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

Abstract

Abstract. 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 occumng colonic volvulus and can serve as a reference for subsequent studies on attenuating bowel injury.

Use of Pelvic Flexure Biopsies to Predict Survival After Large Colon Torsion in Horses

“…Microscopic evaluation of morphologic change provides an assessment of the extent of the tissue injury that has occurred at the time of biopsy. Various experimental models have been developed whereby large colon torsion was created in vivo or blood flow to the colon was reduced to 20% of baseline to investigate the physiological effects of large colon torsion 1,7,8,12,13,18 . Although the experimental protocols vary with regard to the type of strangulating obstruction (ischemic or hemorrhagic) and its duration, colonic biopsy specimens taken to evaluate the effects of ischemia have generally yielded a consistent pattern of morphologic changes.…”

“…Superoxide anion, hydroxyl radical, singlet oxygen, and hydrogen peroxide formation exacerbate the ischemic injury 4–6 . The poor prognosis for survival after surgical correction of colon torsion is associated with the microvascular damage that occurs and results in necrosis of the mucosal layer 7,8 …”

Ultrastructural changes in the equine colonic mucosa after ischaemia and reperfusion

“…Intestinal I/R injury can be identified early by increase in capillary and epithelial permeability (Snyder et al . 1992; Darien et al . 1995).…”

“…Intestinal I/R injury can be identified early by increase in capillary and epithelial permeability (Snyder et al 1992;Darien et al 1995). First histological signs of colonic mucosal damage are characterised by lifting of small clusters of epithelial cells, their detachment from the basement membrane and subsequently death by apoptosis or necrosis (Meschter et al 1991;Snyder et al 1992).…”

Use of an extracorporeal circuit to evaluate effects of ischemia and reperfusion of the equine large colon

“…7,8 To increase our understanding of the pathogenesis of ischemia and reperfusion injury of the large colon during torsion, various experimental models have been developed to evaluate the progression of tissue injury and, once the injury had been created, to evaluate the efficacy of various pharmaceutics for attenuating tissue damage. [9][10][11][12][13][14][15][16][17] Although results of those studies have enhanced our understanding of injury during colonic torsion, inherent complications have been associated with those models. In general, the study design requires a large number of personnel for extended periods of time and requires maintaining a horse for the duration of the study or recovery of a horse after anesthesia and surgery followed by euthanasia at a predetermined time.…”