This Article Abstract Full Text (PDF) All Versions of this Article: 47/3/482    most recent 01.HYP.0000201540.91234.8fv1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Thakali, K. Articles by Watts, S. W. Search for Related Content PubMed PubMed Citation Articles by Thakali, K. Articles by Watts, S. W. Pubmed/NCBI databases Compound via MeSH Substance via MeSH Hazardous Substances DB CALCIUM COMPOUNDS CALCIUM, ELEMENTAL HYDROGEN PEROXIDE OUABAIN SODIUM CHLORIDE Medline Plus Health Information High Blood Pressure Related Collections Other Vascular biology

(Hypertension. 2006;47:482.)
© 2006 American Heart Association, Inc.

Original Articles

Pleiotropic Effects of Hydrogen Peroxide in Arteries and Veins From Normotensive and Hypertensive Rats

From the Department of Pharmacology and Toxicology, Michigan State University, East Lansing.

Correspondence to Keshari Thakali, B445 Life Sciences Building, Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824-1317. E-mail thakalik{at}msu.edu

	Abstract

Top Abstract Introduction Methods Results Discussion References

 
Hydrogen peroxide causes vascular contraction and relaxation and contributes to the pathogenesis of hypertension. We hypothesized that the contractile state of blood vessels governs whether H₂O₂ causes contraction or relaxation. Hydrogen peroxide (1 µmol/L to 1 mmol/L) concentration-dependently contracted thoracic aorta and vena cava from sham normotensive and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The maximal contraction to H₂O₂ was 3 times greater in DOCA aorta compared with sham aorta but unchanged in DOCA vena cava compared with sham vena cava. In prostaglandin F₂ (20 µmol/L)–contracted aorta and vena cava from sham and DOCA rats, H₂O₂ (1 µmol/L to 1 mmol/L) induced a concentration-dependent relaxation that was impaired in DOCA aorta but not DOCA vena cava. In contrast, in KCl (30 mmol/L)-contracted vessels, maximal H₂O₂-induced contraction was enhanced 15-fold in sham aorta and 5-fold in DOCA aorta but only 2-fold in sham vena cava. Tetraethylammonium (10 mmol/L), BAY K 8644 (100 nmol/L), and ouabain (1 mmol/L) all enhanced maximal aortic H₂O₂-induced contraction, whereas only ouabain enhanced venous H₂O₂-induced contraction. The removal of extracellular Ca²⁺ reduced H₂O₂-induced contraction in KCl-contracted aorta, whereas maximal venous H₂O₂-induced contraction (under basal conditions) was unchanged. Our data suggest that differences in arterial and venous K⁺ channel activity and extracellular Ca²⁺ influx are responsible for differences in arterial and venous contraction to H₂O₂. In DOCA-salt hypertension, arterial but not venous contraction to H₂O₂ is enhanced, and relaxation to H₂O₂ is reduced.

Key Words: contraction • relaxation • arteries • veins

	Introduction

Top Abstract Introduction Methods Results Discussion References

 
H₂O₂ is capable of modifying vascular tone in complex manners. Whereas vessels in some vascular regions contract to H₂O₂,^1–5 others relax in the presence of H₂O₂.^6–10 Lucchesi et al⁹ observed in mouse mesenteric resistance arteries that the same concentration of H₂O₂ could induce either contraction or relaxation, depending on K⁺ channel activity. Because of differences in species, vascular bed studied, and experimental design, no consensus has been reached on the mechanisms that govern the vasoactive properties of H₂O₂. We reported previously that H₂O₂ contracts both rat thoracic aorta and vena cava but that aortic contraction to H₂O₂ was minimal (<10% of maximal contraction to an adrenergic agonist) compared with venous H₂O₂-induced contraction (>80% of maximal contraction to an adrenergic agonist).¹¹ The focus of the present study was to determine why there are differences in arterial and venous contraction to H₂O₂. We hypothesized that in rat thoracic aorta, we previously observed minimal H₂O₂-induced contraction, because the predominant arterial response to H₂O₂ is relaxation.

