Reduction in the incidence of radiation-induced tumors in rats after restriction of food intake.

In our inbred colony of Sprague-Dawley rats, fractionated total-body x-ray irradiation (150 rads five times at weekly intervals; 1 rad = 0.01 gray) increased the incidence of tumors from 22% to 93% in females and from 5% to 59% in males [Gross, L. & Dreyfuss, Y. (1979) Proc. Natl. Acad. Sci. USA 76, 5910-5913]. In experiments reported here, we investigated the influence of reduced food intake on the incidence of radiation-induced tumors in Sprague-Dawley rats. All rats in both groups received fractionated total-body x-ray irradiation similar to that specified above. Among the irradiated rats on full (ad lib) diet (five to six pellets of Purina Rodent Lab Chow per day, each) were 14 females and 9 males, and all (100%) developed tumors (or leukemia) at an average age of 13.7 months in females and 13.4 months in males. Among the litter mates on restricted diet (two pellets of Purina Rodent Lab Chow per day, each), only 9 out of 29 females (31%) developed tumors at an average age of 18.2 months and 1 out of 15 males (6.7%) developed a tumor at 9 months of age. In the full diet group, the majority of tumors developing in females were benign. Among the 9 irradiated males, 1 developed leukemia and the remaining 8 developed tumors; 7 of them were examined, 6 were found malignant, and 1 was benign. In the restricted diet group, of the 9 tumors that developed in females, 4 were malignant and 5 were benign. The tumor that developed in 1 male was a sarcoma.