Dietary beta-carotene in rat models of gastrointestinal cancer.

The effect of dietary beta-carotene (BC) was investigated in models of gastric and colonic carcinogenesis. Male Wistar rats were fed a diet with 0.4% BC during weaning, then 0.2% BC throughout. Cancer in the stomach and small intestine was induced by giving 80 mg/l N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in drinking water for 52 wk, but BC failed to affect carcinogenesis under these conditions, although the incidence of gastric adenocarcinoma was reduced slightly. Neoplastic and nonneoplastic lesions in the liver, skin, and pancreas were also present to a similar extent with BC feeding and without BC. Colorectal cancer was induced by six 2 mg intrarectal infusions of MNNG per rat over a 3-wk period, with the rats held another 22 wk without an inhibitory effect by BC. Thus, 0.2% dietary BC failed to influence significantly the development of neoplasia induced by a direct-acting carcinogen in the gastrointestinal tract.