Endothelium‐independent relaxation to cannabinoids in rat‐isolated mesenteric artery and role of Ca 2+ influx

Three cannabinoid receptor agonists, anandamide (CB 1 receptor‐selective) and the aminoalkyl‐indoles, JWH 015(2‐methyl‐1‐propyl‐ 1 H‐indol‐3‐yl)‐1‐napthalenylmethanone; (CB 2 receptor‐selective), R ‐(+)‐WIN 55,212‐2 ( R ‐(+)‐[2,3‐dihydro‐5‐methyl‐3‐(4‐morpholinylmethyl)pyrrolol[1,2,3‐de]‐1,4‐benzoxazin‐6‐yl]‐1‐napthalenylmethanone; slightly CB 2 receptor‐selective), as well as the enantiomer S ‐(−)‐WIN 55,212‐3( S ‐(−)‐[2,3‐dihydro‐5‐methyl‐3‐(4‐morpholinylmethyl)pyrrolol[1,2,3‐de]‐1,4‐benzoxazin‐6‐yl]‐1‐napthalenylmethanone; inactive at cannabinoid receptors), induced endothelium‐independent relaxation of methoxamine‐precontracted isolated small mesenteric artery of rat. KCL (60 m M ) precontraction did not affect relaxation to the aminoalkylindoles, but reduced that to anandamide. SR14176A ( N ‐(piperidin‐1‐yl)‐5‐(4‐chlorophenyl)‐1‐(2,4‐dichlorophenyl)‐4‐methyl‐ 1 H‐pyrazole‐3‐carboxamide; 3 μ M ; CB 1 receptor antagonist) inhibited relaxation only to JWH 015 and anandamide. Neither AM 251 ( N ‐(piperidin‐1‐yl)‐5‐(4‐iodophenyl)‐1‐(2,4‐dichlorophenyl)‐4‐methyl‐ 1 H‐pyrazole‐3‐carboxamide; CB 1 antagonist) nor SR 144528 ( 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; CB 2 antagonist; both at 3 μ M ) affected any of the relaxations. Vanilloid receptor desensitisation with capsaicin reduced anandamide relaxation; addition of SR 141716A (3 μ M ) then caused further inhibition. SR 141716A did not affect capsaicin‐induced relaxation. The aminoalkylindoles inhibited CaCl 2 ‐induced contractions in methoxamine‐stimulated vessels previously depleted of intracellular Ca 2+ . These inhibitory effects were greatly reduced or abolished in ionomycin‐(a calcium ionophore) contracted vessels. Anandamide also caused vanilloid receptor‐independent, SR 141716A‐ (3 μ M ) insensitive, inhibition of CaCl 2 contractions. In conclusion, the aminoalkylindoles JWH 015, R‐(+)‐WIN 55,212‐2 and S‐(−)‐WIN 55,212‐3 relax rat small mesenteric artery mainly by inhibiting Ca 2+ influx into vascular smooth muscle. Anandamide causes vasorelaxation by activating vanilloid receptors, but may also inhibit Ca 2+ entry. Relaxation to JWH 015 and anandamide was sensitive to SR 141716A, but there is no other evidence for the involvement of CB 1 or CB 2 receptors in responses to these compounds.British Journal of Pharmacology (2003) 139 , 585–597. doi: 10.1038/sj.bjp.0705280