Effects of A1 and A2A adenosine receptor ligands in mouse acute models of pain

The effects of selective A(1) and A(2A) adenosine receptor compounds in two mouse models of acute nociception were studied: acetic acid-induced writhing and the hot plate assays. Stimulation of A, receptors by 2-chloro-N-6-cyclopentyl-adenosine (CCPA, 0.01-0.1 mg/kg, i.p.; A(1)K(i) = 6 nM) or blockade of A(2A) receptors by 5-amino-7-(beta-phenylethyl)-2-(8-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH58261, 1-10 mg/kg, i.p.; A(2A)K(i) = 1.3 nM) produced anti-nociceptive effects. At the highest dose tested, CCPA and SCH58261 reduced the number of writhings by 79 and 99%, respectively. On the contrary, the A(1) antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (A(1)K(i) = 2.8 nM) and the A(2A) agonist 2-(4-[2-carboxyethyl])phenethylamino-5'-N-ethylcarboxamido-adenosine-hydrochloride (GGS21680) produced pro-nociceptive effects in both tests. These findings suggest for the first time that blockade of A(2A) adenosine receptors produces anti-nociceptive effects. (C) 2002 Published by Elsevier Science Ireland Ltd.