Effects of curcumin, morphine and naloxone on the experimentally-induced paw edema in rats

In this study, effects of curcumin (active substance of turmeric), morphine (an opioid receptor agonist) and naloxone (an opioid receptor antagonist) in separate and combined treatments have been investigated on the paw edema induced by formalin in rats. Subcutaneous injection of formalin (50μl, 2.5%) in the ventral surface of the hind paw induced a considerable edema in the paw that lasted up to 24h after formalin injection. Chronic oral administration of curcumin (30 and 60mg/kg, 15 days) and subcutaneous injection of morphine (1mg/kg) significantly (p<0.05) decreased the paw edema induced by formalin. Naloxone (1mg/kg) used alone was without effect, whereas pretreatment with naloxone (1mg/kg) before morphine (1mg/kg) significantly (p<0.05) prevented the suppressive effect of morphine on the paw edema. The reducing effect of curcumin on the paw edema was potentiated by morphine, whereas naloxone did not change the anti-edematous effect of curcumin. Curcumin (30mg/kg, 15 days) in the presence of naloxone (1mg/kg) plus morphine (1mg/kg) treatment, produced an anti- edematous effect, which resembled the one following administration of curcumin (30 mg/kg, 15 days) alone. Present findings indicate that curcumin may produce an anti-edematous effect. The endogenous opioid system may involve in modulation of local edema. In addition, morphine may potentiate the anti-edematous effect of curcumin.