Determination of Peripheral Catechol O-methyltransferase (COMT) Activity in vivo using $[2-^{14}C]-3',4'-Dihydroxyacetophenone$

For the determination of peripheral COMT activity, we synthesized $[2-^{14}C]-3',4'-dihydroxyacetophenone([^{14}C]-DHAP)$, a model substrate closely related to catecholamines, which cannot be attacked by monoamine oxidase. After i.v.-injection of $[^{14}C]-DHAP$ in living animals, only 3',4'-dihydroxy-acetophenone (3',4'-DHAP) and 3'-methoxy-4'-hydroxyacetophenone (3'-MHAP) were detected in blood by thin layer radio chromatography. It could be speculated that 3',4'-DHAP was primarily O-methylated by COMT, followed by subsequent conjugations. The concentration of 3',4'-DHAP, a substrate for COMT, in blood at 5 min after injection of $[^{14}C]-DHAP$, were similar in all animals. The rate of 3'-MHAP formation can be therefore used as an indicator for peripheral COMT activity. The velocity of methylation in 15 min after i.v.-administration of $[^{14}C]-DHAP$ was $0.28\;{\mu}g/ml{\cdot}min$. From these results, 3',4'-DHAP was shown to be used as an appropriate substrate to determine the COMT activity in vivo.