Contribution of serum albumin to the transport of orally administered L-tryptophan into liver of rats with L-tryptophan depletion

The role of serum albumin in the transport of orally administered L-tryptop han (Trp) into rat tissues was examined using analbuminemic and Sprague-Daw ley (SD) rats with and without alpha-methyl-DL-tryptophan (AMT)-induced Trp depletion. Trp was orally administered to rats 16h after AMT or 0.85% NaCl administration, when liver tryptophan 2,3-dioxygenase and protein syntheti c activities in AMT-treated rats were similar to those of 0.85% NaCl-treate d rats. After oral Trp administration, regardless of the presence or absenc e of Trp depletion, free serum Trp concentrations were similar in the analb uminemic and SD rats, while total serum Trp concentrations were lower in an albuminemic rats than in SD rats. Although liver, brain, and muscle Trp con centrations after oral Trp administration under Trp depletion were lower in analbuminemic rats than in SD rats, the ratio of the liver Trp concentrati on in analbuminemic rats to that in SD rats was smaller than that of the br ain or muscle Trp concentration. These results suggest that variations in s erum albumin levels could affect the transport of orally administered Trp i nto the liver of rats with Trp depletion.