Influence of a chronic environmental stress on the incidence of methylcholanthrene-induced tumors.

The influence of a chronic environmental stress, living in a 2 degrees environment, on the incidence of methylcholanthrene-induced tumors in albino female Simonsen rats, a Sprague-Dawley-derived strain, was studied. The results indicated that the metabolic rate was double for rats kept at 2 degrees, compared with those kept at 25 degrees. Exposure to 2 degrees for life, with no other treatment, reduced median life expectancy to 560 days compared with 686 days for rats kept at 25 degrees. Transfer to a 2 degrees environment after 250 days at 25 degrees reduced the incidence of spontaneous tumors, while transfer to 25 degrees after 250 days at 2 degrees increased the incidence of tumors compared to that for rats always kept at 25 degrees. Exposure to an environmental temperature of 2 degrees immediately following a carcinogenic stimulus (3-methylcholanthrene, 2 mg s.c.) significantly reduced the incidence of tumors compared to that in rats kept at 25 degrees but did not change tumor induction time. The reduced tumor incidence may have resulted from inhibition of the carcinogenic transformation by chronic stress. The survival time of rats with 3-methylcholanthrene induced tumors was not significantly less in a 2 degrees environment than it was at 25 degrees.