MORPHOLOGIC CHANGES AND XANTHINE-OXIDASE ACTIVITY IN THE EQUINE JEJUNUM DURING LOW-FLOW ISCHEMIA AND REPERFUSION

Objective-To determine whether xanthine oxidase and dehydrogenase acti vities are altered during low flow ischemia and reperfusion of the sma ll intestine of horses. Animals-5 clinically normal horses without his tories of abdominal problems. Procedure-With the horse under general a nesthesia, a laparotomy was performed and blood flow to a segment of t he distal jejunum was reduced to 20% of baseline for 120 minutes and w as then reperfused for 120 minutes. Biopsy specimens were obtained bef ore, during, and after ischemia for determination of xanthine oxidase and dehydrogenase activities, and for histologic and morphometric anal yses. Results-Percentage of xanthine oxidase activity (as a percentage of xanthine oxidase and dehydrogenase activity) was not altered durin g ischemia and reperfusion. An inflammatory response developed and pro gressed during ischemia and reperfusion. Mucosal lesions increased in severity after ischemia and reperfusion. Mucosal surface area and volu me decreased during ischemia and continued to decrease during reperfus ion. Submucosal volume increased slightly during ischemia, and continu ed to increase during reperfusion. Conclusions and Clinical Relevance- Evidence for conversion of xanthine dehydrogenase to xanthine oxidase during ischemia was not found. Factors other than production of reacti ve oxygen metabolites may be responsible for progressive epithelial lo ss, decrease in mucosal surface area and volume, and increase in submu cosal volume observed in this study. Other methods of determining xant hine oxidase activity that detect the enzyme in sloughed epithelial ce lls should be used to better define the importance of this pathway in jejunal reperfusion injury in horses.