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Hypertension. 2007;50:663-671
Published online before print August 13, 2007, doi: 10.1161/HYPERTENSIONAHA.107.089748
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(Hypertension. 2007;50:663.)
© 2007 American Heart Association, Inc.

Original Articles

Differential Regulation of NADPH Oxidase in Sympathetic and Sensory Ganglia in Deoxycorticosterone Acetate–Salt Hypertension

Xian Cao; Xiaoling Dai; Lindsay M. Parker; David L. Kreulen

From the Departments of Physiology (X.C., L.M.P., D.L.K.), Neurology and Ophthalmology (D.L.K.), Pharmacology and Toxicology (X.D.), and Neuroscience Program (X.C., X.D., D.L.K.), Michigan State University, East Lansing.

Correspondence to David L. Kreulen, Department of Physiology, 2201 Biomedical Physical Sciences, Michigan State University, East Lansing, MI 48824. E-mail dkreulen{at}msu.edu


*    Abstract
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We demonstrated recently that superoxide anion levels are elevated in prevertebral sympathetic ganglia of deoxycorticosterone acetate–salt hypertensive rats and that this superoxide anion is generated by reduced nicotinamide-adenine dinucleotide phosphate oxidase. In this study we compared the reduced nicotinamide-adenine dinucleotide phosphate oxidase enzyme system of dorsal root ganglion (DRG) and sympathetic celiac ganglion (CG) and its regulation in hypertension. The reduced nicotinamide-adenine dinucleotide phosphate oxidase activity of ganglion extracts was measured using fluorescence spectrometry of dihydroethidine; the activity in hypertensive dorsal root ganglion was 34% lower than in normotensive DRG. In contrast, activity was 79% higher in hypertensive CG than normotensive CG. mRNA for the oxidase subunits NOX1, NOX2, NOX4, p47phox, and p22phox were present in both CG and DRG; mRNA for NOX4 was significantly higher in CG than in DRG. The levels of mRNA and protein expression of the membrane-bound catalytic subunit p22phox and of the regulatory subunits p47phox and Rac-1 were measured in CG and DRG in normotensive and hypertensive rats. p22phox mRNA and protein expression was greater in CG of hypertensive rats but not in DRG. Compared with normotensive controls, p47phox mRNA and protein, as well as Rac-1 protein, were significantly decreased in hypertensive DRG but not in CG. Immunohistochemical staining of p47phox showed translocation from cytoplasm to membrane in hypertensive CG but not in hypertensive DRG. This suggests that reduced nicotinamide-adenine dinucleotide phosphate oxidase activation in sympathetic neurons and sensory neurons is regulated in opposite directions in hypertension. This differential regulation may contribute to unbalanced vasomotor control and enhanced vasoconstriction in the splanchnic circulation.


Key Words: superoxide • sympathetic ganglia • sensory ganglia • NADPH oxidase • rat • hypertension


*    Introduction
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The splanchnic circulation is of great importance in regulating systemic blood pressure. It receives {approx}60% of the cardiac output and contains approximately one third of the total blood volume.1 The splanchnic circulation is innervated by both the sympathetic division of the autonomic nervous system (prevertebral sympathetic ganglion neurons, including celiac ganglia [CGs] and superior and inferior mesenteric ganglia) and by spinal sensory nerves (dorsal root ganglia neurons [DRGs]). Elevated sympathetic nervous system activation has been shown in various types of hypertension.2,3 In particular, sympathetic ganglionic blockade can reduce the arterial blood pressure increase in deoxycorticosterone acetate (DOCA)–salt hypertension,4 indicating an important role of sympathetic ganglia in the development and maintenance of salt-induced hypertension. On the other hand, sensory nerves play a counterregulatory role in preventing increases in blood pressure through either afferent baroreceptor-mediated mechanisms5 or efferent release of vasodilatory neuropeptides, such as calcitonin gene-related peptide and substance P.6,7 Altered synthesis or release of these vasodilator neuropeptides occurs in genetic and experimental hypertensive animal models.8–10

Reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase is an enzyme that catalyzes the production of superoxide anion (O2•–) from oxygen and NADPH and is considered the predominant source of O2•– in hypertension.11 It is a complex enzyme consisting of 2 membrane-bound components (p22phox and NOX) and 3 components in the cytosol (p47phox or NOXA1, p67phox or NOXO1, and p40phox) plus a GTPase (Rac-1 or Rac-2).12 Activation of NADPH oxidase involves the translocation of regulatory elements from the cytoplasm to combine with catalytic subunits in the membrane.13 NADPH oxidase was first identified in phagocytes.14 It plays a vital role in the nonspecific host defense against pathogens by generating large (millimolar) quantities of O2•– during the respiratory burst.15 More recently, the presence of NADPH oxidase in nonphagocyte cell types has been well identified. This is especially true in cardiovascular system–related tissues, such as the vascular endothelium,16 vascular smooth muscle,17 kidney cortex,18 and nervous system.19 Unlike in neutrophils, the NADPH oxidase in these tissues makes O2•– in small amounts for purposes of signaling under physiological conditions.20 However, excessive amounts of O2•– production leads to a variety of intracellular signaling events that ultimately may cause dysfunction of the system.21 This brings more attention to the pathophysiological role of this enzyme system in the regulation of cardiovascular diseases, such as hypertension.

Elevated NADPH oxidase-derived O2•– production in the vasculature22 and sympathetic neurons,23 accompanied by enhanced endothelin (ET)-1 signaling24 and increased sympathetic system activity,4 are characteristic of DOCA-salt hypertension. Studies using this hypertensive animal model have shown that elevated arterial ET-1 levels lead to enhanced vascular O2•– production via the ETA receptor/NADPH oxidase pathway,25 whereas in prevertebral sympathetic ganglia, O2•– levels are increased because of enhanced activation of the ETB/NADPH oxidase pathway.23 Although sensory neurons are known to participate in innervating the vasculature, the regulation of NADPH oxidase activity in sensory neurons has not been investigated in DOCA-salt hypertension. Possible differential regulation of O2•– in sympathetic and sensory ganglion neurons in cardiovascular diseases has been shown in apolipoprotein E–deficient mice, in which the level of O2•– is increased in sympathetic ganglia neurons but not in nodose sensory neurons.26

In this study, we measured the O2•– levels and the expression of NADPH oxidase subunits in sympathetic ganglia (CGs) and sensory ganglia (DRGs) and compared the expression levels in both normotensive and hypertensive conditions. We tested the hypothesis that NADPH oxidase is regulated differentially in sympathetic and sensory ganglia in DOCA-salt hypertension, in which the enzyme system is upregulated in CGs but not in DRGs.


*    Methods
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 *Methods
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An expanded Methods section can be found in an online data supplement available at http://hyper.ahajournals.org.

Animals
Animal procedures were followed in accordance with the institutional guidelines of Michigan State University. DOCA-salt hypertensive (HT) rats and normotensive (NT) rats were prepared as described previously.23 The mean systolic arterial pressures for the HTs and NTs were 206.3±5.06 mm Hg and 119.7±3.5 mm Hg, respectively.

Tissue Harvest
Rats were euthanized with a lethal dose of sodium pentobarbital (65 mg/kg IP), and the CG and DRG (spinal levels T13-L2) from HT and NT rats were removed and cleaned for further processing.

Measurement of NADPH Oxidase Activity
Activity of NADPH oxidase was measured using fluorescence spectrometry of dihydroethidine in tissue homogenates of DRG and CG from NT rats and HT rats as described previously.27 Freshly prepared ganglia homogenates were incubated with dihydroethidine (10 µmol/L), salmon testes DNA (0.5 mg/mL), and the substrate for NADPH oxidase, ß-NADPH (0.1 mmol/L), for 30 minutes at 37°C in a dark chamber before measuring fluorescence (excitation: 485±40 nm; emission: 590±35 nm) with a fluorescence plate reader. A parallel control group was analyzed in each run with no substrate added into the reaction. The enzyme activity was measured as total fluorescence units per minute per milligram of tissue homogenate. NT rat ganglia were normalized to 100% in both CGs and DRGs independently. Experimental results are presented as the percent changes of fluorescence from NT to HT rats.

RT-PCR and Quantitative Real-Time RT-PCR
Total RNA was isolated from the ganglia using RNeasy Mini kit (Qiagen). The cDNA was synthesized, and PCR or quantitative real-time RT-PCR (qPCR) was performed. All of the primers were derived from the Rattus Norvegicus gene (National Center for Biotechnology Information GenBank). Primer sequences are shown in the Table. PCR products were analyzed on agarose gel. qPCR was performed using the Mx3000P QPCR system (Stratagene). Relative expression ratio calculation and statistical analysis were performed by Pair Wise Fixed Reallocation Randomization Test (http://www.gene-quantification.info) using the Relative Expression Software Tool (REST).28


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  		Table. Primer Sequences for NADPH Oxidase Subunits NOX1, NOX2, NOX4, p47phox, and p22phox; ß-actin; and GAPDH

Protein Isolation and Western Blotting
Tissues were homogenized, and total protein isolation or subcellular fractionation was performed by centrifugation. Protein quantification was performed using a Bradford protein assay. Equal amounts of protein were separated by 7.5% to 15% SDS-PAGE and transferred to polyvinylidene fluoride membrane. The membranes were incubated overnight with the primary antibodies for p22phox, p47phox, and Rac-1 and for 1 hour with the secondary antibody. Immunoreactivity was detected using a chemiluminescence kit.

