Effect of exercise training on nitric oxide and superoxide/H2O2signaling
pathways in collateral-dependent porcine coronary arterioles
Wei Xie,2,3Janet L. Parker,1,3,4and Cristine L. Heaps1,2,4
1Michael E. DeBakey Institute for Comparative Cardiovascular Science and Biomedical Devices,2Department of Veterinary
Physiology and Pharmacology, Texas A & M University,3Department of Systems Biology and Translational Medicine,
4Cardiovascular Research Institute, The Texas A & M University Health Science Center, College Station, Texas
Submitted 6 October 2011; accepted in final form 6 February 2012
Xie W, Parker JL, Heaps CL. Effect of exercise training on nitric
oxide and superoxide/H2O2 signaling pathways in collateral-dependent
porcine coronary arterioles. J Appl Physiol 112: 1546–1555, 2012. First
published February 9, 2012; doi:10.1152/japplphysiol.01248.2011.—
Endothelial nitric oxide (NO) synthase (NOS) has been shown to
contribute to enhanced vascular function after exercise training. Re-
cent studies have revealed that relatively low concentrations of reac-
tive oxygen species can contribute to endothelium-dependent vasodi-
lation under physiological conditions. We tested the hypothesis that
exercise training enhances endothelial function via endothelium-
derived vasodilators, NO and superoxide/H2O2, in the underlying
setting of chronic coronary artery occlusion. An ameroid constrictor
was placed around the proximal left circumflex coronary artery to
induce gradual occlusion in Yucatan miniature swine. At 8 wk
postoperatively, pigs were randomly assigned to sedentary (pen-
confined) or exercise-training (treadmill-run: 5 days/wk for 14 wk)
regimens. Exercise training significantly enhanced concentration-
dependent, bradykinin-mediated dilation in cannulated collateral-
dependent arterioles (?130 ?m diameter) compared with sedentary
pigs. NOS inhibition reversed training-enhanced dilation at low bra-
dykinin concentrations in collateral-dependent arterioles, although
increased dilation persisted at higher bradykinin concentrations. Total
and phosphorylated (Ser1179) endothelial NOS protein levels were
significantly increased in arterioles from collateral-dependent com-
pared with the nonoccluded region, independent of exercise. The
H2O2 scavenger polyethylene glycol-catalase abolished the training-
enhanced bradykinin-mediated dilation in collateral-dependent arteri-
oles; similar results were observed with the SOD inhibitor diethyldi-
thiocarbamate. Fluorescence measures of bradykinin-stimulated H2O2
levels were significantly increased by exercise training, independent
of occlusion. The NADPH inhibitor apocynin significantly attenuated
bradykinin-mediated dilation in arterioles of exercise-trained, but not
sedentary, pigs and was associated with significantly increased protein
levels of the NADPH subunit p67phox. These data provide evidence
that, in addition to NO, the superoxide/H2O2 signaling pathway
significantly contributes to exercise training-enhanced endothelium-
mediated dilation in collateral-dependent coronary arterioles.
chronic coronary occlusion; ischemic heart disease; hydrogen perox-
AN IMBALANCE BETWEEN VASODILATOR and vasoconstrictor influ-
ences of endothelium is a critical consequence of the patho-
genic process of endothelial dysfunction, which is character-
ized by decreased vasodilation, a proinflammatory state, and
smooth muscle proliferation (2, 4). An important feature of this
altered vasoreactivity is impaired nitric oxide (NO) bioavail-
ability and/or elevated oxidant stress (22, 30). Previous studies
have shown that exercise training enhances endothelium-de-
pendent relaxation and endothelial NO synthase (eNOS)
mRNA expression and protein levels in coronary arteries and
arterioles of control animals (29, 45). Exercise training has also
been reported to enhance the contribution of NO and K?
