Antinociceptive Effects of Alpinia katsumadai via Cyclooxygenase-2 Inhibition

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Alpinia katsumadai has been widely used in traditional Chinese and Korean medicine to treat a variety of conditions including emesis and gastric disorders such as gastric pain and distended abdomen. To investigate the antinociceptive potential and mechanism of A. katsumadai, ethanolic extracts of A. katsumadai were assayed on cyclooxygenase-2 and evaluated for analgesic activity based on phenylbenzoquinone (PBQ)-induced writhing and carrageenan-induced hyperalgesia tests. A. katsumadai extracts inhibited the cyclooxygenase-2 enzyme activity in a dose-dependent fashion at an <TEX>$IC_{50}$</TEX> value of 0.044 <TEX>${\mu}g$</TEX>/ml. A. katsumadai extract (30-300 mg/kg, orally (p.o.) administered) significantly inhibited PBQ-induced writhing. This inhibition was judged not to be a false positive because a Rota-rod test revealed no difference in muscular coordination when compared to the controls. With regard to the carrageenan-induced hyperalgesia, A. katsumadai extract (30-300 mg/kg, p.o.) produced a significant, dose-dependent increase in the withdrawal response latencies. Naloxone did not reverse the analgesic effect of A. katsumadai extract in the carrageenan-induced hyperalgesia. Taken together, these results suggest that the antinociceptive activity of A. katsumadai is not related to the opioid receptor. A. katsumadai extract has remarkable, non-opioidreceptor-mediated analgesic effects on PBQ-induced writhing and carrageenan-induced hyperalgesia that occur via cyclooxygenase-2 inhibition.