N-ARACHIDONYLETHANOLAMIDE RELAXATION OF BOVINE CORONARY-ARTERY IS NOTMEDIATED BY CB1 CANNABINOID RECEPTOR

It has been reported that the endogenous cannabinoid N-arachidonyletha nolamide (AEA), commonly referred to as anandamide, has the characteri stics of an endothelium-derived hyperpolarizing factor in rat mesenter ic artery. We have carried out studies to determine whether AEA affect s coronary vascular tone. The vasorelaxant effects of AEA were determi ned in isolated bovine coronary artery rings precontracted with U-4661 9 (3 X 10(-9) M). AEA decreased isometric tension, producing a maximal relaxation of 51 +/- 9% at a concentration of 10(-5) M. Endothelium-d enuded coronary arteries were not significantly affected by AEA. The C B1 receptor antagonist SR-141716A (10(-6) M) failed to reduce the vaso dilatory effects of AEA, suggesting that the CB1 receptor is not invol ved in this action of AEA. Because AEA is rapidly converted to arachid onic acid and ethanolamine in brain and liver by a fatty acid amide hy drolase (FAAH), we hypothesized that the vasodilatory effect of AEA re sults from its hydrolysis to arachidonic acid followed by enzymatic co nversion to vasodilatory eicosanoids. In support of this hypothesis, b ovine coronary arteries incubated with [H-3]AEA for 30 min hydrolyzed 15% of added substrate; similar to 9% of the radiolabeled product was free arachidonic acid, and 6% comigrated with the prostaglandins (PGs) and epoxyeicosatrienoic acids (EETs). A similar result was obtained i n cultured bovine coronary endothelial cells. Inhibition of the FAAH w ith diazomethylarachidonyl ketone blocked both the metabolism of [H-3] AEA and the relaxations to AEA. Whole vessel and cultured endothelial cells prelabeled with [H-3]arachidonic acid synthesized [H-3]PGs and [ H-3]EETs, but not [H-3]AEA, in response to A-23187. Furthermore, SR141 716A attenuated A-23187-stimulated release of [H-3]arachidonic acid, s uggesting that it may have actions other than inhibition of CB1 recept or. These experiments suggest that AEA produces endothelium-dependent vasorelaxation as a result of its catabolism to arachidonic acid follo wed by conversion to vasodilatory eicosanoids such as prostacyclin or the EETs.