channel activity to basal tone, as well as increase protein
content of eNOS and phosphorylated eNOS (Ser1179) in small
coronary arteries from pigs subjected to chronic coronary
artery occlusion/stenosis (19). Exercise training-induced im-
provements in vascular function have been shown to contribute
to enhanced myocardial perfusion and contractile function in
vascular disease states (16, 17). However, despite remarkable
evidence for therapeutic benefits of physical activity, the pri-
mary mechanisms by which regular exercise improves vascular
function in the setting of coronary artery disease have not been
While reactive oxygen species (ROS) have been implicated
in the development of clinical pathophysiology of the cardio-
vascular system, additional studies have suggested that, at
relatively low concentrations, ROS, such as superoxide and
H2O2, can function as physiological signaling molecules (8, 9,
11, 27). Furthermore, recent studies have revealed that inhibi-
tion of NADPH oxidase reduced bradykinin-induced superox-
ide and H2O2 production (26) and attenuated endothelium-
dependent dilation in human coronary arterioles (26) and rat
skeletal muscle arterioles (46). Interestingly, a small number of
recent reports indicate that the ROS H2O2may function as a
potential mediator of exercise training-induced adaptations in
vascular reactivity (46). Thus we sought to assess the contri-
bution of the NO and superoxide/H2O2signaling pathways to
exercise training-enhanced, endothelium-dependent dilation in
collateral-dependent coronary arterioles and to begin to explore
the underlying mechanisms that may contribute to adaptations
in these signaling pathways.
MATERIALS AND METHODS
Experimental animals and surgical procedures. All procedures
were in accordance with “Principles for the Utilization and Care of
Vertebrate Animals Used in Testing, Research and Training” and
were approved by the Institutional Animal Care and Use Committee
at Texas A & M University in accordance with the Association for the
Accreditation of Laboratory Animal Care procedures. In addition, all
protocols and methods conformed to the National Institutes of Health
(NIH) Guide for the Care and Use of Laboratory Animals [Depart-
ment of Health and Human Services Publication No. (NIH) 85-23,
Office of Science and Health Reports, Bethesda, MD]. Adult female
Yucatan miniature swine (Sinclair Research Center, Auxvasse, MO)
were surgically instrumented with an ameroid constrictor around the
proximal left circumflex coronary (LCX) artery, as described in detail
Address for reprint requests and other correspondence: C. L. Heaps, Dept. of
Physiology & Pharmacology, MS4466, College of Veterinary Medicine &
Biomedical Sciences, Texas A & M Univ., College Station, TX 77843 (e-mail:
J Appl Physiol 112: 1546–1555, 2012.
First published February 9, 2012; doi:10.1152/japplphysiol.01248.2011.
8750-7587/12 Copyright © 2012 the American Physiological Societyhttp://www.jappl.org1546
previously (21, 33). Animals were preanesthetized with glycopyrro-
late (0.004 mg/kg im), midazolam (0.5 mg/kg im), and ketamine (20
mg/kg im), and surgical anesthesia was induced with 3% isoflurane.
Animals were then intubated, and anesthesia was maintained with
2–3% isoflurane-balance O2 during aseptic surgery. During the sur-
gical procedure, animals received the following drugs as necessary:
pancuronium (0.1 mg/kg) or vecuronium bromide (0.1 mg/kg) and
lidocaine (1 mg/kg iv). Immediately following surgery, pigs received
ketoprofen (Ketofen, 3.0 mg/kg iv). Prior to surgery and during
surgical recovery, animals received buprenorphine hydrochloride (0.1
mg/kg iv) or butorphanol tartrate (0.5 mg/kg) every 3–6 h as needed
for pain relief. The antibiotic Naxcel (cetiofur sodium, 4 mg/kg im)
was administered 24 h before surgery, immediately prior to surgery,
and for 2 days following surgery. For the most efficient use of our
pigs, we utilize multiple tissue preparations (e.g., vascular, cardiac,
skeletal muscle, blood, and cerebral) from each animal, so that
numerous experiments can be conducted concurrently. Thus, while a
large number of pigs were used for the studies described here, we
make every effort to maximize the use of these animals.
Exercise training. At 8 wk postoperatively, animals were randomly
assigned to a sedentary (n ? 48) or an exercise-training (n ? 44)
group. Sedentary pigs were confined to their pens, while exercise-
trained animals underwent a progressive treadmill exercise-training
program, 5 days/wk for 14 wk, as described previously (12, 15, 20).
At termination, skeletal muscle citrate synthase activity and heart-to-
body weight ratio were measured to evaluate effectiveness of the
exercise-training regimen, as described previously (15, 21).
