Platelet monoamine oxidase in affective disorders.

Platelet monoamine oxidase (MAO) activity was determined with tryptamine as substrate for 61 drug-free patients who had a primary major depressive disorder and for 32 normal controls. Although there were no significant differences between the mean platelet MAO activity of 19 bipolar patients (4.94 nmoles/hr/mg of protein), 42 unipolar patients (4.97 nmoles), and the controls (4.78 nmoles), an analysis of variance indicated that the variance of the bipolar group was significantly greater than that of the other groups. This suggests that there may be subgroups of bipolar patients that differ in their platelet MAO activity but that appear to be distinct from the bipolar I vs bipolar II classification.