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1 Experimental Research Laboratory, Section of Cardiology, Department of Medicine, Baylor College of Medicine, Houston, Texas 77030; 2 Experimental Research Laboratory, Division of Cardiology, University of Louisville, Louisville, Kentucky 40292; and 3 Department of Biomedical Sciences, College of Allied Health, University of South Alabama, Mobile, Alabama 36688
Previous studies in conscious pigs have
demonstrated that a sequence of ten 2-min coronary occlusion/2-min
reperfusion cycles renders the heart relatively resistant to myocardial
stunning 24 h later [late preconditioning (PC) against
stunning] by an unknown mechanism. Since oxygen radicals
contribute importantly to myocardial stunning and since antioxidant
enzymes have been reported to be upregulated 24 h after PC in dogs and
rabbits, we tested the hypothesis that late PC against stunning is
related to an increase in endogenous antioxidant defenses. Chronically instrumented conscious pigs underwent a sequence of ten 2-min coronary
occlusion/2-min reperfusion cycles (preconditioned group, n = 11) or received no intervention
(control group, n = 5). Twenty-four hours later, pigs were killed and the myocardial levels of Mn superoxide dismutase (SOD), Cu-Zn SOD, catalase, glutathione (GSH) peroxidase, GSH reductase, GSH, GSH disulfide,
-tocopherol, and ascorbate were measured. There were no
differences in any of the enzymatic or nonenzymatic antioxidants
between the ischemic and nonischemic regions in the preconditioned
group or between the control and the preconditioned group. Thus, when a
marked protection against stunning was present (24 h after PC), no
alteration in antioxidant defenses was observed. These results indicate
that, in conscious pigs, late PC against myocardial stunning is not mediated by increased endogenous antioxidant defenses, thereby refuting
one of the major current hypotheses regarding this phenomenon.
superoxide dismutase; catalase; glutathione peroxidase; glutathione reductase; tocopherol; ascorbate
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