The Effect of Substance P on the Peristaltic Reflex When Acting on the Outside of the Isolated Guinea Pig Ileum

Abstract

Abstract Substance P (30–100 units) when acting on the outside of the isolated guinea pig ileum abolished the peristaltic reflex. Small doses (4 units) occasionally potentiated peristalsis. The block produced by high doses could not be overcome by intraluminal injections of 5-HT or substance P itself. The effect of nicotine was reduced or abolished in the presence of high doses of substance P. The high doses can also block the response of the gut to the small doses of the same substance. It is concluded that the blocking effect of substance P takes place between the synapse in the peristaltic reflex arc and the effector cell in the plain muscle.