Objective—To identify and characterize motilin receptors
in equine duodenum, jejunum, cecum, and large
colon and to determine whether erythromycin lactobionate
competes with porcine motilin for binding to
Sample Population—Specimens of various segments
of the intestinal tracts of 4 adult horses euthanatized for
reasons unrelated to gastrointestinal tract disease.
Procedure—Cellular membranes were prepared from
smooth muscle tissues of the duodenum, jejunum,
pelvic flexure, and cecum. Affinity and distribution of
motilin binding on membrane preparations were determined
by use of 125I-labeled synthetic porcine motilin.
Displacement studies were used to investigate competition
between 125I-labeled synthetic porcine motilin
and erythromycin lactobionate for binding to motilin
receptors in various segments of bowel.
Results—Affinity of 125I-labeled synthetic porcine motilin
for the equine motilin receptor was estimated to be
6.1nM. A significantly higher number of motilin receptors
was found in the duodenum than in the pelvic flexure
and cecum. The jejunum had a significantly higher
number of motilin receptors than the cecum.
Erythromycin lactobionate displacement of 125I-labeled
porcine motilin from the equine motilin receptor did not
differ significantly among various segments of bowel.
Conclusions and Clinical Relevance—Motilin receptors
were found in the duodenum, jejunum, pelvic
flexure, and cecum of horses. The highest number of
motilin receptors was in the duodenum, and it
decreased in more distal segments of bowel.
Erythromycin lactobionate competed with motilin
binding in the equine gastrointestinal tract. This suggests
that 1 of the prokinetic actions of erythromycin
in horses is likely to be secondary to binding on
motilin receptors. (Am J Vet Res 2002;63:1545–1550)