Paraventricular Nucleus Angiotensin Ⅱ Contributes To Hypertension In Chronic Intermittent Hypoxia Rats Through Reactive Oxygen Species

BackgroundObstructive sleep apnea syndrome (OSAS) is a high incidence rate sleep disordered breathing disease in normal population, which is closely related to the occurrence of hypertension. The primary damage mechanism and pathophysiological features of OSAS include chronic intermittent hypoxia (CIH), sleep interruption and increased negative intrathoracic pressure, Where CIH is considered to be the main cause of hypertension. Recent studies have shown that the paraventricular nucleus (PVN) is an important nucleus in cardiovascular activity integration, Neurons in the PVN project to the intermediolateral cell column of the thoraco-lumbar spinal cord and the rostral ventrolateral medulla (RVLM), its dysfunction may be an important cause of CIH induced enhanced sympathetic nerve activity. Central reactive oxygen species (ROS) plays an important role in the increased sympathetic nerve activity when hypertension. Another important neurotransmitter that regulate blood pressure is brain angiotensin Ⅱ (Ang Ⅱ). Therefore, we hypothesized that ROS and Ang Ⅱ in PVN are closely related to hypertension induced by CIH.Aim(1) Ang Ⅱ-ROS pathway in PVN on the effect of blood pressure in chronic intermittent hypoxia rats;(2) To observe the effect of reducing the level of Ang Ⅱ in rats on hypertension induced by CIM, and to provide evidence for the prevention and treatment of hypertension induced by OSAS.MethodsMale SD rats were randomly divided into control group and CIH group (8 h/d,15 d), micro injection of PVN nucleus in rat brain by using brain stereotactic apparatus, mean arterial pressure (MAP) was measured by carotid artery intubation, and the content of Ang II and ROS in PVN was measured by ELISA method. The protein expression of angiotensin II type 1 receptor and NADPH oxidase 2 (NOX 2) were measured by Western Blot. The total superoxide dismutase (T-SOD) in PVN was measured by kit. The rat tail artery systolic blood pressure (SBP) was measured by using the tail cuff.1. The effect of chronic intermittent hypoxia on rat blood pressure The male SD rats were randomly divided as Control and CIH group. After 15 days of intermittent hypoxia, using the tail cuff measure two groups of rat tail artery blood pressure and observe the effect of CIH on rat blood pressure.2. The effect of CIH on PVN Ang II and its receptor The content of Ang II in Control and CIH group was measured by ELISA method, and the protein expression of Ang II type 1 receptor (AT1R) was detected by Western Blot.3. The effect of CIH on ROS, NOX 2 and T-SOD in PVN The content of ROS in PVN were measured by ELISA method, the protein expression of NOX 2 in PVN was detected by Western Blot and the activity of total superoxide dismutase (T-SOD) in PVN was measured by kit.4. The effect of bilateral PVN injection different concentration of Tempol on blood pressure in ratsRats were divided into Control group and CIH group, bilateral PVN microinjection different concentration of ROS scavenger Tempol (0.2 nmol,2 nmol,20 nmol) change ROS levels and observe the effect of acute changes in the PVN ROS levels on blood pressure in rats.5. The effect of bilateral PVN micro injection of Tempol on the function of Ang II Rats were divided into Control group and CIH group, respectively microinjection in bilateral PVN of Tempol (20 nmol), within 5 min reinjection of Ang Ⅱ (0.3nmol) to observe ROS on the effect of Ang Ⅱ.6. The effect of oral take Captopril (40 mg/kg/d) on blood pressure in rats Rats were divided into Control group, CIH group, Control+Cap group, CIH+Cap group. Rat tail artery systolic blood pressure (SBP) was measured by tail cuff at 1st,5th, 10th,15th days, respectively.7. The effect of oral take Captopril on Ang II and AT1R in PVN After 15 days CIH, the content of Ang II in each group was measured by ELISA method, and the protein expression of Ang II type 1 receptor (AT1R) was detected by Western Blot.8. The effect of oral take Captopril on ROS, NADPH Oxidase and T-SOD in PVN After 15 days CIH, the content of ROS in PVN were measured by ELISA method, the protein expression of NOX 2 in PVN was detected by Western Blot and the activity of total superoxide dismutase (T-SOD) in PVN was measured by kit.Results1. CIH can significantly increase blood pressure in rats;2. CIH can significantly increase the content of Ang II and ATIR protein expression in PVN;3. CIH can significantly increase The content of ROS and NOX 2 protein expression in PVN,T-SOD activity was significantly decreased;4. Microinjection of Tempol in bilateral PVN can reduce blood pressure in rats, and the CIH group decreased more significantly;5. Microinjection of Tempol in bilateral PVN could inhibit the boost effect induced by Ang II, and the inhibition of CIH group was more significant;6. Long-term administration of Captopril can reduce the blood pressure induced by the CIH, but can not be reduced to the normal level;7. Long-term administration of Captopril can significantly decrease the content of Ang II and its receptor protein expression in PVN compared with CIH group;8. Long-term administration of Captopril can significantly decrease the content of ROS and NOX 2 protein expression in PVN compared with CIH group.Conclusion(1) Angiotensin Ⅱ in paraventricular nucleus contributes to hypertension in chronic intermittent hypoxia rats. Which might partly mediated by reactive oxygen species.(2) Long-term administration of Captopril significantly inhibited blood pressure elevation in chronic intermittent hypoxia rats, which might be associated with Ang Ⅱ-ROS pathway in PVN.