Gastric acid secretion and drinking in the Atlantic cod (Gadus mothua) during acidic or hyperosmotic perfusion of the intestine

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Abstract
Cods were equipped with cannulae for drainage of the stomach and for separate perfusion of the stomach and intestine. Acidity, volume, and osmolality of the gastric outflow were measured. During perfusion of the intestine with a near‐isosmotic saline (1 part sea‐water, 2 parts distilled water, '33% SW) and the stomach with pure (‘100%’) SW, gastric acid output was high and volume output slightly above the infused volume. The osmolality of the gastric perfusate decreased during passage of the stomach. It was concluded that no drinking occurred, and that the decreased osmolality was due to dilution by gastric secretions and osmotically lost water. When substituting the isosmotic intestinal perfusion to a dehydrating perfusion (100% SW), gastric acid secretion was depressed but volume output was unaffected. Also perfusion of the intestine with acidified 33% SW depressed gastric acid secretion and in addition increased volume and osmolality of the gastric outflow. The results suggest that perfusion of the intestine depresses the drinking reflex and that this depression is surmounted by intestinal acidification. Possible mediators of the intestinal feed‐back mechanism for the inhibition of gastric acid secretion are discussed.