The Influence of a Chronic Environmental Stress on Radiation Carcinogenesis

Abstract

The influence of a chronic environmental stress on the incidence of radiation-induced tumors, lens opacities, and survival times was determined. Female CFN rats were exposed to whole-body irradiation with either 300 rad of fission neutrons, 600 rad of 250 kV x rays, or sham irradiation. Within each irradiated group, rats were assigned to one of four environments: exposure to 25/sup 0/C until irradiated and immediately returned to (1) a 25/sup 0/C or (2) a 2/sup 0/C environment for duration of life; acclimation to a 2/sup 0/C environment for 40 days, irradiated, then returned to (3) a 2/sup 0/C or (4) a 25/sup 0/C environment. Postirradiation exposure to the 2/sup 0/C compared to the 25/sup 0/C environment reduced tumor incidence in the x- and neutron-irradiated groups, but reduced incidence of lens opacities only in the neutron-irradiated group. A 2/sup 0/C environment before and after irradiation produced similar results. Return of the 2/sup 0/C acclimated rats to a 25/sup 0/C environment increased incidence of tumors and lens opacities in the x-ray group, but reduced incidence of both in the neutron-irradiated rats. Chronic exposure to 2/sup 0/C reduced the tumor incidence of nonirradiated rats but did not change the incidence of lens opacities.more » Median life expectancy was reduced by exposure to the 2/sup 0/C environment. The data are consistent with the hypothesis that a chronic environmental stress initiated immediately after a carcinogen, in this study x or neutron radiation, may inhibit the malignant transformation. In view of other published data the stress-induced increase in metabolic rate may be an important factor in the inhibition.« less