title: Preconditioning threshold of brief pressure overload of the left ventricle.
abstract: BACKGROUND
  We previously reported that pressure overload of the left ventricle reduced myocardial infarct (MI) size in rabbits. The threshold of pressure overload was investigated in this study.
  
  
  METHODS
  Pressure overload of the left ventricle was induced by partial snare of the ascending aorta in anesthetized, open-chest rabbits. Systolic left ventricular pressure (SLVP) was elevated 50% or 30% above baseline value by varying the degree of partial snaring. Different duration of pressure overload, including 10 minutes, 5 minutes, 3 minutes, or 2 minutes, was applied to determine the threshold of protective effects. Ischemic preconditioning was elicited by two 10-minute coronary artery occlusions and reperfusions. Ten minutes after different pretreatment, 1 hour occlusion of the left anterior descending coronary artery followed by 3 hours reperfusion was done to induce MI. The size of area at risk and MI were determined by blue dye injection and triphenyl tetrazolium chloride staining after experiments.
  
  
  RESULTS
  Pressure overload increase of SLVP 50% above baseline value for 10 minutes, 5 minutes, and 3 minutes significantly reduced MI size (18.5 ± 3.6%, 21.4 ± 1.9% and 21.6 ± 1.7%, respectively, vs. 26.6 ± 1.0% in the control group, mean ± standard deviation, p < 0.01). A 30% increase of SLVP by pressure overload for 10 minutes, 5 minutes and 3 minutes also significantly decreased MI size (20.5 ± 2.5%, 21.6 ± 2.3%, and 21.5 ± 2.3%, p < 0.01). Ischemic preconditioning significantly decreased MI size (19.9 ± 2.8%, p < 0.001). Pressure overload to elevate SLVP 50% or 30% above baseline value for 2 minutes did not significantly alter MI size (25.0 ± 2.3% and 26.0 ± 1.7%, p = 0.122 and p = 0.457). Two episodes of 2 minutes pressure overload did not significantly decrease MI size (25.0 ± 2.2% and 25.5 ± 2.2%, p = 0.118 and p = 0.281). The hemodynamics, area at risk, and mortality were not significantly different among all groups of animals.
  
  
  CONCLUSIONS
  Pressure overload to raise SLVP either 50% or 30% above baseline value reduced MI size. A minimum duration of 3 minutes was necessary to induce the protective effects.
authors.affiliation: Division of Cardiovascular Surgery, Department of Surgery, National Yang-Ming University School of Medicine, and Taipei Veterans General Hospital, Taipei, Taiwan, ROC.
authors.forename: Fei-Yi
authors.initials: FY
authors.lastname: Wu
authors.forename: Chen-Yuan
authors.initials: CY
authors.lastname: Hsiao
authors.forename: Chih-Pei
authors.initials: CP
authors.lastname: Ou-Yang
authors.forename: Chang-Chi
authors.initials: CC
authors.lastname: Lai
authors.forename: Yi-You
authors.initials: YY
authors.lastname: Wang
authors.forename: Zen-Chung
authors.initials: ZC
authors.lastname: Weng
authors.forename: Cheng-Hsiung
authors.initials: CH
authors.lastname: Huang
mesh_terms: D000818:Animals; D006352:Heart Ventricles; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods*; D009203:Myocardial Infarction / Q000517:prevention & control*; D011312:Pressure; D011817:Rabbits
keywords: ischemic preconditioning; left ventricular pressure overload; myocardial infarction; rabbits