Relationship between serotoninergic measures in blood and cerebrospinal fluid simultaneously obtained in humans.

The relationships between the concentration of serotonin (5-HT) and related metabolites in human blood and CSF have been studied. 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 less than 0.02), and plasma 5-HIAA correlated with the CSF 5-HIAA/5-HT ratio (r = 0.508, p less than 0.004). The concentration of 5-HIAA in CSF correlated with the plasma 5-HIAA/5-HT ratio (r = 0.405, p less than 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 less than 0.05). The concentrations of IAA in CSF and plasma were strongly correlated (r = 0.899, p less than 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.