Characterization of bombesin effects on canine gastric muscle.

Synthetic bombesin increased the frequency and amplitude of spontaneously occurring contractions of muscle strips from antrum and corpus of the canine stomach in vitro. The effect of bombesin on frequency of contractions in this system was myogenic; was unrelated to receptors for acetylcholine, norepinephrine, substance P, or cholecystokinin; and was independent of extracellular calcium. The effect of bombesin on the amplitude in the circular muscle was unaffected by tetrodotoxin and atropine but locked by verapamil, whereas in the longitudinal muscle it was blocked by tetrodotoxin and atropine. In the circular antral muscle bombesin was approximately 100,000 times more potent than acetylcholine at threshold concentrations and was equipotent to cholecystokinin. The high potency of bombesin and its known presence in gastric nerve fibers make it a candidate for a neurotransmitter function in regulation of gastric mobility.