Histopathological and ultrastructural changes in simulated large colonic torsion and reperfusion in ponies.

This investigation examines the histological and ultrastructural lesions of the colonic mucosa during terminal experimental infarction and subsequent reperfusion. Four ponies were anaesthetised and subjected to surgical torsion of the colon. Biopsies were collected at hourly intervals for 3 h, at which point the torsions were corrected. Circulation was re-established for 2 h and the bowel was re-biopsied at hourly intervals. The ponies were killed while under anaesthesia. During the 3 h experimental infarction, the bowel became macroscopically thickened and dark purple. Histologically, the mucosa degenerated from Grade 0 to Grade 3. Ultrastructurally, there was progressive micro-vascular distension with erythrodiapedesis and damage to the interstitial cells. Spaces developed between the bases and sides of the columnar epithelial cells and sloughing followed subsequently. During the 2 h reperfusion interval, the mucosa continued to degenerate rapidly to a Grade 5, and was characterised by extensive interstitial damage, oedema, cellular swelling, necrosis and mitochondrial damage. The results showed that the experimentally infarcted colonic mucosa degenerated sequentially. Following circulatory reestablishment, continued rapid mucosal degeneration characteristic of reperfusion injury occurred. Reperfusion injury is probably responsible, at least in part, for the often poor outcome of infarcted bowel in horses following surgical correction.