STEREOSPECIFIC EFFECTS OF INTRADUODENAL TRYPTOPHAN ON PYLORIC AND DUODENAL MOTILITY IN HUMANS

Background: L-Tryptophan delays gastric emptying in animals to a greater extent than D-tryptophan, but none of the possible motor mechanisms responsible for this stereospecific effect have been evaluated. Methods: In 11 healthy volunteers antropyloroduodenal pressures were recorded in the fasted state with a sleeve/sidehole manometric assembly during 20-min intraduodenal infusions (2 ml min(-1)) of isotonic L- and D-tryptophan (50 mM, pH5.7) and normal saline (pH 5.5), given in randomized order. Results: Intraduodenal L-tryptophan increased basal pyloric pressure (p < 0.05), whereas D-tryptophan had no effect. In contrast, L- and D-tryptophan both stimulated (p < 0.05) localized phasic pyloric pressure waves, and there was no significant difference in the responses. The number of duodenal pressure waves was greater during infusion of L-tryptophan than during D-tryptophan (p < 0.05). Conclusion: We conclude that intraduodenal tryptophan has stereospecific effects on pyloric and duodenal motility. Although the precise contribution of these differential effects to gastric emptying remains to be clarified, they may be partially responsible for the differences in gastric emptying of D-tryptophan and L-tryptophan.