Endothelium-dependent metabolism by endocannabinoid hydrolases and cyclooxygenases limits vasorelaxation to anandamide and 2-arachidonoylglycerol.
OBJECTIVE
The endocannabinoids, N-arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol (2-AG) are rapidly degraded by fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL). Whilst these lipid mediators are known to modulate vascular tone, the extent to which they are inactivated via local metabolism in the vasculature remains unclear.


METHODS
In rat isolated small mesenteric arteries, the regulatory role of FAAH, MGL and cyclooxygenase (COX) in relaxant responses to anandamide and 2-AG was evaluated by using inhibitors of these enzymes. Relaxations to non-hydrolysable analogues of endocannabinoids and arachidonic acid were also examined.


RESULTS
Relaxation to anandamide but not 2-AG was potentiated by the selective FAAH inhibitor, URB597 (1 microM). In contrast, MAFP (10 microM; an inhibitor of FAAH and MGL) enhanced responses to both anandamide and 2-AG. Inhibition of COX-1 by indomethacin (10 microM) potentiated relaxations to 2-AG, whereas inhibition of COX-2 by nimesulide (10 microM) potentiated anandamide-induced relaxation. With the exception of MAFP, effects of FAAH and COX inhibitors were dependent on the endothelium. Relaxation to methanandamide and noladin ether, the non-hydrolysable analogues of anandamide and 2-AG respectively, were insensitive to the enzyme inhibitors.


CONCLUSIONS
This study shows that local activity of FAAH, MGL and COX, which is present largely in the endothelium, limits the vasodilator action of endocannabinoids in rat small mesenteric arteries. Despite the differential roles played by these enzymes on relaxation to anandamide versus 2-AG, our results suggest that inhibitors of these enzymes enhance the vascular impact of endocannabinoids.
Ho
W-S V
WS
School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, UK. vanessa.ho@nottingham.ac.uk
Randall
M D
MD
D000581:Amidohydrolases / Q000378:metabolism; D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism / Q000494:pharmacology*; D001549:Benzamides / Q000494:pharmacology; D063385:Cannabinoid Receptor Modulators / Q000378:metabolism / Q000494:pharmacology*; D002219:Carbamates / Q000494:pharmacology; D051545:Cyclooxygenase 1 / Q000378:metabolism; D051546:Cyclooxygenase 2 / Q000378:metabolism; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D063388:Endocannabinoids; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005989:Glycerides / Q000378:metabolism / Q000494:pharmacology*; D006867:Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D066298:In Vitro Techniques; D037102:Lectins; D037181:Lectins, C-Type / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D017538:Mesenteric Artery, Superior / Q000187:drug effects / Q000201:enzymology; D063065:Organophosphonates / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000378:metabolism / Q000494:pharmacology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011956:Receptors, Cell Surface; D014664:Vasodilation / Q000187:drug effects*; D014665:Vasodilator Agents / Q000378:metabolism / Q000494:pharmacology*; D000099252:Fatty Acid Amide Hydrolases
D000581:Amidohydrolases; D001095:Arachidonic Acids; D001549:Benzamides; D063385:Cannabinoid Receptor Modulators; D002219:Carbamates; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D016861:Cyclooxygenase Inhibitors; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D005989:Glycerides; D006867:Hydrolases; D037102:Lectins; D037181:Lectins, C-Type; D008565:Membrane Proteins; D063065:Organophosphonates; D053284:Polyunsaturated Alkamides; D011451:Prostaglandin-Endoperoxide Synthases; D011956:Receptors, Cell Surface; D014665:Vasodilator Agents; D000099252:Fatty Acid Amide Hydrolases; C023339:Clec10a protein, rat; C500528:cyclohexyl carbamic acid 3'-carbamoylbiphenyl-3-yl ester; C104810:methyl arachidonylfluorophosphonate; C424442:noladin ether; C088155:methanandamide; C094503:glyceryl 2-arachidonate; C496513:Ptgs1 protein, rat; C489691:Ptgs2 protein, rat; C078814:anandamide