Effect of substance P on contractions of the gallbladder

The effect of substance P on contractions of the gallbladder in dogs (in vivo) and rabbits (in vitro) was examined. Substance P stimulated contraction of the gallbladder, both in vivo and in vitro; however, substance P was not as effective as cholecystokinin. Stimulation of gallbladder contractions in vivo by substance P was not affected by atropine. Stimulation of gallbladder strips in vitro by substance P was not affected by adrenergic antagonists or tetrodotoxin. These findings suggest that substance P may be a direct stimulant of contraction of the smooth muscle of the gallbladder.