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 α1-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 µM, 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-PG1α, 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-PGF1α. We conclude that Ca2+-dependent PLA2, rather than DAG lipase, generates the AA for the production of EDHF in the perfused rat mesenteric bed.
The importance of nitric oxide (NO) and dilator prostaglandins in uterine resistance arterioles was investigated. In pentobarbital anaesthetized rats at dioestrus-2, the uterine microcirculation in vivo was transilluminated by a fibreoptic probe and microvessels (circumferential arterioles) viewed by video microscopy. Arteriolar diameters were measured while increasing concentrations of acetylcholine (ACh), serotonin (5-HT), phenylephrine (PE), or angiotensin II (AII) were applied topically (suffused) over the uterus. Agonists were applied alone or with ibuprofen (IBU; cyclooxygenase inhibitor), N\g=w\-nitro-L-arginine (L-NA; nitric oxide synthase inhibitor) or both. Circumferential arterioles were dilated by ACh and 5-HT (10\m=-\8\p=n-\10\m=-\4mol l \ m=-\ 1) and constricted by PE (10\ m=-\ 8\ p=n-\ 10\ m=-\ 5 mol l \m=-\1) and AII (10\ m=-\ 11\ p=n-\ 10\ m=-\ 7 mol l \ m=-\ 1).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.