APPARENT ABSENCE OF RECOVERY IN ENDOGENOUS COLONY-FORMING CELLS AFTER IRRADIATION UNDER HYPOXIC CONDITIONS.
NAVAL RADIOLOGICAL DEFENSE LAB SAN FRANCISCO CALIF
Pagination or Media Count:
Groups of LAF sub 1 adult mice were subjected to both graded and divided doses of radiation under hypoxic conditions and in air. The endogenous spleen colony-forming unit technique was used to measure the effect of the irradiation on survival of the colony-forming cells. Dose-response curves indicated a D sub 0 of 122 rads in air and 273 rads under hypoxic conditions, an oxygen enhancement ratio of 2.2. Using 2 doses each of 315 rads in air and of 630 rads under hypoxia, survival ratios were obtained for times between 3 and 36 hours. Animals irradiated in air show peaks in the survival ratio at 9 and at 27 hours. The initial peak is probably the result of early repair within the cell and the second peak that of onset of regeneration. The survival ratio of the animals irradiated under hypoxic conditions was not increased but rather fell slightly at times following the initial point. The results suggest that the degree of early cellular repair is markedly decreased and the onset of proliferation is delayed when radiation injury occurs under conditions of hypoxia. Author