Pyrazolopyridine derivatives act as competitive antagonists of brain adenosine A 1 receptors: [ [formula omitted]]GTPγS binding studies

Abstract

The effects of adenosine receptor ligands and three novel pyrazolopyridine derivatives on guanosine-5′- O-(3-[ 35 S ]thio)triphosphate ([ 35 S ]GTPγS) binding to rat cerebral cortical membranes were examined. [ 35 S ]GTPγS binding was stimulated in a concentration dependent manner by several adenosine receptor agonists. The adenosine A 2a receptor selective agonist, 2- p-(2-carboxyethyl)phenethylamino-5′- N-ethylcarboxamidoadenosine (CGS 21680), was ineffective confirming specificity for adenosine A 1 receptor activation. 2-Chloro- N 6-cyclopentyladenosine (CCPA; 10 −7 M)-stimulated [ 35 S ]GTPγS binding was inhibited by xanthine and pyrazolopyridine based adenosine receptor antagonists. The concentration–response curve for CCPA-stimulated [ 35 S ]GTPγS binding was shifted to the right with increasing concentrations of antagonist without significant changes in maximal response. Schild analyses determined p K B values of 8.97, 8.88, 8.21, 8.16, 7.79 and 7.65 for 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), ( R)-1-[( E)-3-(2-phenylpyrazolo[1,5 a]pyridin-3-yl) acryloyl]-2-piperidine ethanol (FK453), 6-oxo-3-(2-phenylpyrazolo[1,5 a]pyridin-3-yl)-1(6 H)-pyridazinebutyric acid (FK838), 9-chloro-2-(2-furyl)[1,2,4]triazolo-[1,5 c]quinazolin-5-amine (CGS 15943), 8-cyclopentyl-1,3-methylxanthine (CPT) and ( R)-1-[( E)-3-(2-phenylpyrazolo[1,5 a]pyridin-3-yl) acryloyl]-piperidin-2-yl acetic acid (FK352), respectively. Schild slopes were close to unity, confirming that these novel pyrazolopyridine derivatives act as competitive antagonists at rat brain adenosine A 1 receptors.