| Background: Hypertension is one of the most important risk factors of heart failure (HF). Hypertension can firstly cause left ventricular concentric hypertrophy (LVH), in which stage cardiac function was nearly normal. Then, with LVH progression, left ventricle dilates, gradually, and finally develop into hypertensive heart failure. Up to date, the mechanism of transition from hypertensive LVH to HF was not completely elucidated. Recently, the abnormal sympathetic nerve distribution and excitation-contraction coupling mechanism in heart failure progression have attracted a lot of attentions, but whether these two mechanisms play a role in the transition from LVH to HF remains unknown.Objective: In the present study, we want to investigate the differences of cardiac sympathetic nerve distribution and functional expression of excitation-contraction coupling related proteins among normotension (NT), LVH and HF, and the relationship between distributions of cardiac sympathetic nerve and the alterations of excitation-contraction coupling related proteins functional expression.Methods: Suprarenal abdominal artery constriction was done to prepare rabbit LV (n=16) and HF (n=12) models. Sham operation (Sham, n=14) rabbits were done the same operations but not caused the artery constriction. After that all rabbits were raised for 8 weeks. 8 weeks later, rabbits were randomly selected from Sham (n=8), LVH (n=8) and HF (n=2), and were determined their electrophysiological indexes in vitro Langendorff perfusion system. The rest rabbits were used to test the following procedures: measurement of cardiac dimensions and ejection fraction with echocardiogram, determination of hemodynamic indexes and serous ANP and NE concentration, quantification of hearts weight, determination of cardiac tissue cAMP concentration, quantificationcardiac collagen fraction and myocardial cross sectional area (MCSA) with picrosirius red staining. Immunohistochemical staining were done with anti-TH antibody to determine the distribution of sympathetic nerve. Proteins functional expression levels of & ARK1, LCC, RYR2, phosphorylated RYR2, FKBP12.6, PLB, phosphorylated PLB, SERCA2 were determined in Cardiac tissue with Western blot methods and corrected with 0 actin concentrations.Results: 8 weeks after the operation, the echocardiogram(Sham, n=14;LVH, n=16;HF, n=7) showed that, compared with those of Sham, Left atrial dimension (LAD), interventricular septum diastolic and systolic thickness (IVSDT, IVSST), left ventricular post wall diastolic and systolic thickness (LVPWDT > LVPWST) of LVH significantly increased (P<0.05), while the left ventricular end-diastolic and end-systolic dimension (LVESD ^ LVEDD), right ventricular dimension (RVD), left ventricular ejection fraction (LVEF) and fraction of area contraction (FAC) did not differ significantly. Compared with those of Sham, LAD, LVESD, LVEDD, RVD of HF increased significantly (P<0.05), and LVEF, FAC decreased significantly (PO.05), while IVSDT, IVSST, LVPWST and LVPWDT did not differ significantly. LAD, LVESD, LVEDD, RVD of HF were significantly higher than those of LVH (P<0.05), and LVEF, FAC, LVPWST of HF was significantly lower than those of LVH (P<0.05), while IVSDT, IVSST, LVPWDT of these two groups did not differ significantly.Hemodynamic examination (Sham, n=6;LVH, n=8;HF, n=5) showed that, the heart rate did not differ significantly among the all three groups. Compared with those of Sham, systolic blood pressure (SBP), diastolic blood pressure (DBP) and left ventricular pressure increasing and decreasing velocity (± dp/dtmax) of LVH were significantly increased (P<0.05), while left ventricular end-diastolic pressure (LVEDP) did not changed significantly. Compared with those of Sham, SBP and LVEDP of HF increased significantly (PO.05), and±dp/dtmax decreased significantly (P<0.05), while DBP did not changed significantly. SBP, DBP and ± dp/dtmax of HF were significantly lower than those of LVH (PO.05), while LVEDP were significantly increased in HF (PO.05).Cardiac weight revealed that, Compared with those of Sham, relative heart weight (H/BW), relative atrial weight (A/BW), relative left ventricular weight (LA/BW), relative ventricular weight (V/BW), relative left ventricular weight (LV/BW) of LVH were significantly increased (P<0.05), while relative right ventricular (RV/BW) did not changed significantly. Compared with those of Sham and LVH, H/BW, A/BW, LA/BW, V/BW, LV/BW and RV/BW of HF were increased significantly (PO.01).Plasmic ANP concentration was significantly increase in HF than those in Sham and LVH (PO.01), while those in the two latter groups did not differ significantly. Plasmic NE