Studies on the transport in vitro of lysine, histidine, arginine and ammonia across the mucosa of the equine colon.

This study investigates how three specific amino acids and ammonia are transported through the mucosa (inner lining) of a horse’s colon using tissue samples. The results showed that the mucosa is mostly impermeable to the amino acids, but ammonia is moved across the lining at significant levels.

Sample Preparation

• The research team prepared disc-shaped samples of stripped mucosa from the proximal ventral colon (the starting point of the large intestine near the small intestine) of eight Shetland cross-breed ponies. These samples were prepared shortly after the ponies were slaughtered.

Incubation Experiments

• The prepared mucosa samples were then fixed in incubation chambers where they were used in experiments to study the movement of three amino acids, namely lysine, histidine and arginine, and ammonia. The duration of these experiments was 150 minutes for amino acids and 90 minutes for ammonia.

Effect of Amino Acid Concentrations

• When the concentration of the amino acids in the mucosal solution was within the physiological range (2.8-3.0 mmol/l, which is considered the normal range in living organisms), no movement of these substances to the other side of the tissue was observed.
• Upon increasing the concentrations by 10-fold, still enough, less than 2% of the total amino acids present in the mucosal solution were found in the solution on the opposite side of the tissue (the serosal side).
• This reveals that the tissue of the proximal colon of the horse is almost entirely impermeable to these specific amino acids.

Transport of Ammonia

• However, ammonia was found to be transported across the mucosal barrier at significant rates, with 63% of the ammonia that disappeared from the mucosal solution being found in the serosal one.
• The results suggest that the transport rates of ammonia are equal to or higher than those observed with the mucosa from the rumen of sheep, which is a different section of the digestive system.