Binding of [3H]haloperidol to dopamine D2 receptors in the rat striatum.
The present study was designed to examine the properties of [3H]haloperidol binding to dopamine D2-receptors in rat striatum membranes, displacement potencies of various chemicals and differences between the affinities of various chemicals and two new 5-hydroxytryptamine (5-HT2) receptor antagonists, MCI-9042, (+/-)-2-(dimethylamino)-1-[[o-(m-methoxyphenetyl)phenoxy]methyl]et hyl hydrogen succinate hydrochloride and one of its metabolites. The plots of specific binding for the striatum membranes obtained from the Scatchard analysis using [3H]haloperidol were monophasic when non-specific binding was determined with 10 microM chlorpromazine, and the Kd and Bmax values were 7.42 +/- 1.03 nM and 1.58 +/- 0.20 pmol (mg protein)-1 (n = 10), respectively. The displacement potencies of D2 receptor, 5-HT2 receptor, histamine H1-receptor, and adrenoceptor antagonists were characterized by [3H]haloperidol binding to D2 receptors. The pKi values of a new antiplatelet agent, MCI-9042, and its metabolite were 5.02 and 5.53, respectively, and these values were lower than those of the D2-receptor antagonists, fluphenazine, spiperone, haloperidol, prochlorperazine, chlorpromazine, thioridazine, and sulpiride. They were also lower than the pKi values of the 5-HT2-receptor antagonists, pirenperone, ketanserin, methysergide, and mianserin. We conclude that the binding site of [3H]haloperidol in the rat striatum is the D2 receptor, that MCI-9042 and its metabolite have lower affinities for D2 receptors than for 5-HT2 receptors, and that this radioreceptor assay is useful for assessing the affinities of various agents.
Department of Pharmacology, Niigata College of Pharmacy, Japan.
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Tsuchihashi
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Sasaki
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Kojima
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Nagatomo
D000818:Animals; D003342:Corpus Striatum / Q000378:metabolism*; D005343:Fibrinolytic Agents / Q000378:metabolism; D006220:Haloperidol / Q000378:metabolism* / Q000493:pharmacokinetics; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism; D013386:Succinates / Q000378:metabolism; D013565:Sympatholytics / Q000494:pharmacology
D005343:Fibrinolytic Agents; D006634:Histamine H1 Antagonists; D017448:Receptors, Dopamine D2; D011985:Receptors, Serotonin; D013386:Succinates; D013565:Sympatholytics; C064294:sarpogrelate; D006220:Haloperidol