title: Deactivation of norepinephrine by peroxynitrite as a new pathogenesis in the hypotension of septic shock.
abstract: BACKGROUND
  Vascular hyporeactivity to catecholamines limits successful treatment of hypotension in septic shock. Large amounts of nitric oxide (NO) and superoxide anion (O(2)(-1).) are produced in response to bacterial endotoxins and/or inflammatory cytokines. NO reacts with O(2)(-1). to form the potentially toxic NO metabolite, peroxynitrite (ONOO(-1)). The purpose of this study was to investigate whether ONOO(-1) decreases the vasocontractile activity of norepinephrine.
  
  
  METHODS
  Norepinephrine was treated with ONOO(-1) or 3-morpholinosydonimine-N-ethyl-carbamine (SIN-1; an ONOO(-1) producer) in a 5 x 10(-2) m sodium phosphate buffer solution at pH 7.4, and absorbance of the product was measured spectrophotometrically at 295 and 370 nm. Norepinephrine pretreated with ONOO(-1) was administered to isolated rat thoracic aortas to observe contractions in functional experiments. The rate constant between norepinephrine and ONOO(-1) was determined via a competition assay with cysteine in functional experiments. Norepinephrine pretreated with ONOO(-1) was injected intravenously into anesthetized rats to measure blood pressure.
  
  
  RESULTS
  Norepinephrine pretreated with ONOO(-1) was confirmed spectrally as oxidized norepinephrine. Norepinephrine pretreated with ONOO(-1) decreased its vasocontractile force in an ONOO(-1) (10(-6), up to 3 x 10(-4) m) concentration-dependent manner (EC(50) = 5.1 x 10(-5) m). The decrease in its force was lower at pretreatment with ONOO(-1) in a lower pH buffer. A rate constant for the ONOO(-1)-norepinephrine reaction was 6 x 10(2) m/s. Norepinephrine (10(-7) m) incubated with SIN-1 (10(-3) m) decreased its vasocontractile force in an incubation time-dependent manner. Administration of norepinephrine pretreated with ONOO(-1) to anesthetized rats caused no significant change in arterial blood pressure.
  
  
  CONCLUSIONS
  These results indicate that norepinephrine was oxidized and deactivated by ONOO(-1). This deactivation may, at least in part, account for the hyporeactivities of vasocontraction to norepinephrine in septic shock.
authors.affiliation: Department of Anesthesiology and Reanimatology, Fukui Medical University, Fukui, Japan. takakura@fmsrsa.fukui-med.ac.jp
authors.forename: Ko
authors.initials: K
authors.lastname: Takakura
authors.forename: Wen
authors.initials: W
authors.lastname: Xiaohong
authors.forename: Kenji
authors.initials: K
authors.lastname: Takeuchi
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Yasuda
authors.forename: Satoru
authors.initials: S
authors.lastname: Fukuda
mesh_terms: D000758:Anesthesia; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001667:Binding, Competitive / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007022:Hypotension / Q000209:etiology / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D008981:Molsidomine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009638:Norepinephrine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D010084:Oxidation-Reduction; D030421:Peroxynitrous Acid / Q000633:toxicity*; D051381:Rats; D017208:Rats, Wistar; D012772:Shock, Septic / Q000150:complications / Q000503:physiopathology*; D014662:Vasoconstrictor Agents / Q000037:antagonists & inhibitors* / Q000494:pharmacology
chemical_list: D014662:Vasoconstrictor Agents; D030421:Peroxynitrous Acid; C002385:linsidomine; D008981:Molsidomine; D009638:Norepinephrine