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.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL074873-09
Application #
8490407
Study Section
Special Emphasis Panel (ZRG1-CVRS-E (02))
Program Officer
Maric-Bilkan, Christine
Project Start
2003-12-01
Project End
2014-06-30
Budget Start
2013-07-01
Budget End
2014-06-30
Support Year
9
Fiscal Year
2013
Total Cost
$387,086
Indirect Cost
$133,549
Name
New York Medical College
Department
Pediatrics
Type
Schools of Medicine
DUNS #
041907486
City
Valhalla
State
NY
Country
United States
Zip Code
10595
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Del Pozzi, Andrew T; Schwartz, Christopher E; Tewari, Deepali et al. (2014) Reduced cerebral blood flow with orthostasis precedes hypocapnic hyperpnea, sympathetic activation, and postural tachycardia syndrome. Hypertension 63:1302-8
Medow, Marvin S; Sood, Shilpa; Messer, Zachary et al. (2014) Phenylephrine alteration of cerebral blood flow during orthostasis: effect on n-back performance in chronic fatigue syndrome. J Appl Physiol (1985) 117:1157-64
Del Pozzi, Andrew T; Pandey, Akash; Medow, Marvin S et al. (2014) Blunted cerebral blood flow velocity in response to a nitric oxide donor in postural tachycardia syndrome. Am J Physiol Heart Circ Physiol 307:H397-404
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Stewart, Julian M (2013) Common syndromes of orthostatic intolerance. Pediatrics 131:968-80
Schwartz, Christopher E; Medow, Marvin S; Messer, Zachary et al. (2013) Spontaneous fluctuation indices of the cardiovagal baroreflex accurately measure the baroreflex sensitivity at the operating point during upright tilt. Am J Physiol Regul Integr Comp Physiol 304:R1107-13

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