Comparative effects of tritiated water and thymidine on the preimplanted mouse embryo in vitro

Preimplanted mouse embryos were cultured in an in vitro-system from the two cell stage to blastocysts. In the control cultures about 92% of the incubated embryos developed to blastocysts. When tritiated compounds like tritiated water or tritiated thymidine were present in the incubation medium the number of blastocysts decreased with increased medium tritiated thymidine was about one thousand times more effective than tritiated water. Tritiated thymidine caused a more pronounced division delay than tritiated water which had a strong effect on the blastulation process. Further studies showed that the incorporation of tritiated thymidine into the DNA lead to high concentrations of tritium in the cell nucleus. Dose calculations are performed for the cell nucleus in the case of incubation with tritiated thymidine as well as with tritiated water. The different action of the tritiated compounds can apparently be explained by the specific incorporation of thymidine into the DNA.