In vivo inhibition of platelet MAO activity by tricyclic antidepressants.

Platelet MAO activity decreased by 40% (p less than .001) in a group of 11 male patients with primary depression after 3 weeks of treatment with either amitriptyline or imipramine. This finding, together with data from previous in vitro studies demonstrating tricyclic-induced inhibition of mitochondrial MAO, suggests that inhibition of MAO plays a role in the clinical action of tricyclic antidepressant drugs.