title: Cardioprotection by postconditioning in conscious rats is limited to coronary occlusions <45 min.
abstract: OBJECTIVE
  Brief episodes of ischemia and reperfusion after a lethal ischemic insult confer cardioprotection, a phenomenon termed "ischemic postconditioning." However, all studies reported to date have been conducted in open-chest animal models. We sought to determine whether postconditioning occurs in conscious animals and whether it protects against severe myocardial injury.
  
  
  METHODS
  Chronically instrumented rats were assigned to a 30- (Subset 1), 45- (Subset 2), or 60-min (Subset 3) coronary occlusion followed by 24 h of reperfusion. In each subset, rats received no further intervention (control), were preconditioned with 12 cycles of 2-min occlusion/2-min reperfusion immediately (early preconditioning; EPC) or 24 h (late preconditioning; LPC) before myocardial infarction, or were postconditioned with 20 cycles of 10-s occlusion/10-s reperfusion immediately after myocardial infarction (20-10 PostC).
  
  
  RESULTS
  With a 30-min occlusion, infarct size (54.4 +/- 2.3% of risk region in control-30) was significantly reduced in EPC-30, LPC-30, and 20-10 PostC-30 groups (by 72, 70, and 47%, respectively; all P < 0.05 vs. control-30). With a 45-min occlusion, infarct size (62.2 +/- 2.4% in control-45) was reduced in EPC-45 and LPC-45 groups (by 47 and 41%, respectively; all P < 0.05 vs. control-45) but not in the 20-10 PostC-45 group [55.4 +/- 2.3%, P = not significant (NS) vs. control-45]. With a 60-min occlusion, infarct size (72.7 +/- 2.2% in control-60) was reduced in the EPC-60 (by 20%, P < 0.05) but not in the LPC-60 (63.6 +/- 2.5%, P = NS) or in the 20-20 PostC group (71.5 +/- 3.4%, P = NS).
  
  
  CONCLUSIONS
  Both early and late ischemic preconditioning as well as ischemic postconditioning confer protection in conscious rats; however, unlike early preconditioning, postconditioning protects only against coronary occlusions <45 min. In the conscious rat, the cardioprotection afforded by postconditioning is limited to mild to moderate myocardial injury.
authors.affiliation: Division of Cardiology, Univ. of Louisville, Louisville, KY 40202, USA.
authors.forename: Xian-Liang
authors.initials: XL
authors.lastname: Tang
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sato
authors.forename: Sumit
authors.initials: S
authors.lastname: Tiwari
authors.forename: Buddhadeb
authors.initials: B
authors.lastname: Dawn
authors.forename: Qiuli
authors.initials: Q
authors.lastname: Bi
authors.forename: Qianhong
authors.initials: Q
authors.lastname: Li
authors.forename: Gregg
authors.initials: G
authors.lastname: Shirk
authors.forename: Roberto
authors.initials: R
authors.lastname: Bolli
mesh_terms: D000818:Animals; D003243:Consciousness; D003327:Coronary Disease / Q000503:physiopathology* / Q000517:prevention & control*; D003402:Creatine Kinase / Q000097:blood; D004562:Electrocardiography; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D009203:Myocardial Infarction / Q000473:pathology / Q000517:prevention & control; D015425:Myocardial Reperfusion; D011897:Random Allocation; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
chemical_list: D003402:Creatine Kinase