Effects of substance P and other neuropeptides on guinea-pig gall-bladder muscle.

Substance P, neurotensin, bombesin and neuropeptide-Y-like immunoreactivities have been identified in nerves in gall-bladder muscle, so we studied the effects of these peptides on guinea-pig gall-bladder muscle in vitro. Substance P (0.1 mumol/l or greater) contracted gall-bladder muscle. Studies with specific antagonists indicated that the response did not involve intramural nerves or the release of acetylcholine, cholecystokinin or histamine. Field stimulation of intramural nerves caused contraction of gall-bladder muscle, but this was unaffected by a substance P antagonist and abolished by atropine. Thus, although substance P contracts gall-bladder muscle by a direct effect, this peptide does not appear to be involved in nerve-mediated gall-bladder contraction. Neurotensin, bombesin and neuropeptide Y had no effect on this preparation.