Objective To observed the effects of X-ray irradiation on myocardial mitochondrial function and role of autophagy in mitochondrial injury.

Methods The rats were divided into sham-irradiation control group, irradiation group and irradiation+3-methyladenine(3-MA) group. Rat in sham-irradiation control group accepted no irradiation, while rat in irradiation group accepted local 20 Gy X-ray irradiation in the chest, the last group accepted 20 Gy X-ray irradiation prior to intraperitoneal injection 2 μl 3-MA. Western blot and real time PCR were used to detect the expression of LC3Ⅱ and Beclin 1 in protein and their mRNA levels. In vitro cardiac function was used to detect the changes of the left ventricular diastolic pressure(LVDP), the maximal rate of rise of pressure in the isovolumetric systolic left ventricle(+dP/dt_max)and the maximal rate of rise of pressure in the isovolumetric diastolic left ventricle(-dP/dt_max).

Results Compared with the sham-irradiation control group, there were the decreased of the LVDP, +dP/dt_max and -dP/dt_max at 21 d, and myocardial mitochondrial injury at 1 d after 20 Gy irradiation. The expression of LC3 and Beclin 1 in protein and mRNA levels increased significantly at 3 h, 6 h, 12 h, 1 d, 2 d, 4 d and 7 d after 20 Gy irradiation, up to peak at 6 h. Compared with irradiation group, intraperitoneal injection 2 μl 3-MA 30 min before irradiation, the expression of LC3Ⅱ and Beclin 1 in protein decreased significantly at 6 h after irradiation, there were the decreased of the LVDP, +dP/dt_max and -dP/dt_max at 14 d, then the irradiation group for 21 days.

Conclusion X-ray irradiation could injury myocardial mitochondrial function and induce autophagy in rat myocardial cell, which was an important factor of myocardial protection.