An investigation into the pharmacological effects of phytocannabinoids and endocannabinoids in human mesenteric arteries

Cannabinoids cause both acute and time-dependent vasodilation/vasorelaxation in a range of vascular beds. The vascular effect of cannabinoids is dependent on the cannabinoid ligand, the species studied and the vascular bed used. To date, there have been four studies that have characterised the effects of cannabinoids in humans. Therefore, the aim of this thesis was to characterise the pharmacological effects of cannabinoids in the human mesenteric artery. Written Informed consent was granted for the use of mesenteric arteries collected from patients at the Royal Derby Hospital. Arteries were dissected from mesenteric tissue and mounted on a Mulvany-Halpern myograph. Arteries were contracted using U46619 and endothelin-1. Concentration-response curves were carried out to the phytocannabinoids THC and CBD; the endocannabinoids AEA and 2-AG; the synthetic cannabinolds CP55,940 and HU-308. The underlying mechanisms of action were assessed using receptor antagonism, enzyme inhibition, endothelium denudation and ion channel manipulation. Experiments to probe the potential for cannabinoids to cause time-dependent vasorelaxation of human mesenteric arteries were also carried out. Post-hoc analysis was conducted on all acute vasorelaxation responses to assess the potential influence of patient characteristics/disease state on cannabinoid responses. All cannabinoids tested, with the exception of HU-308, caused concentration-dependent vasorelaxation of human mesenteric arteries. The synthetic cannabinoid CP55,940 had the greatest Rmax of all the cannabinoids tested. 2-AG had the greatest Rmax of the endocannabinoids tested and CBD had the greatest Rmax of the phytocannabinoids tested. Compared to animal models, cannabinoid efficacy was reduced in human mesenteric arteries. The vasorelaxant effects of 2-AG were mediated through COX-1 metabolism, prostanoid receptor activation (EP4 and IP) and ion channel modulation. The mechanisms underpinning CBD-induced vasorelaxation were CBl and TRPV1 receptor activation, NO release, the endothelium and ion channel modulation. Vasorelaxant responses to AEA were inhibited by antagonism of the CB1 receptor and a putative cannabinoid receptor located on the endothelium (CBe), nitric oxide synthase inhibition and endothelium denudation. Cannabinoid responses were reduced in patients with cardiovascular diseases/disease risk factors including ischaemic heart disease, type-2 diabetes and hypercholesterolemia. Endocannabinoid responses were reduced in patients taking NSAID medication, with some reductions in responses seen to other medication including statins and beta-blockers. CBD and AEA were tested for time-dependent vasorelaxation. Both CBD and AEA were able to cause vasorelaxatlon that gradually increased over time, this was not mediated by the PPARy receptor. This thesis concludes that cannabinoids are able to modulate vascular tone in isolated human mesenteric arteries, and this may be blunted in patients with cardiovascular disease. Furthermore, this thesis presents data suggesting that differences exist between human and animal arterial responses to cannabinoids.