Age at X-irradiation and acute radiation mortality in the adult male rat.

Abstract

Male rats received whole-body single doses of 250-kVp x-rays at various ages ranging from young adulthood to old age. From probit analysis, the ${\rm LD}_{50(30)}$ values for groups exposed at 3 or 7 months of age were 851 and 900 R, respectively. After adjustment for the natural mortality rate, ${\rm LD}_{50(30)}$ values for groups exposed at 17, 21, or 24 months of age were 776, 806, and 747 R, respectively. The mean survival time at the ${\rm LD}_{50(30)}$ for the group exposed at 3 months of age exceeded those for groups irradiated at older ages. The slope of the dose versus survival curve for the youngest group was almost twice that for groups exposed at older ages, reflecting increased variability of the population at older ages. These findings indicate that age at exposure is an important variable to be considered in establishing parameters of acute radiation mortality in adult animals.