N‐arachidonoyl glycine, an endogenous lipid that acts as a vasorelaxant via nitric oxide and large conductance calcium‐activated potassium channels

Abstract

N-arachidonoyl glycine (NAGly) is an endogenous lipid that is structurally similar to the endocannabinoid, N-arachidonoyl ethanolamide (anandamide). While NAGly does not activate cannabinoid receptors, it exerts cannabimimetic effects in pain regulation. Here, we have determined if NAGly, like anandamide, modulates vascular tone. In rat isolated small mesenteric arteries, the relaxant responses to NAGly were characterized. Effects of N-arachidonoyl serine and N-arachidonoyl gamma-aminobutyric acid were also examined. In endothelium-intact arteries, NAGly-induced relaxation (pEC(50%)= 5.7 +/- 0.2; relaxation at 30 microM = 98 +/- 1%) was attenuated by l-NAME (a nitric oxide synthase inhibitor) or iberiotoxin [selective blocker of large conductance Ca(2+)-activated K(+) channels (BK(Ca))], and abolished by high extracellular K(+) concentration. Endothelial removal reduced the potency of NAGly, and the resultant relaxation was inhibited by iberiotoxin, but not l-NAME. NAGly responses were sensitive to the novel cannabinoid receptor antagonist O-1918 independently of endothelial integrity, whereas pertussis toxin, which uncouples G(i/o) proteins, attenuated NAGly relaxation only in endothelium-intact arteries. Treatments with antagonists for CB(1), CB(2) and TRPV1 receptors, or inhibitors of fatty acid amide hydrolase and COX had no effect. The two other arachidonoyl amino acids also induced iberiotoxin- and L-NAME-sensitive relaxations. NAGly acts as a vasorelaxant predominantly via activation of BK(Ca) in rat small mesenteric arteries. We suggest that NAGly activates an unknown G(i/o)-coupled receptor, stimulating endothelial release of nitric oxide which in turn activates BK(Ca) in the smooth muscle. In addition, NAGly might also activate BK(Ca) through G(i/o)- and nitric oxide-independent mechanisms.