1. Rats were subjected to resection of either the distal 50 cm of small bowel, the caecum or a combined ileocaecal operation. The effects on stool production and growth were observed over the following 8 weeks. Subsequently measurements were made at various levels in the remaining gut of intestinal weight, mucosal thickness, mucosal adenosine 3′:5′-phosphate (cyclic AMP) concentration and the water and bile acid content of luminal material.

2. Rapid adaptation, in terms of growth and the production of formed stools, was seen after ile-ectomy or caecectomy. This was slower and less complete after ileocaecectomy. Changes in water content indicated that colonic absorption of water was normal after ile-ectomy but impaired after ileocaecectomy.

3. After ile-ectomy there was growth of the caecum but not colon, whereas after ileocaecectomy there was growth of the remaining colon.

4. The intraluminal bile acid concentration in the small-gut remnant was markedly decreased at 2 weeks with little further change at 8 weeks after ileal resection. The colonic intraluminal bile acid concentration was only modestly increased after ile-ectomy or ileocaecectomy.

5. When studied by a perfusion technique in vivo, deoxycholate (2·5 mmol/l) in intact rats induced a net secretion of water into the colon; by contrast the colon of 8 week ile-ectomized rats absorbed water, although this was at a reduced rate compared with control rats. Deoxycholate increased mucosal cyclic AMP concentrations in the intact rats but not in the ile-ectomized rats.

6. Sodium ricinoleate (5·0 mmol/l) inhibited colonic water absorption and when mixed with deoxycholate (2·5 mmol/l) the effect on water transport was summatory. However, ricinoleate either alone or with deoxycholate did not alter mucosal cyclic AMP concentrations.

7. These results demonstrate that the colon can absorb water effectively after ile-ectomy in spite of being exposed to increased concentrations of luminal bile acids. This may result in part from an altered mucosal response to secretagogues. If so this represents a form of functional adaptation by the colon to ileal resection.

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