Exercise Preconditioning Induced Early And Late Phase Of Cardioprotection: Possible Role Of BNP And Its Receptors

Objective: A short-term high-intensity interval exercise known asexercise preconditioning (EP) have a strong protective effect to heart.Although the effect induced by EP has been confirmed, the underlymechanism of EP has not been elucidated. Brain natriuretic peptide (BNP)may play an important role in the mechanism of EP inducedcardioprotection, but the BNP specific mechanisms and changes are lacking.Therefore, this study probed the cardioprotection of EP on a sustainedhigh-intensity exercise, emphasized BNP as a key mediator refered to EP,disclosed the alteration of BNP and its receptors (natriuretic peptidereceptor, NPR) in early and late protective phase of EP, discussed therelationship between them, providing updated theoretical and experimentalbasis for the study cardioprotective effect and mechanism of EP.Methods:150healthy male SD rats were randomly divided into6groups:Control group (C), HE group took a sustained3h high-intensity treadmillexercise, establishing acute myocardial injury model of rats. EEP group wassubjected to a high-intensity interval exercise protocol on treadmill as EPmodel, sacrificed0.5h after EP. LEP group were subjected to an EPprotocol, sacrificed24h after EP. EEP+HE group took a sustained3hhigh-intensity treadmill exercise after0.5h of EP. LEP+HE group took asustained3h high-intensity treadmill exercise after24h of EP. Myocardialinjury was evlauated quantitatvely in terms of the plasma cardiac troponin I(cTnI), the myocardial ischemia/hypoxia area, and the integral poticaldensity (IOD) of hematoxylin basic fuchsin picric acid (HBFP)staining. Theplasma BNP and amino-terminal brain natriuretic precursor (NT-proBNP)levels was detected by Enzyme-linked immunosorbent assay. BNP, NPR-A,NPR-B, NPR-C mRNA expression in left ventricular of rats were detectedby Real-time PCR assay. BNP, NPR-A, NPR-B, NPR-C protein levels in leftventricular of rats were detected by Western blot. BNP, NPR-A, NPR-B,NPR-C protein distribution in mycardiaum of rats were observed byimmnohistochemistry. Results:(1) Compared with control group, HE group plasma cTnI levelswas significantly increased, myocardium displayed severe myocardialischemia and hypoxia. Compared with HE group, EEP+HE group and LEP+HE group plasma cTnI levels were significantly decreased andmyocardium of myocardial ischemia and hypoxia significantly decreased.(2)In HE group, BNP mRNA, BNP protein levels of left ventricular and BNPmyocardium immunoreactivity positive area and the IOD were significantlyincreased compared with gourp C. Plasma BNP levels were significantlyelevated and there was no significant difference of plasma NT-proBNPlevels in comparison to the C group. There was no significant difference ofthe left ventricular NPR-A、 NPR-C mRNA levels in HE group comparedwith group C. But NPR-B mRNA levels were significantly elevated in HEcompared with C. There was no significant difference of the left ventricularNPR-A protein levels in HE group and the NPR-B、 NPR-C protein levelswere significantly elevated and immunoreactivity positive area and the IODwere significantly increased compared with group C.(3) In EEP and LEPgroup left ventricular, there were significantly elevated of BNP mRNA andBNP protein levels immunoreactivity positive area and the IOD incomparison to the C group. Plasma BNP levels were significantly elevatedof EEP group, there was no significant difference of Plasma BNP levels inLEP group in comparison to the C group. There was no significantdifference of plasma NT-proBNP levels in comparison to the C group. InEEP and LEP group, there were significantly elevated of the NPR-A、NPR-B、NPR-C mRNA and there were significantly elevated of the NPR-A、NPR-B protein levels and immunoreactivity positive area,and NPR-Cprotein levels were significantly decreased,and immunoreactivity positivearea and IOD were significantly decreased in comparison to the C group.(4)Compared with group HE, left ventricular BNP mRNA levels weresignificantly elevated in group EEP+HE&LEP+HE, there was no significantdifference among BNP protein levels but BNP immunoreactivity positivearea and IOD were significantly elevated in group EEP+HE&LEP+HE.Compared with group HE, plasma BNP levels were significantly decreasedin LEP+HE group, plasma NT-proBNP levels were significantly decreasedEEP+HE. Compared with group HE, left ventricular NPR-A、 NPR-B、NPR-C mRNA levels were significantly elevated In EEP+HE&LEP+HE,NPR-A、NPR-B protein levels were significantly increased, but decreased ofthe NPR-C protein levels and immunoreactivity positive area and IOD.(5)In LEP+HE group, left ventricular BNP mRNA significantly elevated of but there was no significant difference of BNP protein levels, immunoreactivitypositive area and IOD compared with group EEP+HE. Compared with groupEEP+HE, group LEP+HE plasma NT-proBNP levels significantly increased.Compared with group EEP+HE, there were no significant difference ofNPR-A、 NPR-B mRNAin group LEP+HE,but NPR-C mRNA levels weresignificantly increased. Compared with group EEP+HE, there were nosignificant difference of left ventricular NPR-A、NPR-B、NPR-C proteinlevels in group LEP+HE, but NPR-B immunoreactivity positive area andIOD were significantly decreased NPR-C immunoreactivity positive areaand IOD were significantly increased in group LEP+HE.Conclusion： A duration of3h high-intensity treadmill exercise causedacute myocardial injury in rats.EP induces the early and late phasecardioproteciton attenuated myocardial injury cuased by3h high-intensitytreadmill exercise. EP could stimulate myocardium synthetise BNP andrelease into systemic circulation, exerting biological effects of BNP. EPincreased expressions of NPR-A and NPR-B in myocardium during the earlyand late phase of cardioprotective effect, reduced expressions of NPR-Ccaused by3h high-intensity treadmill training which indirectly reducedmyocardial cells in the upper reaches of BNP clearance rate, enhanced theeffect of BNP in heart, enhanced myocardial ischemia and hypoxia andoxidative stress tolerance.