1. 5-Hydroxytryptamine (5-HT) is a well known neurotransmitter implicated in mental disorders, tryptophan (Trp) as amino acid precursor may be interesting. 2. A rapid and simple reversed-phase (mu Bondapac C18 as stationary phase) liquid chromatographic method with fluorimetric detection (excitation: 302 nm, emission: 340 nm) is described for the quantitation of 5-hydroxytryptamine (5-HT) and free tryptophan (Trp), in whole blood. 5-fluoro-dl-tryptophan (5-FdlT) was used as internal standard. The mobile phase was 0.01 M phosphate buffer (pH = 4.5) with 0.0025 M 1-heptane sulfonic acid and 15% methanol. 3. In blood of healthy subjects (n = 30), the concentrations were, for 5-HT: 258 +/- 68 ng/ml and for Trp: 5.7 +/- 1.02 micrograms/ml. 4. The assay was used to follow the effect of antidepressant drugs, as a 5-HT reuptake inhibitor (clomipramine) and a monoamine oxidase inhibitor (moclobemide). After 4 week treatments, we observed, with clomipramine by 7 patients (150 mg/day) a highly significant reduction (p < 0.01) in 5-HT levels (77% +/- 12) and with moclobemide by 8 patients (300 or 450 or 600 mg/day) a highly significant increase in 5-HT levels (from 16% to 300% according to the drug dosage). These two drugs did not influence blood Trp concentrations. 5. Assays on whole blood present various advantages: (i) the simplicity for clinical departments (ii) the absence of sample pretreatment and (iii) the assurance that the entire platelet population is assayed since all of the 5 HT in blood is bound to platelets.
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