Anti-nociceptive and anti-inflammatory activities of methanol extract of the leaves of Cajanus cajan.

The leaves of  Cajanus cajan  is used traditionally in several parts of the world for treatment of diseases of inflammatory origin. In this study, the methanol extract of the leaves were assessed for its anti -nociceptive and anti-inflammatory activities using various animal models. The extract (100, 300 and 500 mg/kg), indomethacin (5mg/kg) or distilled water was administered to groups of five rats or mice in each experiment.  A significant (p<0.05) reduction in the number of abdominal writhing movement was observed in mice administered  with 300mg/kg and 500mg/kg of the extract. The extract significantly (p<0.05) inhibited pain sensations particularly from 30 minutes post-administration of the extract as observed in the response time to thermal pain in the hot plate and tail flick test.  A dose-dependent inhibition of pain sensation was observed in the tail flick test from 60 minutes post-administration of the extract (6.00±1.89 seconds, 6.45±1.01± seconds and 7.57±2.77 seconds) and this response was significantly longer than that observed   for mice administered with indomethacin (4.00±0.56 seconds). The extract also inhibited inflammatory responses in the formalin -induced paw lick and albumen-induced paw oedema tests. The inhibition of oedema formation in rats administered with the extract  (500mg/kg) was up to 82% for 90  -120 minutes, while in those administered with indomethacin, the maximum inhibitory effect was 59% at 90 minutes.  The result obtained in this study has established the anti-nociceptive and anti-inflammatory effects of these  leaves. The folkloric uses of  C. cajan for relieve of pain and ailments of inflammatory origin in hereby confirmed.