Objective: To evaluate the analgesic effect of extracts of Alpinia galanga (AG) rhizome in mice and elucidate the possible mechanism for its analgesic action.
Methods: Analgesic action of extracts of AG rhizome was studied in three experimental models of nociception. Albino mice of both sexes weighing 25 to 30 g were used in this study. For the hot-plate test, mice in the five groups with six in each received three different doses of ethanolic extracts of dried rhizome of AG suspended in 2% gum acacia orally, morphine subcutaneously and 2% gum acacia orally, respectively. Reaction time was observed after administration of vehicle or drugs. For the hot-plate test after naloxone pretreatment, mice in the five groups received naloxone subcutaneously 30 min prior to the administration of vehicle or drugs and reaction time was observed as explained above. In the writhing test, writhes were induced by injecting acetic acid intraperitoneally in another 30 mice which were randomly allocated to five groups of six in each and received three different doses of ethanolic extracts of dried rhizome of AG suspended in 2% gum acacia, aspirin suspended in 2% gum acacia and 2% gum acacia orally, respectively. The mice were observed individually for a period of 15 min and the number of writhes was recorded for each animal.
Results: AG treatment significantly increased the latency period in the hot-plate test at all three doses at 30, 60, 90 and 120 min time intervals compared with control group (P<0.05 or P<0.01). Naloxone pretreatment significantly reduced the latency period in hot-plate test for both AG and morphine groups as compared with corresponding groups that did not receive naloxone pretreatment (P<0.05 or P<0.01). AG at all doses significantly reduced the number of writhes compared with control group (P<0.01).
Conclusion: The study confirmed the analgesic effect of AG rhizome and hence justified its use in ethnomedicine for the treatment of pain due to various causes. The probable mechanism of its analgesic action may be central as well as peripheral.

Key words: Alpinia galanga, plant extracts, analgesics, pain measurement, receptors, opioid, mice