A sensitive non-isotopic assay for monoamine oxidase activity in human blood platelets

A sensitive and specific procedure for measuring monoamine oxidase (MAO) activity in human platelets is described. Serotonin is used as substrate and formed 5-hydroxyindoleacetic acid (5-HIAA) is separated by a double microcolumn technique on Sephadex G-10 and Amberlite CG-50 and measured fluorimetrically. MAO activities were 5.11 +/- 1.32 (mean +/- S.D.) nmol/mg protein/hour in male and 7.85 +/- 1.58 in female healthy adults (p less than 0.001). MAO activity measured in 32 depressed patients was in a range of 3.20-10.62 nmol/mg protein/hour, the value not differing from that in the normal subjects. No significant difference was established between three subtypes of depression, in bipolar, unipolar and involutional patients, while significantly higher values were evident in female than in male patients (p less than 0.001).