Calcium-dependent phospholipase A2 mediates the production of endothelium-derived hyperpolarizing factor in perfused rat mesenteric prearteriolar bed.
The isolated, perfused rat mesenteric bed releases a cytochrome P450-linked metabolite of arachidonic acid (AA) as endothelium-derived hyperpolarizing factor (EDHF) in response to acetylcholine and histamine. This study assessed the relative contribution of two AA-generating pathways, phospholipase A2 (PLA2) and diacylglycerol (DAG) lipase, to EDHF-mediated dilation of the rat mesenteric bed. We tested the hypothesis that PLA2-mediated release of AA is essential for the production of EDHF. Mesenteric beds were perfused with physiological salt solution (PSS) containing indomethacin and nitro-L-arginine methyl ester to block cyclooxygenase and nitric oxide synthase, respectively, and constricted with cirazoline (an alpha1-adrenoceptor agonist). Bolus applications of acetylcholine and histamine caused dose-dependent dilation of the constricted beds. The 85-kDa PLA2 inhibitor, arachidonyl trifluoromethyl ketone (AACOCF3), at 3 microM, profoundly blunted decreases in perfusion pressure initiated by 1 nmol acetylcholine (94.3+/-1.7%) and by 100 nmol histamine (88.5+/-3.3%) to 9.6+/-7.5 and 8.6+/-6.0%, respectively. AACOCF3 also blocked cirazoline-stimulated release of 6-keto-PG1alpha, but did not alter the vasodilation initiated by sodium nitroprusside (a nitric oxide donor), cromakalim (a K+ channel activator), or by Na+/K+-ATPase activation, as measured by KCl vasodilation in preconstricted beds perfused with K+-free PSS. The 14-kDa PLA2 inhibitor, oleyloxyethyl phosphorylcholine, also blocked EDHF vasodilation and also significantly inhibited K+ channel activity. Neither the Ca2+-independent PLA2 inhibitor, HELSS [E-6-(bromomethylene)-tetrahydro-3-(1-naphthalenyl)-2H-pyran-2-one], nor DAG lipase inhibitor, RHC-80267 [1,6-bis-(cyclohexyloximino-carbonylamino)-hexane] altered EDHF-mediated vasodilation. However, RHC-80267 blocked cirazoline-stimulated release of 6-keto-PGF1alpha. We conclude that Ca2+-dependent PLA2, rather than DAG lipase, generates the AA for the production of EDHF in the perfused rat mesenteric bed.
Adeagbo
A S
AS
Department of Physiology and Biophysics, School of Medicine, University of Louisville, Ky 40292, USA. ASADEA01@ULKYVM.LOUISVILLE.EDU
Henzel
M K
MK
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D001095:Arachidonic Acids / Q000494:pharmacology; D001160:Arterioles / Q000378:metabolism*; D001685:Biological Factors / Q000096:biosynthesis* / Q000502:physiology; D002118:Calcium / Q000494:pharmacology*; D003512:Cyclohexanones / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D017538:Mesenteric Artery, Superior / Q000378:metabolism*; D010477:Perfusion; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects
D001095:Arachidonic Acids; D001685:Biological Factors; D003512:Cyclohexanones; D004791:Enzyme Inhibitors; C067410:endothelium-dependent hyperpolarization factor; C081565:arachidonyltrifluoromethane; D016718:Arachidonic Acid; C036535:1,6-bis(cyclohexyloximinocarbonyl)hexane; D010741:Phospholipases A; D008071:Lipoprotein Lipase; D054467:Phospholipases A2; D002118:Calcium