Apparent Absence of Recovery in Endogenous Colony-Forming Cells after Irradiation under Hypoxic Conditions

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Abstract
Groups of LAF1 adult mice were subjected to both graded and divided doses of radiations 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 D37 of 83 rads in air and 201 rads under hypoxic conditions, yielding an oxygen enhancement ratio of 2.4. Survival ratios were obtained for times between 3 ana 36 hr. using 2 doses of 260 rads each in air and 520 rads each under hypoxic conditions. The survival ratio in animals irradiated in air shows peaks at 9 and at 27 hr. The survival ratio in animals irradiated under hypoxic conditions was not increased at any time and fell after 4.5 hr. following the initial dose. The results suggest that in the mouse colony-forming cell the degree of early cellular repair is markedly decreased when radiation injury occurs under conditions of hypoxia.