Age at Exposure and the Late Effects of X-Rays. Survival and Tumor Incidence in CAF 1 Mice Irradiated at 1 to 2 Years of Age
A study was made of the effects of age at exposure, during adult life, on the late effects of irradiation. Survival and tumor incidence at autopsy were studied in the adult CAF/sub 1/ mouse irradiated at 1, 1.5, and 2 years of age. This range was extended by reanalyzing data of previous experiments with CAF/sub 1/ mice at 5 months of age and with BALB/c mice irradiated at 5 months, 1.2, and 1.4 years of age. Since the median life span of these mice is about 2.4 years, the ages at exposure, in so far as such a comparison can be made, bracket a period equivalent to that of about 18 to 65 years in man. The present results were compared in detail with the few relevant ones in the literature for other strains of mice. In general, irradiation of old adults tended to have less life- shortening effect than irradiation of young adults, although the difference was not the same in the several strains, owing to genetic or constitutional differences. Sex was also shown to be an important factor in CAF/sub 1/ and other mice. It appeared that during much of adult life the female reacted as if sensitized to low doses but late in life the CAF/sub 1/ female may become less sensitive than the male. These effects were correlated with changes in endocrine balance secondary to ovarian damage that would not be expected to occur in women. Life shortening was not associated with increased neoplasia in older CAF/sub 1/ and BALB/c mice, as is often the case when young animals are irradiated, but with a decrease. In the CAF/sub 1/, irradiation tended to reduce the number of decedents with tumors rather than to reduce the number of tumors per tumorbearing decedent, and the tumorous animal lived as long or longer than the non-tumorous one. The simple concept of premature aging does not approximate a satisfactory explanation of the present results, or those of related experiments. The irradiated mouse is not one that has suddenly been aged at the time of exposure or one whose pattern of aging is normal but proceeding at an accelerated rate. The irradiated mouse is in certain specific respects an abnormal mouse and also one that is aging in an abnormal way. Usually, but not necessarily, it dies sooner than usual, depending in part on age at exposure and sex, as well as on radiation dose. The application in principle to man of some of these resuits with mice is probably justified. It appears reasonable to propose that the hazard of inducing late effects in man is reduced when irradiation occurs in the latter part of life and when the dose is relatively small. (auth)
- Research Organization:
- Univ. of California, San Francisco
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-17-023174
- OSTI ID:
- 4692119
- Journal Information:
- Radiation Research, Vol. 18, Issue 3; Other Information: Orig. Receipt Date: 31-DEC-63; ISSN 0033-7587
- Publisher:
- Radiation Research Society
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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