Abstract
To observe the effect of beta2-adrenergic agonist clenbuterol on ischemia/reperfusion (I/R) injury in isolated rat hearts and hydrogen peroxide (H2O2)-induced cardiomyocyte apoptosis. Isolated rat hearts were subjected to 30 min global ischemia and 60 min reperfusion on a Langendorff apparatus. Cardiac function was evaluated by heart rate, left ventricular end-diastolic pressure (LVEDP), left ventricular systolic pressure, maximal rise rate of left ventricular pressure [+dp/dt(max)], and the coronary effluent (CF). Lactate dehydrogenase (LDH) in the coronary effluent, malondialdehyde (MDA), superoxide dismutase (SOD), and Ca2+-ATPase activity in the cardiac tissue were measured using commercial kits. The apoptotic cardiomyocyte was detected by terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling (TUNEL) assay. Bax/Bcl-2 mRNA levels and the expression of caspase-3 were detected by RT-PCR and immunoblotting, respectively. Cultured newborn rat cardiomyocytes were preincubated with clenbuterol, and oxidative stress injury was induced by H2O2. Cell viability and cardiomyocyte apoptosis were evaluated by flow cytometry (FCM). In the isolated rat hearts after I/R injury, clenbuterol significantly improved diastolic function (LVEDP and CF) and Ca2+-ATPase activity. Treatment with clenbuterol increased SOD activity and decreased the MDA level and LDH release compared with the I/R group (P<0.05). Moreover, clenbuterol decreased apoptosis, which was associated with a reduction in TUNEL-positive cells, Bax/Bcl-2 mRNA, and caspase-3 expression. In H2O2-induced cardiomyocyte injury, clenbuterol increased cell viability and attenuated cardiomyocyte apoptosis. Pretreatment with ICI118551 (selective beta2-adrenergic antagonist) decreased these effects compared with the clenbuterol-treated group (P<0.05). Clenbuterol ameliorated ventricular diastolic function by enhancing Ca2+-ATPase activity and reduced oxidative stress and cardiac myocyte apoptosis in an experimental rat model of myocardium I/R. It decreased cardiomyocyte apoptosis induced by H2O2 in vitro. It plays a key role in the cardiac protection against myocardium I/R injury.
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