Local Vasoconstriction in Postural Tachycardia Syndrome

描述（由申请人提供）：慢性体位不耐受在许多患者中表现为体位性心动过速综合征（POTS）。一种“低流量罐”（LFP）增加血管收缩，增加血管紧张素-II (Ang- II)，减少一氧化氮（NO）和增加活性氧（ROS）。我们假设LFP是由于Ang-II结合血管紧张素1型受体（AT1R）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的增加。ROS包括清除NO产生过氧亚硝酸盐的超氧化物和具有重要血管活性和交感作用的H2O2。全文分为两部分：第一部分探讨Ang-II增加的原因；第二项研究考察了Ang-II对氧化应激、交感神经活动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。研究还将探讨肌肉交感神经活动（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。我们将通过比较LFP患者（N=30）、正常血流罐患者（N=30）和健康志愿者（N=30）来验证这一假设，回答以下问题：1)LFP皮肤微血管NO缺乏是否由Ang-II/氧化酶诱导的氧化应激引起？实验采用皮内微透析探针、激光多普勒血流仪和no依赖的局部加热反应来测量皮肤中的Ang- ii和Ang-(1-7)，并检测罗布麻素/别嘌呤醇对NADPH氧化酶/XO的阻断作用，以及tempol/ebselen对超氧化物/H2O2的还原作用。皮内ROS采用导管内超氧化物和过氧亚硝酸盐反应测定，H2O2采用荧光分光光度法测定。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NO，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NOS异构体是否与LFP有关？皮肤穿刺活检将检测nos -异构体、AT1R和AT2R、ACE2和ACE mRNA表达和蛋白含量。3)中枢交感神经激活和神经血管转导如何导致血管收缩？腓骨微神经造影、腘动脉超声和自发血压振荡将用于评估MSNA、气压反射活性以及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患者的交感神经活动、压力反射功能和直立耐受？中枢和周围神经血管的影响将被检查。5)氯沙坦慢性阻断AT1R能否恢复交感神经活动、压力反射功能和直立耐受性？将对慢性口服氯沙坦治疗LFP进行双盲安慰剂对照研究，并重新评估其对MSNA、压力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. PUBLIC HEALTH RELEVANCE: Chronic orthostatic intolerance due to the postural tachycardia syndrome (POTS) affects over a million Americans, mostly young women, who are prevented from gainful employ or school attendance. While a rapid heart rate (tachycardia) is the hallmark of the illness, patients often have activation of the sympathetic nervous system which remains unexplained. In the current proposal we will perform sophisticated tests of the circulation and nervous systems to study the causes and mechanisms in these patients and we will test drug treatments.