Effect of Age at Irradiation on Life Span in the Male Rat

Abstract

The reduction of life span by a single exposure to ionizing radiation, with displacement of the normal pattern of neoplastic and degenerative diseases toward higher incidences at younger chronologic ages, is well known. Although the relative displacement and importance of these diseases as causes of death are still matters requiring further study, many investigators find it useful to regard radiation as having an aging effect. Evaluation of this concept has led to the realization that the age at exposure has an effect on the degree of life shortening. Unfortunately, there have been few reports in which large numbers of animals have been irradiated at various ages distributed over an extensive proportion of the normal life span. In a recent review of the literature with respect to reduction of life span as a function of age of X-irradiation for mice, Kohn and Guttman (1) concluded that, in general, irradiation of old adults tends to have less life-shortening effect than irradiation of young adults, although the difference is not the same among several strains. For the rat, there is no corresponding body of data in the literature. In designing the present study it was felt that the information most pertinent to the role of age at irradiation could be obtained by maximizing the number of animals and the range of ages at exposure while restricting radiation to a single dose. To this