Postconditioning attenuates myocardial ischemia-reperfusion injury by inhibiting events in the early minutes of reperfusion.
OBJECTIVE
We previously showed that brief intermittent ischemia applied during the onset of reperfusion (i.e., postconditioning) is cardioprotective in a canine model of ischemia-reperfusion. This study tested the hypothesis that the early minutes of reperfusion (R) during which postconditioning (Post-con) is applied are critical to its cardioprotection.


METHODS
In anesthetized open-chest rats, the left coronary artery (LCA) was occluded for 30 min and reperfused for 3 h. All rats were randomly divided into six groups: Control (n=8): no intervention at R; Ischemic preconditioning (IPC) (n=8): the LCA was occluded for 5 min followed by 10 min of R before the index occlusion; Post-con 1 (n=8): after LCA occlusion, three cycles of 10 s R followed by 10 s LCA re-occlusion were applied during the first minute of R; Post-con 2 (n=8): Six cycles of 10 s R and 10 s re-occlusion were applied during the first 2 min of R; Delayed Post-con (n=8): the ligature was loosened for full reflow for the first minute of R, after which the three-cycle Post-con algorithm was applied; Sham (n=6): the surgical procedure was identical to other groups, but the LCA ligature was not ligated.


RESULTS
Infarct size (TTC staining) was 23% smaller in Post-con 1 (40+/-2%*) than in Control (52+/-3%), confirmed by plasma creatine kinase activity (18+/-2* vs. 46+/-6 IU/g protein). There was no further reduction in infarct size with 6 cycles of Post-con (40+/-2.9%, p>0.05 vs. Post-con 1). Meanwhile, infarct size reduction was significantly greater in the IPC group (17+/-3%) than in Post-con1 (p<0.01). The plasma lipid peroxidation product malondialdehyde (MDA, microM/ml) was less after R in IPC and Post-con 1 (0.8+/-0.07* and 0.8+/-0.06*) vs. Control (1.21+/-0.08), consistent with a visual decrease in superoxide anion generation (dihydroethidium staining) in the AAR myocardium after 3 h of reperfusion. Neutrophil accumulation (myeloperoxidase activity, MPO, U/100 g tissue) in the AAR was less in IPC (1.4+/-0.3*) and Post-con 1 (2.5+/-0.3*) vs. Control (5.5+/-0.6). The reductions in infarct size, creatine kinase, MDA and DHE staining were lost with delayed Post-con, while MPO activity remained lower than in Control (3.2+/-0.4*).


CONCLUSIONS
(1) Post-con at onset of R reduces myocardial injury; (2) cardioprotection may be mediated, in part, by inhibiting oxidant generation and oxidant mediated injury; (3) the first minute of R in the rat model is critical to cardioprotection by Post-con; and (4) cardioprotection by Post-con may be independent of neutrophil accumulation in AAR. *p<0.05 Post-con vs. Control.
Kin
Hajime
H
Department of Cardiothoracic Surgery, The Carlyle Fraser Heart Center/Crawford Long Hospital, Emory University School of Medicine, Atlanta, GA 30308-2225, USA.
Zhao
Zhi-Qing
ZQ
Sun
He-Ying
HY
Wang
Ning-Ping
NP
Corvera
Joel S
JS
Halkos
Michael E
ME
Kerendi
Faraz
F
Guyton
Robert A
RA
Vinten-Johansen
Jakob
J
D000818:Animals; D003402:Creatine Kinase / Q000097:blood; D008297:Male; D008315:Malondialdehyde / Q000097:blood; D017202:Myocardial Ischemia / Q000097:blood / Q000473:pathology; D015425:Myocardial Reperfusion / Q000379:methods*; D015428:Myocardial Reperfusion Injury / Q000097:blood / Q000473:pathology / Q000517:prevention & control*; D009206:Myocardium / Q000201:enzymology / Q000473:pathology; D009195:Peroxidase / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley
D008315:Malondialdehyde; D009195:Peroxidase; D003402:Creatine Kinase