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.
Sim-Selley
L J
LJ
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
Brunk
L K
LK
Selley
D E
DE
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