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Differential actions of antiparkinson agents at multiple classes of monoaminergic receptor. II. Agonist and antagonist properties at subtypes of dopamine D2-like receptor and alpha1/alpha2-adrenoceptor. PDF

Newman-Tancredi A, Cussac D, Audinot V, Nicolas JP, De Ceuninck F, Boutin JA, Millan MJ.
J Pharmacol Exp Ther. 2002 Nov;303(2):805-14.

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The accompanying multivariate analysis of the binding profiles of antiparkinson agents revealed contrasting patterns of affinities at diverse classes of monoaminergic receptor. Herein, we characterized efficacies at human hD2-SHORT (S), hD2-LONG (L), hD3, and hD4.4 receptors and at halpha2A-, halpha2B-, halpha2C-, and halpha1A-adrenoceptors (ARs). As determined by guanosine 5'-O-(3-[35S]thio)triphosphate ([35S]GTPgammaS) binding, no ligand displayed "full" efficacy relative to dopamine (100%) at all "D2-like" sites. However, at hD2S receptors quinpirole, pramipexole, ropinirole, quinerolane, pergolide, and cabergoline were as efficacious as dopamine (Emax100%); TL99, talipexole, and apomorphine were highly efficacious (79-92%); piribedil, lisuride, bromocriptine, and terguride showed intermediate efficacy (40-55%); and roxindole displayed low efficacy (11%). For all drugs, efficacies were lower at hD2L receptors, with terguride and roxindole acting as antagonists. At hD3 receptors, efficacies ranged from 33% (roxindole) to 94% (TL99), whereas, for hD4 receptors, highest efficacies (approximately 70%) were seen for quinerolane, quinpirole, and TL99, whereas piribedil and terguride behaved as antagonists and bromocriptine was inactive. Although efficacies at hD2S versus hD2L sites were highly correlated (r = 0.79), they correlated only modestly to hD3/hD4 sites (r = 0.44-0.59). In [35S]GTPgammaS studies of halpha2A-ARs, TL99 (108%), pramipexole (52%), talipexole (51%), pergolide (31%), apomorphine (16%), and quinerolane (11%) were agonists and ropinirole and roxindole were inactive, whereas piribedil and other agents were antagonists. Similar findings were obtained at halpha2B- and halpha2C-ARs. Using [3H]phosphatidylinositol depletion, roxindole, bromocriptine, lisuride, and terguride displayed potent antagonist properties at halpha1A-ARs. In conclusion, antiparkinson agents display diverse agonist and antagonist properties at multiple subtypes of D2-like receptor and alpha1/alpha2-AR, actions, which likely contribute to their contrasting functional profiles.