Contractile response of longitudinal and circular smooth muscles of guinea pig stomach and ileum to substance P.

The mechanical activity of longitudinal and circular smooth muscle preparations from fundus, corpus, and antrum of guinea pig stomach and distal ileum of guinea pig were recorded and the effect of substance P (SP) was measured. In physiological concentrations (10(-13) - 10(-7) mol/l) SP activates the tone of circular muscle strips from fundus and corpus of guinea pig stomach. Quite opposite is the situation with respect to the SP tonic activation in the muscle layers of guinea pig ileum. Here SP activates only the tone of longitudinal muscle layers. In these concentrations SP induces no or only very small contractile response in longitudinal muscle strips of fundus and corpus and in circular muscle preparations of distal ileum. The greater sensitivity to SP appears to result for the longitudinal muscle layer of ileum followed by the circular layer of fundus and corpus.