The effects of the close intraarterial administration of motilin on intestinal myoelectric and contractile activities were examined in 37 dogs. After anesthetization or decerebration, a segment of proximal jejunum was instrumented serosally with electrodes and stain gauges. A mesenteric artery supplying a short length of this segment was cannulated for the injection of motilin and other agents. Motilin (0.03-0.3 μg) caused: (1) a series (1-5 min) of phasic contractions and electrical response activity (ERA) bursts locally; (2) a short (15-60 sec) series of phasic contractions and ERA bursts aborally followed by relaxation; and (3) a series of phasic contractions and ERA bursts whose onset migrated 3.7±1.0 cm orally. The length of orad response increased to 6.6±1.9 cm in the decerebrate dogs (P<0.01). No other tested agent, including serotonin, bethanechol, morphine, dopamine, substance P, neurotensin, somatostatin, vasoactive intestinal peptide, bombesin, pentagastrin, cholecystokinin octapeptide, prostaglandin F2α or leucine-enkephalin, cuased similar responses. All motilin responses were mediated by neural pathways consisting of both nicotinic and muscarinic receptors. The similarity of responses and mechanisms of action of the motilin-activated contractile response with the intrinsic mucosal reflex suggested that motilin may mediate this reflex.
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