New contributions from basic science to understanding the effects of monoamine oxidase inhibiting antidepressants.

Recent studies have provided almost conclusive evidence for the existence of the two separate MAO isozymes previously postulated to exist on the basis of indirect evidence. Important differences in the proportions and distribution of these two enzyme forms across species and in various tissues are responsible for some puzzling anomalies in earlier studies and contribute to differences in behavioral responses, blood pressure changes, and toxic responses to tyramine and other sympathomimetic agents. Substrate-selective, irreversible inhibitors, as well as several new classes of reversible MAO-A and MAO-B selective inhibitors, may provide a spectrum of clinical effects different from the nonselective irreversible MAO inhibitors.