Effect of Isoprenaline on Bethanechol-Stimulated Gastric Acid Secretion and Mucosal Blood Flow in Dogs with Gastric Fistula

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Abstract
The purpose of this study was to elucidate the effect of the β-adrenoceptor stimulation by isoprenaline on cholinergic-stimulated gastric acid secretion and mucosal blood flow in conscious dogs with gastric fistula. Isoprenaline, a β1- and β2-agonist, was used alone and in conjunction with selective blockade of β2 and β1 receptors. A low dose of isoprenaline had no significant effect, whereas higher doses had a significant antisecretory effect. The antisecretory effect was significantly blocked by the β1-adrenoceptor blocker practolol but not by H 35/25. a β2-adrenoceptor blocker. The dose-response curve with five doses of bethanechol with and without isoprenaline was in accordance with a non-competitive inhibition. There was no significant effect on gastric mucosal blood flow, indicating that the acid inhibition was not secondary to changes in blood flow. The inhibitory effect of isoprenaline seems to be mediated by the β1 receptors and with an action primarily on the ‘gastrinergic receptors’.