Tryptophan: a precursor for the endogenous synthesis of norharman in man

We investigated whether in healthy subjects L-tryptophan may serve as a pre cursor for the endogenous synthesis of the beta -carboline norharman. For t his purpose subjects, smokers as well as non-smokers, received 0 or 1.2 g o f an oral dose of tryptophan. Smokers started the experiment 2 h after cess ation of smoking. Plasma levels of tryptophan and norharman were measured 1 00 and 125 min after the start of the experiment. The levels of both compou nds were significantly higher in the group receiving tryptophan. Norharman concentrations in the plasma of smokers were significantly higher than in t he non-smoking subjects under both experimental conditions. These results a dd some proof to the hypothesis that in humans tryptophan may serve as a pr ecursor for the synthesis of norharman. (C) 2001 Published by Elsevier Scie nce Ireland Ltd.