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

Abstract

1. 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. 2. 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-1 had no cannabinoid psychoactivity. 3. Intraplantar injection of carrageenan (1% w v-1) elicited a time-dependent increase in paw volume and thermal hyperalgesia. 4. 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-1 and indomethacin 5 mg kg-1, given p.o. 1 h before carrageenan, also reduced the inflammatory parameters in a time-dependent manner. 5. The selective CB2 cannabinoid 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-1 p.o. 1 h before nabilone and palmitoylethanolamide, prevented the anti-oedema and antihyperalgesic effects of the two cannabinoid agonists 3 h after carrageenan. 6. 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.