Endothelium-independent relaxation to cannabinoids in rat-isolated mesenteric artery and role of Ca2+ influx

1 Three cannabinoid receptor agonists, anandamide (CB1 receptor-selective) and the aminoalkylindoles, JWH 015(2-methyl-1-propyl-1H-indol-3-yl)-1-napthalenylmethanone; (CB2 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 CB2 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 mM) precontraction did not affect relaxation to the aminoalkylindoles, but reduced that to anandamide. 2 SR14176A (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3- carboxamide; 3 mM; CB1 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-1H- pyrazole-3-carboxamide; CB1 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; CB2 antagonist; both at 3 mM) affected any of the relaxations. 3 Vanilloid receptor desensitisation with capsaicin reduced anandamide relaxation; addition of SR 141716A (3 muM) then caused further inhibition. SR 141716A did not affect capsaicin-induced relaxation. 4 The aminoalkylindoles inhibited CaCl2-induced contractions in methoxamine-stimulated vessels previously depleted of intracellular Ca2+. These inhibitory effects were greatly reduced or abolished in ionomycin-(a calcium ionophore) contracted vessels. Anandamide also caused vanilloid receptor-independent, SR 141716A-(3 muM) insensitive, inhibition of CaCl2 contractions. 5 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 Ca2+ influx into vascular smooth muscle. Anandamide causes vasorelaxation by activating vanilloid receptors, but may also inhibit Ca2+ entry. Relaxation to JWH 015 and anandamide was sensitive to SR 141716A, but there is no other evidence for the involvement of CB1 or CB2 receptors in responses to these compounds.