In a duration-of-life study, male Sprague-Dawley rats were exposed to 220 rads of fast neutrons as juveniles (1 month of age), young adults (3 months), middle-aged adults (10, 15 months), or old adults (21 months) and compared with their sham-irradiated littermates at intervals using a variety of criteria of radiation injury. In all five age groups, there was a deficit in body weight that persisted throughout life. The magnitude of this deficit was inversely related to age at exposure. Decreased food and water consumption were seen throughout life in the group irradiated as juveniles and, to a lesser extent, after exposure as young or middle-aged adults. These consummatory changes appeared related to the changes in body size. An age-associated marked increase in water consumption per unit metabolic size occurred earlier (than in controls) in animals exposed as juveniles or as young adults. Proportions of exposed groups with one or more palpable tumors were in excess of control values after exposure at all except the oldest age in spite of significant life-shortening after exposure at the three younger ages. Proportions of irradiated groups with palpable growths of large size (2.5 cm or more) exceeded those for controls even for the group exposed at 21 months.

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