Adaptation to jejunoileal bypass promotes experimental colorectal carcinogenesis.

The co-carcinogenic potential of 85 per cent jejunoileal bypass (JIB) was tested in male Sprague-Dawley rats (n = 81) given 6 preliminary injections of the selective intestinal carcinogen azoxymethane (total dose 90 mg/kg). Controls had sham JIB. Colorectal adaptation was studied 30 weeks postoperatively in rats given injections of vehicle alone. JIB caused 17-33 per cent increments in colonic length, weight and crypt depth; crypt cell production rate was more than doubled (P less than 0.01). Despite lowering body weight by 27 per cent, JIB increased the median number of colorectal tumours per rat from 3 to 8 (P less than 0.01). The findings suggest that evidence of hyperplasia and dysplasia should be sought in patients receiving subtotal jejunoileal bypass for obesity.