<tex-math>$\text{Deoxycytidine-}2\text{-}{\rm C}^{14}$</tex-math> was injected into rats or mice and the animals were subjected to total body irradiation 1 day later. DNA in organs and metabolites in urine were isolated and their activity determined. Radioactivity in lymphoid organs decreased, whereas the total and specific radioactivity of the deoxycytidine excreted increased on the first day after exposure. This observation indicates that deoxycytidine excreted after irradiation originates from degraded DNA, since the specific activity should decrease if precursors not utilized for DNA syntheses were the main contributors to deoxycytidinuria. Experiments in which <tex-math>${\rm C}^{14}\text{-deoxycytidine}$</tex-math> was given after exposure confirmed this assumption.

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