concentration was significantly increased in LVH and HF, and LVH and HF did not differ significantly. Compared with that of Sham, the concentration of cardiac tissue cAMP of LVH was slightly decreased, but did not have statistical significance. Compare with that of Sham, cAMP concentration of HF was significantly decreased (PO.Ol), while LVH and HF did not differ significantly in cAMP concentration.Electrophysiological indexes comparison between LVH and Sham showed that, pacing threshold, sinus cardiac circle, atrial-ventricular conduction wenckebach's circle length did not differ significantly, while left ventricular effective refractory period was significantly lower in LVH than that in Sham (P<0.01). In LVH group, 6 of 8 rabbits were induced into ventricular fibrillation (VF), while none of rabbit in Sham were induced into VF. The inducement rate of VF was significantly increased in LVH than that in Sham (/*<0.01).Compared with that of Sham, myocardial cross sectional area (MCSA) ofLVH and HF were significantly increased (PO.01), and the latter two groups did not differ significantly. Collagen volume fraction (CVF) and Arterial CVF in LVH and HF were significantly increased than that in Sham (PO.01), while the latter two groups did not differ significantly.Anti-TH sympathetic nerve immunohistochemical staining showed that, compared with those of Sham, left ventricular sympathetic nerve highest density and average density were significantly decreased in LVH (PO.05), while regional heterogeneity of left ventricular sympathetic nerve did not differ significantly. Compared with those of Sham, left ventricular sympathetic average density were significantly decreased in HF (PO.05), and the regional heterogeneity was significantly increased in HF(PO.05), while the highest density in these two groups did not differ significantly. Compared with those of Sham, the right ventricular sympathetic nerve highest density and average density of LVH and HF were increased slightly, but not statistical significantly. And the right ventricular sympathetic nerve regional heterogeneity of HF were significantly increased than that of Sham (PO.05), while that did not differ significantly between LVH and Sham.Western blot results showed that, compared with those of Sham, the protein levels of 0 ARK1, RYR2, phosphorylated RYR2, FKBP12.6 and PLB/SERCA2 of LVH increased significantly (PO.05), and protein levels of LCC, PLB, SERCA2 of LVH decreased significantly (PO.05), while relative RYR2 phosphorylation ratio, FKBP12.6/RYR2, phosphorylated PLB, relative PLB phosphorylation ratio did not differ significant between these two groups. Compared with those of Sham, the protein levels of P ARK1, phosphorylated RYR2, relative RYR2 phosphorylation ratio of HF were significantly increased (PO.05), and the protein levels of LCC, RYR2, FKBP12.6, PLB, phosphorylated PLB, SERCA2, PLB/SERCA2 of HF decreased significantly (PO.05), whileFKBP12.6/RYR2, relative PLB phosphorylation ratio did not differ significantly between these two groups. Compared those of LVH, the protein levels of LCC, RYR2, FKBP12.6, PLB and PLB/SERCA2 of HF decreased significantly (PO.05), and the protein levels of 3 ARK1, phosphorylated RYR2, FKBP12.6/RYR2, phosphorylated PLB, relative PLB phosphorylation ratio, SERCA2 of HF did not significantly differ from those of LVH, while the relative RYR2 phosphorylation ratio increased significantly in HF than that in LVH (P<0.05).Conclusions: Even though sympathetic nerve was activated in LVH and HF, the cardiac sympathetic nerve density decreased in LVH and HF, and the sympathetic nerve regional heterogeneity increased significantly in HF compared with that in Sham. The results that protein level of P ARK1 elevated and the concentration of cAMP decreased in LVH and HF, suggested that the function of P receptor pathway deceased in LVH and HF.The protein levels of PLB, phosphorylated PLB, SERCA2, LCC decreased in LVH and HF. The protein levels of RYR2, FKBP12.6, phosphorylated RYR2 significantly elevated in LVH, and the relative RYR2 phosphorylation ratio slightly increased, but had no statistical significance. The protein levels of RYR2, FKBP12.6 decreased significantly, while the protein level of phosphorylated RYR2 and the relative RYR2 phosphorylation ratio elevated significantly in HF compared with that in Sham. The relative RYR2 phosphorylation ratio was higher in HF than that in LVH. These above results suggested that the functional expression of RYR2 and FKBP12.6 differed significantly between LVH and HF, and this may be partly account for the mechanism of transition from LVH to HF.
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