[Estroprogestational drugs and the ultimate embyogenesis in the rat]

Cyclic female rats were fed with ethinodiol diacetate plus mestranol (EDM) for periods of 45 to 180 days. They were mated during prooestrus, on the first cycle following the end of the treatment. Results were as follows: 1. The cycle is blocked about eight days after starting E.D.M. The longer the treatment, the later rats resume their cycle. 2. Degeneration of the ova before implantation and embryonic mortality are slightly augmented when fecundation takes place within two days after stopping E.D.M.; whereas from the third cycle on, the quality of th ova is identical to the control group. The ova are euploid; they are more fragile to hypotonic shock than the ova of the control animals. No influence of E.D.M. upon meiotic or mitotic processes could be demonstrated. Those experiments do no allow any inference to the human species, but they are inkeeping with the observations of Boué et al. on women.