Hypertrophy of ileal smooth muscle after construction of ileal reservoir in the rat.

An experimental model of the continent ileostomy reservoir used in clinical practise has been adapted for rats in order to evaluate changes in the smooth muscle layers of the ileal wall. The reservoir was constructed in the distal part of ileum, with intestinal continuity in order to avoid emptying problems. The rats were sacrificed 3-7 months after construction of the reservoir. There was a significant dilatation of the reservoir with a 26-fold increase in the mean reservoir volume. Morphometric studies of the smooth muscle in the intestinal wall revealed an increased thickness of the circular and longitudinal layers after construction of the reservoir (p less than 0.001). The number of muscle cell nuclei per section in samples of the ileal reservoir was reduced (p less than 0.01), whereas the mean size of the individual nuclei was greater (p less than 0.001). These results indicate that the enormous dilatation of this ileal reservoir is related to a clear hypertrophy of the smooth muscle layer. Whether there is a concomitant hyperplasia remains to be studied.