Influence of a chronic environmental stress on radiation carcinogenesis

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 250C until irradiated and immediately returned to (1) a 250C or (2) a 20C environment for duration of life; acclimation to a 20C environment for 40 days, irradiated, then returned to (3) a 20C or (4) a 250C environment. Postirradiation exposure to the 20C compared to the 250C environment reduced tumor incidence in the x- and neutron-irradiated groups, but reduced incidence of lens opacities only in the neutron-irradiated group. A 20C environment before and after irradiation produced similar results. Return of the 20C acclimated rats to a 250C 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 20C reduced the tumor incidence of nonirradiated rats but did not change the incidence of lens opacities. Median life expectancy was reduced by exposure to the 20C 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