Relation of Embryonic and Fetal X-Irradiation to Life Time Average Weights and Tumor Incidence in Mice.

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Abstract
Summary and Conclusions 1. Control or normal male CF1 mice show lifetime average weights in excess, of comparable CF1 females. 2. Exposure of the CF1 mouse embryo or fetus at various stages to 100 r X-rays reduces its lifetime average weight significantly below the parallel controls, particularly for the males. 3. The month at which the peak weight was reached varied for the sexes, being 12 to 15 for the males and 13 to 30 for the females, suggesting greater variations in response of the females to growth inhibition by X-irradiation of the embryonic stages. 4. Exposure to 100 r on gestation days 11, 12, and 13 had the greatest effect on reducing the average weight of both males and females. This is the period of greatest skeletal growth activity. 5. Tumor incidence was higher among the females than among the males (4 to 1 ratio) among those X-irradiated in utero. Tumor incidence among the controls was low, but even there the incidence was higher among the females. The evidence for any increment in tumorigenesis following embryonic or fetal X-irradiation was equivocal. 6. The long time sequelae of embryonic and fetal radiation relate to growth and total body weight (permanent stunting) more than to tumorigenesis.