Inhibitory effects of SR141716A on G-protein activation in rat brain

Eur J Pharmacol. 2001 Mar 2;414(2-3):135-43. doi: 10.1016/s0014-2999(01)00784-1.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Benzoxazines
  • Brain / drug effects*
  • Brain / metabolism
  • Calcium Channel Blockers / pharmacology
  • Camphanes / pharmacology
  • Dose-Response Relationship, Drug
  • GTP-Binding Proteins / antagonists & inhibitors
  • GTP-Binding Proteins / metabolism
  • Guanosine 5'-O-(3-Thiotriphosphate) / antagonists & inhibitors*
  • Guanosine 5'-O-(3-Thiotriphosphate) / metabolism
  • Male
  • Morpholines / pharmacology
  • Naphthalenes / pharmacology
  • Piperidines / pharmacology*
  • Pyrazoles / pharmacology*
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Cannabinoid
  • Receptors, Drug / antagonists & inhibitors*
  • Receptors, Drug / metabolism
  • Rimonabant
  • Sodium Chloride / pharmacology

Substances

  • Benzoxazines
  • Calcium Channel Blockers
  • Camphanes
  • Morpholines
  • Naphthalenes
  • Piperidines
  • Pyrazoles
  • Receptors, Cannabinoid
  • Receptors, Drug
  • SR 144528
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Sodium Chloride
  • Win 55212-2
  • GTP-Binding Proteins
  • Rimonabant