Effect of Isoprenaline on Bethanechol-Stimulated Gastric Antral Motility in Dogs with Gastric Fistula

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Abstract
The purpose of the present study was to evaluate the effect of isoprenaline on gastric antral motility in conscious dogs with gastric fistula, using intraluminal strain-gauge transducers. Infusion of bethanechol increased the motility for both frequency and strength. Isoprenaline, a β1- and β2-agonist, was used alone and in conjuction with selective blockade of β1 and β2 receptors. The stimulated antral motility was dose-dependently inhibited by isoprenaline. The effect was significantly blocked by the β1 + β2-adrenoceptor blocker propranolol and by using in conjunction the β1-adrenoceptor blocker practolol and the β2-adrenoceptor blocker H 35/25. H 35/25 and particularly practolol reduced the effect of isoprenaline to some extent, but the reduction was not of statistical significance. This indicates that isoprenaline acts on antral motility through both β2 and β1 receptors. Dose-response experiments with five logarithmically increasing doses of bethanechol and one dose of isoprenaline showed inhibition of a non-competitive type.