Enhancement of mammary carcinogenesis by a high-fat diet in Fischer, Long-Evans, and Sprague-Dawley rats.

The relationship between dietary fat and mammary carcinogenesis was examined by feeding a high-fat or a low-fat purified diet, differing only in fat and carbohydrate content, to Fischer, Long-Evans, and Sprague-Dawley rats. An additional group of rats from each strain was fed a nonpurified laboratory diet for comparison. The rats were given an i.v. dose of N-nitrosomethylurea (50 mg/kg body weight) at 50 days of age. The results showed that (a) a high-fat purified diet significantly enhanced mammary carcinogenesis; (b) a nonpurified laboratory diet retarded mammary carcinogenesis compared to a low-fat purified diet; (c) rats on three different diets had a similar body weight gain; (d) the susceptibility of N-nitrosomethylurea-induced mammary carcinogenesis in the three strains of rats was in the order of Sprague-Dawley > Fischer > Long-Evans; and (e) Fischer rats appeared to be better suited for further systematic studies of dietary fat and mammary carcinogenesis.