Intraperitoneal and intravenous injections of tracer quantities of3 H- or14 C-labeled deoxycytidine (CdR) were used to investigate the biologic half-life, the miscible pool size, and the turnover rate of CdR in normal and x-irradiated rats. The specific activity of highly purified CdR isolated from blood plasma samples taken at various times after injection of the tracer CdR was used as the basis for calculating these values. The mean values observed for normal rats were: biologic half-life 116 minutes, miscible pool 790 μg/rat (100 to 180 grams), and turnover rate 7.0 mg per 24 hours per rat. The miscible pool of CdR appeared to be nonuniform, with the intracellular concentration appreciably higher than the general body-water concentration. About one-third of the total miscible CdR appeared to be intracellular. After relatively low doses of whole-body x-irradiation (50 to 100 rads), there were alterations in the turnover kinetics of CdR, but the presence of a non-steady state made computation of the above three values impossible. However, the data are fully consistent with an increase in the miscible pool size of CdR, occurring as early as 1 hour postirradiation. The data do not provide information as to the mechanism for this apparent increase.

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