Deamination of β-phenylethylamine by monoamine oxidase—Inhibition by imipramine

The oxidative deamination of tyramine (Tyr), 5-hydroxytryptamine (5-HT), and β-phenylethylamine (PEA) by mitochondrial preparations of rabbit lung and brain was inhibited by imipramine. This tricyclic iminodibenzyl antidepressant drug was most effective in decreasing the deamination of PEA: at 1 × 10 −4M imipramine, deamination of PEA, Tyr and 5-HT was inhibited by approximately 70, 45 and 45 per cent, respectively, when either lung or brain mitochondrial monoamine oxidase (MAO) preparations were used. Imipramine-induced inhibition of MAO was shown to be of a mixed type based on Lineweaver-Burk plots, but was found to be completely reversible. The desmcthyl and didesmethyl derivatives of imipramine were equally as effective as the parent drug in inhibiting the deamination of PEA, whereas the N-oxide analog of imipramine was less effective as an inhibitor of this reaction. These results support the premise that the action of imipramine as a clinically effective antidepressive agent may be related to its inhibitory effect on the specific form of MAO which deaminates PEA.