Local Vasoconstriction in Postural Tachycardia Syndrome

描述(由申请人提供)：在许多患者中，慢性立位耐受性表现为体位性心动过速综合征(POTS)。一种类型的“低流量锅”(LFP)增加了血管收缩，伴随着血管紧张素-II(Ang-II)的增加，一氧化氮(NO)的减少，以及活性氧(ROS)的增加。我们推测，LFP是由于Ang-II与血管紧张素1型受体(AT1R)结合，激活NADPH氧化酶或黄嘌呤氧化酶(XO)产生ROS而引起的中枢交感神经活动或神经血管交感神经转导增加所致。ROS包括清除NO以产生过氧亚硝酸盐的超氧化物，以及发挥重要的血管活性和交感神经作用的过氧化氢。该提案包括两个部分：第一部分探索Ang-II增加的原因；第二部分研究Ang-II对氧化应激、交感神经活性和神经血管转导的影响。皮肤将继续作为替代组织来探索NO、Ang-II和ROS。研究还将探索肌肉交感神经活动(MSNA)、外周血流量和动脉血压之间的联系以及潜在的治疗方法。通过比较LFP患者(N=30)、正常血流盆患者(N=30)和健康志愿者(N=30)来验证这一假设，以回答以下问题：1)LFP中微血管NO缺乏是否由Ang-II/Oxx诱导的氧化应激引起？实验使用皮肤内微透析探头、激光多普勒血流仪和NO依赖的局部热反应来检测皮肤中的Ang-II和Ang-(1-7)，并观察用apocynin/别嘌呤醇阻断NADPH氧化酶/XO以及用temol/ebselen减少超氧化物歧化/过氧化氢的影响。用超氧化物和过氧亚硝酸根在皮内的反应测定皮内ROS，用荧光分光光度法测定过氧化氢。我们将在以后的实验中确定抗坏血酸钠和氯沙坦是否能改善皮肤一氧化氮，并将皮肤反应与静脉注射抗坏血酸和口服氯沙坦的全身反应联系起来。2)皮肤血管紧张素-II受体和一氧化氮合酶亚型是否与LFP有关？皮肤穿孔活检将测定一氧化氮合酶亚型、AT1R和AT2R，以及ACE2和ACE的mRNA表达和蛋白含量。3)中枢交感神经兴奋和神经血管转导如何参与血管收缩？将使用腓神经显微照相术、腓动脉超声和自发性血压振荡来评估MSNA、压力感受器反射活动以及MSNA对外周阻力的神经血管转导。4)静脉注射抗氧化剂抗坏血酸能否恢复LFP的交感神经活性、压力反射功能和立位耐力？将检查中枢和外周神经血管的影响。5)氯沙坦慢性阻断AT1R能否恢复交感神经活动、压力反射功能和立位耐力？慢性口服氯沙坦治疗LFP的双盲、安慰剂对照研究将重新评估其对MSNA、压力感受器反射和神经血管转导的影响。

DESCRIPTION (provided by applicant): Chronic orthostatic intolerance takes the form of postural tachycardia syndrome (POTS) in many patients. One type of "Low flow POTS" (LFP) has increased vasoconstriction associated with increased angiotensin-II (Ang- II), reduced nitric oxide (NO), and increased reactive oxygen species (ROS). We hypothesize that LFP is due to increased central sympathetic activity or neurovascular sympathetic transduction caused by Ang-II binding to angiotensin type 1 receptors (AT1R) activating NADPH oxidase or Xanthine oxidase (XO) to produce ROS. ROS include superoxide which scavenges NO to produce peroxynitrite, and H2O2 which exerts important vasoactive and sympathetic effects. The proposal comprises two parts: the first explores causes of increased Ang-II; the second examines effects of Ang-II on oxidative stress, sympathetic activity and neurovascular transduction. Skin will continue as a surrogate tissue to explore NO, Ang-II and ROS. Studies will also explore connections among muscle sympathetic nerve activity (MSNA), peripheral blood flow, and arterial BP as well as potential treatments. The hypothesis will be tested by comparing patients with LFP (N=30), to patients with normal flow POTS (N=30), and to healthy volunteers (N=30) to answer the following questions: 1) Is cutaneous microvascular NO deficiency in LFP caused by Ang-II/oxidase induced oxidative stress? Experiments use intradermal microdialysis probes, laser Doppler flowmetry, and the NO-dependent local heating response to measure Ang-II and Ang-(1-7) in the skin, and to examine the effects of NADPH oxidase/XO blockade with apocynin/allopurinol, and superoxide/H2O2 reduction with tempol/ebselen. Intradermal ROS are measured using intracatheter reactions of superoxide and peroxynitrite while H2O2 is assessed using fluorescent spectrophotometry. We will determine if sodium ascorbate and losartan improve cutaneous NO and will correlate skin responses with systemic responses to intravenous ascorbic acid and oral losartan in later experiments. 2) Do cutaneous angiotensin-II receptors and NOS isoforms contribute to LFP? Skin punch biopsies will determine NOS-isoform, AT1R and AT2R, and ACE2 and ACE mRNA expression and protein content. 3) How do central sympathetic activation and neurovascular transduction contribute to vasoconstriction? Peroneal microneurography, popliteal artery ultrasound, and spontaneous BP oscillations will be used to assess MSNA, baroreflex activity, and the neurovascular transduction of MSNA to peripheral resistance. 4) Can intravenous infusion of the antioxidant ascorbic acid restore sympathetic activity, baroreflex function and orthostatic tolerance in LFP? The central and peripheral neurovascular effects will be examined. 5) Can chronic AT1R blockade with losartan restore sympathetic activity, baroreflex function and orthostatic tolerance? A double blind, placebo controlled study of chronic oral losartan treatment in LFP will be performed with reassessment of its effects on MSNA, baroreflex, and neurovascular transduction.