Reversal of lipopolysaccharide‐induced thermal and behavioural hyperalgesia by quercetin

Lipopolysaccharide (LPS), a major constituent of the outer membrane of the cell wall of gram‐negative bacteria, is known to cause inflammatory pain. Quercetin, a dietary flavonoid, is claimed to have antiinflammatory activity in a few experimental studies. However, it is not known whether quercetin can reverse the hyperalgesia that is secondary to the inflammation. The aim of the present study was to evaluate the effect of quercetin on LPS‐induced alteration of pain perception in mice. Central perception of pain was assessed with the tail‐flick and hot plate methods and behavioural hyperalgesia was assessed by noting the animal's reactions such as redness, paw licking, and rearing after the intraplantar injection of LPS (10 μg/paw). Local administration of LPS induced significant hyperalgesia when measured by both central effects and behavioural reactions. Quercetin (50 and 100 mg/kg), like dexamethasone (0.5 mg/kg), attenuated central and behavioural hyperalgesia. This effect of quercetin was sensitive to reversal by naloxone (2 mg/kg). Our results thus indicate that quercetin protects against LPS‐induced hyperalgesia through modulation of the opioidergic system. Drug Dev. Res. 58:248–252, 2003.