METABOLIC-FATE OF THE SYMPATHONEURAL IMAGING AGENT 6-[F-18]FLUORODOPAMINE IN HUMANS

We examined the metabolism of 6-[F-18]fluorodopamine, by assaying arte rial plasma concentrations of radioactivity, 6-[F-18]fluorodopamine, a nd 6-[F-18]fluorodopamine metabolites in untreated subjects or subject s given desipramine to block neuronal uptake of catecholamines or tyra mine to displace vesicular amines. After the 3-min 6-[F-18]fluorodopam ine infusion, plasma 6-[F-18]fluorodopamine levels declined precipitou sly, total radioactivity declining slowly. After 30 min, the main iden tified metabolite was 6-[F-18]fluorodopamine-sulfate. Desipramine atte nuated the rapid increase in plasma 6-[F-18]fluorodihydroxyphenylaceti c acid levels, and tyramine briefly increased 6-[F-18]fluorodopamine l evels. Neither drug affected 6-[F-18]fluorodopamine-sulfate levels. Th e results indicate that soon after 6-[F-18]fluorodopamine infusion, pl asma radioactivity corresponds mainly to 6-[F-18]fluorodopamine metabo lites; that sympathetic nerves rapidly remove 6-[F-18]fluorodopamine, which then undergoes oxidative deamination in the neuronal cytoplasm a nd sequestration in sympathetic vesicles; and that sulfoconjugation of [F-18]fluorodopamine occurs extraneuronally.