Immunohistochemistry
Fresh ganglia were fixed in 10% formalin, embedded in paraffin, and sectioned into 5-µm sections and mounted onto glass slides. Normal goat serum was used as a protein block followed by incubation in p47phox primary antibody. Incubation of biotinylated secondary antibody was followed by incubation with Nova Red chromogen. Slides were counterstained with Lerner 2 hematoxylin, then dehydrated. Images were collected using standard bright-field microscopy.

Data Analysis
Data are presented as mean±SE of the mean. Statistical significance of NADPH oxidase activity, Western blotting, and immunohistochemistry data were assessed by Student’s t test using Prism 4.0 software (GraphPad Software). qPCR data statistical significance was assessed by the Pair Wise Fixed Reallocation Randomization Test using REST software.


*    Results
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Expression of NADPH Oxidase mRNA in Normal Rat DRG and CG
PCR amplicons of NADPH oxidase subunits p47phox, p22phox, NOX1, NOX2, and NOX4 were detected in RNA extracts of DRG and CG from normal rats that did not receive DOCA-salt treatments (Figure 1A). These amplicons were at the expected sizes of 221, 282, 324, 245, and 261 bp, respectively. PCR products from CG ganglia were consistent with our previous findings in dissociated CG neurons.27 However, DRG NOX4 mRNA was barely detectable on the regular PCR gel compared with CG. qPCR was then performed to determine the relative expression levels of NOX4 in normal DRGs and CGs. Results showed that the expression ratio of NOX4 in DRGs and CGs was 0.077 (Figure 1B; P<0.05 versus CG; n=7).


Figure 1
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  		Figure 1. NADPH oxidase subunits are expressed in DRGs and CGs. A, PCR amplicons for NOX1, NOX2, p47phox, p22phox, and ß-actin were present on ethidium bromide-stained agarose gels from DRGs (top) and CGs (bottom). PCR step with no cDNA template added (NTC) and reverse-transcription step without adding the transcriptase enzyme (No RT) were performed as negative controls. B, qPCR results show that the NOX4 mRNA level is significantly lower in DRGs then in CGs in normal rats. The expression ratio of NOX4 in DRGs versus CGs is 0.077 (n=7 normal rats). Relative expression value calculation and statistical analysis were performed by REST software. The randomization test output from REST is listed in table format (right) attached to the bar graph. *Significance (P<0.05) vs CG.

NADPH Oxidase Activity in DRGs and CGs in NT and HT Rats
Tissue homogenates of DRGs and CGs from NT and HT animals were incubated with the NADPH oxidase substrate ß-NADPH, and the formation of O2•– was detected in the reaction mixture. The NADPH oxidase activity of DRG homogenates from HT rats was 34% lower than the activity of homogenates from NT animals (Figure 2; P<0.05 versus NT; n=3). This result demonstrates that the NADPH oxidase enzymatic activity in tissue homogenates of HT DRGs is less than this activity in NT DRGs. Meanwhile, the NADPH oxidase activity in HT CGs is 78.6% higher than NT CGs (P<0.05 versus NT; n=6).27


Figure 2
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  		Figure 2. NADPH oxidase activity is lower in DRGs from DOCA-salt HT rats than from NT control rats but is higher in HT CGs than NT CGs. ß-NADPH was used as the NADPH oxidase substrate. Results represent the percent changes of dihydroethidine fluorescence intensity in the ganglia homogenate from no- substrate controls to substrate-treated groups in both HT and NT rats. The NADPH oxidase activity of DRG homogenates from HT rats was 34% lower than from NT animals (n=3; left); meanwhile, the NADPH oxidase in HT CGs is 78.6% higher than NT CGs (n=6; right).27 *Significance (P<0.05) vs NT.

