Anandamide-induced vasorelaxation in rabbit aortic rings has two components: G protein dependent and independent

The endogenous cannabinoid anandamide (arachidonylethanolamide) produces vasorelaxation in different vascular beds. In the present study, we found that anandamide and a metabolically stable analog, methanandamide, produced dose-dependent (10 nM-10 muM) vasorelaxation of similar to80% in a rabbit aortic ring preparation in an endothelium-dependent manner. Non-endothelium-dependent vasorelaxation was observed to be a maximum of 20-22% at >10 muM methanandamide. The efficacious CB1 receptor analogs desacetyllevonantradol (10 muM) and WIN55212-2 (10 muM) failed to produce vasorelaxation; however, the endothelium-dependent vasorelaxation evoked by methanandamide was partially (75%) blocked by the CB1 receptor antagonist SR141716A. The VR1 vanilloid receptor antagonist capsazepine or the calcitonin gene-related peptide (CGRP) antagonist CGRP-(8-37) partially attenuated (25%) the vasorelaxation in endothelium-intact preparations and greatly reduced the response in endothelium-denuded preparations. Pretreatment of aortic rings with N-G-nitro-L-arginine methyl ester completely blocked the methanandamide-, capsaicin-, and CGRP- induced vasorelaxation. Pretreatment of aortic rings with pertussis toxin attenuated the methanandamide-induced vasorelaxation in endothelium-intact aortic rings, indicating the involvement of G(i/o) proteins in the vasorelaxation; however, pertussis toxin treatment failed to block the endothelium-independent response. Thus, in the rabbit aorta, methanandamide- induced vasorelaxation exhibits two components: 1) in endothelium-intact rings, an SR141716A-sensitive, non-CB1 receptor component that requires pertussis toxin-sensitive G proteins and nitric oxide (NO) production; and 2) in endothelium-denuded rings, a component that is mediated by VR1 vanilloid receptors and possibly by the subsequent release of CGRP that requires NO production but is independent of pertussis toxin-sensitive G proteins.