Pyrazolopyridine derivatives act as competitive antagonists of brain adenosine A(1) receptors: [S-35]GTP gamma S 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 ade nosine 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 activ ation. 2-Chloro-N-6-cyclopentyladenosine (CCPA; 10(-7) M)-stimulated [S-35] GTP gamma S binding was inhibited by xanthine and pyrazolopyridine based ad enosine receptor antagonists. The concentration-response curve for CCPA-sti mulated [S-35]GTP gamma S binding was shifted to the right with increasing concentrations of antagonist without significant changes in maximal respons e. 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-phe nylpyrazolo[1,5a]pyridin-3-yl) acryloyl]-2-piperidine ethanol (FK453), 6-ox o-3-(2-phenylpyrazolo[ 1,5a]pyridin-3-yl)-1(6H)-pyridazine butyric acid (FK 838), 9-chloro-2-(2-furyl)[1,2,4]triazolo-[1,5c]quinazolin-5-amine (CGS 159 43), 8-cyclopentyl-1,3-methylxanthine (CPT) and (R)-1-[(E)-3-(2-phenylpyraz olo[1,5a]pyridin-3-yl) acryloyl]-piperidin-2-yl acetic acid (FK352), respec tively. Schild slopes were close to unity, confirming that these novel pyra zolopyridine derivatives act as competitive antagonists at rat brain adenos ine A(1) receptors. (C) 1999 Elsevier Science B.V. All rights reserved.