Hypertension is associated with changes in vascular reactivity. Specifically, vasoconstriction to agonists, such as serotonin,¹² phenylephrine,¹³ and H₂O₂,¹⁴ is enhanced, whereas endothelial-dependent relaxation is reduced. Changes in vascular smooth muscle membrane potential¹⁵ and Ca²⁺ handling¹³ have been proposed to account for enhanced vasoconstriction in hypertension and endothelial dysfunction responsible for reduced endothelial-dependent relaxation.^13,16 However, most of these experiments were performed in arteries, and it is unclear whether similar changes in venous reactivity occur in hypertension. Increasing evidence suggests that increased venous tone, in addition to increased arterial resistance, is important in hypertension,¹⁷ because mean circulatory filling pressure, an index of venomotor tone, is increased in hypertension.^18,19 Increased venoconstriction in splanchnic veins can lead to significant increases in cardiac output and, consequently, increases in blood pressure. We questioned how arterial and venous reactivity to H₂O₂ changed in hypertension and hypothesized that the vascular response to H₂O₂, be it contraction or relaxation, would change in the established phase of mineralocorticoid hypertension.

	Methods

Top Abstract Introduction Methods Results Discussion References

 
Animals
All of the animal studies were performed in accordance with institutional guidelines of Michigan State University. Male Sprague-Dawley rats (250 to 300 g; Charles River Laboratories, Inc) underwent uninephrectomy and implantation of a deoxycorticosterone acetate (DOCA) pellet (200 mg/kg) under isoflurane anesthesia. DOCA-treated rats drank water supplemented with 1.0% NaCl and 0.2% KCl, whereas sham rats drank normal tap water. Systolic blood pressures were measured using the standard tail-cuff method. In experiments comparing sham and DOCA responses, sham normotensive and DOCA-salt hypertensive rats were paired.

Isolated Tissue Bath Protocol
Thoracic aorta and vena cava were removed from anesthetized male Sprague-Dawley rats (pentobarbital, 60 mg/kg, IP); placed in physiological salt solution (PSS) containing (in mmol/L): NaCl, 130; KCl, 4.7; KH₂PO₄, 1.18; MgSO₄ 7H₂O, 1.17; CaCl₂ 2H₂O, 1.6; NaHCO₃, 14.9; dextrose, 5.5; and CaNa₂EDTA, 0.03 (pH 7.2); and prepared for measurement of isometric tension as described previously.¹¹ Cumulative concentration response curves to H₂O₂ (1 µmol/L to 1 mmol/L) were performed in aorta and vena cava as follows: (1) under quiescent conditions; (2) after KCl (30 mmol/L) contraction; or (3) after prostaglandin (PG)F₂ (20 µmol/L) contraction. When inhibitors were used, they or vehicle were added for 1 hour before performing cumulative H₂O₂ (1 µmol/L to 1 mmol/L) concentration response curves. In Ca²⁺-free experiments, tissues were washed 3 times at 10-minute intervals with Ca²⁺-free PSS plus EGTA (0.15 mmol/L) and then were washed 3 times at 10-minute intervals with Ca²⁺-free PSS before performing cumulative H₂O₂ concentration response curves.

Data Analysis
Data are presented as mean±SE of the percentage of the initial contraction to phenylephrine (PE; aorta, 10 µmol/L) or norepinephrine (NE; vena cava, 10 µmol/L). In tissues contracted with KCl (30 mmol/L), contraction to H₂O₂ was calculated as the contraction above the maximal KCl response. In tissues contracted with PGF₂ (20 µmol/L), relaxation was calculated as a percentage of contraction to PGF₂ (20 µmol/L). Agonist EC₅₀ values were calculated using a nonlinear regression analysis using the algorithm (effect=maximum response/1+EC₅₀/agonist concentration; GraphPad Prism). When a clear maximum response was not obtained, the EC₅₀ values calculated were considered estimates, with the true EC₅₀ value greater than or equal to the calculated value. When comparing 2 groups, the appropriate Student t test was used, and when comparing 3 groups, 1-way ANOVA with Bonferroni’s post-hoc test was performed. In all of the cases, a P value 0.05 was considered statistically significant.

