Contractile response to a cannabimimetic eicosanoid, 2-arachidonoylglycerol, of longitudinal smooth muscle from the guinea-pig distal colon in vitro

Abstract

The effect of 2-arachidonoylglycerol, a cannabimimetic eicosanoid, was studied on mucosa-free longitudinal muscle strips isolated from the guinea-pig distal colon. In the presence of indomethacin (3 μM) and N G-nitro- l-arginine (100 μM), 2-arachidonoylglycerol (10 nM–10 μM) produced concentration-dependent and tetrodotoxin (1 μM)-sensitive contractions of the longitudinal muscle strips. The contractions were markedly attenuated in the presence of atropine (0.2 μM), and partially by hexamethonium (100 μM) pretreatment. The response to 2-arachidonoylglycerol was mimicked with N-arachidonoylethanolamine (anandamide, 0.1–30 μM), another cannabimimetic eicosanoid, but the cannabinoid CB 1/CB 2 receptor agonist, R-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3,-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN55,212-2) (0.1–10 μM), and the vanilloid receptor agonist, (all Z)-(4-hydroxyphenyl)-5,8,11,14-eicosatetraenamide (AM 404) (10–30 μM), were without effect. The cannabinoid CB 1 receptor antagonist, N-piperidino-5-(4-chlorophenyl)-l-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-caroxamide (SR141716A) (1 μM), the cannabinoid CB 2 receptor antagonist, [ N-[1 S]-endo-1,3,3-trimethyl bicyclo [2.2.1] heptan-2-yl]-5-(4-chloro-3-methylphenyl)-l-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) (1 μM), and the vanilloid receptor antagonist, capsazepine (10 μM), did not shift the concentration–response curve for 2-arachidonoylglycerol to the right. The contractile action of 2-arachidonoylglycerol was also partially attenuated in the presence of nordihydroguaiaretic acid (10 μM), a lipoxygenase inhibitor. These results indicate that 2-arachidonoylglycerol produces contraction of longitudinal muscle of the guinea-pig distal colon via mainly stimulation of myenteric cholinergic neurones, and that neither cannabinoid CB 1/CB 2 receptors nor vanilloid receptors contributed to the response. The present results suggest the possibility that lipoxygenase metabolites may also contribute, at least in part, to the contractile action of 2-arachidonoylglycerol.