Experimental colitis as a promoter in large-bowel tumorigenesis

To study the effect of acetic acid colitis on 1,2-dimethylhydrazine-induced colon tumorigenesis, fischer 344 male rats, 10 weeks of age, were divided into three groups: one receiving 5% acetic acid enema (subgroup 1a); one receiving 10% acetic acid enema (subgroup 1b); and one not receiving acetic acid enema (group 2). Colitis developed in rats in groups 1a and 1b, resulting in early death in some cases. Rats of all three groups received the same subcutaneous dose of dimethylhydrazine given once a week for 20 weeks starting at 11 weeks of age; they were killed at 31 weeks after the first dimethylhydrazine injection. The percentage of animals having tumors in the large bowel was greatest in subgroup 1b and least in group 2. The mean number of large-bowel tumors per animal in which large-bowel had developed was determined in each group. The mean number of subgroup 1 was greater than that of group 2 and also greater than that of groups 1a and 2 combined. The results of the study suggest that colonic mucosal injury may render the colonic epithelium susceptible to tumor induction by carcinogens in the fecal stream.