Chemicals
Acetylcholine, H₂O₂ (30%), norepinephrine, and phenylephrine were solubilized in water; tetraethylammonium and ouabain were solubilized in dimethylsulfoxide; 4-aminopyridine (4-AP) was solubilized in 1N HCl (pH 7.4); and BAY K 8644 was solubilized in ethanol and were purchased from Sigma Chemical Co. Endothelin 1 was purchased from Bachem. Glibenclamide was solublized in DMSO and purchased from Calbiochem.

	Results

Top Abstract Introduction Methods Results Discussion References

 
H₂O₂-Induced Contraction Was Enhanced In Aorta From Hypertensive Rats
Systolic blood pressure was significantly higher in DOCA salt rats (176±6 mm Hg) compared with sham rats (112± 3 mm Hg). Aorta and vena cava from sham normotensive and DOCA-salt hypertensive rats contracted to exogenously added H₂O₂ (1 µmol/L to 1 mmol/L; Figure 1 and Tables 1 and 2). Maximal H₂O₂-induced contraction was significantly enhanced in aorta from DOCA-salt hypertensive rats (sham aorta: 3.7±0.7% of initial PE contraction; DOCA aorta: 11.3±2.5) but unchanged in vena cava from DOCA-salt hypertensive rats compared with their normotensive counterparts (sham vena cava: 84.9±13.4% of initial NE contraction; DOCA vena cava: 72.7±16.9). Consistent with our previous findings,¹¹ we observed that aortic H₂O₂-induced contraction was significantly smaller than venous H₂O₂-induced contraction when H₂O₂-induced contraction was calculated as a percentage of initial adrenergic challenge.

View larger version (20K): [in this window] [in a new window]   Figure 1. H2O2 (1 µmol/L to 1 mmol/L) contracted both rat thoracic aorta (A) and vena cava (B) in a concentration-dependent manner, and this contraction was enhanced in aorta but not vena cava from DOCA-salt hypertensive rats (aorta: n=9 to 11; vena cava: n=4). Points represent mean±SEM. *Statistically significant difference between Sham and DOCA (P<0.05).

View this table: [in this window] [in a new window]   TABLE 1. Maximal H2O2-Induced Contraction of Aorta and Vena Cava From Sham Normotensive and DOCA-Salt Hypertensive Rats Under Basal Conditions or After KCl (30 mmol/L) Contraction and Maximal H2O2-Induced Relaxation of Aorta and Vena Cava From Sham Normotensive and DOCA-Salt Hypertensive Rats After PGF2 (20 µmol/L) Contraction

View this table: [in this window] [in a new window]   TABLE 2. Estimated EC50 Values (–log mol/L) for H2O2-Induced Contraction of Aorta and Vena Cava From Sham Normotensive and DOCA-Salt Hypertensive Rats Under Basal Conditions and After KCl (30 mmol/L) Contraction and Estimated EC50 Values (–log mol/L) for H2O2-Induced Relaxation of Aorta and Vena Cava From Sham Normotensive and DOCA-Salt Hypertensive Rats After PGF2 (20 µmol/L) Contraction

Vascular Response to H₂O₂ Varied Depending on the Contractile State of the Blood Vessels
H₂O₂ (1 µmol to 1 mmol/L) induced relaxation of aorta (Figure 2A) and vena cava (Figure 2B) when vessels were contracted with PGF₂ (20 µmol/L; data summarized in Tables 1 and 2 ). H₂O₂-induced relaxation was significantly rightward shifted in aorta from DOCA-salt hypertensive rats compared with normotensive rats [sham aorta estimated EC₅₀ (–log mol/L): 4.0±0.1; DOCA aorta estimated EC₅₀ (–log mol/L): 3.4±0.1] but was unchanged in vena cava from DOCA-salt hypertensive rats [sham vena cava estimated EC₅₀ (–log mol/L): 4.1±0.2; DOCA vena cava estimated EC₅₀ (–log mol/L): 3.7±0.1]. When PGF₂ cumulative concentration response curves were performed in sham and DOCA aorta, there were no differences in EC₅₀ values or maximal PGF₂-induced contraction (data not shown), suggesting that differences in PGF₂ contraction were not responsible for differences in sham and DOCA aortic H₂O₂-induced relaxation after PGF₂ contraction.

