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1 Gastrointestinal Unit and 2 Department of Surgery, Centre Hospitalier de l'Université de Montréal; and 3 Department of Chemistry, Université du Québec à Montréal, Montreal, Quebec, Canada H2X 3J4
Motilin is an intestinal peptide that
stimulates contraction of gut smooth muscle. The motilin receptor has
not been cloned yet, but motilin-receptor agonists appear to be potent
prokinetic agents for the treatment of dysmotility disorders. The aim
of this study was to determine neural or muscular localization of motilin receptors in human upper gastrointestinal tract and to investigate their pharmacological characteristics. The binding of
125I-labeled motilin to tissue membranes prepared from
human stomach and duodenum was studied; rabbit tissues were used for
comparison. Solutions enriched in neural synaptosomes or in smooth
muscle plasma membranes were obtained. Various motilin analogs were
used to displace the motilin radioligand from the various tissue
membranes. The highest concentration of human motilin receptors was
found in the antrum, predominantly in the neural preparation. Human motilin receptors were sensitive to the NH2-terminal
portion of the motilin molecule, but comparison with rabbit showed that
both species had specific affinities for various motilin analogs
[i.e., Mot-(1
9), Mot-(1
12), Mot-(1
12)
(CH2NH)10-11, and erythromycin]. Motilin receptors obtained from synaptosomes or muscular plasma membranes of human antrum expressed different affinity for two motilin-receptor agonists, Mot-(1
12) and Mot-(1
12)
(CH2NH)10-11, suggesting that they
correspond to specific receptor subtypes. We conclude that human
motilin receptors are located predominantly in nerves of the antral
wall, are functionally (and probably structurally) different from those
found in other species such as the rabbit, and express specific
functional (and probably structural) characteristics dependent on their
localization on antral nerves or muscles, suggesting the existence of
specific receptor subtypes, potentially of significant physiological or
pharmacological relevance.
gastrointestinal motility; regulatory peptides; receptor subtypes
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