Morphologic changes and xanthine oxidase activity in the equine jejunum during low flow ischemia and reperfusion.

The research investigates the impact of low flow ischemia – a condition of restricted blood supply – and reperfusion – the restoration of blood supply – on the small intestine of horses. Specifically, it explores changes in the activity of two enzymes, xanthine oxidase and dehydrogenase, and their potential link to intestinal injuries.

Methodology

• Five normal horses without abdominal problems were selected and put under general anesthesia.
• A laparotomy – a surgical procedure involving an incision into the abdominal cavity – was performed to access the distal jejunum, a segment of the small intestine.
• Ischemia was induced by reducing blood flow to the jejunum to 20% of its normal level for a duration of two hours. This was followed by reperfusion, where the blood flow was restored for another two hours.
• Throughout the experiment, biopsy samples were taken at different intervals for analysis of xanthine oxidase and dehydrogenase activities, as well as for histological and morphometric studies to assess changes in tissue structure and form.

Results

• The research found that the proportion of xanthine oxidase activity (relative to the combined activity of xanthine oxidase and dehydrogenase) remained unchanged during both low flow ischemia and reperfusion.
• An inflammatory response, along with increasing severity of mucosal lesions — damage or inflammation on the inner lining of the intestine – were observed during these periods.
• The surface area and volume of the mucosal (innermost layer) of the jejunum diminished during ischemia and continued to decrease during reperfusion.
• In contrast, the volume of the submucosal layer (the layer beneath the mucosal layer) slightly increased during ischemia and continued to grow during reperfusion.

Conclusions

• The study did not find evidence supporting a change in xanthine dehydrogenase into xanthine oxidase during ischemia. This contradicts the belief that the production of reactive oxygen metabolites by xanthine oxidase contributes to damage in ischemic conditions.
• The observed epithelial loss, diminishing mucosal surface area and volume, and the increase in submucosal volume might be due to factors other than the production of reactive oxygen metabolites.
• The researchers suggest using methods that can detect xanthine oxidase in sloughed (shed) epithelial cells for a more accurate understanding of its role in intestinal injuries caused by reperfusion in horses.