Interaction Between The Angiotensin Converting Enzyme Or Angiotensin Type 1 Receptor And NMDA Receptor In The Paraventricular Nucleus Contribute To Sympathoexcitation In Heart Failure

Interaction Between the Angiotensin Converting Enzyme or Angiotensin Type 1 Receptor and NMDA Receptor in the Paraventricular Nucleus Contribute to Sympathoexcitation in Heart FailureCongestive heart failure (CHF) is a malignant clinical symptom accompanied by decreased cardiac output and aggravated heart function in progress. It is the main complication of various kinds of cardiovascular disease especially in coronary artery disease. The elevated sympathetic nerve activity is the most important characteristic symptom of CHF, which is a major factor contributing to the worsen heart function of CHF. Inhibition of sympathoexcitation is the basic therapy for CHF. The mechanism(s) of it remained to be unresolved. It has been considered that left ventricular dynamics and overactive renin-angiotensin system are the cardinal manifestation of CHF. Recent studies pointed to a central mechanism that contributes to the vicious cycle of volume accumulation, elevated sympathetic nerve discharge and declining heart function in CHF. Central neurohumoral excitation induced a sympathetic dysfunction.The activation of sympathetic preganglionic neurons is controlled directly by the paraven-tricular nucleus (PVN) and the rostral ventrolateral medulla (RVLM). PVN of the hypothalamus is an important region that mediate sympathetic nerve outflow. The increased neuronal excitation accompanied by neurohumoral changes in PVN in HF rats. It will contribute to the aggravated heart function and increased sympathetic nerve activity. The renin-angiotensin system is a major component of the neuroendocrin system. ANGⅡ, the central member of RAS, carries out its functions via AT1 receptors. AT1 receptors and angiotensin converting enzyme have been identi-fyied in the PVN, RVLM and nucleus tractus solitarii(NTS). They may play an essential role in regulating sympathetic nerve activity and cardiovascular function. Injection of ANGⅡinto PVN induced an augment in renal sympathetic nerve activity (RSNA). And the brain ACE activity plays an important role in the baseline RSNA in normal rats.It is necessary for us to investigate the central mechanism(s) of CHF.A number of neurotransmitters in PVN play a key role in regulating sympathetic nerve activity and cardiovascular function. The glutamatergic system is the most important one. The increased glutamatergic mechanisms within the PVN induced the overacting of sympathetic drive in CHF. Functional studies have indicated that glutamatergic mechanisms in the PVN are involved in the accommodation of cardiovascular reflexes. It has been reported that functional NMDA receptor is one of the main subtype of ionotropic glutamate receptor, which was composed of at least one NR1 subunit in combination with one or more NR2 subunits. The function of NMDA receptor may be limited to NR1 subunit. Recent studies from Li et al found that in rat with CHF, stimulation of the NMDA receptor in the PVN has been shown to induce increased fire of renal sympathetic nerve. In contrast, microinjection of the NMDA receptor antagonist into the PVN caused significant decreases in BP, HR and RSNA in rats with HF. Furthermore, the norepinephrine level in the PVN was increased during heart failure and influe-nce sympathetic outflow. The basic RSNA is largely due to diminish in basal GABAergic synaptic activity. It is considered that the alterations in neuronal transmissions in the PVN of HF rats play a key role in the regulation of RSNA.In a vitro study, neurons was incubated with ANGⅡ, which have both AT1-R and NMDAR1.can be observed a dose-dependent increase in the expression of NMDAR1 protein, In addition losartan can prevent it, the expression of NMDAR1 can not be upregulated. ANGⅡcan promote the activation of neuronal mechanisms of glutamate, increase NMDAR1 protein expression, There may be interactions between RAS and GLU system in the central nervous systemThe purposes of the present study are:(1) investigate the changes of ACE and AT1-R within