Antiinflammatory action of endocannabinoid palmitoylethanolamide and the synthetic cannabinoid nabilone in a model of acute inflammation in the rat

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Abstract
The antiinflammatory activity of synthetic cannabinoid nabilone in the rat model of carrageenan‐induced acute hindpaw inflammation was compared with that of the endocannabinoid palmitoylethanolamide and the nonsteroidal antiinflammatory drug indomethacin. Preliminary experiments in rats used a tetrad of behavioural tests, specific for tetrahydrocannabinol‐type activity in the CNS. These showed that the oral dose of nabilone 2.5 mg kg−1had no cannabinoid psychoactivity. Intraplantar injection of carrageenan (1% w v−1) elicited a time‐dependent increase in paw volume and thermal hyperalgesia. Nabilone (0.75, 1.5, 2.5 mg kg−1, p.o.), given 1 h before carrageenan, reduced the development of oedema and the associated hyperalgesia in a dose‐related manner. Nabilone 2.5 mg kg−1, palmitoylethanolamide 10 mg kg−1and indomethacin 5 mg kg−1, given p.o. 1 h before carrageenan, also reduced the inflammatory parameters in a time‐dependent manner. The selective CB2cannabinoid receptor antagonist {N‐[(1S)‐endo‐1,3,3‐trimethyl bicyclo [2.2.1]heptan‐2‐yl]‐5‐(4‐chloro‐3‐methylphenyl)‐1‐(4‐methylbenzyl)pyrazole‐3 carboxamide} (SR 144528), 3 mg kg−1p.o. 1 h before nabilone and palmitoylethanolamide, prevented the anti‐oedema and antihyperalgesic effects of the two cannabinoid agonists 3 h after carrageenan. Our findings show the antiinflammatory effect of nabilone and confirm that of palmitoylethanolamide indicating that these actions are mediated by an uncharacterized CB2‐like cannabinoid receptor. British Journal of Pharmacology(2002)135, 181–187; doi:10.1038/sj.bjp.0704466