Effects of chronic monoamine oxidase inhibitor treatment on biogenic amine metabolism in rat brain.

The effects of acute and chronic administration of phenelzine and tranylcypromine on rat brain monoamine metabolism have been examined. Peak increases in norepinephrine, dopamine and 5-hydroxytryptamine occurred between 1 and 7 days with monoamine oxidase inhibitor treatments followed by a gradual decline in brain monoamines towards control levels with continued chronic drug administration. There was an associated adaptive increase in tryptophan hydroxylase but no change in tyrosine hydroxylase activity with chronic phenelzine treatment. Tranylcypromine did not affect tryptophan hydroxylase or tyrosine hydroxylase activities but was associated with a significant increase in aromatic amino acid decarboxylase activity after 14 and 21 days of treatment.