Lethal Effects of X-Irradiation and Injection of Radioactive Phosphorus on Rats in Relationship to Age

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Abstract
The LD50(30) of rats exposed to whole-body X-irradiation when 21 and 32 days old were, respectively, 360 r and 420 r. Animals exposed when 60 or 100 days old did not differ in sensitivity, the LD50(30) being 758 r for both ages combined. The change in sensitivity from weaning to maturity seems to be greater in the rat than in the mouse. The LD50(30) of rats injected with P32 at 21, 32, and 100 days of age were essentially the same, ranging from 3.27 to 3.42 mc/kg. Radiation exposures of various tissues of rats injected with 4.5 mc of P32 per kilogram at 21, 32, and 100 days of age were computed. Exposure of spleen and other soft tissues were inversely related to age, wheras exposure of bone and bone marrow seemed independent of age. The significance of this is discussed. Inhibition but not complete suppression of growth occurred in 21- or 32-day-old rats after exposure to X-rays or P32 injection.