Summary
The regional brain kinetics of (β-11C)-L-dopa and 6-fluoro-(β-11C)-L-dopa was measured in six Rhesus monkeys using positron emission tomography (PET). Radioactivity accumulated specifically in the striatal region and the increase in L-dopa-derived radioactivity utilization with time was calculated using surrounding brain as a reference area, this being devoid of dopaminergic activity. The rate constant for selective striatal utilization i.e. grossly decarboxylation was 0.0110 ± 0.0007 (S.D) and 0.0057 ± 0.0006 min1 for (β-11C)-L-dopa and 6-fluoro-(β-11C)-L-dopa, respectively. After pre-treatment of the monkeys with the peripherally and centrally active catecholamine-O-methyl transferase (COMT) inhibitor Ro 40-7592 10 mg/kg, the decarboxylation rate remained unchanged (0.0112 ± 0.0015 min-1) for (β11C)-L-dopa, whereas an increase in rate was measured for 6-fluoro-(β-11C)L-dopa (0.0092 ± 0.0015 min−1). Differences in the distribution of radiolabelled metabolites i.e. the corresponding O-methyl-L-dopa in the reference area is most probably the reason for the difference in calculated decarboxylation rate seen between the radiotracers. The higher decarboxylation rate measured for 6-fluoro-(β-11C)-L-dopa after blockade of COMT shows that the radiolabelled metabolites i.e. 6-fluoro-O-methyl-(β-11C)-L-dopa significantly contributes to background radioactivity.
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Hartvig, P., Lindner, K.J., Tedroff, J. et al. Regional brain kinetics of 6-fluoro-(β-11C)-L-dopa and (β-11C)-L-dopa following COMT inhibition. A study in vivo using positron emission tomography. J. Neural Transmission 87, 15–22 (1992). https://doi.org/10.1007/BF01253107
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DOI: https://doi.org/10.1007/BF01253107