Morphologic Changes of the Ascending Colon during Experimental Ischemia and Reperfusion in Ponies

The morphologic changes following ascending colon volvulus result from the interaction of inflammatory and coagulation mediators. The objective of this study was to establish a quantifiable histopathologic scoring system to evaluate the serial pathomorphologic changes during ischemia and reperfusion. Such a scoring system could then be applied to subsequent studies designed to attenuate bowel lesions by regulating activity of individual mediators. Ten normal, healthy adult ponies were randomly divided into two equal groups. Following anesthesia and a 30-minute stabilization period, the colon of ponies in the experimental group was twisted 720°: for 2 hours of ischemia and then untwisted for 2 hours of reperfusion. The control ponies underwent 4 hours of anesthesia. Full-thickness colonic biopsy specimens were obtained from the antimessenteric border of the pelvic flexure and prepared for light and transmission electron microscopy at 0, 1, 2, 3, and 4 hours after twisting. The mean histopathology score at 0 hours for control ponies was 1.2 and remained unchanged; the score for the experimental ponies was 1.8 and progressed to 4.2 by 4 hours. At 2 hours of ischemia, there was edema of the submucosa and lamina propria attributable to accumulation of platelets, fibrin, and neutrophils in capillaries of the lamina propria. The morphologic changes in experimental ponies progressed to complete destruction of the mucosa with congestion, hemorrhage, and microvascular thrombosis. Mean histopathology scores of control and experimental ponies were significantly different at 1 hour of ischemia, and lesions progressively worsened through the reperfusion period. The morphologic changes observed in this study accurately reflect those changes reported in horses with naturally occurring colonic volvulus and can serve as a reference for subsequent studies on attenuating bowel injury.