The Metabolism of [18F]6‐Fluoro‐l‐3,4‐Dihydroxyphenylalanine in the Hooded Rat

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Abstract
The metabolism of the positron-emitting compound [18F]6-fluoro-L-3,4-dihydroxyphenylalanine (*F-DOPA) was studied in carbidopa-pretreated male hooded rats. Thirty minutes following carbidopa administration (5 mg/kg i.p.), animals received *F-DOPA (500 .mu.g/kg; specific activity, 175-230 Ci/mol) as an intrajugular bolus. Blood samples were taken at various times between 5 and 90 min, and the plasma was analyzed by HPLC with gamma counting of fractions. *F-DOPA disappeared rapidly from plasma in concert with the formation of the 3-O-methylated metabolite, Me-*F-DOPA. Animals were killed from 5 to 120 min after injection, and the brains were rapidly dissected. The disappearance of *F-DOPA from both vermis and striatal samples was rapid. Me-*F-DOPA, the sole metabolite observed in the vermis, was the major labeled material in the striatum at .gtoreq. 20 min after injection. Fluorodopamine was an important metabolite in the striatum, making up 255 of total radioactivity at early intervals. Striatal samples also contained fluoro-3,4-dihydroxyphenylacetic acid, which constituted .apprx. 10% of the total radioactivity, and traces of two radiolabeled compounds, tentatively identified as fluorohomovanilic acid and fluoro-3-methoxytyramine.

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