The radiolabeled catecholamine analogue (1R, 2S)-6-[(18)F]fluorometaraminol (6-[(18)F]FMR) is a substrate for the neuronal norepinephrine transporter. It has been used as a positron emission tomography (PET) ligand to map sympathetic nerves in dog heart. 6-[(18)F]FMR could be only synthesized with low specific radioactivity, which precluded its use in human subjects. We have recently prepared (1R,2S)-4-[(18)F]fluorometaraminol (4-[(18)F]FMR), a new fluoro-analogue of metaraminol, with high specific radioactivity (56-106 GBq/micromol). In the present study, we demonstrate in rats that 4-[(18)F]FMR possesses similar affinity toward myocardial norepinephrine transport mechanisms as 6-[(18)F]FMR. When compared with control animals, an 80% and 76% reduction in myocardial uptake was observed in animals pretreated with desipramine (an inhibitor of the neuronal norepinephrine transporter) and with reserpine (a blocker of the vesicular storage of monoamines), respectively. The entire radioactivity in rat myocardium represented unmetabolized parent tracer as determined by high performance liquid chromatography analysis of tissue extracts. In dogs, myocardial kinetics of 4-[(18)F]FMR were assessed using PET. A rapid and high uptake was observed, followed by prolonged cardiac retention. A heart-to-lung ratio of 15 was reached 10 min after injection of the radiotracer. Pretreatment with desipramine reduced the heart half-life of 4-[(18)F]FMR by 90% compared with control. Moreover, an infusion of tyramine caused a rapid decline of radioactivity in the heart. This demonstrates that 4-[(18)F]FMR specifically visualizes sympathetic neurons in dog heart. High specific radioactivity 4-[(18)F]FMR is a promising alternative to 6-[(18)F]FMR for myocardial neuronal mapping with PET in humans.
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http://dx.doi.org/10.1016/s0969-8051(00)00082-2 | DOI Listing |
Environ Geochem Health
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Department of Chemistry, Chulalongkorn University, Bangkok, Thailand.
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Akdeniz University, Faculty of Medicine, Department of General Surgery, 07070, Antalya, Turkey.
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Intramural Research Program, National Institute of Mental Health, Bethesda, Maryland;
Cyclooxygenase-2 (COX-2) is present in a healthy brain at low densities but can be markedly upregulated by excitatory input and by inflammogens. This study evaluated the sensitivity of the PET radioligand [C]-6-methoxy-2-(4-(methylsulfonyl)phenyl)--(thiophen-2-ylmethyl)pyrimidin-4-amine ([C]MC1) to detect COX-2 density in a healthy human brain. The specificity of [C]MC1 was confirmed using lipopolysaccharide-injected rats and transgenic mice expressing the human gene, with 120-min baseline and blocked scans using COX-1 and COX-2 selective agents.
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Dipartimento di Geoscienze, Università di Padova, Padova, Italy.
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