Myocardial response to ischemia reperfusion injury in rats after X-ray irradiation

Objective: To observe myocardial tolerance to ischemia/reperfusion (I/R) injury in rats after exposure to X-ray irradiation. Methods: Twelve male rats were randomly divided into control group and radiation group. The rat model of radiation-induced heart disease was established in the radiation group by precordial irradiation with 20.0 Gy of 6 MV X-ray in a single fraction. At 14 days after model establishment, the Langendorff perfusion technique was performed in the two groups and the cardiac parameters including left ventricular developing pressure (LVDP), left ventricular end diastolic pressure (LVEDP), maximal rate of left ventricular pressure rise/fall (+/-LVdp/dt_max), and coronary flow (CF) were recorded. Myocardial infarct size after I/R was compared between the two groups by 2, 3, 5-triphenyltetrazolium chloride staining. Results: After 30 minutes of ischemia and 60 minutes of reperfusion, the irradiation group had a significantly slower CF than the control group (5.64 ± 0.35 vs.8.38 ± 0.52 ml/min, P = 0.002). Moreover, the irradiation group had substantially poorer recovery of cardiac function in isolated hearts compared with the control group, as shown by a significantly reduced LVDP (25.4 ± 2.31 vs. 52.76 ± 2.76 mm Hg(1 mm Hg = 0.133 kPa), P = 0.000), significantly reduced +/-LVdp/dt_max(547.04 ± 78.74 vs. 1100.05 ± 83. 35 mm Hg(1 mmHg = 0.133 kPa)/s, P = 0.001; -408.81 ± 56.74 vs. 813.62 ± 73.82 mm Hg(1 mm Hg = 0.133 kPa)/s, P = 0.002), and a significantly increased LVEDP (85.29 ± 4.61 vs. 65.65 ± 3.65 mm Hg (1 mm Hg = 0.133 kPa), 0.012). X-ray irradiation induced a significantly increased percentage of myocardial infarct size in rats (44.67% ± 0.95% vs. 30.46% ± 0.96%, 0.000). Conclusions: X-ray irradiation can induce coronary injury, reduce myocardial tolerance to I/R injury, and increase myocardial infarct size after I/R in rats. (authors)