Binding of radiolabeled porcine motilin and erythromycin lactobionate to smooth muscle membranes in various segments of the equine gastrointestinal tract.

The study investigates how porcine motilin, a digestive hormone, and erythromycin lactobionate, a type of antibiotic, bind to receptors in different parts of a horse’s gastrointestinal (GI) tract. The research found that both substances had the highest binding affinity in the duodenum and decreased in more distant parts of the GI tract, which implies that erythromycin could function as a prokinetic agent by binding on these receptors.

Research Methodology

• The study was carried out using different parts of the intestinal tracts from four adult horses. These horses were euthanized for reasons unrelated to the GI tract disease, ensuring the integrity of the samples used.
• Smooth muscle tissues were taken from the duodenum, jejunum, the pelvic flexure (part of the large intestine), and the cecum (connecting the small and large intestines). Cellular membranes were prepared from these tissues to study the motilin receptors.
• The affinity and distribution of motilin receptors were determined using a radioactively labelled version of synthetic porcine motilin.
• To evaluate competition between porcine motilin and erythromycin lactobionate, displacement studies were conducted. In these studies, they would measure how much labelled motilin was displaced from the receptors by erythromycin lactobionate.

Research Findings

• The researchers discovered that the labelled porcine motilin had an affinity of 6.1nM for the equine motilin receptor, providing a measure of how strongly the hormone binds to the receptor.
• The number of motilin receptors was significantly higher in the duodenum as compared to the pelvic flexure and cecum.
• Similarly, the number of motilin receptors was significantly higher in the jejunum than in the cecum. This suggests that the receptor’s prevalence may decrease along the GI tract.
• Displacement of the labelled porcine motilin by erythromycin lactobionate did not vary greatly between different parts of the bowel. This suggests that the antibiotic competes consistently with motilin across the GI tract.

Conclusions

• The study finds that motilin receptors are present in different parts of the horse’s intestine, with the greatest number found in the duodenum and decreasing numbers in more distal parts of the GI tract.
• It also finds that erythromycin lactobionate competes with motilin for receptor binding in the horse’s GI tract. This suggests that erythromycin lactobionate’s prokinetic actions (stimulating gut motility) could be due to its binding to motilin receptors.