View larger version (32K): [in this window] [in a new window]   Figure 2. H2O2 relaxed rat thoracic aorta (A) and vena cava (B) from sham and DOCA rats when they were contracted with PGF2 (20 µmol/L) (aorta: n=5; vena cava: n=4). H2O2 contracted rat thoracic aorta (C) and vena cava (D) when they were contracted with KCl (30 mmol/L; aorta: n=6, vena cava: n=5 to 6). Neither NE (E) nor endothelin 1 (F)-induced contraction was enhanced in aorta contracted with KCl (30 mmol/L; aorta: n=4). Points represent mean±SEM. *Statistically significant difference between sham control and sham KCl; Statistically significant difference between DOCA control and DOCA KCl (P<0.05).

The same concentrations of H₂O₂ (1 µmol/L to 1 mmol/L) induced contraction of aorta (Figure 2C) and vena cava (Figure 2D) when vessels were contracted with KCl (30 mmol/L; data summarized in Tables 1 and 2). Maximal H₂O₂-induced contraction was enhanced 15-fold in KCl (30 mmol/L)-contracted sham aorta (sham control: 4.9±0.4% of initial PE contraction; sham KCl: 53.8±6.5) and enhanced 5-fold in DOCA aorta (DOCA control: 14.3±3.3% of initial PE contraction; DOCA KCl: 51.0±8.2) compared with maximal aortic H₂O₂-induced contraction under basal conditions. Maximal H₂O₂-induced contraction was enhanced 2-fold in KCl (30 mmol/L)-contracted sham vena cava (sham control: 80.0±15.7% of initial NE contraction; sham KCl: 175.4±67.7), although venous H₂O₂-induced contraction above KCl-induced contraction was highly variable. Enhanced aortic contraction after KCl (30 mmol/L) contraction occurred specifically for H₂O₂, because KCl (30 mmol/L) contraction did not potentiate maximal aortic contraction to other agonists, such as norepinephrine (Figure 2E) or endothelin 1 (Figure 2F).

Nonspecific K⁺ Channel and Na⁺/K⁺ ATPase Blockade Potentiated Aortic H₂O₂-Induced Contraction
When aorta were incubated with tetraethylammonium (TEA; 10 mmol/L), a nonspecific K⁺ channel blocker, maximal H₂O₂-induced contraction was significantly enhanced in sham and DOCA aorta (Figure 3A; sham control: 3.0±1.4% of initial PE contraction; sham TEA: 61.4±21.0; DOCA control: 13.2±3.1; DOCA TEA: 46.5±9.6) but was unchanged in vena cava (Figure 3B; sham control: 80.7±13.4% of initial NE contraction; sham TEA: 98.0±4.1). Specific K⁺ channel inhibitors, TEA (1 mmol/L) to inhibit Ca²⁺-dependent K⁺ (BK_Ca) channels, glibenclamide (2 µmol/L) to inhibit ATP-dependent K⁺ (K_ATP) channels, and 4-AP (3 mmol/L) to inhibit voltage-gated K⁺ channels, were used individually to determine whether a specific family of K⁺ channels was involved in the potentiation of aortic H₂O₂-induced contraction, but none of these inhibitors potentiated aortic H₂O₂-induced contraction (data not shown). A combination of TEA (1 mmol/L), glibenclamide (2 µmol/L), and 4-AP (3 mmol/L) to achieve more complete K⁺ channel blockade did not potentiate aortic H₂O₂-induced contraction (data not shown). TEA (10 µmol/L to 50 mmol/L) caused a concentration-dependent contraction of thoracic aorta from DOCA-salt hypertensive rats and had no effect on thoracic aorta from normotensive rats or vena cava from normotensive and DOCA-salt hypertensive rats (data not shown).

View larger version (38K): [in this window] [in a new window]   Figure 3. TEA (10 mmol/L), a K+ channel blocker, potentiated aortic (A) but not venous (B) H2O2-induced contraction (aorta: n=7 to 8; vena cava: n=5 to 6). Ouabain (1 mmol/L) potentiated both aortic (C) and venous (D) H2O2-induced contraction (aorta: n=4; vena cava: n=7). Points represent mean±SEM. *Statistically significant difference between sham control and sham TEA; Statistically significant difference between DOCA control and DOCA TEA (P<0.05).

