Spectrophotofluorometry of serotonin in blood platelets.

A rapid sensitive, and reproducible assay for determination of platelet serotonin is reported. Serotonin in extracted into an ascorbic acid solution by freezing and thawing and sonication. Ascorbic acid stabilizes the serotonin in the extract, and added ethanol enhances the final fluorescence of serotonin, which is measured in a concentrated hydrochloric acid medium (activation at 295 nm and emission at 540 nm). The method has an average coefficient of variation of 4.1%; 95% of added standards is accounted for. The average serotonin content of platelets from 15 men, ages 30-65 years, was 0.67 (SE 0.03) microgram/10(9) platelets, which compares favorably with previously reported values. 5-Hydroxyindole compounds such as 5-hydroxyindole-3-acetic acid and 5-hydroxytryptophan interfere with the assay, but there is relatively little of these compounds in platelets.