The development of embryos in the uteri of mice treated with actinomycin D before implantation.

This investigation follows the development of embryos in the uteri of mice in which the differentiation of the implantation chamber has been retarded by the administration of actinomycin D before implantation. For the first 48 h after the induction of implantation both embryonic and extra-embryonic parts of the blastocyst develop, but after 72 h the embryonic parts cease to grow and die. The giant cells and other extra-embryonic tissues, on the other hand, continue to develop for a much longer period, up to 288 h. It is suggested that the actinomycin D, by delaying the formation of the implantation chamber in the endometrium, interferes with the formation of a proper functional connection between the trophoblast and endometrium with the result that the embryo receives insufficient nutrition for its development.