Myoelectric and contractile effects of motilin on dog small intestine in vivo.

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 microgram) caused: a series (1-5 min) of phasic contractions and electrical response activity (ERA) bursts locally; a short (15-60 sec) series of phasic contractions and ERA bursts aborally followed by relaxation; and 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 less than 0.01). No other tested agent, including serotonin, bethanechol, morphine, dopamine, substance P, neurotensin, somatostatin, vasoactive intestinal peptide, bombesin, pentagastrin, cholecystokinin octapeptide, prostaglandin F2 alpha or leucine-enkephalin, caused 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.