Pyrazolopyridine derivatives act as competitive antagonists of brain adenosine A1 receptors:: [35S]GTPγS binding studies

The effects of adenosine receptor Ligands and three novel pyrazolopyridine derivatives on guanosine-5'-O-(3-[S-35]thio)triphosphate [S-35]GTP gamma S) binding to rat cerebral cortical membranes were examined. [S-35]GTP gamma S 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 [S-35]GTP gamma S binding was inhibited by xanthine and pyrazolopyridine based adenosine receptor antagonists. The concentration-response curve for CCPA-stimulated [S-35]GTP gamma S binding was shifted to the right with increasing concentrations of antagonist without significant changes in maximal response. Schild analyses determined pK(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[1,5a]pyridin-3-yl) acryloyl]-2-piperidine ethanol (FK453), 6-oxo-3-(2-phenylpyrazolo[ 1,5a]pyridin-3-yl)-1(6H)-pyridazine butyric acid (FK838), 9-chloro-2-(2-furyl)[1,2,4]triazolo-[1,5c]quinazolin-5-amine (CGS 15943), 8-cyclopentyl-1,3-methylxanthine (CPT) and (R)-1-[(E)-3-(2-phenylpyrazolo[1,5a]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. (C) 1999 Elsevier Science B.V. All rights reserved.