Effects of fecal stream on experimental colorectal carcinogenesis. Morphologic and histochemical changes.

The effect of alteration of fecal stream in the presence of the carcinogen 1.2 Dimethylhydrazine, 2 HCl (DMH) has been studied in rats who have undergone surgical division of the colon to produce emptying and filling loops with areas of both decreased and increased fecal exposure. The progressive development of lesions with increasing severity related to prolonged exposure to carcinogen is demonstrated. These changes are preceded and accompanied by alteration of glycoprotein secretion. In the operated rats (1) neoplastic growth appears enhanced and it arises sooner and more proximally than in nonoperated animals; (2) the lesions show tendency to occur at the site of the anastomosis with relative sparing of the distal colon; and (3) tumors are more numerous in areas with increased fecal concentration (filling and small emptying loops), in contrast with their absence in the distal segment of the long emptying loops. Two possible explanations for this preferential distribution are suggested. First, the increased susceptibility to the carcinogen in a previously traumatized area (anastomotic site). Second, the changes in the carcinogenic effect and bile acid concentration as a result of fecal stasis produced by interference with the normal peristalsis of the bowel due to surgical division. The importance of these observations in planning surgery to the colon is considered.