EFFECTS OF GASTROINTESTINAL HORMONES ON THE ELECTRICAL AND MECHANICAL ACTIVITIES OF THE CAT SMALL INTESTINE

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Effects of gastrointestinal hormones on the electrical and mechanical activities of the smooth muscle of the cat small intestine were examined. Both spontaneous electrical and mechanical activities of the intestinal smooth muscle were inhibited by tetragastrin, pentagastrin and pancreozymin. The spike activity and the phasic contraction of the smooth muscle were depressed by these hormones while the slow waves were maintained. On the other hand, secretin showed an excitatory action on the mechanical activity of the isolated preparation of smooth muscle. Spike activity disappeared and the level of tone was increased gradually. The inhibitory and excitatory actions of each hormone on the mechanical activity were not abolished by the application of atropine and tetrodotoxin. Furthermore, the inhibitory effects of pentagastrin and pancreozymin on the smooth muscle were not antagonized with phenoxybenzamine or propranolol. These results suggest that the inhibitory actions of pentagastrin and pancreozymin on the smooth muscle were not mediated by alpha or beta receptors and not due to the stimulation of an inhibitory nervous system in the gut. Antagonistic relations between secretin and pentagastrin and also between secretin and pancreozymin were observed. The mechanisms of the actions of gastrointestinal hormones are discussed.