the PVN in CHF rats and their contribution to RSNA,these rats received different drug treatment through chronic PVN infusion via osmotic minipump after four weeks. (2) observe the changes of NMDAR1, TH and GAD67 in the PVN in CHF rats and their effects on RSNA. (3) through chronic PVN infusion with AT1-R antagonist, ACEI or AP5 via osmotic minipump, observe the changes of AT1-R or ACE in the PVN, the interaction between RAS and glutamate-ergic mechanisms and its influence on sympathoexcitation.ChapterⅠThe Changes of the Angiotensin Converting Enzyme and Angiotensin Type 1 Receptor in the Paraventricular Nucleus Contribute to Sympathoexcitation in Heart FailureAims:The elevated renin-angiotensin system and sympathetic nerve activity, with aggravated heart function are the cardinal manifestation of congestive heart failure (CHF). The paraventricular nucleus (PVN) of the hypothalamus is an important region that mediate sympathetic nerve outflow. The purposes of the present study are to investigate the expression changes of the angiotensin converting enzyme (ACE) and the angiotensin type 1 receptor (AT1-R) within the PVN in CHF rats and its contribution to RSNA. Methods:Adult male Sprague-Dawley rats weighing 230-250g were implanted with PVN cannulae. A week later, HF was induced by ligation of the left anterior descending coronary artery and SHAM rats underwent the same surgery but did not undergo coronary ligation. Subsequently, animals were PVN treated with the AT1-R antagonist Valsartan (0.05μg/h), ACE inhibitor Lisinopril (0.46μg/h) or vehicle (VEH,0.11μl/h) for 4 weeks. After 4 weeks, Left ventricular function was measured by the hemodynamic parameters. Renal sympathetic nerve discharge was recorded by electrophysiological techniques; Lung/body weight ratio (Lung/BW) and right ventricle/ body weight ratio (RVW/BW) was calculated; Immunohistochemical staining was used for expression of ACE in the hypothalamic paraventricular nucleus; Plasma NE and Angll content were measured using ELISA techniques; Fra-like and AT1-R protein levels of the hypothalamic paraventricular nucleus was measured with Western blot technique. Results:HF rats had a decrease in±dp/dtmax and LV ejection fraction (LVEF), a significant increase in left ventricular end diastolic pressure (LVEDP), sympathetic nerve activity,the expression of Fra-LI (markers of activated neurons), AT1-R and ACE in the PVN, and plasma angiotensinⅡ(ANGⅡ) and norepinephrine (NE) levels when compared with SHAM rats. In contrast, PVN treated with Valsartan or Lisinopril attenuated Fra-LI, AT1-R and ACE expression in the PVN compared with VEH-treated HF rats, and recovered cardiac function partly by elevating±dp/dtmax and reducing LVEDP. The treatment also decreased RVW/BW and lung/BW and reduced plasma levels of NE and ANGⅡ. Conclusion:These findings confirm that activated AT1-R and ACE in the PVN contribute to the increased sympathetic nerve activity and the pathophysiology of congestive heart failure.ChapterⅡThe Changes of NMDA Receptor in the Paraventricular Nucleus Contribute to Sympathoexcitation in Heart FailureAims:A number of neurotransmitters in the paraventricular nucleus (PVN) play a key role in regulating sympathetic nerve activity and cardiovascular function. The glutamatergic system is the most important one. Furthermore, the norepinephrine level in the PVN is increased and GABAergic synaptic activity was diminishe during heart failure and influence sympathetic outflow. The purposes of the present study are observe the changes of NMDAR1, TH and GAD67 in the PVN in congestive heart failure (CHF) rats and its contribution to sympathoexcitation in heart failure. Methods:Adult male Sprague-Dawley rats were implanted with PVN cannulae and HF was induced by ligation of the left anterior descending coronary artery and SHAM rats did not undergo coronary ligation. Subsequently, animals were PVN treated with the NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid (AP5,0.02μg/h) or vehicle (VEH,0.11μl/h) for 4 weeks. After 4 weeks, Left ventricular function was measured by the hemodynamic parameters. Renal sympathetic nerve discharge was recorded by