title: Downregulation of endothelial nitric oxide synthase in rat aorta after prolonged hypoxia in vivo.
abstract: The goal of this study was to determine whether hypoxia alters expression of endothelial nitric oxide synthase (eNOS) in the systemic circulation. Rats breathed either air or 10% oxygen for 12 hours, 48 hours, or 7 days. Thoracic aortas were excised and either mounted in organ bath myographs or frozen in liquid nitrogen for later extraction of protein and RNA. eNOS protein (Western blotting) was decreased (20% of normoxic control) after 12 hours, 48 hours, and 7 days of hypoxia. eNOS mRNA (ribonuclease protection assay) was similarly reduced. Acetylcholine (10(-4) mol/L) reversed phenylephrine (10(-5) mol/L) preconstriction by 53.3+/-5.6% in aortic rings from normoxic rats and 26.1+/-4.8% in rings from rats exposed to hypoxia for 48 hours (P<0.05), with comparable impairment of relaxation by the calcium ionophore A23187 (10(-5) mol/L). Responses to diethylamine nitric oxide and 8-bromo-cGMP were unaffected. Aortic cGMP levels after incubation with acetylcholine (10(-6) mol/L) averaged 14.0+/-1.8 fmol/mg in rings from normoxic rats compared with 8.7+/-1.0 fmol/mg in rings from hypoxic rats (P<0. 05). Similarly, nitrate concentration (by capillary electrophoresis) in the media in which the rings were incubated was reduced in the hypoxic group (5.6+/-0.23 micromol/L for hypoxic rats and 7.8+/-0.7 micromol/L for normoxic rats). Impaired endothelial NO release may handicap the vascular responses that defend vital organ function during hypoxia.
authors.affiliation: Meakins-Christie Laboratories, McGill University, Montréal, Québec, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Toporsian
authors.forename: K
authors.initials: K
authors.lastname: Govindaraju
authors.forename: M
authors.initials: M
authors.lastname: Nagi
authors.forename: D
authors.initials: D
authors.lastname: Eidelman
authors.forename: G
authors.initials: G
authors.lastname: Thibault
authors.forename: M E
authors.initials: ME
authors.lastname: Ward
mesh_terms: D000818:Animals; D001011:Aorta / Q000201:enzymology* / Q000378:metabolism; D006152:Cyclic GMP / Q000096:biosynthesis; D015536:Down-Regulation; D004730:Endothelium, Vascular / Q000502:physiology; D000860:Hypoxia / Q000201:enzymology*; D008297:Male; D008969:Molecular Sequence Data; D009566:Nitrates / Q000097:blood / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014664:Vasodilation / Q000502:physiology
chemical_list: D009566:Nitrates; D012333:RNA, Messenger; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D006152:Cyclic GMP