Cardiac Sympathetic Nerve Remodeling In Heart Failure Rats And The Effect Of Hexarelin On It

Background and purpose:Chronic heart failure(CHF)is a serious clinical syndrome at the end of various cardiovascular diseases,and it is also the leading cause of death from cardiovascular diseases.It has become a major problem in the global medical field.CHF is characterized by decreased left ventricular pump function,increased activation of stress-related hormones,autonomic nervous disorders,cardiac structural remodeling(enlarged ventricular cavity,decreased myocardial cells,thinned ventricular walls and myocardial fibrotic),and cardiogenic cachexia(weight loss and muscle atrophy).The cardiac autonomic nervous system plays an important role in the process of heart failure.At present,a lot of research has been done on the pathogenesis and treatment of CHF.However,the mechanism of cardiac sympathetic remodeling during CHF is not fully elucidated.The literature and previous experimental results of our experimental group confirmed that Hexralin is a synthetic growth hormone-releasing peptide that binds to growth hormone secretagogue receptor(GHSR)1a and the non-GHSR receptor CD36 to exert cardioprotective effect.However,its cardioprotective effect and potential mechanism against chronic heart failure is yet to be demystified.Therefore,we established a rat model of heart failure to investigate the phenomenon of cardiac sympathetic nerve remodeling during CHF;Explore the cardioprotective mechanisms of Hexarelin against heart failure by changing the cardiac sympathetic nerve remodeling,improve the prognosis of CHF,and provide more theoretical basis for the study of the pathogenesis and treatment of chronic heart failure.Method:Eighty male healthy Sprague Dawley rats were randomly selected to form the control group(Ctrl,n=8).The HF model rats were induced via the permanent ligation of left anterior descending(LAD)coronary artery.The sham group underwent the same surgical produre except ligated.Four weeks after the surgery,the surviving ligated rats were separated into the heart failure group(HF,n=32)and the Hexralin intervention group(HF + Hx,n=32).HF + Hx rats were intervented with subcutaneous injection of Hexralin(100ug/kg/d),while the remaining groups were intervented with an equal volume of saline for 4 weeks.Electrocardiogram and echocardiography was used to evaluated left ventricular function in each group of rats;Cardiac pathological changes in each group of rats were observed by hematoxylin and eosin(HE)staining and Masson trichrome staining;The expression of BNP,NGF,TH and GAP43 were detected by immunohistochemical method(SABC);The positive expression level of protein BNP,NGF,TH and GAP43 ware detected and analyesd by Western blotting.Result:1.Heart function test results of experimental rats in each group:(1)The ECG of rats before operation was normal,the law was uniform,and the waveforms were complete;ECG of the rats showed ST-segment arches rising upwards.(2)ECG at 8 weeks after surgery showed:ECG of Ctrl and Sham group were normal;T wave inversion occurred in HF group and HF +Hx group,The inversed T wave of HF group was larger than 0.1 m V and some of rats in HF groups showed pathological Q wave.In the HF + Hx group,the T wave dropped closer to normal level,and the inverted T wave voltage was less than 0.1m V.(3)The results of echocardiography postoperatively showed that the activity of left ventricular in HF and HF+Hx groups were decreased.The movements of ventricular of HF group almost disappeared and left ventricle expanded clearly.Compared with the Ctrl and Sham groups,left ventricular end diastolic diameter(LVEDD),left ventricular end systolic diameter(LVESD),left ventricular end diastolic volume(LVEDV),and left ventricular end systolic volume(LVESV)were significantly increased(P<0.05);Left ventricular fractional shortening(LVFS)and left ventricular ejection fraction(LVEF)decreased significantly(P<0.05).LVEDD,LVESD,LVEDV and LVESV of the HF+Hx group were improved than that of HF group,LVFS and LVEF were increased(P<0.05).2.Cardiac pathological results:(1)HE staining test results: The myocardial tissues of Ctrl group and Sham group were stained evenly,and myocardial cells were arranged regularly.The left ventricular cardiomyocytes in the HF group showed increased myocardial damages that were characterized by myocardial cell loss and loss of cross striations of myocardial fibers,shows myocardial hypertrophy,myocardium fragmention,rupturing,and infiltration of inflammatory cells.These symptoms were improved in HF+Hx group.(2)Masson trichrome staining test results: Red color indicates normal tissues while blue color indicates collagen fibers.The myocardial tissues of the Ctrl group and the Sham group were red and no collagen fibers were deposited;A large area of blue staining was seen in the left ventricular myocardial tissue of the HF group,hyperplastic collagen fiber was obvious.Rats of the HF + Hx group was significantly attenuated the level of fiberssis or deposition of collagen compared with rats of the Ctrl group and the Sham group.3.Test results of immunohistochemistry:The positive expression of BNP protein was significantly increased in the HF group compared with the Ctrl group and the Sham group(P<0.05);the positive expression of the HF + Hx group was significantly decreased compared with the HF group(P<0.05).The positive expression of NGF protein was significantly reduced in the HF group compared with the Ctrl group and Sham group(P<0.05);the positive expression of the HF + Hx group was significantly increased compared with the HF group(P<0.05).The positive expression of TH protein was significantly reduced in the HF group compared with the Ctrl group and Sham group(P<0.05);the positive expression of the HF + Hx group was significantly increased compared with the HF group(P<0.05).The positive expression of GAP43 protein was significantly reduced in the HF group compared with the Ctrl group and Sham group(P<0.05);the positive expression of the HF + Hx group was significantly increased compared with the HF group(P<0.05).4.Western blot detection results:The expression of BNP protein was significantly increased in the HF group compared with the Ctrl group and Sham group(P<0.05);the expression of the HF + Hx group was significantly reduced compared with the HF group(P<0.05).The expression of NGF protein was significantly reduced in the HF group compared with the Ctrl group and Sham group(P<0.05);the expression of the HF + Hx group was significantly increased compared with the HF group(P<0.05).The TH protein expression was significantly reduced in the HF group compared with the Ctrl group and Sham group(p <0.05);the expression of the HF + Hx group was significantly increased compared with the HF group(P<0.05).The expression of GAP43 protein was significantly reduced in the HF group compared with the Ctrl group and Sham group(P<0.05);the expression of the HF + Hx group was significantly increased compared with the HF group(P<0.05).Conclusion:1.Chronic heart failure rats left ventricular myocardial NGF,TH and GAP43 protein expression down-regulated with sympathetic nerve remodeling.2.Hexarelin can effectively inhibit the decline of NGF,TH and GAP43 protein expression,improve cardiac sympathetic nerve remodeling and significantly improve cardiac function.Hint:Inhibiting cardiac sympathetic nerve remodeling may be one of Hexarelin’s important cardioprotective mechanisms.