Decreased tryptophan availability in endogenous depression caused by disturbed plasma leucine clearance

Abstract

• 1.

  1. Brain uptake of tryptophan is regulated in part by competition from other plasma amino acids, e.g. leucine.

• 2.

  2. Following oral L-leucine loading, plasma leucine clearance was normal in 3 depressives but decreased in one depressive who subsequently reacted to L-tryptophan treatment.

• 3.

  3. It is suggested that a disturbed leucine clearance causes dietary leucine to remain elevated in plasma and that this effect, in turn, reduces brain uptake of tryptophan, and serotonin synthesis.