Longitudinal assessment of MAO-, COMT-, and DBH- activity in patients with bipolar depression

This study was carried out to determine whether the activity of regulatory enzymes for biogenic amines are state variables or trait variables for bipolar depression. The activity of MAO, COMT, and DBH in platelets, RBC and serum, respectively, was measured repeatedly in patients with bipolar depression and in matched control subjects. An increase in MAO activity was observed in patients compared to controls, while MAO activity was unrelated to the patient's psychopathological state. COMT activity was higher in female patients than in female controls and was lower in male patients than in male controls, but it failed to be related to the psychopathological state of patients. Relevant differences in serum DBH activity failed to occur either between patients and controls, or in patients during different states of their illness. The findings suggest that the activity of MAO and COMT are trait variables for bipolar depression, while DBH activity is neither a state variable nor a trait variable. it is discussed why only longitudinal studies in contrast to conventional cross-sectional assessments allow a distinction between state and trait variables.