Involvement of opioid receptors in antinociceptive activity of semi purified fraction and β-amyrin isolated from Ricinus communis Linn. leaves in mice

The antinociceptive effect of chloroform extract (RCLC), semi-purified fraction (RC 2 ) and isolated pentacyclic triterpenoid β-amyrin (BA) from the leaves of Ricinus communis in acetic acid-induced abdominal writhing, formalin-induced paw licking and hot-plate test was conducted in mice. The GC-MS study revealed that the RC 2 showed the dominance of diterpenes, triterpenes, fatty acids, sterol and higher alkanes. No obvious behavioral changes, allergic reactions and mortality were observed in acute toxicity studies. Acute administration of the diazepam (1 mg/kg), RC 2 (50 mg/kg) and BA (10 mg/kg) displayed mild sedation in open field test while RCLC (100 mg/kg) showed potent sedative properties. No motor incoordination and neurotoxicity was observed in rota-rod test. RCLC (100 mg/kg), RC 2 (25 and 50 mg/kg) and BA (5 and 10 mg/kg) significantly inhibited the number of abdominal writhing induced by acetic acid and formalin-induced paw licking response. The central and peripheral antinociceptive effects for RCLC and RC 2 in hot-plate were comparable to morphine. The administration of naloxone reversed the antinociceptive effect of morphine, RCLC and RC 2 indicating the involvement of opioid receptors while BA principally showed peripheral antinociceptive effects which may be modulated via peripheral opioid receptors or protein kinase.