(+/-)Tetrahydroanisocycline and (+/-)tetrahydropalmatine binding to D1 and D2 dopaminergic receptors in human putamen.
D1 and D2 dopaminergic receptors were detected in membranes from human putamen by the specific binding of the radiolabelled antagonists [(3)H]SCH 23390 and [(3)H]spiperone, respectively. Competition binding experiments with plant alkaloids isolated from Anisocycla cymosa and their hydrogenated derivatives showed the same order of affinities for both receptor types, i.e. (+/-)tetrahydropalmatine > (+/-)tetrahydroanisocycline > anisocycline > remrefidine. Hydrogenation of anisocycline produced a more pronounced increase in affinity for the D1 receptors (27-fold) than for the D2 receptors (1.5-fold). The affinities of (+/-)tetrahydropalmatine and chlorpromazine were similar for the D1 receptors (K(i) = 0.42 and 0.30 ?M, respectively) but the alkaloid's affinity was appreciably lower for the D2 receptors (K(i) = 0.77 and 0.06 ?M, respectively).
Vauquelin
G
G
Department of Protein Chemistry, Institute of Molecular Biology, Free University Brussels (V.U.B.) Belgium.
De Keyser
J
J
Kanyinda
B
B
Vanhaelen
M
M