• Serotonin;
  • Cerebrospinal fluid;
  • Plasma;
  • Platelets;
  • Monoamine metabolites

Abstract: The relationships between the concentration of serotonin (5-HT) and related metabolites in human blood and CSF have been studies. Plasma tryptophan (TP), 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), and indoleacetic acid (IAA), whole-blood 5-HT, and CSF TP, 5-HT, 5-HIAA, IAA, homovanillic acid, and 3-methoxy-4-hydroxyphenylethylene glycol were determined in 35 unmedicated outpatients who underwent minor surgical operations and had no history of psychiatric or neurological illnesses. Significant correlations were found between the serotoninergic parameters analyzed in blood and CSF. Plasma free 5-HT correlated significantly with CSF 5-HT (r= 0.411, p < 0.02), and plasma 5-HIAA correlated with the CSF 5-HIAA/5-HT ratio (r= 0.508, p < 0.004). The concentration of 5-HIAA in CSF correlated with the plasma 5-HIAA/5-HT ratio (r= 0.405, p < 0.026) (which can be taken as an index of monoamine oxidase type A activity in peripheral tissues) and with the platelet 5-HT/plasma 5-HT ratio (r= 0.375, p < 0.05). The concentrations of IAA in CSF and plasma were strongly correlated (r= 0.899, p < 0.001). The significance of these results and their relationship to the use of “in vivo”measures of 5-HT and related metabolites in plasma and platelets as an index of serotoninergic function in affective disorders are discussed.