Serotonin in blood platelets: Studies on a simple assay

A simple, sensitive assay for aqueous solutions of 5-HT, especially platelet lysates, has been outlined. The precision of the assay is acceptable for routine use (C.V. less than 10%). The fluorescent intensity of 5-HT is reduced drastically when the pH of the medium falls below 1.0, whether the emission intensity is measured at 535 or 335 nm; thus the present assay of 5-HT in near-neutral solution is much more sensitive than the common assays which use a highly acidic environment for measurement of the final fluorescence. Interferences from the indoles TRY and DMT are negligible, but interferences from 5-HTP and 5-HIAA are 10 and 60%, respectively; therefore the assay is not specific for 5-HT. However, ion-exchange chromatography can readily be combined with the present assay to allow specific analysis of 5-HT and other indoles which have similar fluroescent patterns.