Relative effects of ileal resection and bypass on intestinal adaptation and carcinogenesis.

Since ileal resection and ileal bypass are commonly performed in man and might stimulate colonic hyperplasia, their co-carcinogenic potential was explored in male Sprague-Dawley rats (n = 135). One week after 33 per cent distal small-bowel resection, 33 per cent distal small-bowel bypass or distal ileal transection (control), animals started a 6-week course of azoxymethane injections (total dose 90 mg/kg ip). Findings in rats killed at 20 and 25 weeks were similar: bypass produced a higher yield of colorectal tumours (4.0 +/- 0.6 per rat: mean +/- s.e.) than controls (2.4 +/- 0.4; P less than 0.05), but resection caused maximal enhancement (5.2 +/- 0.5: P less than 0.01). In rats killed at 30 weeks, however, tumour yields were almost identical. Overall, resection increased colonic tumour yield by 55 per cent (P less than 0.02) and bypass by 32 per cent. Stathmokinetic measurements of crypt cell production rate (CCPR) at 20 weeks showed similar increases after resection and bypass both in residual functioning small bowel (109-200 per cent: P less than 0.01) and in colorectum (63-100 per cent: P less than 0.05). At 30 weeks these adaptive effects persisted, despite an overall increase in CCPR with age. Loss of functioning ileum enhances experimental colorectal carcinogenesis principally by reducing the latent period for tumour development. Resection has a greater effect than bypass probably by producing earlier hyperplasia, though later adaptive effects are similar.