Effects of tricyclic antidepressants on platelet monoamine oxidase activity

The eight subjects in this study were diagnosed as having primary or secondary depression and were treated with amitriptyline, 100 to 300 mg/day. Activity of platelet monoamine oxidase (MAO), an enzyme responsible for the degradation of biogenic amines, was determined before and after treatment with amitriptyline. Pretreatment values for MAO activity ranged from 17.94 to 44.89 U. After amitriptyline the values ranged from 0.66 to 41.94 U, a mean decrease of 50.2%. These results are consistent with the hypothesis that the tricyclic antidepressants act, at least in part, by inhibition of MAO.