was 100% effective in blocking development of the blastocyst stage. The deleterious effects of the CI-628 were partly prevented by including estradiol-17beta in the medium. PIEs which did not develop appeared degenerating. CI-628, previously designated CN-55,945-27, is a nonsteroidal antiestrogen which acts by displacing estrogen from estrogen receptor sites. Its effect was thought to be due to its antiestrogenic properties. If so, results support the hypothesis that the development of mouse PIEs depends on estrogen which originates in the PIEs.