HPLC assays of 5-HIAA and tryptophan in cerebrospinal fluid and 5-HT and tryptophan in blood: a methodological study with clinical applications.

HPLC methods were developed for the assay of 5-hydroxy-tryptamine (5-HT) and tryptophan in blood after a simple precipitation step, and 5-hydroxy-indolamine acetic acid (5-HIAA) and tryptophan in CSF by direct injection of CSF. Using these methods, CSF and blood contents were studied in drug-free volunteers and patients treated with tricyclic antidepressant (TCA) drugs. Previously reported variations in the CSF concentrations of 5-HIAA with sex and age were confirmed. No significant difference between patients and healthy subjects were seen in the concentrations of tryptophan in blood or CSF, which were significantly positively intercorrelated. There was no intercorrelation between the concentrations of tryptophan and 5-HIAA in CSF. Highly significant differences between patients and healthy subjects in the platelet-content of 5-HT could be ascribed to the TCA medication. Three TCA drugs, amitriptyline, clomipramine, and imipramine, were compared regarding influence on the platelet-content of 5-HT. Patients treated with clomipramine were found to have considerably lower 5-HT values than imipramine- and amitriptyline-treated patients. A logarithmic model indicated a positive correlation between the two serotonin markers studied, i.e., the amount of platelet-bound 5-HT and the CSF concentrations of 5-HIAA.