[Effect of aminopterin on pre-implantation rat embryos cultivated outside the body].

The rat embryos at the stage of 8 blastomeres were explanted in the Biggers' medium with 20% of blood serum from the rats obtained different doses of aminopterin. The marked delay of cleavage rate, morphological anomalies of blastocysts, selective damaging effect of aminopterin upon the inner cells mass (embryoblast) and high resistance of trophectoderm cells against this drug were observed. The role of dihydrololate reductase at the preimplantation developmental stages, the resistance against aminopterin of the early rat embryos within the maternal organism and high sensitivity to this drug of the embryos in vitro are discussed. A conclusion is drawn on the presence of the barrier function of oviducts with respect to aminopterin.