Cannabinoids, including the endogenous ligand arachidonyl ethanolamide (anandamide), elicit not only neurobehavioral but also cardiovascular effects. Two cannabinoid receptors, CB1 and CB2, have been cloned, and studies with the selective CB1 receptor antagonist SR141716A have implicated peripherally located CB1 receptors in the hypotensive action of cannabinoids. In rat mesenteric arteries, anandamide-induced vasodilation is inhibited by SR141716A, but other potent CB1 receptor agonists, such as HU-210, do not cause vasodilation, which implicates an as-yet-unidentified receptor in this effect. Here we show that ''abnormal cannabidiol'' (Abn-cbd) is a neurobehaviorally inactive cannabinoid that does not bind to CB1 receptors, yet causes SR141716A-sensitive hypotension and mesenteric vasodilation in wild-type mice and in mice lacking CB1 receptors or both CB1 and CB2 receptors. Hypotension by Abn-cbd is also inhibited by cannabidiol (20 g͞g), which does not influence anandamide-or HU-210-induced hypotension. In the rat mesenteric arterial bed, Abn-cbdinduced vasodilation is unaffected by blockade of endothelial NO synthase, cyclooxygenase, or capsaicin receptors, but it is abolished by endothelial denudation. Mesenteric vasodilation by Abncbd, but not by acetylcholine, sodium nitroprusside, or capsaicine, is blocked by SR141716A (1 M) or by cannabidiol (10 M). Abn-cbd-induced vasodilation is also blocked in the presence of charybdotoxin (100 nM) plus apamin (100 nM), a combination of K ؉ -channel toxins reported to block the release of an endotheliumderived hyperpolarizing factor (EDHF). These findings suggest that Abn-cbd and cannabidiol are a selective agonist and antagonist, respectively, of an as-yet-unidentified endothelial receptor for anandamide, activation of which elicits NO-independent mesenteric vasodilation, possibly by means of the release of EDHF.

Background and purpose: A nonpsychoactive constituent of the cannabis plant, cannabidiol has been demonstrated to have low affinity for both cannabinoid CB 1 and CB 2 receptors. We have shown previously that cannabidiol can enhance electrically evoked contractions of the mouse vas deferens, suggestive of inverse agonism. We have also shown that cannabidiol can antagonize cannabinoid receptor agonists in this tissue with a greater potency than we would expect from its poor affinity for cannabinoid receptors. This study aimed to investigate whether these properties of cannabidiol extend to CB 1 receptors expressed in mouse brain and to human CB 2 receptors that have been transfected into CHO cells. Experimental approach: The [ 35 S]GTPgS binding assay was used to determine both the efficacy of cannabidiol and the ability of cannabidiol to antagonize cannabinoid receptor agonists (CP55940 and R-( þ )-WIN55212) at the mouse CB 1 and the human CB 2 receptor. Key results: This paper reports firstly that cannabidiol displays inverse agonism at the human CB 2 receptor. Secondly, we demonstrate that cannabidiol is a high potency antagonist of cannabinoid receptor agonists in mouse brain and in membranes from CHO cells transfected with human CB 2 receptors. Conclusions and implications:This study has provided the first evidence that cannabidiol can display CB 2 receptor inverse agonism, an action that appears to be responsible for its antagonism of CP55940 at the human CB 2 receptor. The ability of cannabidiol to behave as a CB 2 receptor inverse agonist may contribute to its documented anti-inflammatory properties.

The cannabinoid analog abnormal cannabidiol [abn-cbd; (Ϫ)-4-(3-3,4-trans-p-menthadien-[1,8]-yl)-olivetol] does not bind to CB 1 or CB 2 receptors, yet it acts as a full agonist in relaxing rat isolated mesenteric artery segments. Vasorelaxation by abncbd is endothelium-dependent, pertussis toxin-sensitive, and is inhibited by the BK Ca channel inhibitor charybdotoxin, but not by the nitric-oxide synthase inhibitor N -nitro-L-arginine methyl ester or by the vanilloid VR1 receptor antagonist capsazepine. The cannabidiol analog O-1918 does not bind to CB 1 or CB 2 receptors and does not cause vasorelaxation at concentrations up to 30 M, but it does cause concentration-dependent (1-30 M) inhibition of the vasorelaxant effects of abn-cbd and anandamide. In anesthetized mice, O-1918 dose-dependently inhibits the hypotensive effect of abn-cbd but not the hypotensive effect of the CB 1 receptor agonist (Ϫ)-11-OH-⌬ 9 -tetrahydrocannabinol dimethylheptyl. In human umbilical vein endothelial cells, abn-cbd induces phosphorylation of p42/44 mitogenactivated protein kinase and protein kinase B/Akt, which is inhibited by O-1918, by pertussis toxin or by phosphatidylinositol 3 (PI3) kinase inhibitors. These findings indicate that abncbd is a selective agonist and that O-1918 is a selective, silent antagonist of an endothelial "anandamide receptor", which is distinct from CB 1 or CB 2 receptors and is coupled through G i /G o to the PI3 kinase/Akt signaling pathway.