electrophysiological techniques; Lung/body weight ratio (Lung/BW) and right ventricle/ body weight ratio (RVW/BW) was calculated; Immunohistochemical staining was used for expression of TH in the hypothalamic paraventricular nucleus; Plasma NE and Angll content were measured using ELISA techniques; NMDAR1 and GAD67 protein levels of the hypothalamic paraventricular nucleus was measured with Western blot technique. Results:HF rats had a decreased 67-kDa isoform of glutamate decarboxylase (GAD67), a significant increase in the expression of NMD A receptor subunit NR1(NMDAR1) and tyrosine hydroxylase(TH) in the PVN, and in plasma levels of norepinephrine (NE) and angiotensinⅡ(ANGⅡ) when compared with SHAM rats. In contrast, PVN treated with AP5 increased GAD67 in the PVN, and PVN treated with AP5 also attenuated NMDAR1 and TH in this region,reduced plasma levels of norepinephrine, angiotensinⅡ, and decreased LVEDP and increased±dp/dtmax. compared with VEH-treated HF rats. Conclusion:These results suggest that NMDAR1 in the PVN in HF is activated and contribute to the increased sympathetic nerve activity. Treatment with NMD A receptor antagonists will be a potential way to delay the process of HF.ChapterⅢInteraction between the Angiotensin Converting Enzyme or Angiotensin Type 1 Receptor and NMDA Receptor in the Paraventricular Nucleus Contribute to Sympathoexcitation in Heart FailureAims:The renin-angiotensin system is a major component of the neuroendocrin system. The angiotensin type 1 receptor (AT1-R) and the angiotensin converting enzyme (ACE) have been identified in the paraventricular nucleus (PVN) and play an essential role in regulating sympathetic nerve activity and cardiovascular function. The glutamatergic system in the PVN also play an important role in regulating sympathetic nerve activity and cardiovascular function. The purposes of the present study are retrieval whether the changes of AT1-R or ACE in the PVN contribute to the activation of glutamatergic mechanisms in congestive heart failure (CHF). And investigate the effect on renal sympathetic nerve activity (RSNA) or the influence to the progre-ssion of CHF. Methods:Adult male Sprague-Dawley rats were implanted with PVN cannulae and CHF was induced by ligation of the left anterior descending coronary artery and SHAM rats did not undergo coronary ligation. Subsequently, animals were PVN treated with AT1-R antagonist Valsartan(0.05μg/h), ACE inhibitor (ACEI) Lisinopril(0.46μg/h), the NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid (AP5,0.02μg/h)or vehicle (VEH, 0.11μl/h) for 4 weeks. After 4 weeks, Left ventricular function was measured by the hemodynamic parameters. Renal sympathetic nerve discharge was recorded by electrophysiological techniques; Lung/ body weight ratio (Lung/ BW) and right ventricle/ body weight ratio (RVW/ BW) was calculated; Immunohistochemical staining was used for expression of ACE and TH in the hypothalamic paraventricular nucleus; Plasma NE and AngⅡcontent were measured using ELISA techniques; Fra-like,AT1-R,NMDAR1 and GAD67 protein levels of the hypothalamic paraventricular nucleus was measured with Western blot technique. Results:HF rats had a decrease in±dp/dtmax, LV ejection fraction (LVEF) and 67-kDa isoform of glutamate decarboxylase (GAD67) in the PVN, a significant increase in left ventricular end diastolic pressure (LVEDP), sympathetic nerve activity, the expression of Fra-LI (markers of activated neurons), AT1-R, ACE, NMDAR1 and TH in the PVN, and plasma angiotensinⅡ(ANGⅡ) and norepinephrine (NE) levels when compared with SHAM rats. In contrast, PVN treated with Valsartan, Lisinopril or AP5 attenuated Fra-LI, AT1-R, ACE, NMDAR1 and TH in the PVN compared with VEH-treated HF rats, increased GAD67 in the PVN and recovered cardiac function partly by elevating±dp/dtmax and reducing LVEDP. The treatment also decreased RVW/BW and lung/BW and reduced plasma levels of NE and ANGⅡ. Conclusion:These results suggest that NMDAR1 in the PVN in HF is activated by increased AT1-R and ACE. Perhaps combination therapy with AT1-R antagonist or ACEI and NMDA receptor antagonist will be a effective way to delay the process of CHF.