Summary
The O-methyl derivative methoxytyrosine accumulated rapidly in rat liver after an intraperitoneal injection of l-dopa (50 mg/kg) in combination with 3-hydroxybenzylhydrazine, an inhibitor of the aromatic amino acid decarboxylase. Methoxytyrosine levels reached a plateau 40–60 min after an i.p. injection of l-dopa, of which the tissue concentration declined monoexponentially. Injection of various doses of l-dopa revealed that methoxytyrosine formation was saturable and followed enzyme kinetics in rat liver. The catechol-O-methyltransferase inhibitors pyrogallol, tropolone and α-propyldopacetamide as well as the inhibitor of the aromatic amino acid decarboxylase benserazide inhibited the formation of methoxytyrosine dose-dependently and concomitantly increased the tissue concentration of dopa.
The accumulation of methoxytyrosine from exogeneously applied l-dopa appears to be a reliable indicator of the in vivo activity of catechol-O-methyltransferase.
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Kehr, W., Zimmermann, R. & Thiede, M. Methoxytyrosine formation as an indicator of catechol-O-methyltransferase activity in rat liver in vivo. Naunyn-Schmiedeberg's Arch. Pharmacol. 300, 19–23 (1977). https://doi.org/10.1007/BF00505075
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DOI: https://doi.org/10.1007/BF00505075