Effect of collateral circulation on intestinal viability following segmental devascularization in the rat

The collateral circulation in the rat small intestine was studied by evaluating the viability of an intestinal segment after its primary mesenteric vascular supply had been interrupted. After ligation of the main mesenteric branches of a 30-cm segment of either jejunum or ileum, viability was assessed immediately by the fluorescence pattern observed under ultraviolet illumination after the peripheral intravenous injection of sodium fluorescein. Viability was assessed again at 48 hours by the fluorescein technique and by gross and histologic examination. With the marginal vessels intact, the collateral circulation was able to sustain 10 per cent of the entire length of small intestine beyond the point of devascularization. On the other hand, when the marginal vessels had been ligated, this length of sustained intestine proved to be negligible. With respect to the above findings, there was no difference in the extent or pattern of collateral circulation at different levels along the small intestine, from proximal jejunum to jejuno-ileal junction to terminal ileum. Systemic infusion of a vasodilator, isoproterenol, was found to substantially decrease the length of small intestine maintained viable by collateral flow. This was associated with a greater decrease in systemic vascular resistance than in mesenteric vascular resistance, which resulted in a drop in mesenteric blood flow. In each of the above studies, the ultimate viability of the intestine by histologic section at 48 hours correlated closely with the fluorescein pattern immediately after devascularization. These studies demonstrate that the collateral circulation of the small intestine is extensive and sufficient to maintain viability in a substantial proportion of the length of the entire intestine. The marginal vessels appear to be the primary collateral conduit, and the contribution by intramural vessels is negligible. The use of an effective dose of a systemic vasodilator cannot be relied upon to increase collateral flow, and may, as in this case, have a paradoxical effect of reducing mesenteric flow due to a lowering of (systemic) perfusion pressure. Finally, the fluorescein technique of viability determination has been shown to be valid, not just for intestinal segments subjected to ischemia and then reperfusion, but now also for acutely devascularized segments that are not revascularized.