Abstract
L-tryptophan is an essential amino acid in human nutrition. The minimum daily requirement for adults is in the range of 175 to 250 mg daily and this is normally exceeded in the average western diet which contains 600 to 1000 mg. Excess tryptophan is normally metabolised through the kynurenine pathway and only 1–2% of tryptophan in the diet is converted to 5-HT. The concept that 5-HT had a part to play in depressive illness evolved after the original observation by Ashcroft & Sharman in 1960 that patients with severe depressive illness had lower levels of the metabolite of 5-HT in cerebrospinal fluid compared with controls. In addition, early papers on the therapeutic efficacy of tryptophan suggested that it was potentially as successful as ECT.
Highlights
L-tryptophan is an essential amino acid in human nutrition
The minimum daily requirement for adults is in the range of 175 to 250 mg daily and this is normally exceeded in the average western diet which contains 600 to lOOOmg.Excess tryptophan is normally metabolised through the kynurenine pathway and only 1-2% of tryptophan in the diet is converted to 5-HT
Subsequent open studies suggest the combination of L-tryptophan, lithium and phenelzine (Barker et al, 1987) or L-tryptophan, lithium and clomipramine (Hale et al, 1987) in severe depressive illness, that is patients who have failed to respond to other adequate treatments including ECT over a minimum period of two years
Summary
DONALDECCLESTONP,rofessor of Psychiatry, Royal Victoria Infirmary, Newcastle Upon Tyne NEI 4LP. L-tryptophan is an essential amino acid in human nutrition. The minimum daily requirement for adults is in the range of 175 to 250 mg daily and this is normally exceeded in the average western diet which contains 600 to lOOOmg.Excess tryptophan is normally metabolised through the kynurenine pathway and only 1-2% of tryptophan in the diet is converted to 5-HT. Early papers on the therapeutic efficacy of tryptophan suggested that it was potentially as successful as ECT. Administration of L-tryptophan led to an increase in the synthesis of 5-HT in brain in animals and in csf in man. As a consequence the use of L-tryptophan as a therapeutic agent was on a sound theoretical basis
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