THE EFFECTS OF PHENELZINE ON SEROTONIN, NORADRENALINE, AND MONOAMINE OXIDASE IN THE RAT

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Abstract
The serotonin, noradrenaline, and monoamine oxidase (MAO) levels in the brain, liver, lung, and kidney of rats treated with phenelzine (β-phenylethylhydrazine) were compared with the levels in the same tissues in untreated rats. The administration of the drug was found to markedly reduce the MAO activity in all tissues in 3 hours. Recovery to a supranormal level occurred in the liver in 72 hours. Kidney MAO activity returned to normal in 36 hours, while brain and lung MAO had not recovered in 72 hours. The serotonin level in the brain, liver, and kidney increased as the enzyme level decreased. No change occurred in the serotonin concentration in the lung. The noradrenaline level in the brain was not altered by the drug, whereas a decrease was noted in the lung and both kidney and liver showed an increase at 3 and 36 hours. It is postulated that the central action of MAO-inhibiting agents is mediated through serotonin. The increase in liver noradrenaline suggests that MAO must play some role in the metabolism of the amine. Since the concentration of serotonin in the lung was not changed when the enzyme was inhibited, it is conceivable that lung tissue may serve as a storage site for serotonin.