Biochemical aspects of tryptophan depletion in primates.

We studied the degree of plasma tryptophan depletion produced by giving normal human males different amounts of a tryptophan-free (T-) amino acid mixture. From the results of this and other studies we concluded that the maximum degree of tryptophan depletion can be produced by a 31.5 g mixture of seven essential amino acids. Administration of a T−amino acid mixture to vervet monkeys lowered tryptophan and 5-hydroxyindoleacetic acid in the cerebrospinal fluid. Levels of tyrosine and the catecholamine metabolites were unchanged. These data support the idea that the effects of T−mixture on mental function in humans which have been reported previously are due to a decrease in 5-hydroxytryptamine. [ABSTRACT FROM AUTHOR]