Effect of substance P on intestinal muscle.

The mode of action of synthetic substance P on intestinal motility was investigated in vitro. Results have indicated that substance P has a major stimulating effect on the intestine by eliciting mechanical contraction and bursts of spike potentials. On a molar basis, substance P was 1.6 X 10(3) times more potent than acetylcholine. Unlike the gastrin peptide analogue caerulein, the effects of which were mediated through the release of acetylcholine from the enteric plexuses, the site of action of substance P appeared to be directly on the muscle cells because its effects were resistant to atropine, tetrodotoxin, and Lioresal. These data strongly suggest a possible physiological role of substance P in the modulation of intestinal longitudinal muscle motor activity.