title: Xenon induces late cardiac preconditioning in vivo: a role for cyclooxygenase 2?
abstract: BACKGROUND
  Xenon induces early myocardial preconditioning of the rat heart in vivo, but whether xenon induces late cardioprotection is not known. Cyclooxygenase-2 (COX-2) has been shown to be an important mediator in the signal transduction of myocardial ischemic late preconditioning (i-LPC). We investigated whether xenon induces late preconditioning (Xe-LPC) and whether COX-2 activity and/or expression are involved in mediating this effect.
  
  
  METHODS
  Anesthetized male Wistar rats were instrumented with a coronary artery occluder. After 7 d of recovery, animals were randomized to 1 of 5 groups each containing 8 animals. The i-LPC group underwent 5 min of coronary occlusion to induce i-LPC. Xe-LPC was achieved by administration of xenon (70 volume%) for 15 min. Additional rats were pretreated with the COX-2 inhibitor NS-398 (5 mg kg(-1) body weight i.p.) with and without Xe-LPC. A group of sham operated animals not undergoing i-LPC or Xe-LPC served as controls (Con). After 24 h, all animals were anesthetized and underwent 25 min of myocardial ischemia induced by tightening of the coronary artery occluder followed by 2 h of reperfusion. Myocardial infarct size was assessed by triphenyltetrazolium chloride staining. In additional experiments, hearts were excised at different time points after preconditioning to investigate COX-2 mRNA and protein expression by polymerase chain reaction and infrared Western blot, respectively.
  
  
  RESULTS
  Both i-LPC and Xe-LPC reduced myocardial infarct size (% of the area at risk) compared with Con (i-LPC: 29 +/- 7%; Xe-LPC 31 +/- 8%, both P < 0.05 vs Con 64 +/- 6%). NS-398 abolished the cardioprotective effect of Xe-LPC (61 +/- 6%, P < 0.05 vs Xe-LPC). COX-2 mRNA and protein expression was only increased in the i-LPC group, but not in the Xe-LPC group.
  
  
  CONCLUSIONS
  Xenon induces late myocardial preconditioning that is abolished by functional blockade of COX-2 activity. In contrast to i-LPC, Xe-LPC did not lead to an increased expression of COX-2 mRNA and protein. These data suggest differences in COX-2 regulation in i-LPC and Xe-LPC.
authors.affiliation: Laboratory of Experimental Intensive Care and Anesthesiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Nina C
authors.initials: NC
authors.lastname: Weber
authors.forename: Jan
authors.initials: J
authors.lastname: Frässdorf
authors.forename: Christoph
authors.initials: C
authors.lastname: Ratajczak
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Grueber
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schlack
authors.forename: Markus W
authors.initials: MW
authors.lastname: Hollmann
authors.forename: Benedikt
authors.initials: B
authors.lastname: Preckel
mesh_terms: D000818:Animals; D051546:Cyclooxygenase 2 / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D006339:Heart Rate; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D009203:Myocardial Infarction / Q000517:prevention & control; D009578:Nitrobenzenes / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D013449:Sulfonamides / Q000494:pharmacology; D014978:Xenon / Q000494:pharmacology*
chemical_list: D009578:Nitrobenzenes; D012333:RNA, Messenger; D013449:Sulfonamides; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D014978:Xenon; D051546:Cyclooxygenase 2; C489691:Ptgs2 protein, rat