Further studies on the carcinogenesis of the colon of the rat with special reference to the absence of intestinal contents.

The proximal and distal ends of the ascending, transverse and descending colon of 67 Sprague-Dawley rats were severed and stitched to the abdominal wall. The remaining colon was anastomosed end to end. The disarticulated colon loop was rinsed 30 times over 15 days to remove all traces of intestinal contents. The animals were then given subcutaneous injections of 1,2-dimethylhydrazine (21 mg/kg body weight) for 27 weeks. During that period, the isolated loops were rinsed with saline once a week. The rats were killed after seven months of treatment. Eighty-five tumors developed in the 67 animals: 20 in the isolated loops and 65 in the end-to-end anastomosed colon. The carcinogen employed reached the colonic loop through the circulation and induced (independently of bile acids) mucosal changes that led to the development of colonic tumors.