Synthesis and in vivo distribution in the rat of a dopamine agonist: N-([11C]methyl)norapomorphine

A method for the rapid production and purification of 10,11-dihydroxy-N-([C-11]methyl)norapomorphine ([C-11]APO), a dopamine agonist (DA), is described. The potency of this ligand for studying the D2-receptors was examined. The label was introduced by N-methylation of norapomorphine hydrobromide with no-carrier-added (n.c.a) [C-11]CH3I, produced from cyclotron-produced [C-11]carbon dioxide. In 60 min (EOB) a radiochemical yield of 15% (corrected for decay) was achieved, based on [C-11]CH3I. The specific activity ranged from 5 to 11 GBq/mu mol. The distribution, after intravenous injection, was studied in rats. The radioactivity level in the striatum was higher than in the cerebellum and frontal cortex and was decreased after D2-blockade. The highest uptake ratio (1.47) was found at 30 min after injection. Dopamine depletion with reserpine did increase the striatum/cerebellum ratio at a low dosage of [C-11]APO (10 nmol/kg). High uptakes of [C-11]apomorphine were found in the lungs, liver and kidneys.