title: The protection of ischaemic preconditioning can be reinstated in the rabbit heart after the initial protection has waned.
abstract: OBJECTIVE
  Preconditioning the heart with 5 min of ischaemia followed by reperfusion renders the myocardium resistant to infarction from subsequent ischaemia. This protection lasts for about 1 h. The aim of this study was to test whether the protection could be reinstated with a second episode of preconditioning after protection from an initial episode had worn off.
  
  
  METHODS
  To induce infarction animals experienced 30 min of coronary artery occlusion and then 3 h reperfusion. Ischaemic preconditioning was accomplished with 5 min of coronary branch occlusion. In one group of rabbits the subsequent reperfusion period was prolonged to 2 h to permit protection to wear off before the 30 min coronary occlusion was initiated. In another group a second 5 min coronary occlusion was performed at the end of the 2 h reperfusion. After 10 min of reperfusion the 30 min ischaemic period began. Control animals experienced only the 30 min ischaemia and 3 h reperfusion. Infarct volume was measured with tetrazolium and expressed as a percentage of the ischaemic zone volume.
  
  
  RESULTS
  Average infarct size in seven control rabbits [36.0 (SEM 2.0)% of the ischaemic zone] was not significantly different from that in eight rabbits with the prolonged coronary occlusion occurring 2 h after the preconditioning stimulus [28.6 (2.9)% infarction]. In contrast infarcts were significantly smaller in the re-preconditioned group of seven rabbits [8.3 (4.2)%] and comparable to those previously seen with a single preconditioning stimulus followed 10 min later by the 30 min occlusion [6.1 (1.8)%].
  
  
  CONCLUSIONS
  The rabbit heart can be protected with a second preconditioning stimulus after protection from an initial period of preconditioning has subsided.
authors.affiliation: University of South Alabama, College of Medicine, Mobile 36688.
authors.forename: X M
authors.initials: XM
authors.lastname: Yang
authors.forename: S
authors.initials: S
authors.lastname: Arnoult
authors.forename: A
authors.initials: A
authors.lastname: Tsuchida
authors.forename: D
authors.initials: D
authors.lastname: Cope
authors.forename: J D
authors.initials: JD
authors.lastname: Thornton
authors.forename: J F
authors.initials: JF
authors.lastname: Daly
authors.forename: M V
authors.initials: MV
authors.lastname: Cohen
authors.forename: J M
authors.initials: JM
authors.lastname: Downey
mesh_terms: D000818:Animals; D005260:Female; D008297:Male; D009203:Myocardial Infarction / Q000473:pathology / Q000517:prevention & control*; D017202:Myocardial Ischemia / Q000473:pathology; D015425:Myocardial Reperfusion / Q000379:methods*; D009206:Myocardium / Q000473:pathology; D011817:Rabbits; D013997:Time Factors