Mature mice of two inbred strains, BALB/c and C57BL, were subjected to whole-body irradiation to determine the LD/sub 50(30). The LD/sub 50/ increased with decreasing dose rate when the dose rate was approximately 5 r/min or less. For each dose rate, survival times were analyzed according to isolethality groups by pooling the survival times of decedent mice. Deaths fell in either of two ranges, intermediate and absolute, according to the expected LD calculated for the original exposure dose group. Mice irradiated at approximately 5 r/min and/ or less died later than those irradiated at approximately 18 r/min. This was most pronounced in the C57BL strain at the absolute isolethal level. BALB/c mice showed only a slight tendency toward this effect, and this has been attributed to a greater dependence of death on marrow injury in this strain. It is concluded that the prolongation in survival time found for the lower dose rates reflects greater or more rapid recovery in the intestinal crypt cells than in the bone marrow cells. The concept of differential recoverability from radiation injury is discussed. (auth)
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Robert F. Kallman (1962) studied this question.