A simple, specific, radioenzymatic assay for picogram quantities of serotonin or acetylserotonin in biological fluids and tissues

The assay is specific and sensitive to approximately 5 pg of serotonin and thus can be used to measure serotonin levels in single brain nuclei or microliter quantities of biological fluids and can be easily adapted for the direct measurement of N -acetylserotonin.

Abstract

This report describes several modifications of the original radioenzymatic assay for serotonin (4) which increase the sensitivity of the assay 10-fold as well as enhance its reliability. Serotonin is converted to [3H]melatonin, in two steps. First, serotonin is acetylated to N-acetylserotonin by acetic anhydride. The N-acetylserotonin is then incubated with hydroxyindole-O-methyltransferase and S-[methyl-3H]adenosyl methionine and is converted to [3H]melatonin. The radioactive melatonin is extracted with toluene-isoamyl alcohol (7:3), dried, reconstituted, isolated by one-dimensional, silica gel, thin-layer chromatography, and counted in a liquid scintillation counter. The assay is specific and sensitive to approximately 5 pg of serotonin and thus can be used to measure serotonin levels in single brain nuclei or microliter quantities of biological fluids. The assay can be easily adapted for the direct measurement of N-acetylserotonin. A large number of samples can be assayed in a single working day.