Effects of isopropylnoradrenaline on tachyphylaxis of gastrin stimulated gastric acid secretion and mucosal blood flow in the anaesthetized cat.

1. Gastric acid and mucosal blood flow responses to sustained gastrin stimulation were studied in anaesthetized cats. 2. Acid and mucosal blood flow showed identical rates of tachyphylaxis to both large (maximal) and small doses of gastrin. 3. Isopropylnoradrenaline infused either intravenously or close arterially to the stomach produced increases in blood flow unrelated to time following the peak response to large doses of gastrin, whereas increases in acid secretion appeared to be a part removal of the acid tachyphylaxis. 4. During stimulation by small doses of gastrin, isopropylnoradrenaline increased both blood flow and acid secretion above the peak responses to gastrin alone. 5. Increases in gastrin stimulated acid and mucosal blood flow were also produced by expansion of the blood volume by dextran-saline infusions. 6. The physiological significance of these findings is discussed. 7. It is concluded that tachyphylaxis of gastric acid secretion to gastrin may be a function of the primary tachyphylaxis of mucosal blood flow.