A Comparative Study on the Mechanism of Action of Morphine on Gastric Acid Secretion in Dogs

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Abstract
While researching the mechanisms of gastric secretagogue action of morphine, the effects of hexamethonium, atropine and secretin on morphine-induced gastric secretion were studied, and were compared with those on food-, histamineand tetrapeptide-induced gastric secretion in conscious dogs, and on histamine-, tetrapeptide and bethanecol-induced gastric secretion in anesthetized dogs. Effect of acute bilateral vagotomy on the gastric secretion was also investigated in anesthetized dogs. Results are discussed in relation to the mechanisms involved in the stimulation and inhibition of gastric secretion, and the following suggestions are made. Direct vagal excitation of oxyntic glands and endogenous gastrin plays an important role in food-induced secretion in innervated and denervated fundic pouches, respectively. Exogenous gastrin stimulates gastric secretion activating cholinergic post-ganglionic nerve fibers in conscious dogs. In anesthetized dogs, however, exogenous gastrin induces its secretagogue action mainly by a direct action on oxyntic glands. A close similarity was observed between morphine-induced secretion and food-induced secretion in denervated fundic pouches when inhibitory activities of drugs were compared. It is thus concluded that endogenous gastrin plays an important role in the gastric secretion induced by morphine.