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September 1983

Ratio of Plasma Tryptophan to Five Other Amino Acids in Depressed Subjects: A Follow-up

Author Affiliations

The Institute of Psychiatric Research Indiana University Medical Center 791 Union Dr Indianapolis, IN 46223

Arch Gen Psychiatry. 1983;40(9):1033-1034. doi:10.1001/archpsyc.1983.01790080115018

To the Editor.—  In a study from our institute of unipolar depressed subjects, improvement in depressive symptoms was significantly correlated to increases in the ratio of the total plasma concentration of tryptophan to the sum of the concentrations of five of the competitors with tryptophan for entry into the CNS: valine, leucine, isoleucine, phenylalanine, and tyrosine.1 In that study, the ratio appeared to be a state indicator of depression, at least in subjects who demonstrated a rapid improvement in their symptoms. The study was carried out in hospitalized subjects over a five-day period, during which no treatment was provided. Following is a brief report of the results of a follow-up study on that ratio in a treated inpatient sample of depressed patients. We were interested in using the ratio to distinguish clinical subtypes of unipolar depressive disorders and as a state indicator of depression over a longer time period.

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