D2-dopamine receptor and cx,radrenoreceptor-mediated analgesic response of quercetin

Quercetin, a biot1avonoid (100-300 mg/kg) produced dose dependent increase in tail-flick latency, the analgesic effect bei ng sensitive to reversa l by naloxone (1 mg/kg) . Prior trea tment with haloperidol (I mg/kg), 0 1/02 receptor antagoni st haloperidol , sulpiridc (50 mg/kg), a selective O2 receptor antagonist, yohimbine (5 mg/kg), a a2-adrenoreceptor antagoni st but not by SCH 23390 a, selective 0 1 receptor antagonist blocked this response. Apomorphine (I mg/kg) a mixed 0 1/02 dopamine receptor agonist, and quinpirolc (0.5 mg/kg), a selecti ve O2 receptor agoni st also produced antinociception, that was reversed by haloperidol (I mg/kg), sulpiride (50 mg/kg), but not by yohimbine (5 mg/kg). The anti nociceptive action of quercetin (200 mg/kg) was potentiated by O2 agonist quinpirole (0.2 mglkg). Dopamine 0 1 receptor agonist SKF38393 (10 and IS mg/kg) fai led to aIter the anli noc icepti ve effect of quercetin (200 mg/kg). Quercetin (200 mglkg) reversed reserpine (2 Il1g/kg-4 hr) induced hyperalgesia, which was reversed by su lpiride but not by yohimbine. Thus, a role of dopamine O2 and a~-ad rcnoreccptors is postulated in the antinoeiceptive action of quercetin.