Intestinal Transport of Tryptophan and Its Analogs

A comparative study of the intestinal transport of DL-tryptophan and its 1-methylindole (tryptophan-l-Me) and benzo[b]thiophene (tryptophan-S) analogs has been carried out in vitro, using the everted intestinal sac of the rat and hamster. Both tryptophan and tryptophan-S are actively transported across the intestine, while tryptophan-l-Me is not actively transported. The active transport of tryptophan is competitively inhibited by tryptophan-S, suggesting a similar carrier, while tryptophan-l-Me is not an inhibitor of tryptophan transport, suggesting little or no interaction with the carrier. The transport of tryptophan and tryptophan-S is depressed at concentrations (10 mM), and all three amino acids produce subtle alterations in the barrier properties of the sacs, as evidenced by increased tetraethylammonium bromide-14C diffusion.