Radiotoxicities of [³H]thymidine and of [³H]arginine compared in mouse embryos in vitro

Tritium that is bound to organic molecules is of special risk for living systems, in particular when such molecules are components of the cell nucleus. Therefore, [³H]thymidine and [³H]arginine were studied for radiotoxicity in early mammalian embryo development. Starting with the two-cell stage, mouse embryos were incubated in vitro with [³H]thymidine or [³H]arginine at either 370 Bq/ml (10 nCi/ml) or 925 Bq/ml (25 nCi/ml). Development in vitro was followed up to the formation of the inner cell mass at 192 h postconception (p.c.). There was no difference in radiotoxicity of the two substances with respect to cell proliferation; however, formation of blastocysts, hatching of blastocysts, trophoblast outgrowth, and formation of inner cell mass were impaired more strongly by [³H]arginine than by [³H]thymidine when the external exposure concentrations were the same. Similarly, micronuclei were seen in blastocysts at 96 h p.c. at higher frequency after incubation with [³H]arginine. However, uptake of [³H]arginine by the embryos was considerably faster than that of [³H]thymidine, and this most probably accounts for the apparent difference in radiotoxicity.