Quantification of tissue damage in the feline small intestine during ischaemia‐reperfusion: the importance of free radicals

Intestinal ischaemia is accompanied by characteristic mucosal lesions, which can be graded according to a six‐grade system proposed by Chiu et al. (1970). This report describes a continuous grading system which makes it possible to quantify the intestinal damage in connection with ischaemia‐reperfusion. The present morphometric method is based on quantitative histological analysis of intestinal biopsies performed on 200 histological sections from 44 cat experiments. Radical formation was quantified by infusing close i.a. a spin trap, OXANOH, which produces a secondary stable radical, OXANO‐, after reacting with radicals in the tissue. OXANO‐ concentration was determined in venous blood samples with electron spin resonance. We demonstrate a highly significant correlation between the grading system of Chiu et al. (1970) and the morphometric analysis of this study. The tissue damage was located exclusively in the intestinal villi. Comparing the mucosal damage that occurs during 60 min of intestinal ischaemia (superior mesenteric artery pressure 15–25 mmHg) with that seen during the first 30 min reperfusion this study shows that the villus damage occurring during ischaemia is at least twice as large as the aggravation seen upon reperfusion. Furthermore, the authors demonstrate a significant correlation between rate of radical formation and villus tissue damage particularly during the first 30 min after ischaemia. It is concluded that the proposed quantitative morphological method represents a non‐discrete grading system for evaluating tissue damage in connection with ischaemia‐reperfusion in the small intestine. The ischaemia itself inflicted a more severe damage to the intestine than reperfusion. A significant correlation between damage and radical formation was demonstrated during the reperfusion. However, the results suggest that factors other than radical formation are of importance in explaining the tissue damage upon reperfusion. The nature of these factors is presently unknown.