Alterations in colonic arterial and venous plasma neuropeptide concentrations in horses during low-flow ischemia and reperfusion of the large colon.

This study investigates how the concentrations of certain neuropeptides in the blood change in horses when the large colon experiences periods of reduced blood flow, also known as ischemia, followed by restoring of blood flow or reperfusion. The neuropeptides being studied include Vasoactive Intestinal Peptide (VIP), Calcitonin Gene-related Peptide (CGRP), and Substance P (SP), which are present in the blood flowing to and from the colon.

Research Design and Methodology

• The experiment was conducted on ten adult horses that were anesthetized.
• In six of these horses, colonic ischemia was experimentally induced by reducing blood flow to the large colon to 20 percent of normal (marked as baseline, or BL) and maintained it at this level for three hours. Then the blood flow was restored and monitored for another three hours.
• Different physiological variables including heart rate and colonic arterial pressure were continuously monitored and recorded every 30 minutes.
• Blood samples were collected from both colonic arteries (CA) and colonic veins (CV) at fixed intervals during the ischemia and reperfusion. The plasma extracted from these samples was used to measure concentrations of VIP, CGRP, and SP using a technique called radioimmunoassays.
• In another group of four horses, only the VIP and CGRP levels in blood from CA and CV were measured, at shorter intervals during the first hour of the experiment.

Results and Findings

• Heart rate saw a significant increase at the 5.5 and 6 hour marks of the experiment, but changes in other systemic hemodynamic variables were not statistically significant.
• During the ischemia phase, a significant decrease in blood flow to the colon was observed. When blood flow was restored (reperfusion), it was observed to rebound to an amount significantly more than the baseline value within 5 minutes, and this elevated level was maintained throughout the rest of the reperfusion period of three hours.
• Colonic arterial pressure dropped significantly during ischemia, but it returned to baseline value by 3.25 hours after reperfusion began.
• Colonic venous pressure did not change during the ischemia phase, but it increased significantly past the baseline after 3.25 hours into reperfusion, and stayed elevated for the rest of the experiment.
• Concentrations of VIP in the CV were significantly increased by as early as 0.25 hours into ischemia, but it returned to baseline value by 3.25 hours into reperfusion.
• Levels of CGRP in the CV increased noticeably at 3.25 hours into ischemia, but returned to baseline value by 3.5 hours into reperfusion.

Conclusion

The research showed that during a period of reduced blood flow (ischemia) in the large colon of horses, there is an increase in the concentration of the neuropeptide VIP in the blood from the colonic vein (CV). Later when blood flow is restored (reperfusion), the concentrations of both the CGRP and SP neuropeptides were observed to increase in blood from both colonic artery (CA) and vein. This study provides valuable insights into the impacts of ischemia and reperfusion on the neuropeptide concentrations and could be pivotal for the understanding of equine colic conditions.