Antinociceptive activity and toxicological study of aqueous leaf extract of Justicia gendarussa Burm. F. in rats

According to Sri Lankan traditional medicine, leaves of Justicia gendarussa Burm. F. possesses analgesic action. But, validity of this claim has not been scientifically assessed. This study examined the oral antinociceptive potential of aqueous leaf extract (ALE) of J. gendarussa in rats using different concentrations (1500, 2000 and 3000 mg/kg). The results showed moderate and significant (P<0.05) antinociceptive action when tested in hot plate but not in tail flick test. This antinociceptive action had a rapid onset (2 h), moderate duration of action (2-4 h) and was dose-related. However, its antinociception effect was 2-5 folds weaker than morphine. In addition, ALE significantly impaired both phases of formalin test of nociception. Naloxone blocked the antinociceptive activity of ALE. Collectively, these observations suggest that ALE mediates its antinociception centrally at supraspinal and peripheral sites via opioid receptor mechanisms, and is effective against neurogenic and continuous inflammatory pain. In addition, ALE showed strong antioxidant activity which could also contributes to its antinociception. ALE was well tolerated (in terms of overt clinical signs, hepatic, renal and haemotoxicities). Phytochemical screening revealed the presence of alkaloids, flavonoids, saturated steroidal saponins or triterpinoidal saponins and amino acids and/or amines in ALE. It is concluded that ALE of J. gendarussa possesses safe, moderate oral antinociceptive activity.