Inhibitory effects of SR141716A on G-protein activation in rat brain.
N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR141716A), a cannabinoid CB(1) receptor antagonist, has inverse agonist effects in cannabinoid CB(1) receptor-expressing cell lines, brain and peripheral organs. These studies characterized SR141716A-inhibited G-protein activity by measuring [35S]GTPgammaS binding. Maximal inhibition of basal [35S]GTPgammaS binding in cerebellar membranes was 50%. The EC(50) value for inhibition of [35S]GTPgammaS binding was 4.4 microM, whereas the K(e) for inhibition of R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate (WIN 55,212-2)-stimulated [35S]GTPgammaS binding was 0.6 nM. [35S]GTPgammaS autoradiography was used to examine the regional specificity of SR141716A inhibition. SR141716A inhibited basal [35S]GTPgammaS binding in all regions examined, with inhibition ranging from approximately 20% in caudate-putamen to 40% in hippocampus. These studies demonstrate that SR141716A is a competitive antagonist at nanomolar concentrations, whereas it inhibits basal receptor-mediated G-protein activity at micromolar concentrations. These data suggest that the apparent inverse agonist effect is either not cannabinoid CB(1) receptor-specific or that SR141716A is binding to different sites on the cannabinoid CB(1) receptor to produce inverse agonist versus competitive antagonist effects.
Department of Pharmacology and Toxicology and Institute for Drug and Alcohol Studies, Virginia Commonwealth University Medical College of Virginia, 1112 East Clay St., Box 980524, 23298, Richmond, VA, USA. ljsimsel@hsc.vcu.edu
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D000818:Animals; D048588:Benzoxazines; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D001892:Camphanes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology*; D011720:Pyrazoles / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000077285:Rimonabant; D012965:Sodium Chloride / Q000494:pharmacology
D048588:Benzoxazines; D002121:Calcium Channel Blockers; D001892:Camphanes; D009025:Morpholines; D009281:Naphthalenes; D010880:Piperidines; D011720:Pyrazoles; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; C110630:SR 144528; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D012965:Sodium Chloride; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D019204:GTP-Binding Proteins; D000077285:Rimonabant