Preparation of coronary arterioles. After the 14-wk exercise-
training protocol or sedentary confinement, pigs were anesthetized
using xylazine (Rompun, 2.25 mg/kg im), ketamine (35 mg/kg im),
and pentothal sodium (30 mg/kg iv), and heparin was administered
(1,000 U/kg iv). Animals were intubated and ventilated with room air,
and a left lateral thoracotomy was performed in the fourth intercostal
space. Hearts were removed, placed in Krebs bicarbonate buffer
(0–4°C), and weighed. Visual inspection at the ameroid occluder
during dissection of the LCX artery indicated 100% occlusion in all
animals used in this study. With the aid of a dissection microscope,
size-matched arterioles (?130 ?m) were isolated from subepicardial
regions of the nonoccluded left anterior descending (LAD) artery and
the collateral-dependent LCX artery in areas free from infarct.
Microvessel cannulation and experimental protocols. Isolated ar-
terioles were transferred to a Lucite vessel chamber containing phys-
iological saline solution, cannulated, and pressurized for assessment
of vascular reactivity, as described in detail previously (18). Arterioles
underwent a 1-h equilibration period, during which the vessels estab-
lished a stable level of basal tone. Arterioles were further precon-
stricted with endothelin-1 until a preconstriction level of ?30–70% of
maximal diameter was attained. For experiments in which pharmaco-
logical inhibitors were utilized, arterioles were preconstricted to the
same level (?30–70%) using the inhibitor plus endothelin-1, as
previously described (18). Pharmacological inhibitors included the
NOS inhibitor N?-nitro-L-arginine methyl ester (L-NAME, 300 ?M),
the H2O2scavenger polyethylene glycol (PEG)-catalase (1,000 U/ml),
an inhibitor of SOD [diethyldithiocarbamate (DETC), 1 mM], and an
inhibitor of NADPH oxidase (apocynin, 100 ?M). Additional vehicle
control data were collected in the presence of the PEG compound at
the same concentration (2.5 mg/ml) used in the PEG-catalase studies.
Concentration-response curves were determined in response to cumu-
lative concentrations of bradykinin or nitroprusside. All drugs were
added directly to the tissue bath. Because our preliminary experiments
suggested that arterioles subjected to repeated exposures to bradykinin
exhibit tachyphylaxis, each arteriole underwent only a single concen-
tration-response curve to bradykinin in the absence or presence of
Immunoblots. Additional coronary arterioles (?100–150 ?m di-
ameter, 10–15 mm total length) were dissected from the nonoccluded
and collateral-dependent myocardial regions, quick-frozen in liquid
N2, and stored at ?80°C for immunoblot analysis. Arterioles were
homogenized in 40 ?l of 2? lysis buffer [20 mM Tris·HCl, 50 mM
NaCl, 0.1% Triton X-100, 1% each protease and phosphatase inhibitor
cocktails (catalog nos. 539131 and 524625, respectively, Calbio-
chem), and 3 mM EGTA] by freeze-thaw cycles and vortexed ap-
proximately six to eight times. Protein concentration was determined
by bicinchoninic acid protein assay kit (Pierce). Arteriole lysate (12
?g of total protein) was subjected to 12.5% SDS-PAGE, transferred to
polyvinylidene difluoride membranes, and probed overnight with
primary antibody, as described in detail previously (12). Primary
antibody dilutions were as follows: eNOS (1:250), phosphorylated
eNOS (Ser1179, 1:750), the NADPH oxidase subunits Nox1 (1.1
?g/ml), Nox2 (1:500), Nox4 (1:500), p47phox (1:1,250), and
p67phox (1:250), and ?-actin (1:5,000) at 4°C overnight. After
they were washed, the membranes were incubated with the appro-
priate horseradish peroxidase-conjugated species-specific anti-IgG
(diluted 1:50,000–1:100,000 depending on primary antibody) for 2
h at 25°C. Peroxidase activity was detected using SuperSignal
West Dura substrate. Scanning densitometry was used to quantify
signal density from luminograms. Normalization for potential
loading differences was accomplished using the ratio of densitom-
etry signals for proteins of interest to ?-actin.
Fluorescent detection of H2O2. In additional studies, bradykinin-
mediated changes in H2O2 were detected in real time with the
cell-permeable fluorescent indicator 5-(and 6)-chloromethyl-2=,7=-di-
chlorodihydrofluorescein diacetate (DCF). Pressurized coronary arte-
rioles (?100–150 ?m) were loaded intraluminally by delivery of
DCF (5 ?M) into the arteriole through a cannulating micropipette.