NADPH Oxidase Subunit mRNA Levels in DRGs and CGs in NT and HT Rats
p22phox and p47phox mRNA were both present in DRGs and CGs as shown above, and these subunits are critical in mediating the NADPH oxidase enzyme activity.12,29 We, therefore, compared the levels of p22phox and p47phox mRNA in RNA extracts of DRGs and CGs from NT and HT rats using qPCR. The mRNA level of p22phox in CG was significantly greater in HT animals compared with NT by the factor 1.776 (P<0.05 versus NT rats; n=7 NT rats; n=6 HT rats), whereas its level was unchanged in DRG (Figure 3A). On the other hand, p47phox mRNA was significantly lower in HT DRGs compared with NT DRGs. The relative expression ratio of p47phox mRNA in HT DRGs to NT DRGs is 0.379 (P<0.05 versus NT rats; n=7 NT rats; n=5 HT rats), whereas there was no significant difference between p47phox mRNA in NT CGs and HT CGs (Figure 3B).


Figure 3
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  		Figure 3. p22phox mRNA level is higher in CGs in HT animals vs NT controls, and p47phox mRNA is lower in HT DRGs than in NT DRGs. A, mRNA level of p22phox in CGs was significantly greater in HT animals compared with NT animals by the factor 1.776 (n=7 NT rats; n=6 HT rats), whereas its level was unchanged in DRGs. B, p47phox mRNA was significantly lower in HT DRGs compared with NT DRGs. The relative expression ratio of p47phox mRNA in HT DRGs to NT DRGs is 0.379 (n=7 NT rats; n=5 HT rats), whereas there was no significant difference between p47phox mRNA in NT CGs and HT CGs. All of the qPCR data are normalized to GAPDH. Results are shown in table form from REST software analysis output (right) and in graphical form (left). *Significance (P<0.05) vs NT.

NADPH Oxidase Subunit Protein Expression Levels in CGs and DRGs in NT and HT Rats
In addition to p22phox and p47phox, we also measured Rac-1 protein expression levels in the ganglia in NT and HT rats, because the protein expression of this regulatory factor has been associated with NADPH oxidase activity in the nervous system.30 The protein expression of p22phox, p47phox, and Rac-1 in CGs and DRGs was examined by Western blotting analysis. The expression of p22phox was greater in HT CGs than in NT CGs (P<0.05 versus NT rats; n=6), and this paralleled its greater mRNA levels shown above. Similar to its unchanged mRNA levels in DRGs, the p22phox protein expression was not significantly different between NT and HT rats (Figure 4A). In CGs, there was no difference between NT and HT rats in the amounts of p47phox and Rac-1 in total protein fractions. Meanwhile, HT DRGs showed a different pattern in the expression of these 2 subunits. There was a profound downregulation of p47phox (P<0.05 versus NT rats; n=4; Figure 4B), as well as a significant decrease in Rac-1 expression (P<0.05 versus NT rats; n=3; Figure 4C) in total protein preparation.


Figure 4
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  		Figure 4. Western blot data from ganglia homogenate reveal that p22phox, p47phox, and Rac-1 are present in DRGs and CGs and are differentially regulated in HT and NT animals. A, There is no significant difference in the amount of p22phox protein expression in NT DRGs vs HT DRGs (left), whereas it is higher in HT CGs than in NT CGs (right; n=6). Representative blots are shown below each figure. B, p47phox protein is significantly decreased in HT DRGs vs NT DRGs (left; n=4) but is not different between NT and HT CGs (right). C, Protein expression of Rac-1 is lower in HT DRGs than in NT DRGs (n=3), and there is no significant difference between Rac-1 protein levels in NT and HT CGs. All of the data are normalized to actin before statistical analysis. *Significance (P<0.05) vs NT.

We also analyzed the p47phox expression in CGs and DRGs with immunohistochemistry. In both CGs and DRGs there was intense staining associated with the neuron cell bodies with little or no staining of intercellular elements. Compared with NT CGs, there was a significant redistribution of p47phox to the plasma membrane of neurons in the HT CGs (P<0.05 versus NT rats; n=7 neurons in NT CGs; n=14 neurons in HT CGs; Figure 5A). We observed a similar redistribution pattern in Western blotting of CG subcellular fractions; in HT CGs there was lower expression of p47phox in cytosolic fractions accompanied by greater p47phox expression in membrane fractions (Figure 5B). On the other hand, immunohistochemical staining of DRGs showed that the total p47phox staining was decreased in HT DRGs as compared with NT DRGs (P<0.05 versus NT rats; n=61 neurons in NT DRGs; n=91 neurons in HT DRGs; Figure 6). This is consistent with our Western blotting data in which there was decreased p47phox protein expression in HT DRGs (see Figure 4). However, there was no p47phox redistribution from cytosol to membrane in HT DRGs. This suggests that the translocation of p47phox from the cytoplasm to the plasma membrane may contribute to the elevated NADPH oxidase activity in HT CGs, whereas in HT DRGs the lack of this translocation, as well as the decreased expression of total p47phox protein, could contribute to the lower activity level of the enzyme.


