Specific opiate effects on dextran-induced inflammation in rats

The effects of opiates were investigated in two models of acute inflammation in rats. Morphine (0.1-10 mg/kg, i.p.) inhibited by 50% the paw edema induced by interdigital injection of 1% dextran solution. Low but not high doses of naltrexone produced a similar degree of inhibition. Naltrexone (10 mg/kg, i.p.) completely prevented morphine antiedema effect. Local anesthesia of the hindleg with lidocaine neither modified dextran-induced paw edema nor morphine inhibitory effects. Morphine (10 mg/kg, i.p.) enhanced by 50% skin vascular permeability induced by intradermically injected 1% dextran solution. Again, naltrexone prevented morphine effects. The obtained results suggest a specific modulatory role of opiates in the acute inflammatory responses of the rat.