Platelet MAO deamination of serotonin in depressed patients. Changes after imipramine treatment and clinical correlations

Monoamine oxidase (MAO) in blood platelets has been used as a model to study MAO in the central nervous system, where disorders in serotonergic systems are thought to occur in depression. Inconsistent changes in platelet MAO of depressed patients have been reported when several substrates other than serotonin (5-HT) have been used. To correlate changes in platelet MAO activity with the enzyme activity in central serotonergic systems, the platelet MAO activity of depressed patients (first unmedicated and then after 3 weeks and 2 months of imipramine treatment) and normal controls was measured using 5-HT as substrate. The results showed that there is a steady, measurable platelet MAO activity with that substrate. This activity was significantly higher in unmedicated depressed patients than in controls, and it decreased progressively with imipramine treatment, reaching a normal level when the patients were clinically recovered from depression after 2 months of therapy.