Arachidonic acid metabolites, hydrogen peroxide, and EDHF in cerebral arteries

1 Cerebrovascular Research Laboratory, Department of Anesthesiology, and 2 Division of Cardiovascular Sciences, Department of Medicine and Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas Submitted 10 October 2004 ; accepted in final form 21 April 2005 We tested the hypotheses that EDHF in rat middle cerebral arteries (MCAs) involves 1 ) metabolism of arachidonic acid through the epoxygenase pathway, 2 ) metabolism of arachidonic acid through the lipoxygenase pathway, or 3 ) reactive oxygen species. EDHF-mediated dilations were elicited in isolated and pressurized rat MCAs by activation of endothelial P2Y 2 receptors with either UTP or ATP. All studies were conducted after the inhibition of nitric oxide synthase and cyclooxygenase with N -nitro- L -arginine methyl ester (10 µM) and indomethacin (10 µM), respectively. The inhibition of epoxygenase with miconazole (30 µM) did not alter EDHF dilations to UTP, whereas the structurally different epoxygenase inhibitor N -methylsulfonyl-6-(2-propargyloxyphenyl)hexanoic acid (20 or 40 µM) only modestly inhibited EDHF at the highest concentration of UTP. An antagonist of epoxyeicosatrienoic acids, 14,15-epoxyeicosa-5( Z )-enoic acid, had no effect on EDHF dilations to UTP. Chronic inhibition of epoxygenase in the rat with 1-aminobenzotriazol (50 mg/kg twice daily for 5 days) did not alter EDHF dilations. The inhibition of the lipoxygenase pathway with either 10 µM baicalein or 10 µM nordihydroguaiaretic acid produced no major inhibitory effects on EDHF dilations. The combination of superoxide dismutase (200 U/ml) and catalase (140 U/ml) had no effect on EDHF dilations. Neither tiron (10 mM), a cell-permeable scavenger of reactive oxygen species, nor deferoxamine (1 or 10 mM), an iron chelator that blocks the formation of hydroxyl radicals, altered EDHF dilations in rat MCAs. We conclude that EDHF dilations in the rat MCA do not involve the epoxygenase pathway, lipoxygenase pathway, or reactive oxygen species including H 2 O 2 . adenosine triphosphate; endothelium; endothelium-derived hyperpolarizing factor; epoxyeicosatrienoic acids; epoxygenase; hydroxyl radical; lipoxygenase; reactive oxygen species; superoxide anion; uridine triphosphate Address for reprint requests and other correspondence: R. M. Bryan, Jr., Dept. of Anesthesiology, Rm. 434D, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030 (E-mail: Rbryan{at}bcm.tmc.edu )