| Abstrakt: |
Calcium-mobilizing G protein-coupled receptor (GPCR) agonists, such as angiotensin II (AngII), endothelin and vasopressin induce vasoconstriction. Activation of AT1 angiotensin- and other Gq/11 protein-coupled receptors leads to diacylglycerol (DAG) formation, which can be converted to 2-arachidonoylglycerol (2-AG), an important endocannabinoid by the effect of DAG lipase (1,2). Cannabinoids via CB1 cannabinoid receptors (CB1R) have peripheral hypotensive and vasodilator actions. We tested the hypothesis that 2-AG release can modulate the vasoconstrictor action of AngII and other calcium-mobilizing hormones in rodent vascular tissue. Male Wistar rats (300-350g), C57BL6 and CB1R knockout mice (21-25g, 3) were anaesthetised with pentobarbital (50mg kg-1 ip.). Rat skeletal muscle (gracilis) arterioles and mouse saphenous arteries were isolated, pressurized and subjected to microangiometry. Also, rats (200-250g) were anaesthetised and aorta was removed for vascular smooth muscle cell (VSMC) isolation. Vascular expression of CB1R was demonstrated with immunohistochemistry. In accordance with the functional relevance of these receptors WIN55212, a CB1R agonist caused vasodilation, which was absent in CB1R knockout mice. In gracilis arterioles dose-dependent vasoconstrictions for AngII, norepinephrine (NE), endothelin, vasopressin and prostaglandin (PG)F2α were obtained. Inhibition of CB1Rs with neutral antagonist O2050 in gracilis arterioles augmented the vasoconstriction induced by AngII, NE, endothelin and vasopressin (from 29.1±5.8% to 47.5±3.2% and from 38.8±7.6% to 76.3±4.8%, effects of 10nM AngII and 1µM NE, respectively, p<0.05) but did not influence the contractile effect of PGF2α (45.6±9.9% and 36.9±9.8% at 1µM, n.s.). Inhibition of CB1Rs enhanced AngII-induced vasoconstrictor action in saphenous arteries of wild type, but not of CB1R knockout mice. Inhibition of DAG lipase by tetrahydrolipstatin (THL) also augmented the vasoconstrictor effect of AngII, suggesting the role of 2- AG in CB1R activation. In VSMCs AngII-stimulated 2-AG formation was inhibited by THL but potentiated by JZL184, an inhibitor of monoacylglycerol lipase, an enzyme catalyzing degradation of 2-AG. Inhibition of CB1R also increased the sustained phase of AngII-induced calcium signal and this effect was found to be independent of nitric oxide synthase activity and of endothelial function. These data demonstrate that vasoconstrictor effects of calcium mobilizing GPCR agonists are physiologically attenuated by agonist-induced endocannabinoid release and consequent CB1R activation. It is proposed that this effect may serve as a beneficial control mechanism by moderating the microvascular tone in high contractile states. [ABSTRACT FROM AUTHOR] |
