Evidence for a defective platelet L-tryptophan transport in depressed patients

Int Clin Psychopharmacol. 1993 Summer;8(2):87-93. doi: 10.1097/00004850-199300820-00002.


The kinetic characteristics of platelet L-tryptophan uptake were investigated in 23 untreated depressed patients and 18 healthy volunteers. A significant increase of 50% in the apparent Michaelis constant (Km) was observed in depressed patients compared with controls, without significant change in the maximal velocity (Vmax). After 1 month of successful antidepressant treatment the mean Km value decreased significantly and reached the control value. This result raises the possibility that the decrease in platelet tryptophan uptake affinity is a state-dependent marker for depression. It is likely that the transport alteration results in a decrease in platelet tryptophan accumulation. The effect of this peripheral membrane defect on brain serotonin function is discussed.

MeSH terms

  • Administration, Oral
  • Adult
  • Aged
  • Antidepressive Agents / therapeutic use
  • Blood Platelets / drug effects
  • Blood Platelets / metabolism*
  • Cells, Cultured
  • Depressive Disorder / blood*
  • Depressive Disorder / drug therapy
  • Female
  • Humans
  • Male
  • Middle Aged
  • Tryptophan / pharmacokinetics*


  • Antidepressive Agents
  • Tryptophan