Abstract: Objective: In order to provide the experimental basis for the prevention of exercise-induced cardiac injury, we evaluated the effects of nuclear factor erythroid-2-related factor2(Nrf2) on the changes of cardiac function and electrocardiogram in rats after exhaustive exercise. Methods: SD rats were randomly divided into 5 groups (n=6):control group (Con), exhaustied exercise group (EE), 6h, 12 h, 24 h recovery from exhaustied exercise group(EER6 EER12 EER24). The animal models of exercise-induced myocardial injury were established according to Thomas' method.Rats were forced to swim until they were exhausted.The electrocardiograms were recorded in conscious rats. Cardiac function of rats was recorded and analyzed by Millar pressure-volume system. The changes of catalase(CAT), glutathione peroxidase(GPX), Nrf2 and reactive oxygen speies(ROS) were detected by ELISA, respectively. Results: ①Compared with the control group and recovery groups(EER6, EER12, and EER24), the heart rate (HR), left ventricular end systolic pressure (Pes), arterial elasticity (Ea), the maximum rate of left ventricular pressure rise (dP/dt_max), peak rate of left ventricular pressure decline (-dP/dt_min) and left ventricular end diastolic pressure volume relationship curve slope (ESPVR) in the EE group decreased significantly, while left ventricular end diastolic volume (Ved), Pes, left ventricular end systolic volume (Ves), stroke volume, and Tau value increased significantly. Besides, HR, Pes, dP/dt_max, -dP/dt_min in recovery groups were significantly different with those in EE group, but there had no difference with those in the Con group. ②Compared with the control group, heart rate was increased, QT intervals were prolonged P wave, R wave and ST segments were increased in EE and recovery groups, but the changes of above-mentioned indexes in recovery groups had no statistical significant difference with those in EE group.③ Compared with the control group,the contents of ROS, Nrf2 were increased in EE group, while the content of GPX was decreased. Moreover, the content of CAT in EER6 group was the lowest in all groups. ④ The level of Nrf2 in serum was positively correlated with ROS and -dP/dt_min, and negatively correlated with HR, Ea. The level of ROS in Serum was positively correlated with EF, -dP/dt_min, and was negatively correlated with HR, Ea, dP/dt_max. Conclusion: Exhausted exercise caused changes of cardiac bioelectricity, impaired both the cardiac systolic and diastolic function, especially the diastolic disfunction. However, with recovery time after exhausted exercise prolonged, cardiac systolic and diastolic function recovered gradually, which was related to the reduced oxidative stress levels modulated by the increased Nrf2-induced changes of GPX and CAT.

Key words: cardiac function, acute exhaustive exercise, oxidative stress, Nrf2, rats