Mechanisms of bicarbonate secretion in the equine colon ex vivo.

The research investigates how bicarbonate (a chemical compound often used for digestion) is secreted in different parts of the horse’s colon and how a medication called phenylbutazone impacts this process.

Methods

• The research was conducted with 14 healthy horses.
• 10 horses were anesthetized and their colon mucosa segments from the right dorsal colon (RDC) and right ventral colon (RVC) were examined to observe bicarbonate secretion using the pH Stat method.
• The impact of phenylbutazone (PBZ), a commonly used medication for horses, on bicarbonate secretion was observed specifically in the RDC of 4 additional horses.

Findings

• The research affirmed the existence of three distinct mechanisms for bicarbonate secretion in the horse’s colon that had previously been identified in a mouse model.
• The RDC exhibited a greater ability for ‘electrogenic’ bicarbonate secretion that is independent of chloride compared to RVC. This was statistically significant with a P value of 0.04.
• In the RDC, secretion of bicarbonate was found to decrease with the application of PBZ. This was found to be statistically significant, with a P value less than 0.02. The same was not studied further in the RVC due to low basic secretion.

Conclusion

• The researchers found that bicarbonate secretion in the RDC could have a key role in the horse’s colon physiology, as this area experiences strong microbial fermentation that may require bicarbonate secretion to buffer short-chain fatty acids.
• Interference with this bicarbonate secretion by PBZ could lead to mucosal buffering disruption and contribute to conditions associated with right dorsal colitis (an inflammatory bowel disease affecting horses).