Effect of intestinal microflora and dietary fat on 3,2'-dimethyl-4-aminobiphenyl-induced colon carcinogenesis in F344 rats.

The effect of dietary fat and intestinal microflora on colon and small intestinal carcinogenesis was studied in weanling male F344 germfree and conventional rats fed semipurified diets containing low and high fat. At 7 weeks of age, all animals, except vehicle-treated groups, received weekly s.c. injections of 50 mg 3,2'-dimethyl-4-aminobiphenyl (DMAB) per kg body weight for 20 weeks. The DMAB- and vehicle-treated germfree and conventional rats fed high- and low-fat diets were autopsied 20 weeks after the last injection of DMAB. The incidence of colon, small intestinal, ear duct, and skin tumors was lower in germfree rats than in the conventional animals. The incidence and multiplicity of DMAB-induced colon tumors were higher in conventional rats fed the high-fat diet than in the conventional animals fed the low-fat diet; however, the tumor incidence did not differ significantly between the high- and low-fat-fed germfree animals. Dietary fat had no effect on the incidence of small intestinal tumors in both germfree and conventional rats.