Cardiac Sympathetic Nerve Norepinephrine Transporter And ?-adrenergic Receptor Internalization Of Rat Under Immobilization

Objectives:Stress cardiomyopathy is an acute serious cardiovascular adverse event induced by environment or mental factors,which receive great attention in recent years.The clinical manifestations is similar to acute coronary syndrome.Patients' plasma norepinephrine level and cardiac injury markers elevated,ventricular morphology appear apex ballooning.The exact pathogenesis is not fully clear at present.It's well accepted that abnormal sympathetic nerve activity is the key pathogenesis at present.Catecholamine release results in acute myocardial injury and blood vessel function change,which is the main inducement of SC.Besides,it is accepted that coronary artery spasm and microvascular dysfunction are associated with SC.The sympathetic nerve play important role in cardiovascular regulatory function via activating ?-AR in myocardial cells,the activation intensity of ?-AR have important influence on cardiac function.Norepinephrine transporter is located in nerve terminals,which has vital effect on regulating norepinephrine level in the synaptic cleft and terminating nerve impulse signal.It is learned that different subtypes of ?-AR in myocardium have different influence to cardiac function after stress,the uptake function of cardiac sympathetic nerve is abnormal in SC patients.However,the exact mechanism and the correlation between uptake function and ?-AR expression in myocardium is not fully clear.Therefore,we establish immobilization-stress cardiomyopathy model with rats to observe the neurotransmitter in cardiac sympathetic nerve—NET and ?-AR expression,which can explain the role of cardiac sympathetic nerve system changes in SC patients.1 Established SC model of SD rats by acute immobilization(13 rats in IMO group,13 rats in control group).2 Used Powerlab physiograph to monitor the change of electrocardiogram and hemodynamics,ultrasonic cardiogram to observe the change of cardiac morphology.3 Real-time polymerase chain reaction(real-time PCR)was performed to detect the NET mRNA expression in MC-SGC and ?-AR mRNA expression in heart.4 Western blot was used to detect the NET,?1-AR and ?2-AR protein expression in IMO group and control group.5 Myocardial tissue of left ventricular was cut into slices to observe the morphology of myocardial cell with haematoxylin-eosin staining.6 Enzyme-linked immno sorbent assay(ELISA)was performed to detect the plasma NE and cTnI levels after IMO 30 min and 2h.Results:1 General condition and echocardiogram:Body weight,left ventricle weight and heart weight of IMO group have no difference with control group.One rat in IMO group appeared apex ballooning,ventricle morphological change of the rest of IMO rats were not obvious.2 ECG monitoring:There were significant difference between two groups after IMO.RR interval,heart rate,Q amplitude,R amplitude and ST height of IMO groups were higher than control rats.3 Hemodynamic monitoring: There were significant difference between two groups after carotid artery intubations.Compared with control rats,left ventricle max pressure,mean pressure and ±dP/dt of IMO group were significantly elevated.4 In RT-PCR analyses,the NET mRNA expression in MC-SGC of IMO group was 6.81 times as much as the control group.The ?1-AR and ?2-AR mRNA expression in heart of IMO group were respectively 0.39 and 8.54 times as much as the control group.5 In western blot analyses,the sympathetic nerve total NET expression Methods: and cytoplasm NET expression in heart of IMO rats had no difference with control group,however,membrance NET of IMO rats reduced.The sympathetic nerve total ?1-AR expression and membrance ?1-AR in heart of IMO rats reduced,however,cytoplasm ?1-AR expression of IMO rats had no difference with control group.The sympathetic nerve total ?2-AR expression and membrance ?2-AR in heart of IMO rats increased,however,cytoplasm ?2-AR expression of IMO rats had no difference with control group.6 Inflammatory cell infiltration,myocardial cell edema and necrosis appeared in the heart of IMO rats with HE staining.7 In ELISA analyses,plasma NE and cTnI level of IMO group were elevated compared with control group after IMO 30 min.Plasma NE and cTnI level of IMO group were also elevated compared with control group after IMO 2h.Besides,the level of plasma cTnI of IMO group after IMO 2h was higher compared with 30 min.Conclusions:1 Stress cardiomyopathy model can be established by acute immobilization.2 Acute immobilization of rats result in plasma NE and cTnI levels elevating significantly,the level of plasma cTnI of IMO group after IMO 2h is higher compared with 30 min.Besides,inflammatory cell infiltration,myocardial cell edema and necrosis appear in the heart of IMO rats.3 The membrane NET expression on cardiac sympathetic nerve of IMO rats reduced,but the total and cytoplasm NET expression have no change,which show that the location of NET change and result in the abnormal NE reuptake ability.Meanwhile,the NET mRNA expression in MC-SGC elevated,it is considered the compensatory response to the location change.4 Acute immobilization of rats cause membrane ?1-AR and total ?1-AR expression on cardiac sympathetic nerve decreased,which can reduce myocardial toxic effects.The up-regulation of membrane ?2-AR and total ?2-AR expression on cardiac sympathetic nerve is beneficial to cardiac function.