The Influence of Strain on Acute X-Ray Lethality in the Mouse: II. Recovery Rate Studies

Abstract

The rate of recovery from a single, whole-body exposure to X-rays (250-kvcp, HVL, 1.6 mm Cu, tissue-dose rate about 35 r/min.) was determined with the two-fraction technique for each of 5 types of adult mice (100 to 200 days old). A tissue dose of 350 r was given and changes in the LD50/28 at various times from 1 to 14 days thereafter was determined. The initial dose of 350 r was equal to 53 to 63% of the LD50/28 of previously untreated mice. The data could be treated as though injury had decreased as an exponential function of time. Some evidence, however, suggested that a 12-hour latent period preceded exponential recovery. The half-recovery times (RT50) in days were as follows: A/He, 1.7; BALB/c, 3.1; C3H, 1.9; C57BL, 1.4. The CAF1 hybrid from the cross BALB/c x A/He had an RT50 of 2.1. It was concluded that constitutional factors, presumably genetic in origin, influenced the RT50. No evidence for a significant amount of irreversible injury was found. The temporal distribution of deaths during the 28 days after exposure was studied as a function of strain, X-ray dose, and fractionation interval. It was concluded that fractionation did not fundamentally change the distributions, although it did perturb them.