Na⁺/K⁺ ATPase blockade using ouabain (1 mmol/L) significantly enhanced maximal sham aortic H₂O₂-induced contraction (Figure 3C; sham control: 2.3±0.9% of initial PE contraction; sham ouabain: 29.3±5.6) and maximal sham venous H₂O₂-induced contraction (Figure 3D; sham control: 19.1±9.3% of initial NE contraction; sham ouabain: 249.2±41.6). Ouabain (1 mmol/L) did not contract rat thoracic aorta or vena cava from sham normotensive rats.

Extracellular Ca²⁺ Influx Was Required for Aortic but Not Venous H₂O₂-Induced Contraction
Removal of extracellular Ca²⁺, using Ca²⁺-free PSS in the presence of EGTA, significantly reduced aortic H₂O₂-induced contraction in the presence of elevated extracellular KCl (30 mmol/L) from sham normotensive rats (sham KCl/control: 36.8±6.1% of initial PE contraction; sham KCl/Ca²⁺-free: 3.8±1.5; Figure 4A). This maneuver also significantly reduced KCl-induced contraction (data not shown). Removal of extracellular Ca²⁺ did not significantly reduce maximal venous H₂O₂-induced contraction (Figure 4B) from sham normotensive rats (sham control: 71.1±14.5% of initial NE contraction; sham Ca²⁺-free: 72.0±7.9). L-type Ca²⁺ channel activation using BAY K8644 (100 nmol/L), which did not contract sham normotensive aorta or vena cava, significantly potentiated maximal sham aortic H₂O₂-induced contraction (sham control: 4.5±0.7% of initial PE contraction; sham BAY K8644: 19.9±5.5; Figure 4C) but not maximal sham venous H₂O₂-induced contraction (sham control: 84.6±17.3% of initial NE contraction; sham BAY K8644: 76.6±11.9; Figure 4D).

View larger version (37K): [in this window] [in a new window]   Figure 4. In the absence of extracellular Ca2+, aortic H2O2-induced contraction after KCl (30 mmol/L) was significantly reduced (A), whereas maximal venous H2O2-induced contraction under quiescent conditions was unchanged (B; aorta: n=4; vena cava: n=4). L-type Ca2+ channel activation with BAY K 8644 (100 nmol/L) significantly potentiated aortic (C) but not venous (D) H2O2-induced contraction under quiescent conditions (aorta: n=7; vena cava: n=4). Points represent mean±SEM. *Statistically significant difference from control (P<0.05).

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
Pleiotropic Effects of H₂O₂ on Vascular Tone
H₂O₂ is a complex signaling molecule capable of having multiple seemingly contradictory effects on vascular smooth muscle tone. Why H₂O₂ causes relaxation in some vessels and contraction in others has been the topic of many investigations, but as to date no definitive conclusion has been reached as to how H₂O₂ causes such pleiotropic effects. Moreover, there has not been a comparison of the vasoactive properties of H₂O₂ in arteries and veins. Lucchesi et al⁹ observed that when K⁺ channel function was compromised, (ie, in the presence of elevated extracellular [K⁺]), H₂O₂ caused contraction. However, if K⁺ channel function was not compromised (in phenylephrine-contracted vessels), H₂O₂ induced relaxation. Our results suggest that a common phenomenon–we propose K⁺ channel blockade–induced by elevated extracellular [K⁺], K⁺ channel blockade, or Na⁺/K⁺ ATPase blockade allows H₂O₂ to cause contraction. Stimulation of K⁺ channel opening, specifically, K_Ca, K_ATP, and K_V, has been implicated as a mechanism of H₂O₂-induced relaxation.²⁰ Thus, we hypothesize that H₂O₂ normally opens some K⁺ channels, but when these K⁺ channels are unable to open, the contractile pathways activated by H₂O₂ are revealed. Another possible explanation for our data are that elevated extracellular [K⁺], K⁺ channel blockade, or Na⁺/K⁺ ATPase blockade depolarize smooth muscle, and this depolarization mediates H₂O₂-induced contraction. Like KCl-induced contraction, PGF₂-induced contraction is accompanied by smooth muscle depolarization, but PGF₂-induced depolarization involves Cl^– efflux and Na⁺ influx, with no reported changes in K⁺ channel activity.²¹ In PGF₂-contracted aorta and vena cava, K⁺ channel function may be uncompromised, permitting H₂O₂-induced relaxation to be observed. Thus, our data suggest that K⁺ channel function determines the end vascular response, contraction or relaxation, to H₂O₂, and we observed that this dependence on K⁺ channel function does not differ between arteries and veins.

