STEREOSPECIFIC EFFECTS OF TRYPTOPHAN ON GASTRIC-EMPTYING AND HUNGER IN HUMANS

The amino acid tryptophan (tryp) is a potent: inhibitor of gastric emp tying in both animals and humans. Animal studies suggest that this eff ect may be specific for the L-enantiomer. The effects of D- and L-tryp tophan on gastric emptying, intragastric distribution and appetite in humans were evaluated. Ten volunteers ingested 300 mt of either L-tryp (50 mmol/L), D-tryp (50 mmol/L) or normal saline labelled with Tc-99m sulfur colloid on three occasions, separated by between 3 and 7 days. Hunger and fullness were measured with a visual analogue scale at - 2 , 15, 30 and 60 min after ingestion of each drink. Saline emptied fast er from the stomach than both L-tryp and D-tryp (P < 0.05) and D-tryp emptied faster than L-tryp (P < 0.005). Emptying from the proximal sto mach was fastest for saline (P < 0.05) and faster for D-tryp than L-tr yp (P < 0.005). Emptying from the distal stomach was faster for saline than both D- and L-tryp (P < 0.05). A reduction in hunger (P < 0.05) and a non-significant trend for an increase in fullness were observed after all three drinks. At 60 min, fullness was greater after L-tryp t han after ingestion of D-tryp (P < 0.01). These observations indicate that the effect of tryptophan on gastric emptying in humans is stereos pecific, consistent with the concept that stereospecific receptors for tryptophan exist in the human small intestine.