Vasoactive intestinal peptide. An inhibitor of feline gastric smooth muscle in vitro.

Dose-response characteristics of feline corpus circular muscle were studied in vitro for three neuropeptides individually and with vasoactive intestinal peptide. Bombesin, substance P, and cholecystokinin-octapeptide each elicited concentration-dependent isometric contractions that were reduced by 10(-8) M or 10(-7) M vasoactive intestinal peptide (P less than 0.01). The concentration of each neuropeptide producing a half-maximal response was increased more than one logfold to greater than or equal to 10(-6) M by vasoactive intestinal peptide. Tetrodotoxin blocked responses to bombesin (P less than 0.001) and reduced responses to substance P (P less than 0.05), but had no effect on responses to cholecystokinin-octapeptide (P greater than 0.1). These results demonstrate inhibition of neuropeptide responses of gastric smooth muscle and support vasoactive intestinal peptide as an inhibitory regulator of gastric motor function.