Effects of acute and chronic phenelzine on regional monoamine metabolism in rats and its potentiation by deuterium substitution.

Phenelzine is a monoamine oxidase inhibitor with antidepressant properties. The present study investigated effects of acute (1-2 mg kg-1 4 h s.c.) and chronic (0.25-2 mg kg-1 day-1 Alzet miniosmotic pumps, 13 days s.c.) administration of phenelzine on regional monoamine metabolism in rats. The effects of these phenelzine treatments were compared with those of equivalent doses of a deuterated form of the drug (phenelzine-d4). The following brain regions and compounds were assessed using high performance liquid chromatography with electrochemical detection: Striatum: dopamine, DOPAC, HVA, 5-HT, 5-HIAA; hypothalamus: dopamine, 5-HT, 5-HIAA, noradrenaline; hippocampus: 5-HT, 5-HIAA, noradrenaline; frontal cortex: dopamine, noradrenaline, 5-HT, 5-HIAA. Acute drug administration increased levels of dopamine, 5-HT and noradrenaline with the exception of dopamine in the hypothalamus and frontal cortex and 5-HT in the hypothalamus. DOPAC, HVA and 5-HIAA levels were decreased. After chronic administration amine levels increased with the exception of dopamine administration amine levels increased with the exception of dopamine in the hypothalamus. The respective acid metabolites were also decreased. These effects of phenelzine were markedly potentiated by deuterium which was substituted for hydrogen in the side chain. The potentiation of these effects was enhanced with chronic administration, differences between phenelzine and phenelzine-d4 effects being more marked at lower doses.