Plasma Tryptophan and Five Other Amino Acids in Depressed and Normal Subjects

Marian K. DeMyer, Philip A. Shea, Hugh C. Hendrie, Norman N. Yoshimura

Research output: Contribution to journalArticle

92 Scopus citations


Decreases in brain serotonin levels have been implicated in the pathogenesis of human depression. While circulating levels of tryptophan (TRP) might possibly reflect concentration of brain serotonin, a more relevant peripheral measure may be the ratio of plasma TRP to five other neutral amino acids (TRP/5aa ratio). In depressed subjects and normal controls, plasma TRP (free and total), phenylalanine (PHE), tyrosine (TYR), leucine, isoleucine, and valine were measured on three days. When depression was most severe, depressed patients had lower TRP/5aa ratios and total TRP levels and higher PHE and TYR levels. After the patients' conditions improved, these differences disappeared. As Hamilton depression scores improved, the plasma TRP/5aa ratios increased significantly. This finding tends to support the idea that changes in brain serotonin level reflect changes in depression severity.

Original languageEnglish (US)
Pages (from-to)642-646
Number of pages5
JournalArchives of general psychiatry
Issue number6
StatePublished - Jun 1981
Externally publishedYes

ASJC Scopus subject areas

  • Arts and Humanities (miscellaneous)
  • Psychiatry and Mental health

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