Flow was stopped, and the dye was incubated in the arteriole for 10
min. Flow was resumed for an additional 10 min to eliminate the
fluorescent indicator from the arterioles and perfusion pipettes. The
arteriole was allowed to equilibrate for an additional 10 min prior to
start of experimentation. Albumin-free solutions were utilized to
avoid potential interference with DCF fluorescence detection (47).
After equilibration, a region of interest was selected, and changes in
fluorescence intensity were observed (NIS Elements, Nikon) using an
epifluorescence microscopy system. Arterioles were excited with a
175-W xenon arc lamp with a 475-nm interference filter (Lambda
DG-4, Sutter Instruments). Fluorescence emission was captured at
515 nm every 30 s and reflected to an interline transfer, progressive-
scan, cooled charge-coupled device video camera (CoolSNAP HQ,
Photometrics) with a dichroic mirror. The microscope was equipped
with an ?10 oil immersion objective, numerical aperture of 0.3. Basal
fluorescence was obtained for 3 min; then arterioles were exposed to
bradykinin (10?12or 10?10M), and fluorescent images were acquired
every 30 s for 5 min. An equal number of arterioles from each of the
four vessel treatment groups received 10?12or 10?10M bradykinin.
Arterioles were exposed to exogenous H2O2, PEG-catalase, and
nitroprusside in various combinations to verify specificity of DCF.
Although DCF is oxidized by other peroxides in addition to H2O2,
other investigators have demonstrated complete inhibition of agonist-
stimulated fluorescence by addition of catalase (3, 24, 51).
Solutions and pharmacological agents. L-NAME, apocynin, PEG-
catalase, PEG, and DETC were purchased from Sigma. Endothelin-1
was purchased from Peninsula Laboratories. DCF was obtained from
Invitrogen. Primary antibodies against the following proteins were
utilized for these studies: eNOS (catalog no. 610297) and phosphor-
ylated eNOS (Ser1179, catalog no. 612392) purchased from BD
Biosciences; Nox1 (catalog no. abs5831) from Abcam; Nox4 (catalog
no. NB110-58851) and ?-actin (catalog no. NB400-501) from Novus;
and Nox2 (catalog no. SC-20782), p47phox (catalog no. SC-14015),
and p67phox (catalog no. SC-7662) from Santa Cruz Biotechnology.
Physiological saline solution contained 145 mM NaCl, 4.7 mM KCl,
2.0 mM CaCl2, 1.17 mM MgSO4, 3.0 mM MOPS, 1.2 mM NaH2PO4,
5.0 mM glucose, 2.0 mM pyruvate, 0.02 mM EDTA, and 1% bovine
serum albumin, pH 7.4.
Exercise, Occlusion, eNOS, Superoxide/H2O2 Signaling • Xie W et al.
J Appl Physiol • doi:10.1152/japplphysiol.01248.2011 • www.jappl.org
15. Griffin KL, Laughlin MH, Parker JL. Exercise training improves
endothelium-mediated vasorelaxation after chronic coronary occlusion. J
Appl Physiol 87: 1948–1956, 1999.
16. Hambrecht R, Adams V, Erbs S, Linke A, Krankel N, Shu Y, Baither
Y, Gielen S, Thiele H, Gummert JF, Mohr FW, Schuler G. Regular
physical activity improves endothelial function in patients with coronary
artery disease by increasing phosphorylation of endothelial nitric oxide
synthase. Circulation 107: 3152–3158, 2003.
17. Hambrecht R, Wolf A, Gielen S, Linke A, Hofer J, Erbs S, Schoene N,
Schuler G. Effect of exercise on coronary endothelial function in patients
with coronary artery disease. N Engl J Med 342: 454–460, 2000.
18. Heaps CL, Jeffery EC, Laine GA, Price EM, Bowles DK. Effects of
exercise training and hypercholesterolemia on adenosine activation of
voltage-dependent K?channels in coronary arterioles. J Appl Physiol 105:
19. Heaps CL, Mattox ML, Kelly KA, Meininger CJ, Parker JL. Exercise
training increases basal tone in arterioles distal to chronic coronary
occlusion. Am J Physiol Heart Circ Physiol 290: H1128–H1135, 2006.
20. Heaps CL, Parker JL, Sturek M, Bowles DK. Altered calcium sensi-
tivity contributes to enhanced contractility of collateral-dependent coro-
nary arteries. J Appl Physiol 97: 310–316, 2004.
