Alteration Of Cardiac Troponin I During Cardioprotection Of Exercise Preconditioning

Objective: Exercise preconditioning(EP)can significantly alleviate the myocardial ischemia and hypoxia injury caused by long-term and intensive exercise by inducing endogenous protective effects on the heart.Cardiac biomarker cTnI has the characteristics of high specificity and sensitivity.It is an ideal index for detecting exercise-induced myocardial injury.Under the background of cardioprotection of exercise preconditioning,while taking cTnI as the research core,this study compared the characteristics of myocardial injury and protection on plasma cTnI and expression of cTnI in myocardial tissue,explored the relationship between plasma cTnI content and expression of cTnI in myocardial tissue of EP myocardial protection effect,and further explored the characteristics of ischemic and hypoxic injury site of exercise myocardium,so as to provide new evidence for myocardial protection of EP.Methods: 120 adult male Sprague-Dawley rats were randomly assigned into 6 groups,20 in each group,as a Group for comparision(Group C),early exercise preconditioning group(EEP group),late exercise preconditioning group(LEP group),exhaustive group(EE group),early exercise preconditioning + exhaustive group(EEP + EE group)and late exercise preconditioning + exhaustive group(LEP + EE group).EP model was established by a high-intensity intermittent treadmill exercise,and exhaustive myocardial injury model was established by a longtime high intensity treadmill exercise.hematoxylin-eosin staining(HE),chromotrope 2R brilliant green staining(C-2R-BG)and cTnI immunohistochemical staining were used to observe the location of myocardial ischemia-hypoxia injury,and to evaluate the extent of myocardial injury and protection,as well as the effect of ischemia-hypoxia injury on the expression of cTnI in tissues.The content and expression of cTnI in myocardial tissues were detected by cTnI immunohistochemistry and Western blotting.Chemiluminescence assay was used to detect plasma cTnI content,and the correlation between plasma cTnI content and tissue cTnI expression was analyzed to evaluate the relationship between them in the protective effect of EP on myocardium,so as to provide a new theoretical and experimental basis for the study of exercise-induced myocardial injury and protection.Results: 1.Evaluation of exercise-induced myocardial injury and the degree of protection: Compared with group C,plasma cTnI levels in EE group increased significantly,a large number of bright red positive areas appeared in myocardial tissue of EE group,and MOD value increased significantly(P < 0.05).There was no significant change between EEP group and LEP group.Compared with EE group,plasma cTnI levels in EEP+EE group and LEP+EE group decreased significantly,and the area of bright red positive areas in myocardial tissue decreased significantly,MOD value increased significantly(P < 0.05).Compared with EEP+EE group,the plasma cTnI content and MOD value of ischemia-hypoxia staining in LEP+EE group decreased significantly(P < 0.05).Interestingly,a large number of randomized observations under low power microscopy showed that the bright red positive areas of myocardial ischemia and hypoxia staining were mostly concentrated in the endocardium and papillary muscles.2.The results of adjacent sections staining: HE staining,C-2R-BG staining and cTnI immunohistochemical staining showed that exercise-induced myocardial ischemia and hypoxia injury could weaken the positive expression of cTnI immunoreactivity in tissues,and even lead to hypoinfection.3.Alteration of cTnI expression in myocardial tissue: Quantitative analysis of positive expression of cTnI immunohistochemical staining showed that compared with group C,there was no significant change in MOD value in EEP group and LEP group,while MOD value in EE group,EEP+EE group and LEP+EE group decreased significantly(P < 0.05),suggesting that exhaustive exercise resulted in the decrease of positive expression of cTnI in myocardial tissue.Compared with EE group,MOD in EEP + EE group and LEP + EE group increased significantly,suggesting that EP increased the expression of cTnI in myocardium after exhaustive exercise.However,the results of cTnI immunoblotting test showed that there was no significant difference between groups,but there was a downward trend in EE group.4.The relationship between plasma cTnI levels and the expression of cTnI in myocardium: The correlation analysis showed that after exhaustive exercise-induced myocardial injury,the expression of cTnI in myocardium decreased gradually with the increase of plasma cTnI levels.Conclusion: 1.Exercise-induced myocardial ischemia and hypoxia injury mostly occurs in the subendocardial myocardium.2.The effect of late exercise preconditioning on exhaustive myocardial ischemia and hypoxia injury is stronger than that of early exercise preconditioning.3.The increase of plasma cTnI after exhaustive exercise mainly comes from myocardial ischemia and hypoxia.