To our surprise, specific pharmacological inhibition of BK_Ca, K_ATP, or voltage-dependent K⁺ channels (K_V) or a combination of these K⁺ channel inhibitors did not potentiate aortic H₂O₂-induced contraction as did TEA (10 mmol/L) or KCl (30 mmol/L). We speculate that TEA (10 mmol/L) and KCl (30 mmol/L) caused a greater degree of K⁺ blockade than individual K⁺ channel blockers and that greater K⁺ channel blockade was necessary for enhanced aortic H₂O₂-induced contraction. However, without electrophysiological data, we cannot compare the degree of K⁺ channel blockade between the different treatments, and this idea must remain a speculation.

Differences in Arterial and Venous H₂O₂-Induced Contraction
Under basal conditions, veins contract more robustly to H₂O₂ than do arteries,¹¹ and why this occurs is unknown. Differences in the activity of catalase and glutathione peroxidase (antioxidant enzymes that degrade H₂O₂) in arteries and veins may explain why basal contractile responses to H₂O₂ varied between arteries and veins. However, because pharmacological manipulations elicited both contraction and relaxation to H₂O₂ in arteries and veins, we chose to take a more mechanistic rather than a molecular approach to understanding differences in arterial and venous H₂O₂-induced contraction. Increasing extracellular K⁺ and Na⁺/K⁺ ATPase blockade both potentiated aortic and venous H₂O₂-induced contraction, possibly through indirectly increasing intracellular Ca²⁺. Interestingly, K⁺ channel blockade did not potentiate venous H₂O₂-induced to the same degree that it potentiated aortic H₂O₂-induced contraction. This suggests that if compromising K⁺ channel activity reveals H₂O₂-induced contraction, then veins have less tonic K⁺ channel activity than arteries under basal conditions. Differences in K⁺ channel expression in arteries and veins may explain why K⁺ channel blockade failed to significantly potentiate venous H₂O₂-induced contraction. Li et al²² observed differences in mRNA expression of K_ATP channels in arteries and veins; specifically, rat aorta expressed low levels of K_ATP channel mRNA, whereas vena cava had no detectable K_ATP channel mRNA. To our knowledge, it is unknown whether there are other arterial and venous differences in K⁺ channel expression and whether different ion channels determine membrane potential, although membrane potential is the same in arterial and venous smooth muscle cells.²³

Differences in arterial and venous Ca²⁺ handling may contribute to differences in arterial and venous contraction to H₂O₂. The literature regarding the role of Ca²⁺ in H₂O₂-induced contraction is controversial. In pulmonary arteries, H₂O₂-induced contraction was independent of extracellular Ca²⁺ influx,^1,2 whereas in canine basilar arteries and rat thoracic aorta, H₂O₂-induced contraction was dependent on extracellular Ca²⁺ influx and release of intracellular Ca²⁺.^5,24 In perspective with the other studies examining the role of Ca²⁺ in H₂O₂-induced contraction, there appears to be species, experimental condition–specific, and vessel-specific differences in the role of extracellular influx of [Ca²⁺] in H₂O₂-induced contraction. We observed that H₂O₂-induced contraction in rat thoracic vena cava did not require extracellular Ca²⁺ influx, whereas aortic H₂O₂-induced contraction was dependent on extracellular Ca²⁺ influx. We also observed that L-type Ca²⁺ channel activation potentiated aortic H₂O₂-induced contraction (but to a lesser extent than with TEA or increased extracellular K⁺ treatment) and had no effect on venous H₂O₂-induced contraction. Thus, we concluded that differences in K⁺ channel activity and extracellular Ca²⁺ influx account for differences in arterial and venous contraction to H₂O_2.

