title: Endothelial nitric oxide synthase-independent release of nitric oxide in the aorta of the spontaneously hypertensive rat.
abstract: In the aorta of male spontaneously hypertensive rats (SHR), but not in that of normotensive Wistar-Kyoto rats (WKY), contractions to phenylephrine obtained in the presence of L-NAME [inhibitor of nitric oxide synthase (NOS)] and indomethacin (inhibitor of cyclooxygenase) are inhibited by an unknown endothelium-derived factor. The present study aimed to identify the mechanism underlying this endothelium-dependent inhibition in the SHR aorta. Aortic rings of male SHR and WKY, with and without endothelium, were suspended in organ chambers in the presence of indomethacin and L-NAME for the measurement of isometric tension. Contractions to phenylephrine were smaller in SHR aortae with endothelium than in those without, but were similar in the two types of preparations of WKY aortae. The endothelium-dependent, NOS-independent inhibition of phenylephrine-induced contraction was abolished by oxyhemoglobin [extracellular NO scavenger], carboxy-PTIO (NO scavenger) and ODQ (inhibitor of soluble guanylyl cyclase). It was unmasked not only by indomethacin but also by apocynin (antioxidant), but inhibited by diphenyleneiodonium (inhibitor of flavoproteins including cytochrome P450 reductase). The cytochrome P450 reductase protein expression was similar in SHR and WKY aortae. However, the level of nitrate and nitrite, substrates of cytochrome P450 reductase, were higher in SHR than WKY plasma and aortae. Therefore, in SHR but not WKY aortae, eNOS-independent NO is formed by cytochrome P450 reductase.
authors.affiliation: Department of Pharmacology and Pharmacy, University of Hong Kong, Hong Kong SAR, China.
authors.forename: Yingzi
authors.initials: Y
authors.lastname: Zhao
authors.forename: Paul M
authors.initials: PM
authors.lastname: Vanhoutte
authors.forename: Susan W S
authors.initials: SW
authors.lastname: Leung
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism*; D003022:Clotrimazole / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D004730:Endothelium, Vascular / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009566:Nitrates / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D009861:Onium Compounds / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D015398:Signal Transduction / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D009566:Nitrates; D009573:Nitrites; D009861:Onium Compounds; D014662:Vasoconstrictor Agents; D010656:Phenylephrine; D009569:Nitric Oxide; C007517:diphenyleneiodonium; D052250:Nitric Oxide Synthase Type III; D009251:NADPH-Ferrihemoprotein Reductase; D003022:Clotrimazole; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin