Plasma levels of catecholamines and dihydroxyphenylglycol during antidepressant drug treatment.

Plasma norepinephrine, epinephrine, and 3,4-dihydroxyphenylglycol levels were measured in depressed outpatients treated in a double-blind controlled clinical trial with 150 mg/day of amitriptyline or 60 mg/day of phenelzine for 6 weeks. Both antidepressant drug treatments were associated with a significant decline in plasma dihydroxyphenylglycol concentrations, which was more pronounced with phenelzine. Plasma norepinephrine levels also declined during phenelzine but not amitriptyline treatment, and the posttreatment values correlated with clinical improvement with the monoamine oxidase inhibiting drug. Reductions in norepinephrine and dihydroxyphenylglycol correlated highly with the degree of platelet monoamine oxidase inhibition. Mechanisms of these antidepressant drug effects on amine metabolism and their implications are discussed.