Factors influencing the anticarcinogenic efficacy of selenium in dimethylbenz[a]anthracene-induced mammary tumorigenesis in rats.

The present study was designed to investigate the effect of selenium supplementation on dimethylbenz[a]anthracene-induced mammary tumorigenesis in female Sprague-Dawley rats fed either a 5 or 25% corn oil diet, denoted as low fat (LF) or high fat (HF), respectively. Selenium supplementation of LF and HF diets were begun at 21 days of age. In Experiment 1, rats (50 days of age) were given 5 mg of dimethylbenz[a]-anthracene p.o. and were supplemented with 0.1 (adequate level), 0.5, 1.5, and 2.5 ppm of selenium (as sodium selenite) in the diet. The total number of tumors found were as follows (30 rats/group): 26, 23, 19, and 10, respectively, in the LF group; and 65, 66, 41, and 21, respectively, in the HF group. In experiment 2, rats (50 days of age) were given 10 mg of dimethylbenz[a]anthracene, and selenium was added to the diets at 0.1, 2,5, and 5.0 ppm. Tumor yields were found to be 71, 32, and 15, respectively, in the LF group and 135, 85, and 46, respectively, in the HF group. There was also a trend towards a longer latency period of tumor appearance with selenium supplementation. In conclusion, high dietary selenium levels are able to protect against mammary tumorigenesis, but rats on a HF diet still develop more tumors than those on a LF diet at comparable selenium supplementation.