Ultrastructural mucosal injury after experimental ischemia of the ascending colon in horses.

This study investigates the progression of ultrastructural injury in the horse’s ascending colon during experimentally induced ischemia, highlighting earlier occurrence of mucosal congestion in horses with obstructed colonic venous circulation compared to those with both arterial and venous obstruction. The experimental protocol did not induce any significant morphological changes in the control horses.

Experimental Procedure

• The experiment was conducted on 6 halothane-anesthetized horses whose ascending colonic function was disrupted by two types of vascular occlusion, one 24cm proximal and the other distal to the pelvic flexure, thereby inducing ischemia.
• In all horses, a transmural vascular compression was performed. For three horses, the procedure obstructed the colonic venous circulation while for the other three, both the arterial and venous circulation was obstructed.
• As a comparison, two additional horses were anesthetized but not subjected to the vascular occlusion procedures. These control horses were used to identify any potential morphological changes induced by the experimental protocol itself.
• Full-thickness colonic biopsy specimens were obtained at predetermined time intervals ranging from immediate post-procedure to 5 hours post procedure. These samples were examined with light and transmission electron microscopy.

Findings

• The colon of control horses did not manifest any noticeable morphological changes, thereby indicating that the experimental protocol was not causing alterations.
• Mucosal congestion, generally a symptom of ischemia, was observed via light microscopy. This appeared earlier in the horses with obstructed colonic venous circulation than in horses with both arterial and venous obstruction.
• At the cellular level, initial alterations like inter- and intracellular vacuolation and loss of staining were seen to impact groups of superficial luminal epithelial cells.
• Glandular epithelial cells, on the other hand, exhibited delayed alterations, evident in both the obstructed groups by 2 hours post procedure.
• By the end of the experiment (4.5 to 5 hours), 100% sloughing of all epithelium observed, indicating significant cellular injury due to the induced ischemia.

Through this procedure and subsequent observation, the researchers are better able to understand the progression and impact of ischemia in equine gastro-intestinal health, especially in regards to colonic venous versus arterial and venous obstruction.