Effect of substance P on mechanical and myoelectrical activities of stomach and small intestines in conscious dog.

The effect of Substance P (SP) on the intestine in situ of the dog was investigated. Five female dogs were used. At the same time, mechanographic recordings, using balloon kymography, were taken, while the myoelectric activity was recorded by means of electrography. Differences in SP action on the mechanogram and electromyogram of the stomach and the small intestines were reflected in the following phenomena: (a) SP in the doses used was less active on the ileum than on the stomach; (b) SP increased basal tonus but inhibited peristaltic contraction; (c) SP acted predominantly on spike discharges in the electromyogram. These results are likely to support the assumption that SP acts as a physiological modulator of smooth muscle activity.