title: Conscious rabbits become tolerant to multiple episodes of ischemic preconditioning.
abstract: Although ischemic preconditioning protects myocardium from infarction in isolated hearts and in anesthetized open-chest animals, its effects have not been examined in unanesthetized animals. Furthermore, it is unknown whether animals become tolerant to multiple episodes of ischemic preconditioning. Rabbits were chronically instrumented with a balloon occluder around a major branch of the left coronary artery for reversible coronary occlusion, a left atrial catheter for radioactive microsphere injections, ECG electrodes for monitoring of myocardial ischemia, and, in some cases, a carotid artery catheter for pressure measurements and timed withdrawal of reference arterial blood samples. Eight control rabbits underwent a 30-minute coronary occlusion and then 180 minutes of reperfusion. Five of the eight rabbits developed ventricular tachycardia or fibrillation during ischemia, and infarct size averaged 37.7 +/- 2.6% of the risk area. Eight rabbits experienced a 5-minute coronary occlusion and 10 minutes of reperfusion before the 30-minute occlusion. In these preconditioned animals, potentially fatal arrhythmias during ischemia were significantly reduced (one of eight, P < .05), and infarct size was much smaller (5.6 +/- 1.1%, P < .0001). The difference could not be explained by hemodynamics or collateral blood flow, which were nearly identical in the two groups. But when the 30-minute coronary occlusion was preceded by 40 to 65 five-minute occlusions during a 3- to 4-day period in seven animals, protection was markedly attenuated. Potentially lethal arrhythmias were very common, and infarct size averaged 26.5 +/- 2.9%, substantially larger than in rabbits with only one preconditioning occlusion (P < .0001).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Division of Cardiology, University of South Alabama College of Medicine, Mobile 36688.
authors.forename: M V
authors.initials: MV
authors.lastname: Cohen
authors.forename: X M
authors.initials: XM
authors.lastname: Yang
authors.forename: J M
authors.initials: JM
authors.lastname: Downey
mesh_terms: D000818:Animals; D003097:Collateral Circulation; D003250:Constriction; D006339:Heart Rate / Q000502:physiology; D009203:Myocardial Infarction / Q000473:pathology*; D017202:Myocardial Ischemia / Q000503:physiopathology*; D011817:Rabbits; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000209:etiology / Q000503:physiopathology