Radioactive  2-fluorodopamine is also available. It is used for drug transport system related studies. dopamine is converted to norepinephrine (NE) by dopamine β-hydroxylase (DBH) and stored in vesicles in the neurons. Released NE in synaptic junctions is either inactivated by COMT in postsynaptic cells or transported by a NE transporter (NET) into the nerve terminals (uptake-1). Dopamine is also efficiently transported by NET. At extraneuronal locations, DAT is present in placenta and lung endothelial cells and NET is present in stomach and pancreas. There are also three non-neuronal transporters functioning in peripheral tissues such as the heart, liver, kidney, intestine, blood vessels, retina, and placenta. These uptakes by non-neuronal cells are termed uptake-2.After transported into sympathetic nerve ending by uptake-1, 6-[18F]FDA is rapidly converted to 6-[18F]fluoronorepinephrine (6-FNE) by DBH in neuronal vesicles (5). 6-[18F]FDA is also metabolized via mitochondrial monoamine oxidase to yield [18F]6-fluoro-3,4-dihydroxyphenylacetic acid (FDOPAC). In nonneuronal cells, 6-[18F]FDA is converted by COMT sequentially to O-[18F]methoxytyramine and [18F]6-fluorochomovanillic acid (FHVA).