ABSTRACT
A study was made of the action upon the rabbit embryo of various agents administered to pregnant animals in doses which did not seriously upset maternal health. The pre-implantation blastocyst, examined as a flat mount, was the principal object of study, but observations were also made on ovulation, fertilization, cleavage, nidation, and subsequent phases of pregnancy.
To facilitate comparison between embryos from normal and treated animals 5-to 7-day-old blastocysts from untreated animals, grouped according to size, were classified into 6 developmental stages, depending upon the degree of maturity of the embryonic disc. Additional procedures which served to evaluate the condition of blastocysts and their uterine environment were: mitotic counts made in the abembryonic part of the trophoblast, chemical determinations of certain characteristic constituents of blastocyst fluid, and measurement of carbonic anhydrase activity in the endometrium. .
The experimental agents comprised hormones, colchicine derivatives, several polyfunctional alkylating compounds, metabolic analogues, a sulphonamide inhibitor of carbonic anhydrase, and substances endowed with teratogenic, hepatotoxic, radiation-protective, and hypoglycaemia-inducing properties; total body exposure to X-rays was also investigated.
Results obtained at various stages of pregnancy with the different treatments are described and discussed; several results relating to blastocysts are illustrated by photomicrographs.
Among significant general findings emerging from the study are: the speed with which exogenous agents are transmitted to embryos even before uterine attachment; differential drug sensitivity, frequently evident in the pre-implantation blastocysts, as between the embryonic disc and trophoblast, the former usually being more susceptible; and variability in response, both individual and between litters, of the embryos to parenterally administered agents.
It is suggested that the blastocyst flat mount preparation could be adapted as a conveniently rapid and simple procedure for the screening of cytostatic and other growth-modifying agents.