Inhibitory ?2-Adrenergic mechanism regulating gastric secretion in pylorus-ligated rats

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Abstract
Several α-adrenoceptor agonists given intracerebroventricularly or subcutaneously to rats were assessed for their effects on gastric secretion under condition of pylorus ligation. Intracerebroventricular injection of α-adrenoceptor agonists reduced gastric secretion, in the following order (relative potency, clonidine = 1): oxymetazoline (100) > clonidine (1) > methoxamine (0.024) > phenylephrine (0.003). The antisecretory effects of oxymetazoline and clonidine given intracerebroventricularly were antagonized with yohimbine administered by the same route. Subcutaneous injection of α-adrenoceptor agonists also reduced gastric secretion, in the following order (relative potency, clonidine = 1): clonidine (1) > oxymetazoline (0.3) ≫ phenylephrine (0.001) ∼ methoxamine (0.0006). Oxymetazoline, when given intracerebroventricularly, was most effective in decreasing the volume and titratable acidity of gastric secretion. Pretreatment with 6-hydroxydopamine intracerebroventricularly (250 μg/rat × 2; 72 and 120 h before) reduced the antisecretory effect of clonidine given intracerebroventricularly. Thus, gastric secretion appears to be regulated in an inhibitory manner by α2-, but not by α1- in the central and peripheral nervous systems, in pylorus-ligated rats.

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