Inhibitory effects of selenium on 1,2-dimethylhydrazine and methylazoxymethanol acetate induction of colon tumors.

Sprague-Dawley rats were injected weekly with either 1,2-dimethylhydrazine (DMH) or methylazoxymethanol acetate (MAM). Addition of 4 ppm selenium (sodium selenite) in the drinking water reduced the number of rats developing DMH-induced colon tumors from 13 to 6 groups of 15 each. The total number of tumors observed in these two groups was 39 in the DMH treated and 11 in the DMH plus selenium. The incidence of MAM-induced tumors was 93% (14/15) with the selenium additive and 100% (14/14) when MAM was administered without the selenium supplement. However, selenium decreased the total number of colon tumors induced by MAM to 42 tumors as compared to a total of 73 tumors in rats receiving only MAM. Both carcinogens induced tumors with a higher frequency in the transverse colon as compared to either the proximal or distal colon. Selenium at this level did not affect the weight gain of the animals.