Relationship between changes in plasma amino acids and depression in alcoholic patients

The authors studied the relationship between changes in amino acid precursors of biogenic amines and depression in 42 alcoholic patients with a secondary depression. Tryptophan and amino acids competing with it for brain entry were measured in the plasma of depressed alcoholics, nondepressed alcoholics, and control subjects. The ratio of tryptophan to its competitors was significantly lower in depressed patients than in nondepressed patients and controls. The decreased ratio was due primarily to decreased tryptophan and increased tyrosine and phenylalanine values. A decreased tryptophan ratio is known to result in decreased brain tryptophan and may contribute to depression through a deficiency of brain serotonin.