TYROSINE INHIBITS INTESTINAL-PHASE GASTRIC-ACID SECRETION

Background. Intestinal infusion of leucine augments the maximal gastri c-acid secretory response to pentagastrin and serves as a bioassay for intestinal-phase acid secretion. Another action of leucine is to decr ease tyrosine flux into neural tissues. We hypothesized that the mecha nism of leucine-stimulated acid secretion involves its ability to alte r tyrosine absorption. Methods. We administered tyrosine intrajejunall y and intravenously to anesthetized, vagotomized rats during maximal p entagastrin stimulation and measured acid output in response to intraj ejunal infusion of leucine. Results. Intrajejunal tyrosine produced a dose-dependent inhibition of leucine-stimulated acid secretion but onl y mild effects on acid secretion in response to pentagastrin alone. In travenous tyrosine infusions also decreased acid secretion in response to intestinal leucine but required much higher doses. Conclusions. Ty rosine exerts a specific inhibitory effect on leucine-stimulated acid secretion, which is mediated intraluminally. Because tyrosine is an im portant regulator of adrenergic nervous system activity, we speculate that the mechanism of leucine-stimulated acid secretion may involve mo dulation of the sympathetic nervous system, thereby affecting acid sec retion.