Infarct limitation of the second window of protection in a conscious rabbit model.
OBJECTIVE
Myocardial protection associated with ischemic preconditioning (PC) wanes within an hour or two. It has recently been observed, however, that a delayed phase of protection appears about 24 h after ischemic PC in anesthetized rabbits and dogs which might be related to synthesis of cytoprotective proteins. We tested whether a second window of protection could be induced in conscious rabbits.


METHODS
Rabbits chronically instrumented with a coronary artery occluder and ECG electrodes experienced a 30-min coronary occlusion followed by 3 h reperfusion. Infarct size was measured with triphenyltetrazolium chloride.


RESULTS
35.7 +/- 2.3% of the risk zone infarcted in control animals. PC with 4 cycles of 5-min coronary occlusion/10-min reperfusion 24 h prior to the 30-min ischemia decreased infarction to 24.1 +/- 1.4% of the risk zone (P < 0.01). During the 30-min occlusion 3 of 7 non-PC rabbits developed ventricular fibrillation, while this arrhythmia did not occur in the 7 PC animals (P < 0.1). Myocardial hsp70 content in PC rabbits was twice that in controls. Collateral blood flow was not different in the two groups.


CONCLUSIONS
A second window of protection exists in conscious rabbits which minimizes both infarction and arrhythmias, and cytoprotective protein content is increased in the myocardium of protected animals.
Yang
X M
XM
Department of Physiology, University of South Alabama College of Medicine, Mobile 36688, USA.
Baxter
G F
GF
Heads
R J
RJ
Yellon
D M
DM
Downey
J M
JM
Cohen
M V
MV
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D009203:Myocardial Infarction / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control; D017202:Myocardial Ischemia / Q000378:metabolism*; D015425:Myocardial Reperfusion; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D011817:Rabbits; D013997:Time Factors
D018840:HSP70 Heat-Shock Proteins