Isolated bowel segment (Iowa Model 1): technique and histological studies.

An isolated bowel segment (IBS) is a viable loop of bowel that is completely free of its mesenteric attachments. We created an IBS by staged procedures: (1) myoenteropexy between the undersurface of the abdominal wall muscle and a jejunal loop that is exteriorized at both ends as mucous fistulae; and (2) division of the IBS mesentery several weeks later. Viability of the IBS is preserved by vascular collaterals that develop at the myoenteropexy during the interval between these two procedures. In this study, histological observation of the IBS was performed to retrospectively determine the optimal interval required for adequate collateral circulation to develop. Twenty-eight rats were subdivided into seven groups of four rats each; each group underwent mesenteric division of the IBS at successive 1-week intervals after myoenteropexy (1 to 7 weeks). The bowel wall structures were histologically examined under light microscopy for each group after mesenteric division. Ischemic changes were observed in the groups in which the intervals were shorter than 6 weeks. With the time interval longer than 6 weeks, no ischemic changes were observed in the intramural ganglia and muscle layers and minimal changes were noted in the mucosa. This study concluded that an IBS can be safely created in the rat that preserve normal bowel structures when its mesentery is divided 7 weeks after myoenteropexy.