A selective tonic activation of gastrointestinal smooth muscle by substance P.

Mechanical and electrical activity of smooth muscle preparations from fundus, corpus, and antrum of guinea-pig stomach and from distal ileum of guinea-pig were recorded, and the effects of Substance P were examined. Substance P activated selectively the tonic activity of corpus, fundus, and ileum of guinea-pig before and after blockade of phasic contractions. The tonic activation of Substance P is accompanied by increasing of number and amplitude of spike discharges and by decreasing of amplitude of slow potentials in corpus. The tonic activation of Substance P is potentiated parallel with reduction of Ca++ up to 0.6 mmol.