The influence of oral tyrosine and tryptophan feeding on plasma catecholamines in man.

We investigated the effects of oral tyrosine (7.5 g/day) and oral tryptophan (3 g/day) feeding with regular meals in normal male volunteers using a double-blind cross-over design with a "run in" period for acclimatization. Oral tyrosine feeding significantly decreased both free and conjugated plasma norepinephrine concentrations while oral tryptophan feeding did not have such an effect. Since alpha adrenergic stimulation in certain areas of the CNS has been shown to decrease peripheral sympathetic tone, we postulate that dietary tyrosine supplementation in man causes an increase in brain catecholaminergic activity which in turn leads to a decrease in peripheral sympathetic activity as evidenced by the decrease in plasma catecholamines.