Demethylation of l-3-methoxytyrosine in vivo.

After administration of purified l-C-3-methoxytyrosine ( l-C-3-MTO) to rats, the fractions of labelled amino acids, catecholamines and phenolcarboxylic acids of urine and brain have been separated by column chromatography. Prior to performing the quantitative determinations, the individual metabolites of each urinary fraction and of the cerebral catecholamine fraction were isolated by paper chromatography using different systems. Susbtantial amounts of C-3,4-dihydroxyphenylacetic acid (C-DOPAC) as well as some C-3,4-dihydroxyphenylalanine (C-DOPA) and traces of dopamine (DA) appeared in the urine. Furthermore, small amounts of C-DA and C-norepinephrine were found in the brain with two different chromatographic systems. The urinary excretion of C-DOPAC and C-DA was increased by pretreatment with dopacetamide, an inhibitor of catechol-3-O-methyl-transferase. A possible contamination of the l-C-3-MTO with traces of l-C-DOPA as a major source of the dihydroxylated metabolites has been ruled out. It is concluded that part of l-3-MTO undergoes demethylation in vivo and that the finding of DA in brain and urine after administration of l-3-MTO is not an artifact. [ABSTRACT FROM AUTHOR]