Effects of acetylsalicylic acid on serum protein binding and metabolism of tryptophan in man

Abstract

In normal persons, ingestion of aspirin causes a release of tryptophan from its binding site on serum albumin. There is a fall in bound and total serum tryptophan concentrations and a rise in free tryptophan concentrations. The urinary excretion of 3-hydroxyanthranilic acid is decreased, that of xanthurenic acid is increased and that of 3-hydroxykynurenine was increased in 4 out of 6 subjects, indicating an effect on the enzyme systems involved in the metabolism of tryptophan. Conjugates of these metabolites were shown to interfere with the method of assay of the unconjugated hydroxy acids by column chromatography. To overcome this difficulty all urine samples were first boiled in molar hydrochloric acid to hydrolyse any conjugates present. Any results obtained using non-hydrolysed urines would be misleading. This work shows that it is important to take account of the drugs used in treatment before ascribing changes in tryptophan metabolism to pathological states.