21. Heaps CL, Sturek M, Price EM, Laughlin MH, Parker JL. Exercise
training restores adenosine-induced relaxation in coronary arteries distal to
chronic occlusion. Am J Physiol Heart Circ Physiol 278: H1984–H1992,
22. Heitzer T, Schlinzig T, Krohn K, Meinertz T, Munzel T. Endothelial
dysfunction, oxidative stress, and risk of cardiovascular events in patients
with coronary artery disease. Circulation 104: 2673–2678, 2001.
23. Ismail S, Sturrock A, Wu P, Cahill B, Norman K, Huecksteadt T,
Sanders K, Kennedy T, Hoidal J. NOX4 mediates hypoxia-induced
proliferation of human pulmonary artery smooth muscle cells: the role of
autocrine production of transforming growth factor-?1 and insulin-like
growth factor binding protein-3. Am J Physiol Lung Cell Mol Physiol 296:
24. Kang LS, Reyes RA, Muller-Delp JM. Aging impairs flow-induced
dilation in coronary arterioles: role of NO and H2O2. Am J Physiol Heart
Circ Physiol 297: H1087–H1095, 2009.
25. Kober T, Konig I, Weber M, Kojda G. Diethyldithiocarbamate inhibits
the catalytic activity of xanthine oxidase. FEBS Lett 551: 99–103, 2003.
26. Larsen BT, Bubolz AH, Mendoza SA, Pritchard KA Jr, Gutterman
DD. Bradykinin-induced dilation of human coronary arterioles requires
NADPH oxidase-derived reactive oxygen species. Arterioscler Thromb
Vasc Biol 29: 739–745, 2009.
27. Larsen BT, Gutterman DD, Sato A, Toyama K, Campbell WB, Zeldin
DC, Manthati VL, Falck JR, Miura H. Hydrogen peroxide inhibits
cytochrome p450 epoxygenases: interaction between two endothelium-
derived hyperpolarizing factors. Circ Res 102: 59–67, 2008.
28. Lassegue B, Clempus RE. Vascular NAD(P)H oxidases: specific fea-
tures, expression, and regulation. Am J Physiol Regul Integr Comp Physiol
285: R277–R297, 2003.
29. Laughlin MH, Pollock JS, Amann JF, Hollis ML, Woodman CR,
Price EM. Training induces nonuniform increases in eNOS content along
the coronary arterial tree. J Appl Physiol 90: 501–510, 2001.
30. LeBlanc AJ, Shipley RD, Kang LS, Muller-Delp JM. Age impairs Flk-1
signaling and NO-mediated vasodilation in coronary arterioles. Am J
Physiol Heart Circ Physiol 295: H2280–H2288, 2008.
31. Lee YM, Kim BJ, Chun YS, So I, Choi H, Kim MS, Park JW. NOX4
as an oxygen sensor to regulate TASK-1 activity. Cell Signal 18: 499–
32. Levada-Pires A, Lambertucci R, Mohamad M, Hirabara S, Curi R,
Pithon-Curi T. Exercise training raises expression of the cytosolic com-
ponents of NADPH oxidase in rat neutrophils. Eur J Appl Physiol 100:
33. Liu YP, Gutterman DD. Vascular control in humans: focus on the
coronary microcirculation. Basic Res Cardiol 104: 211–227, 2009.
34. Martyn KD, Frederick LM, von Loehneysen K, Dinauer MC, Knaus
UG. Functional analysis of Nox4 reveals unique characteristics compared
with other NADPH oxidases. Cell Signal 18: 69–82, 2006.
35. Matoba T, Shimokawa H, Nakashima M, Hirakawa Y, Mukai Y,
Hirano K, Kanaide H, Takeshita A. Hydrogen peroxide is an endothe-
lium-derived hyperpolarizing factor in mice. J Clin Invest 106: 1521–
36. Miura H, Bosnjak JJ, Ning G, Saito T, Miura M, Gutterman DD. Role
for hydrogen peroxide in flow-induced dilation of human coronary arte-
rioles. Circ Res 92: E31–E40, 2003.
37. Mohazzab KM, Kaminski PM, Wolin MS. NADH oxidoreductase is a
major source of superoxide anion in bovine coronary artery endothelium.
Am J Physiol Heart Circ Physiol 266: H2568–H2572, 1994.
