Effects of age factors on hypothermia-induced reduction of ischemia-reperfusion injury in isolated rat hearts

Abstract

Objective To evaluate the effects of age factors on hypothermia-induced reduction of ischemia-reperfusion(I/R)injury in isolated rat hearts. Methods Pathogen-free healthy aged male Sprague-Dawley rats, aged 18-20 months, weighing 400-600 g, and young rats, aged 4-6 months, weighing 280-350 g, were used in the study.After the animals were anesthetized with intraperitoneal chloral hydrate and heparinized, their hearts were excised and perfused with K-H solution in a Langendorff apparatus.Twenty-four isolated hearts of aged rats were assigned into 2 groups(n=12 each)using a random number table: I/R group(group AI/R)and hypothermia group(group AH). Twenty-four isolated hearts of young rats were assigned into 2 groups(n=12 each)using a random number table: I/R group(group YI/R)and hypothermia group(group YH). Perfusion was suspended for 30 min followed by 120 min reperfusion to establish the model of I/R.The temperature was maintained at 37 ℃ during the whole process in AI/R and YI/R groups.The hearts were perfused with 34 ℃ K-H solution until 120 min of reperfusion starting from onset of reperfusion in AH and YH groups.At 30 min of equilibration(T0)and 15, 30, 60 and 120 min of reperfusion(T1-4), heart rate(HR), left ventricular developed pressure(LVDP), the maximum rate of increase in left ventricular pressure(+ dp/dtmax), and the minimum rate of increase in left ventricular pressure(+ dp/dtmin)were recorded.Six hearts from each group were randomly selected at T4, and myocardial specimens were obtained for determination of ATP, superoxide dismutase(SOD)and malondialdehyde(MDA)levels and myocardial infarct size(IS). Results Compared with group YI/R, HR was significantly decreased at T1-4, ATP and SOD levels were increased, and the MDA content and myocardial IS were decreased in group YH, and the HR, LVDP, + dp/dtmax and + dp/dtmin at T0 and ATP and SOD levels at T4 were significantly decreased, and the MDA content and myocardial IS were increased in group AI/R(P<0.05). Compared with group YH, HR, LVDP, + dp/dtmax and + dp/dtmin at T0 and ATP and SOD levels at T4 were significantly decreased, and the MDA content and myocardial IS were increased in group AH(P<0.05). Compared with group AH, the levels of ATP and SOD were significantly decreased, and the MDA content and myocardial IS were increased in group AI/R(P<0.05). Conclusion Age factors affect the efficacy of hypothermia in reducing I/R injury in isolated rat hearts, and hypothermia provides better cardioprotection for young rats than for aged rats. Key words: Age factors; Hypothermia, induced; Myocardial reperfusion injury