The effect of doses of mixed gamma-neutron radiations or 14-MeV neutrons on the urinary excretion of deoxypyrimidines calculated as deoxycytidine equivalent (CdR) was evaluated as a biodosimeter in rats. The rats were exposed to doses in the range from 22 to 780 rads. The excretion of CdR equivalent in the urine of irradiated rats during the 4- to 12-hour postirradiation interval was a function of dose over the range of 22-376 rads. The response was similar for the different types of radiations. In a group of 10 rats exposed to the same does of x-rays (50, 150, or 450 rads) on 3 successive days, the 4- to 12-hour postirradiation excretion of CdR equivalent was dose dependent after the initial exposure but not after the second and third exposures. The total CdR equivalent excretion after an accumulated dose of 150-1350 rads approximated that of an equal single dose. The disappearance of circulating lymphocytes paralleled the urinary excretion of CdR equivalent. After lymphocytes had essentially disappeared following two 450-rad doses of x-rays, a third dose of 450 rads induced less excretion of CdR equivalent by irradiated rats than by unirradiated control animals. Calculations of the amount of CdR equivalent excreted per deleted circulating lymphocyte suggest that there are other radiosensitive cells that contribute to deoxypyrimidinuria.

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