To evaluate the lifetime health effects of exposure to ionizing radiation during development, 1,680 beagles received wholebody exposures to60 Co γ rays or sham exposures. Eight groups of 120 dogs each received mean doses of 15.6-17.5 or 80.8-88.3 cGy in early, mid- or late gestation, at 8, 28 or 55 days after breeding, or at 2 days after birth. Another group of 120 dogs received a mean dose of 82.6 cGy as 70-day-old juveniles and one group of 240 dogs received a mean dose of 81.2 cGy as 365-day-old young adults. Sham irradiations were given to 360 controls. Sexes were equally represented. There was no significant effect of irradiation on mean survival times in any groups. In 1,343 dogs allowed to live out their life span, chronic renal disease was a common cause of mortality, and irradiation in the late fetal or juvenile periods potentiated this disease, resulting in increased mortality due to renal failure. This was consistent with earlier findings of the high radiosensitivity of the kidney in the perinatal period. Hypothyroidism associated with atrophic thyroiditis was decreased by irradiation, a finding contrary to expectation and not easily explained. Diabetes mellitus was increased by irradiation in the mid- and late gestation and juvenile periods, a finding which is intriguing based on early reports of a similar finding in atomic bomb survivors. Though convulsive seizures were a common cause of mortality in the dogs, there was no evidence for increased risk associated with prenatal irradiation as has been reported in humans. Genetic analyses indicated that renal disease, hypothyroidism, diabetes mellitus and convulsive seizures all had a heritable component, but that this did not influence or bias the radiation responses evaluated.

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