The effects of ischemia and reperfusion on mucosal respiratory function, adenosine triphosphate, electrolyte, and water content in the ascending colon of ponies

Objective- The purpose of this study was to examine the effects of ischemia and reperfusion on the biochemical integrity of equine colonic mucosa to assess the relative roles of ischemic- and reperfusion-induced damage. Study Design- Two hours of no-flow ischemia experimentally induced by 720 degrees counterclockwise ascending colon volvulus followed by 2 hours reperfusion after derotation. Animals- Ten ponies. Methods- Ascending colon biopsies were obtained every hour for measurement of mucosal adenosine triphosphate (ATP), water, sodium, and potassium content. Additional samples were homogenized for assay of mitochondrial respiratory function. Results- ATP content diminished 92% after ischemia and recovered to only 44% of control levels (P <.001 versus controls) after 2 hours reperfusion. Reperfusion increased mucosal water and decreased sodium and potassium content for the duration of the experiment. Both NADPH-(pyruvate) and FADH-linked (succinate) respiration decreased after ischemia and did not recover during reperfusion indicating electron transport chain dysfunction. Conclusions- Two hours ischemia induced severe metabolic dysfunction in equine colon mucosa which persisted throughout reperfusion. Unequivocal evidence of injury specific to reperfusion was not observed in this study suggesting that much of the damage observed during reperfusion may be a continuation of injury induced during the ischemic period and not specific to reperfusion per se. Clinical Relevance- This study suggests that greater efforts to metabolically support ischemically injured mucosa may be an important aspect of obtaining improved survival of horses affected by ascending colon volvulus (ACV). (C) Copyright 1997 by The American College of Veterinary Surgeons.