[Studies on lysis of the blastocyst coverings in the rabbit: effect of uterine environment].

The effect of uterine environment on lysis of the blastocyst coverings in the rabbit was studied in vivo and in vitro. After transplantation of 4, 5, and 6 days post coitum old blastocysts in foster does, the stage of pregnancy of which differed ± 2 days from the corresponding age of the blastocysts and after in vitro culture of 4 day old blastocysts, we investigated histologically the protease activity and the structure of the blastocyst coverings. The experiments revealed that only an exact synchronous in vivo medium is capable of initiating lysis or of support started lysis, although growth of the blastocysts seemed to be normal in foster uteri as well as in culture dishes. A series of figures on structural changes of the blastocyst between the 4 and the 8 day post coitum is compiled.