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Decreased plasma tryptophan levels in major depression
P J Cowen1, M Parry-Billings, E A Newsholme
1University Department of Psychiatry, Littlemore Hospital, Oxford, U.K.
Journal of Affective Disorders
|January 1, 1989
Summary
Depressed patients have lower plasma tryptophan levels and a reduced ratio of tryptophan to other neutral amino acids. This suggests decreased brain tryptophan availability in depression, independent of neuroendocrine response.
Area of Science:
- Neuroscience
- Biochemistry
- Psychiatry
Background:
- Tryptophan is a precursor to serotonin, a neurotransmitter implicated in mood regulation.
- Alterations in amino acid metabolism have been observed in patients with major depressive disorder.
Purpose of the Study:
- To investigate plasma tryptophan levels and their relationship with neutral amino acids in depressed patients compared to healthy controls.
- To explore the potential impact of reduced tryptophan availability on brain function in depression.
Main Methods:
- Measurement of total plasma tryptophan concentrations.
- Analysis of the ratio of total tryptophan to other neutral amino acids.
- Comparison between 12 depressed patients and 12 normal controls.
Main Results:
- Significantly lower total plasma tryptophan was found in depressed patients.
- The ratio of total tryptophan to neutral amino acids was decreased in depressed individuals.
- No correlation was observed between basal tryptophan levels and neuroendocrine response to tryptophan infusion.
Conclusions:
- Depressed patients exhibit altered plasma tryptophan metabolism.
- Reduced tryptophan availability to the brain may be a contributing factor in depression.
- Basal tryptophan levels do not predict neuroendocrine response in this cohort.