Indoleamine compartmentation in human blood.

Improved methods are described for the fluorimetric determination of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and tryptophan (TRP) in plasma, platelet and RBC blood compartments. The methods for 5-HT and 5-HIAA utilize ion exchange chromatography and allow simultaneous determinations to be made on the same blood sample. The tryptophan assay is a modification of an existing extraction method. All of the 5-HT in whole blood was found to be associated with the platelet fraction (122.6 ng/ml), whereas all 5-HIAA was distributed between the plasma (78.3 ng/ml) and RBC (124.0 ng/ml) compartments. Tryptophan was found in all three compartments although the majority of this amino acid was in the plasma (4.3 microgram/ml) and RBC (1.7 microgram/ml) fractions.