A new method for rapidly and simultaneously decreasing serotonin and catecholamine synthesis in humans.

Objective: The administration of amino acid (AA) mixtures that are selectively deficient either in tryptophan or phenylalanine plus tyrosine can decrease serotonin or catecholamine synthesis, respectively. In the present study, we assessed whether a mixture that was simultaneously deficient in tryptophan, phenylalanine and tyrosine could induce sufficient protein synthesis that plasma levels of all 3 monoamine precursors would decrease.
Design: Ten healthy volunteers (5 male, 5 female) were administered a tryptophan/phenylalanine/tyrosine-deficient AA mixture in an open-label study. Plasma concentrations of large neutral AAs were measured before and 5 hours after mixture ingestion.
Results: The tryptophan/phenylalanine/tyrosine-deficient mixture lowered plasma concentrations of the 3 AAs by 67;, 78% and 77%, respectively (p < or = 0.001); their ratio to other large neutral AAs was decreased more, namely, by 87%, 90% and 90% (p < or = 0.001). Mood lowering was seen on 3 subscales of the bipolar Profile of Mood States, that is, elated-depressed, composed-anxious and clearheaded-confused, as well as 2 visual analog scales, bored and irritated (p < or = 0.05).
Conclusions: Acute tryptophan/phenylalanine/tyrosine depletion may be a suitable new method for rapidly decreasing serotonin and catecholamine transmission simultaneously.