Figure 5
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  		Figure 5. p47phox protein is redistributed in the CG neurons in HT animals vs NT controls. A, Immunohistochemistry reveals p47phox protein localization in CG neurons (shown in red). Left 3 panels are CGs from NT rats and right 3 panels are HT CGs (top to bottom: x20, x100 oil objective, no primary antibody controls). Representative images show that p47phox protein is present in most cells within the ganglia. The membrane localization of p47phox is significantly higher in HT CGs than in NT CGs (arrow), indicating a translocation of this protein from the cytoplasm to the plasma membrane. Plots of the density measurements are shown to the right of the micrographs. In HT CGs there was a significant increase in plasma membrane density (*P<0.05 vs NT; n=7 neurons in NT CG; n=14 neurons in HT CG), but no change in total (plasma membrane+cytoplasm) staining density. B, Western blot performed on CG subcellular fraction protein shows that, in cytosol fraction, NT CG has higher p47phox protein expression than HT CG. However, in membrane-rich fraction, HT CG has more p47phox than NT CG. Membranes are stripped and reprobed with Pan-cadherin, a plasma membrane marker, indicating membrane-rich protein preparation (n=5, pooled ganglia).


Figure 6
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  		Figure 6. Immunohistochemistry reveals p47phox localization in DRG neurons. The left 3 panels are DRG sections from NT rats and the right 3 panels are from HT rats (top to bottom: x20, x100 oil objective, no primary antibody controls). The micrographs show p47phox staining (red) throughout the cytoplasm of the ganglion cell bodies with limited membrane localization in both NT and HT DRGs. Plots of the density measurements are shown to the right of the micrographs. The total amount of p47phox is significantly lower in HT DRG than in NT. (*P<0.05 vs NT; n=61 neurons in NT DRG; n=91 neurons in HT DRG).


*    Discussion
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 up arrowMethods
 up arrowResults
 *Discussion
down arrowReferences
 
In this study we have shown for the first time that, in DOCA-salt hypertension, NADPH oxidase–derived reactive oxygen species production is regulated in opposite directions in sympathetic ganglion neurons and in primary sensory neurons. Whereas O2•– production and NADPH oxidase activity are increased in sympathetic ganglia in HT rats,23,27 they are decreased in DRGs. The expression of NOX4 is much higher in CGs than in DRGs. Furthermore, p22phox is increased in HT CGs, whereas p47phox and Rac-1 are decreased in HT DRGs. Finally, p47phox is translocated from the cytoplasm to the plasma membrane in HT CGs but not in DRGs.

NADPH oxidase activity can be determined by 2 major factors: the capability of different NOX isoforms to catalyze electron transfer reactions and/or the availability of the cytosolic regulatory subunits. The expression pattern and level of the core protein, as well as the regulatory subunits, can affect the enzyme activity level. First, the differential regulation of NADPH oxidase activity in CGs and DRGs in hypertension may be because of their differences in the expression of NOX isoforms. The formation of the catalytic core of NADPH oxidase between either one of the NOX isoforms and p22phox is essential for the production of O2•–.31 However, whereas the activation of catalytic complexes made with NOX1/NOX2 and p22phox requires the addition of cytosolic regulatory subunits, such as p47phox or the GTPase Rac32, NOX4-p22phox produces O2•– constitutively without combining with other subunits.33 Different from the other 2 isoforms, the expression of NOX4 is much higher in CGs than in DRGs. It is then conceivable that, because a large part of the oxidase in CGs where NOX4 expression is high contains only NOX4-p22phox, the p22phox increase that we observed in HT CGs may be responsible for the elevated oxidase activity even if the expression levels of regulatory subunits p47phox and Rac-1 were unchanged.

