Effects of imipramine, nomifensine and d-amphetamine on type B monoamine oxidase, cyclic AMP phosphodiesterase and dopamine-beta-hydroxylase.

The three dissimilar structural antidepressant drugs, imipramine, nomifensine and d-amphetamine, were compared for their effects on type B monoamine oxidase, cyclic AMP phosphodiesterase and dopamine-beta-hydroxylase. Three antidepressant drugs caused a dose-dependent inhibition on type B monoamine oxidase. Of the three drugs, imipramine had a most potent effect. Unlike d-amphetamine, both imipramine and nomifensine inhibited the cyclic AMP phosphodiesterase activity at concentrations more than 10(-4)M. No effect was observed below this concentration. All drugs seemed to have little or no effects on the partially purified dopamine-beta-hydroxylase activity. The weak inhibitory effects of nomifensine on these three enzymes may not be attributable to its antidepressant properties. Morphine had no effect on the three enzyme activities.