Effects of leucine on brain serotonin

Evaluation of the relative potency of individual competing amino acids to tryptophan transport in endogenously depressed patients

There is evidence that the plasma ratio of tryptophan to five competing amino acids may predict the response of depressed patients to treatment with L-tryptophan. The relative potency of the individual competitors had been evaluated retrospectively. Phenylalanine consistently reduced, and isoleucine slightly reduced the predictive value of the plasma tryptophan ratio. The ratio of tryptophan to the sum of valine, leucine, and tyrosine was identified as most predictive for the therapeutic response. The L-tryptophan responders showed a normal plasma total tryptophan concentration as did the nonresponders, whereas the concentration of the three competitors was significantly elevated. It is concluded that while the plasma ratio of tryptophan to the sum of valine, leucine, and tyrosine is a useful predictor of the course of depressives on L-tryptophan, it does not definitely separate out the L-tryptophan responders from the control subjects.

Regional brain studies on indoles and tyrosine in Mongolian gerbils during nutrition with artificial mixtures high in branched chain amino acids compared to a protein rich diet

Up till now evidence is lacking regarding the regional distribution of indoles, like tryptophan (TRP), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) as well as tyrosine (TYR) in the brains of Mongolian gerbils. Therefore using a microdissection technique and pooling regional brain samples, it can be shown that there is a regional distribution of 5-HT and 5-HIAA in the brain of Mongloian gerbils which is highest in the raphe + reticular formation system followed by the rest of the brainstem and lenticular nuclei. A longterm fast (22 hours) increases TRP and 5-HIAA but not 5-HT, indicating an increase in the turnover rate of 5-HT. Brain TYR and TRP are only slightly increased after a protein rich diet, whereas 5-HT and 5-HIAA are not changed. Artificial nutrition with amino acid mixtures highly concentrated with branched chain amino acids lead to a decrease of TYR and TRP as well as 5-HT and 5-HIAA. Competing amino acid as well as inhibition of 5-HT synthesis is suggested to be responsible for these effects. Mongolian gerbils show higher brain values of TRP and lower ones of TYR in comparison with other species of mice. In peripheral organs, specially in the liver and lung, similar effects are observable. However, the changes are only mild in comparison to that observed in the brain. Moreover, TYR and TRP are significantly increased in peripheral organs after a protein rich diet.

Plasma amino acids as an index for subgroups in manic depressive psychosis: correlation to effect of tryptophan

Two biochemical distinct groups of manic depressive patients seem to be present. One group showed a normal pattern of plasma amino acids and was resistant to oral tryptophan medication. Another group, characterized by a relative deficiency of tryptophan in plasma as measured by the ratio of total plasma tryptophan to competing amino acids, responded readily to tryptophan treatment. No significant differences could be demonstrated in the free tryptophan, total tryptophan, percentage of free tryptophan or kynurenine in the plasma between patients and controls. The findings are discussed in view of changes in the transport conditions of tryptophan from plasma into the brain.