Comparison of amino acids bathing the oxyntic gland area in the stimulation of gastric secretion.

This study was undertaken to compare the ability of L- and D-isomers of amino acids bathing the oxyntic gland area to stimulate acid secretion in conscious dogs with Heidenhain pouch (HP), gastric fistula (GF) and pancreatic fistula (PF). Acid outputs from HP were determined by an intragastric titration method when amino acid solutions were perfused into HP at various concentrations, pH values, and distention pressures. Only L-isomers of all natural amino acids were found to stimulate acid secretion, whereas D-isomers of amino acids tested were completely inert in this respect. The comparison of the secretagogue activity of amino acids shows that L-histidine among essential amino acids and glycine among nonessential amino acids exhibited the strongest stimulation of acid outputs, reaching, respectively, 52 and 40% of the maximal response to histamine. Decreasing the pH of L-histidine solution perfused into HP in sequential order from 5.0 to 1.0 resulted in a stepwise reduction of acid output, falling at pH 1.0 to about 40% of the peak response achieved at pH 5.0. Local irrigation of HP by 2% xylocaine and intravenous infusion of atropine (100 mug per kg per hr) or metiamide (2.9 mg per kg per hr) reduced but did not abolish HP response to chemical stimulation and the pH dependency of this response. We conclude that only L- and not D-isomers of amino acids bathing the oxyntic gland area stimulate acid secretion by a local, gastrin-independent mechanism sensitive to distention pressure and pH.