Different contractile effects of substance P on the intestine of mammals.

The contractile effect of substance P was examined on the longitudinal muscle of isolated sections of the gut of cat, guinea-pig, rabbit, and rat. Substance P caused contraction of all intestinal regions investigated, but there were marked qualitative and quantitative differences in the contractile responses to substance P. Low concentrations of substance P that did not cause tonic contraction (0.22--2.2 nM), increased the phasic longitudinal contractions observed in the ileum of cat, pig, and rabbit. Higher concentrations induced a tonic longitudinal contraction of the ileum, which in the cat, pig and rat was accompanied by facilitation and in the rabbit by inhibition of the phasic contractions. While in the ileum of guinea-pig and rabbit the maximal longitudinal contraction induced by substance P was equal to the maximal effect of acetylcholine, the maximal response to substance P was only about 50% of that to acetylcholine in the ileum of cat, pig, and rat. The jejunum, ileum and colon of the rabbit responded to substance P and acetylcholine was similar maximal contractions, but the jejunum appeared to be most and the ileum least sensitive to substance P. The results suggest qualitatively and quantitatively different roles of substance P in the intestinal motility of different mammals.