Striatal kinetics of [11C]-(+)-nomifensine and 6-[18F]fluoro-L-dopa in Parkinson's disease measured with positron emission tomography

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Abstract
The kinetics in brain of the dopamine reuptake blocking agent [11C]‐(+)‐nomifensine and the L‐dopa analogue 6‐[18F]fluoro‐L‐dopa were compared in 3 patients with idiopathic Parkinson's disease and age‐matched healthy volunteers using positron emission tomography. Regional uptake was analyzed and quantified according to a 3‐compartment model. Retention of both tracers in striatal regions of the parkinsonian patients were reduced compared with the healthy volunteers mainly in the putamen, while the caudate nucleus was only mildly affected. The reductions were considerably less than the decrease previously reported postmortem for striatal dopamine content in the basal ganglia of patients with Parkinson's disease. A fairly constant ratio between 6‐[18F]fluoro‐L‐dopa utilization and [11C]‐(+)‐nomifensine binding in the caudate nucleus and the putamen were found in both groups unrelated to the size of the estimated parameters. This indicates that a limiting factor for the utilization of exogenous levodopa in Parkinson's disease may be a reduced transport capacity for the amino acid into the dopaminergic terminals.