A Comparison of 11C-Labeled L-DOPA and L-Fluorodopa as Positron Emission Tomography Tracers for the Presynaptic Dopaminergic System (original) (raw)

1999, Journal of Cerebral Blood Flow & Metabolism

DOPA) and L-fluorodopa were used as tracers for the func tional state of the presynaptic dopamine system in anesthetized monkeys with positron emission tomography, The radiotracer disposition in brain tissue and plasma were studied and effects induced by pharmacologic challenges were evaluated, 6R-L erythro-5,6,7,8-tetrahydrobiopterin (6R-BH 4) increased the striatal influx tate constant, e.g., striatal Ki for L-[[3-1 IqDOPA, but it induced no effect on the K;-value using L-[[3-1 I Cj-6fluorodopa. Studies of radiolabeled tracer and metabolites in plasma showed substantial differences between the two tracers. At baseline conditions, 60% unchanged L-[[3-IIC1DOPA was detected in plasma 50 minutes after tracer injection and the 3-0-methylated fraction accounted for 25% of total radioactiv ity. FOfL-[[3-IICj-6-fluorodopa, the relation was inverse; about Positron emission tomography (PET) and radiolabeled 3,4-Dihydroxy-phenyl-L-alanine (L-DOPA) have been used to study presynaptic dopaminergic function in vivo for several years. L-DOPA has been radiolabeled with different positron-emitting nuclides, II C-labeled L-DOPA in �-position, L-[�_ II C]DOPA, and ls F-labeling in 6 po sition on the aromatic ring giving the analogue L-6e S F]fluorodopa (Fig. 1), are commonly used today. These tracers have both been shown to reveal the pre synaptic dopaminergic function in healthy and patho logic states of humans (Garnett et aI., 1983; Hartvig et