Studies on the Incorporation of Tritiated Thymidine in Desoxyribonucleic Acid in Mouse Tissues and on Its Radiation Effects

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Abstract
Summary Studies are reported which were designed to check for possible disadvantageous effects of labelling DNA with tritiated thymidine of high specific activity in long-term experiments. Three series of mice were injected with 200μc, 20 μc and 5 μc of the substance per mouse, and one series received 4 μc per mouse of 14C-labelled thymidine. The total activity was recorded, and the degree of labelling was investigated in autoradiographs at intervals up to 120 days after injection in seven different tissues. The results indicate that cellular death due to radiation from the label occurs in mice labelled with a dose of 200 μc, and possibly also with a dose of 20 μc per mouse (about 1 μc/g). The incorporation of thymidine in several tissues does not increase proportionately to the amount available, indicating a pool effect that might be due to thymidine existing as a normal intermediate. The findings may have implications for the use of tritiated thymidine as a label for DNA in autoradiographic studies.