Influence of L-3-methoxytyrosine on monoamine synthesis in rat brain

Rats were injected i.p. with L-3-methoxytyrosine, 100 or 300 mg/kg. One h later brain, liver, heart and blood plasma were analyzed for catecholamines and their precursors. In brain Dopa as well as dopamine and noradrenaline levels were unchanged, while demethylation of L-3-methoxytyrosine might have occurred in peripheral organs since Dopa levels in liver and dopamine in heart were elevated. 3-Methoxytyramine could not be detected in brain and liver after treatment with L-3-methoxytyrosine. Monoamine synthesis in vivo was measured in whole brain by determining the accumulation of Dopa and 5-hydroxytryptophan 30 min after the i.p. injection of NSD 1015(3-hydroxybenzylhydrazine HC1, 100 mg/kg), an inhibitor of the aromatic amino acid decarboxylase. L-3-Methoxytyrosine attenuated the formation of Dopa and 5-hydroxytryptophan by about 25% in brain tissue. The effect was paralleled by a decrease in the brain concentration of tryptophan.