The effect of tryptophan and a tryptophan/5-hydroxytryptophan combination on indoles in the brains of rats fed a tryptophan deficient diet

Abstract

Rats maintained on a tryptophan deficient diet had reduced brain and serum tryptophan and brain 5-hydroxyindolacetic acid levels compared to controls. 5-Hydroxytryptophan and L-tryptophan administered to these deficient rats in a combination (5:95) produced a greater elevation of indolamines and tryptophan in the brain than either amino acid alone. In rats maintained on a normal diet the urinary output of 3-hydroxykynurenine was considerably reduced by treatment with the combination of amino acids as compared to tryptophan treatment. 5-Hydroxytryptophan reduced the induction of kynurenine synthesis in the liver produced by tryptophan, implying that it is capable of inhibiting the enzyme tryptophan pyrrolase in vivo. It is suggested that the possession by 5-hydroxytryptophan of tryptophan pyrrolase inhibitory properties may make the administration of the combination a better treatment of depressed patients exhibiting an indolamine deficit than either amino acid alone.

Comparison of the Antidepressant Action of Tryptophan, Tryptophan/5-Hydroxytryptophan Combination and Nomifensine

“…had been shown to be a pyrrolase inhibitor. Clark et al [1975] used the model of tryptophan-deficient rats to study to what extent a combination of tryptophan with 5-HTP would be more effective in elevating the cerebral tryptophan and serotonin levels than the administration of tryptophan on its own. They were able to show that the combination produced higher concentrations than would have been expected from the sum of the two amino-acids.…”