Calcium-dependent phospholipase A2 mediates the production of endothelium-derived hyperpolarizing factor in perfused rat mesenteric prearteriolar bed

• Published in: Journal of vascular research Vol. 35; no. 1; p. 27
• Main Authors: Adeagbo, A S, Henzel, M K
• Format: Journal Article
• Language: English
• Published: Switzerland 01-01-1998
• Subjects: Animals; Arachidonic Acid - metabolism; Arachidonic Acids - pharmacology; Arterioles - metabolism; Biological Factors - biosynthesis; Biological Factors - physiology; Calcium - pharmacology; Cyclohexanones - pharmacology; Endothelium, Vascular - metabolism; Endothelium, Vascular - physiology; Enzyme Inhibitors - pharmacology; Lipoprotein Lipase - antagonists & inhibitors; Lipoprotein Lipase - metabolism; Male; Mesenteric Artery, Superior - metabolism; Perfusion; Phospholipases A - antagonists & inhibitors; Phospholipases A - metabolism; Phospholipases A2; Rats; Rats, Sprague-Dawley; Vasodilation - drug effects
• ISSN: 1018-1172
• DOI: 10.1159/000025562

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.