Importance of the fecal stream on the induction of colon tumors by azoxymethane in rats.

The effect of the fecal stream on intestinal carcinogenesis with azoxymethane was studied in male rats. Colostomies were performed approximately 2 cm distal to the cecum in 50 Sprague-Dawley rats to produce a 20-cm segment of nonfunctional large bowel; an additional 50 animals were left intact. Each of these groups was divided equally and was fed a normal diet or a diet containing 2% cholestyramine by weight. All animals were given azoxymethan s.c. At the end of 7 months all rats were sacrificed. The animals with colostomies developed significantly fewer tumors in the defunctionalized bowel than did intact animals in the same bowel segment. Cholestyramine appeared to increase the tumor yield in the large bowel of the intact animals but had no effect on the number of tumors in the defunctionalized bowel. Further, the intact animals on both dietary regimens developed a greater number of large tumors in the distal 20 cm of bowel. The results show that the fecal stream alters the carcinogenic activity of azoxymethane in the large bowel of the rat. It also appears that the carcinogen can reach its target tissue by a route other than the fecal stream.