Lithium-induced changes in plasma amino acid levels during treatment of affective disorders.

Plasma amino acid (AA) profiles were determined in patients with bipolar affective disorders before and during treatment with lithium (Li) carbonate. After 90 days of Li intake, there were moderately (20-60%) but significantly decreased plasma levels of isoleucine, leucine, and valine. After 150 days of Li intake, the plasma lysine was also significantly decreased (12%). No significant changes in plasma levels were noted for any of the other 17 AAs that were studied. Since isoleucine, leucine, and valine are important competitors of tryptophan uptake at the blood-brain barrier, these observations suggest a possible mechanism for the therapeutic activity of Li, i.e., the enhancement of brain serotonin levels.