38. Mueller CF, Laude K, McNally JS, Harrison DG. ATVB in focus:
redox mechanisms in blood vessels. Arterioscler Thromb Vasc Biol 25:
39. Pagano PJ, Ito Y, Tornheim K, Gallop PM, Tauber AI, Cohen RA. An
NADPH oxidase superoxide-generating system in the rabbit aorta. Am J
Physiol Heart Circ Physiol 268: H2274–H2280, 1995.
40. Rajagopalan S, Kurz S, Münzel T, Tarpey M, Freeman BA, Grien-
dling KK, Harrison DG. Angiotensin II-mediated hypertension in the rat
increases vascular superoxide production via membrane NADH/NADPH
oxidase activation. Contribution to alterations of vasomotor tone. J Clin
Invest 97: 1916–1923, 1996.
41. Roth DM, Maruoka Y, Rogers J, White FC, Longhurst JC, Bloor CM.
Development of coronary collateral circulation in left circumflex ameroid-
occluded swine myocardium. Am J Physiol Heart Circ Physiol 253:
42. Rush JW, Turk JR, Laughlin MH. Exercise training regulates SOD-1
and oxidative stress in porcine aortic endothelium. Am J Physiol Heart
Circ Physiol 284: H1378–H1387, 2003.
43. Rush JWE, Laughlin MH, Woodman CR, Price EM. SOD-1 expres-
sion in pig coronary arterioles is increased by exercise training. Am J
Physiol Heart Circ Physiol 279: H2068–H2076, 2000.
44. Sato A, Sakuma I, Gutterman DD. Mechanism of dilation to reactive
oxygen species in human coronary arterioles. Am J Physiol Heart Circ
Physiol 285: H2345–H2354, 2003.
45. Sessa WC, Pritchard K, Seyedi N, Wang J, Hintze TH. Chronic
exercise in dogs increases coronary vascular nitric oxide production and
endothelial cell nitric oxide synthase gene expression. Circ Res 74:
46. Sindler AL, Delp MD, Reyes R, Wu G, Muller-Delp JM. Effects of
ageing and exercise training on eNOS uncoupling in skeletal muscle
resistance arterioles. J Physiol 587: 3885–3897, 2009.
47. Subramaniam R, Fan XJ, Scivittaro V, Yang JQ, Ha CE, Petersen
CE, Surewicz WK, Bhagavan NV, Weiss MF, Monnier VM. Cellular
oxidant stress and advanced glycation endproducts of albumin: caveats of
the dichlorofluorescein assay. Arch Biochem Biophys 400: 15–25, 2002.
48. Thengchaisri N, Shipley R, Ren Y, Parker J, Kuo L. Exercise training
restores coronary arteriolar dilation to NOS activation distal to coronary
artery occlusion: role of hydrogen peroxide. Arterioscler Thromb Vasc
Biol 27: 791–798, 2007.
49. Ungvari Z, Wolin MS, Csiszar A. Mechanosensitive production of
reactive oxygen species in endothelial and smooth muscle cells: role in
microvascular remodeling? Antioxid Redox Signal 8: 1121–1129, 2006.
50. Van Buul JD, Fernandez-Borja M, Anthony EC, Hordijk PL. Expres-
sion and localization of NOX2 and NOX4 in primary human endothelial
cells. Antioxid Redox Signal 7: 308–317, 2005.
51. Zafari AM, Ushio-Fukai M, Akers M, Yin Q, Shah A, Harrison DG,
Taylor WR, Griendling KK. Role of NADH/NADPH oxidase-derived
H2O2 in angiotensin II-induced vascular hypertrophy. Hypertension 32:
52. Zhou M, Widmer RJ, Xie W, Jimmy Widmer A, Miller MW, Schr-
oeder F, Parker JL, Heaps CL. Effects of exercise training on cellular
mechanisms of endothelial nitric oxide synthase regulation in coronary
arteries after chronic occlusion. Am J Physiol Heart Circ Physiol 298:
53. Zhou MS, Raij L. Cross-talk between nitric oxide and endothelium-
derived hyperpolarizing factor: synergistic interaction? J Hypertens 21:
Exercise, Occlusion, eNOS, Superoxide/H2O2 Signaling • Xie W et al.
J Appl Physiol • doi:10.1152/japplphysiol.01248.2011 • www.jappl.org