Alterations And Mechanisms Of CNP And Its Receptor During Exercise Preconditioning-induced Cardioprotection

Objective:exercise preconditioning (EP) has a strong Cardioprotective ffect to heart, and its effect has been confirmed. The mechanisms of EP ill under discuss. C type natriuretic peptide (CNP) is a vasodilatory olypeptide. CNP plays a very important role in functional homeostasis of ardiovascular system, through the combination of its receptor B type atriuretic peptide receptor (NPR-B). In this study, under the background of P, we probed the cardioprotection of EP on a sustained high-intensity xercise, and emphasized CNP and its receptor as a key mediator refered to P. So that we can afford new evidences to EP induced cardioprotection and pdate the theoretical basis for development of training programs.Methods:150 adult male Sprague-Dawley rats were randomly assigned nto 6 groups as a Group for comparison (Group C); high-intensity exercise HE); early exercise preconditioning group (EEP); late exercise reconditioning group (LEP); early exercise preconditioning plus high xercise group (EEP+HE); late exercise preconditioning plus high exercise roup (LEP+HE). EEP and LEP were subjected to a high-intensity interval xercise protocol, as EP model. Useing a high-intensity treadmill exercise eads to exercise-induced myocardial injury. Then the lever of cTnI was letected by chemiluminescent immunoassay. HE staining was used to )bserve the changes in ventricular structure. Hematoxylin-basic ’uchsin-picric acid (HBFP)staining and Chromotrope 2R-Brilliant green 2R) staining were evaluated the degree of myocardial ischemia/hypoxia. The change of CNP in plasma was detected by enzyme inked mmunosorbent assay. Expression of CNP mRNA in left ventricular of rats vas detected by Real-time PCR assay. The change of CNP in myocardium vas detected by immunohistoChemistry and Western blot. Expression of NPR-B was detected by immunofluorescence and Western blot.Results:1. Myocardial injury and the degree of protection:compared with roup C, a significant increase in HE group plasma cTnl levels, cardiac issue shows large flake crimson hypoxic-ischemic change(P<0.05). compared with HE group, EEP+HE and LEP+HE group plasma cTnl levels were significantly reduced, the area of myocardial ischemia and tissue hypoxia significantly reduced(P< 0.05).2. The plasma CNP levels: compared with HE group, EEP+HE and LEP+HE group CNP plasma levels were significantly increased(P<0.05).3. CNP mRNA in situ hybridization of myocardial tissue:Within the group C myocardial tissue, CNP mRNA hybridization signal was brown small lump in endothelial cells and was yellow granules in myocytes. Compared with EEP and LEP group, EEP+HE and LEP+HE group CNP mRNA hybridization signal area significantly increased, integrated optical density was significantly higher (P< 0.05). Compared with EEP+HE group, LEP+HE group CNP mRNA hybridization signal area significantly increased, integrated optical density was significantly higher(P<0.05).4. The fluorescence quantitative PCR results: compared with EEP and LEP group, EEP+HE and LEP+HE group CNP mRNA levels were significantly increased(P< 0.05). Compared with EEP+HE group, LEP+HE group CNP mRNA levels were significantly increased(P< 0.05).5. CNP immunohistochemical results:In group C myocardial tissue, CNP immunoreactivity was brown granular, dispersed in cardiomyocytes and endothelial cells cytoplasm. Compared with C group, HE group, EEP and LEP group CNP immunoreactivity myocardial tissue area was larger, integrated optical density was significantly higher(P< 0.05). Compared with HE group, EEP+HE and LEP+HE group CNP immunoreactivity myocardial tissue area was larger, integrated optical density was significantly higher(P< 0.05). Compared with LEP group LEP+HE group CNP immunoreactivity myocardial tissue area was larger, integrated optical density was significantly higher(P<0.05).6. Western blot analysis of CNP in myocardial tissue:compared with group C, HE group CNP myocardial tissue levels tended to increase, but not a significant difference(P> 0.05); EEP and LEP group CNP myocardial tissue was significantly higher(P<0.05). Compared with HE, EEP+HE and LEP+HE group CNP levels were significantly increased in myocardial tissue(P< 0.05). Compared with LEP, LEP+HE group CNP levels were significantly increased in myocardial tissue(P<0.05).7. NPR-B immunofluorescence results in myocardial tissue:In group C myocardial tissue, NPR-B immunoreactivity was bright red, patchy distribution in the periphery of a small number of myocardial cell membrane. Compared with C group, HE group, EEP and LEP myocardial tissue area of NPR-B immune response significantly increased, integrated optical density was higher(P< 0.05). Compared with HE, EEP and LEP+HE group, EEP+HE group myocardial tissue area of NPR-B significantly increased the immune response, integrated optical density was significantly higher(P<0.05).8. Myocardial tissue NPR-B Western blot results:compared with group C, HE group, EEP group and LEP myocardial tissue NPR-B levels were significantly increased(P<0.05). Compared with HE group, EEP+HE and LEP+HE group myocardial tissue NPR-B levels were significantly increased(P< 0.05). Compared with EEP group, EEP+HE group myocardial tissue NPR-B levels were significantly increased(P<0.05). Compared with LEP group, LEP+HE group myocardial tissue NPR-B levels were significantly increased(P<0.05).Conclusion:1. EP can attenuate high-intensity exercise-induced myocardial injury in the early and the late phases of cardioprotection, especially during the early phase of EP.2. The increased level of plasma CNP involved in EP induced cardioprotection.3. Myocardial cells have the function of synthesis and secretion of CNP. EP can induce myocardium to produce CNP and NPR-B increase, and through CNP/NPR-B pathway to mediate EP early and late phase cardioprotection.4. EP can improve cardiac tissue CNP mRNA levels, and promote CNP expression. CNP can bind myocardial NPR-B and through autocrine or paracrine way to act early and late cardioprotection.