Neutrophil accumulation in the large colon of horses during low-flow ischemia and reperfusion.

The research investigates whether during diminished blood flow conditions and its subsequent restoration (ischemia and reperfusion) in the large colon of horses, neutrophils, a type of white blood cells, increase. The study notes a significant accumulation of neutrophils during such conditions which suggests their role in reperfusion injury.

Research procedure

• The researchers carried out evaluations using histomorphologic/morphometric (microscopic analysis of tissue structure and dimensions), leukocyte scintigraphy (imaging procedure that uses radioactive markers to visualize neutrophils), and myeloperoxidase (an enzyme that increases with neutrophil activity) activity assessments.
• A total of 24 adult horses were separated into three groups. Group 1 consisted of 6 barrier-removed (sham-operated) horses, Group 2 was comprised of 9 horses undergoing six hours of ischemia, and Group 3 had 9 horses subjected to three hours of ischemia followed by three hours of reperfusion.
• For Groups 2 and 3, low-flow ischemia of the large colon was implemented by reducing colonic arterial blood flow to 20% of the baseline level.
• Radiolabeled or isotopically marked neutrophils were injected into the horses. This action allowed tracking and visualization of these white blood cells.
• Full-thickness biopsy specimens of the left ventral colon were taken at the start and at 30-minute intervals over six hours to examine activities associated with neutrophils.

Results and findings

• No differences were observed in baseline mucosal neutrophil index, neutrophil numbers, mucosal radioactivity, or myeloperoxidase activity among all groups or over time in group-1 horses.
• During ischemia, there was a noticeable accumulation of neutrophils in the colonic mucosa. This accumulation was observed further upon reperfusion (as indicated by neutrophil index and mucosal neutrophil numbers).
• Particularly in Group 3, the neutrophil accumulation was significantly greater during reperfusion than the corresponding periods during ischemia in Group 2 horses.
• Ten minutes into the reperfusion in Group 3, the neutrophil numbers considerably increased in the venules (small veins). The numbers were significantly higher in Group 3 compared to Group 2 during the recovery period from 3 to 6 hours.
• The mucosal radioactivity, representative of neutrophil presence, increased at reperfusion in Group 3 horses. There was a notable trend towards higher mucosal radioactivity in Group 3 compared to Group 2 throughout 3 to 6 hours.
• No differences were discovered in myeloperoxidase activity among or within any group over time, which means the enzyme did not contribute to variations observed on neutrphils activity.

Conclusion

In the large colon of horses, neutrophils were found to aggregate during low-flow ischemia and reperfusion. This accumulation was detectable by leukocyte scintigraphy and histologic examination, but not by myeloperoxidase activity measurements. The accumulation of neutrophils, therefore, could potentially contribute to the injury caused to the colon during reperfusion following ischemia.