Antinociceptive activity of aqueous extract of Pachyptera hymenaea (DC.) in mice

The standardized aqueous extract of leaves of Pachyptera hymenaea (DC.) belonging to family Bignoniaceae was investigated for possible antinociceptive effect in mice. Three different models were used to study the effects of extract on nociception, namely acetic acid-induced writhing test, formalin test (paw licking test) and tail flick test in mice. The extract was administered 1h prior to pain induction in the dose range of 25, 50 and 75mg/kg orally. The extract at the given dose range reduced the acetic acid induced nociception by 44.03, 52.90 and 62.46% respectively. The extract reduced formalin effect in both the phases of experiment by 32.36, 41.94, 54.29% and 35.39, 50.17, 55.86% respectively. In the tail flick study, animals' reaction time were increased by 22.69, 38.24 and 40.26% at the above selected doses respectively at 120min after drug administration. Naloxone (2mg/kg; s.c.) significantly antagonized the effect of extract in formalin and tail flick method, while partially antagonized the effect in writhing test. However caffeine completely reverted the extract effect in both the phases of formalin test. Results of these studies revealed that the extract have significant antinociceptive activity in the used models with a possible involvement of central mechanism and adenosine system.