Interactions of aromatic amino acids with gastric secretagogues in humans

To determine the interactions of phenylalanine and tryptophan with gastric secretagogues, acid secretory studies were performed in 10 healthy subjects. Phenylalanine and tryptophan potentiated the gastric secretory responses following low doses of pentagastrin, whereas their effects on acid secretion stimulated by low doses of histamine or the cholinergic bethanecol were additive. Phenylalanine and tryptophan did not increase maximal acid output stimulated by pentagastrin, histamine, or bethanecol. Doses of the H2-receptor antagonist ranitidine, the prostaglandin E1 analogue misoprostol, atropine, and somatostatin that produced approximately 50% inhibition of pentagastrin-stimulated acid secretion significantly inhibited phenylalanine- and tryptophan-stimulated acid secretion. After the combination of either phenylalanine or tryptophan with pentagastrin, the H2-receptor antagonist significantly inhibited gastric acid secretion, whereas somatostatin, atropine, and the prostaglandin E1 analogue were not effective. These results indicate that both phenylalanine and tryptophan potentiate gastric acid secretion stimulated by a submaximal dose of pentagastrin, whereas their effects on histamine- and bethanecol-stimulated secretion are additive. The potentiating effects of phenylalanine and tryptophan on pentagastrin-stimulated acid secretion depend, at least in part, on intact histamine pathways.