Myogenic and neurogenic motor-stimulating actions of motilin in the rabbit stomach

• Published in: Japanese Journal of Pharmacology 1997, Vol.73 (suppl.1), p.79-79
• Main Authors: Kitazawa, Takio, Kihara, Yoshiko, Taneike, Tetsuro
• Format: Article
• Language: English
• ISSN: 0021-5198; 1347-3506
• DOI: 10.1016/S0021-5198(19)44822-1

The present experiment was designed to determine muscle layer and regional differences, and the mechanism of contractile responses of motilin in the rabbit stomach. The effect of Leu^13 -porcine motilin (LMT) on gastric motility was investigated using anesthetized rabbits (in vivo) and isolated muscle strips (in vitro). In vivo study： LMT, given i.v. at a dose of 0.3 to 10 μg/kg, stimulated motor activity of the antrum but not of the corpus. The excitatory response of LMT was potentiated by neostigmine (30 μg/kg) and abolished by atropine (3mg/kg), but cervical vagotomy did not decrease the response of LMT. Stimulation of peripheral end of the vagus (17V, 3msec duration, 20sec) caused frequency-dependent (1- 10Hz) contraction of the antrum through the cholinergic neural pathway. LMT potentiated the vagal stimulation-induced response. In vitro study： LMT(1nM - 1 μM) caused contraction of the gastric antrum (both circular and longitudinal smooth muscles). Atropine (1 μM) and tetrodotoxin (1 μM) failed to decrease the contractile response of LMT. On the other hand, muscle strips from the corpus and fundus were insensitive to LMT. Electrical field stimulation (EFS) of the gastric muscle strips caused a frequency-dependent cholinergic contraction. LMT potentiated the EFS-induced contraction in the antrum but not in the corpus and fundus without affecting the response of acetylcholine. The potentiation was more conspicuous in the circular muscle than in the longitudinal muscle and was decreased by LMT-induced desensitization. The results indicate that 1) myogenic and neurogenic motilin receptors are distributed heterogenously in the stomach, and that 2) only the neurogenic motilin receptor is functional in anesthetized rabbits.