MONOAMINE OXIDASE CATALYZED DEGRADATION OF PHENELZINE-1-14C AN IRREVERSIBLE INHIBITOR OF MONOAMINE OXIDASE .2.

Rats receiving approx. 2.5 mg kg of phenelzine-1-14C by the intraperitoneal route were placed in metabolism cages and their urine collected for 24 hr. Phenylacetic-1-14C acid was recovered as a major metabolite. Pretreatment of the animals with tranylcypromine (10 mg kg) or pargyline (100 mg kg) prior to injection of radioactive phenelzine markedly reduced the urinary excretion of phenylacetic-1-14C acid and the excretion of other unidentified metabolites appeared to increase. Inhibition of monoamine oxidase (MAO) with tranylcypromine or pargyline had no effect on the urinary excretion of an equimolar dose of phenylacetic-1-14C acid administered by the same route. Therefore, pretreatment of rats with tranylcypromine or pargyline appears to have decreased the bioconversion of the injected phenelzine to phenylacetic acid. These results provide further evidence that phenelzine, in addition to being an irreversible inhibitor, is also a substrate of MAO in the intact animal. © 1969.