Inhibition of the electrical and mechanical activities of the intestinal smooth muscle by pentagastrin.

Spontaneous electrical activity of the intestine smooth muscle of the cat consisted of slow waves and spikes. The spike activity and the slow wave generation were inhibited by pentagastrin and tetragastrin. Phasic contraction corresponding with the electrical activity was also abolished by pentagastrin and tetragastrin. Adrenaline showed the inhibitory action on the spike activity and phasic contraction, but slow waves persisted against adrenaline. Propranolol depressed this inhibitory action produced by adrenaline, while it did not block the inhibitory action by pentagastrin. The inhibitory effect of pentagastrin was not influenced by caffeine or theophylline. Imidazole depressed slightly the inhibitory action of pentagastrin. Verapamil inhibited the spike activity. Additional application of pentagastrin after verapamil produced further inhibition of both slow wave generation and phasic contraction. These results suggest that the inhibitory action produced by pentagastrin on the electrical and mechanical activities is directly on the smooth muscle cell membrane mediated through a mechanism other than via beta-receptors. It is also suggested that the primary action of pentagastrin is to inhibit the generation of slow waves of the intestinal smooth muscle.