Second, differences in the availability of regulatory subunits can affect NADPH oxidase activity. For example, in NOX1- or NOX2-based NADPH oxidase, O2•– generation is regulated by the concentration of p47phox and Rac-1,34–36 and inhibition of p47phox or Rac-1 expression can result in a decrease in O2•– production.30,37 Therefore, the decreased expression of p47phox and Rac-1 in HT DRGs, where the NOX1 and NOX2 dominate, is likely to result in lower oxidase activity. Moreover, NADPH oxidase activation involves the translocation of regulatory subunits from the cytoplasm to combine with catalytic core in the membrane. The redistribution of regulatory subunits can be another indicator for oxidase activity level. There is increased membrane-bound p47phox in HT CG but not in HT DRG, indicating that the translocation of p47phox may contribute to enhanced oxidase activity in HT CG, whereas the lack of this translocation accompanied by decreased total p47phox expression may explain the attenuated oxidase activity in HT DRG.

In hypertension, enhanced NADPH oxidase activity and expression occur in various tissue types, including vasculature,25,38 kidney,18 and the nervous system.27,39 There is a positive correlation between reactive oxygen species levels in the nervous system and sympathetic neuronal activity in hypertension. For example, removal of extracellular O2•– or reactive nitrogen species within the rostral ventrolateral medulla by microinjection of superoxide dismutase reduces sympathetic nervous system activity in animals subjected to oxidative stress40; also, intravenous administration of the superoxide dismutase mimetic Tempol lowers mean blood pressure and renal sympathetic nervous system activity in the DOCA-salt hypertensive model.41 Activation of ETB receptors increases O2•– production in prevertebral sympathetic ganglia both in vitro23 and in vivo.42 In these ganglia, ETB receptor expression and NADPH oxidase-derived O2•– generation are elevated in DOCA-salt hypertension.23 Because DOCA-salt hypertension is characterized by sympathetic hyperactivation, elevated O2•– levels in sympathetic ganglia may directly or indirectly contribute to the hypertension.

The relationship of changes in reactive oxygen species levels in sensory neurons to blood pressure regulation is not known but could be related to interactions between sensory neurons and sympathetic ganglionic neurons1,43 or of sensory nerves directly with the vasculature. In salt-sensitive hypertension, synthesis and release of vasoactive neuropeptides from sensory ganglia innervating the splanchnic circulation are increased,10,44 and this may play a role in blood pressure regulation,45 but it is not known whether these are related to the observed decreases in the activity of NADPH oxidase.

One of the important findings of the present study is that NADPH oxidase activity is decreased in extracts of spinal sensory ganglia in hypertension; this is in contrast to sympathetic ganglia, where it is increased in hypertension. Both types of ganglia are made up of neurons and satellite cells, but in both types, the presence of the enzyme appears limited to the neurons. Dorsal root ganglia are a mixture of neurons with different functional and neurochemical properties, and only a subset of the neurons innervates the vasculature and release neuropeptides. Sensory nerve fibers that innervate the systemic blood vessels contain the vasodilatory neuropeptides calcitonin gene-related peptide and substance P,46 and subsets of dorsal root ganglion neurons are labeled with calcitonin gene-related peptide (33%) substance P (23%)47 or NO synthase (12%).48 Thus, if decreased NADPH oxidase activity in dorsal root ganglia is associated with changes in activity of the peptide-containing vascular neurons, it is possible that these changes could contribute to hypertension.

Perspectives
The splanchnic vasculature is innervated by sympathetic nerves, which are vasoconstrictor, and by sensory nerves, which are vasodilator. The NADPH oxidase system that is responsible for generation of O2•– is regulated differently in these 2 types of nerves in DOCA-salt hypertension. We suggest that O2•– overproduction evoked by the increased NADPH oxidase in sympathetic ganglia may play a role in the increased neurogenic vasoconstriction. Decreased oxidase activity in sensory ganglia may also enhance blood vessel tone or it may be a response to increased blood pressure. Further studies are needed to unravel the mechanisms underlying the fine tuning of NADPH oxidase-derived reactive oxygen species levels and neuronal activities in these ganglia and how these contribute to the development and maintenance of DOCA-salt hypertension.


*    Acknowledgments
 
Sources of Funding

This work was supported by grants from the National Institutes of Health (P01HL70687) and Michigan State University to D.L.K.

Disclosures

None.

Received February 28, 2007; first decision March 19, 2007; accepted July 24, 2007.


*    References
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 up arrowMethods
 up arrowResults
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 *References
 

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The Continuing Saga of Neuronal Oxidative Stress in Hypertension: Nox, Nox Who's There, and Where?
Hypertension, October 1, 2007; 50(4): 600 - 602.
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