DOCA-Salt Hypertension Is Associated With Changes in Arterial Reactivity to H₂O₂
We observed that H₂O₂-induced contraction was significantly enhanced in aorta but not vena cava from DOCA-salt hypertensive rats compared with sham normotensive rats, consistent with observations that arterial contraction to other agonists, such as norepinephrine and serotonin, are enhanced in DOCA-salt hypertension.¹³ Enhanced H₂O₂-induced contraction has been observed in arteries from spontaneously hypertensive rats.^3,14 Enhanced arterial vasoconstriction in hypertension has largely been attributed to increased Rho kinase¹³ and L-type Ca²⁺ channel activity.²⁵ Changes in membrane potential and K⁺ channel activity also occur in hypertension and may be involved in arterial hyperresponsiveness. Arterial smooth muscle cells from spontaneously hypertensive rats are depolarized compared with normotensive Wistar-Kyoto rats.^15,26,27 The depolarization of hypertensive arterial smooth muscle cells may mediate increased Rho kinase activity and L-type Ca²⁺ channel activity in hypertension, because arterial smooth muscle depolarization with high concentrations of KCl increases RhoA activity²⁸ and expression of the pore-forming _1C subunit of the L-type Ca²⁺ channel.²⁵ We observed that aortic H₂O₂-induced contraction requires extracellular Ca²⁺ influx and conclude that both enhanced Rho kinase and L-type Ca²⁺ channel activity may account for enhanced aortic but not venous H₂O₂-induced contraction in DOCA-salt hypertension.

In addition to enhanced sensitivity to a number of vasoconstrictors, reduced vasodilation because of endothelial dysfunction is another vascular contractile change that accompanies hypertension.^13,29 We observed reduced H₂O₂-induced relaxation in PGF₂-contracted aorta from hypertensive rats compared with normotensive rats, and our results are consistent with the observation that H₂O₂-induced relaxation is reduced in mesenteric arteries from spontaneously hypertensive rats.²⁰ It is interesting to note that the contractile changes that occurred in arteries from DOCA-salt hypertensive rats (enhanced contraction to H₂O₂ and reduced relaxation to H₂O₂) were not observed in vena cava from hypertensive rats.

Changes in K⁺ channel activity may drive changes in arterial contractility observed in hypertension. Total K⁺ currents are reduced in arterial smooth muscle cells from spontaneously hypertensive rats,²⁶ but the expression and functional activity of Ca²⁺-activated K⁺ channels, specifically BK_Ca channels, is increased in hypertension, whereas K_V channel activity is reduced.^16,26,30 We observed that TEA (10 µmol/L to 50 mmol/L) caused a concentration-dependent contraction of thoracic aorta from DOCA-salt hypertensive rats, suggesting that arteries from DOCA-salt hypertensive rats display increased BK_Ca channel activity as demonstrated by Xu et al.³¹ However, we have not performed electrophysiological experiments to confirm our tissue bath results. Despite increased BK_Ca channel activity in arteries from DOCA-salt hypertensive rats (which would tend to hyperpolarize smooth muscle cells and prevent contraction), basal H₂O₂-induced contraction was enhanced in arteries from hypertensive rats, and we hypothesize that this was because of either increased Rho kinase or L-type Ca²⁺ channel activity. Our data also suggest that H₂O₂-induced relaxation in aorta likely does not occur via BK_Ca channel opening, because in DOCA aorta where there was an apparent increase in BK_Ca channel activity, reduced H₂O₂-induced relaxation was observed. Interestingly, we did not observe similar changes in K⁺ channel activity in veins from DOCA-salt hypertensive rats.

Perspectives
The vascular effects of H₂O₂ are complex, and the mechanisms of H₂O₂-induced contraction differ between arteries and veins, specifically the dependence on extracellular Ca²⁺ influx and K⁺ channel activity differ in arteries and veins. DOCA-salt hypertension is accompanied by increased H₂O₂-induced contraction and reduced H₂O₂-induced relaxation in arteries but not in veins. It is difficult to predict the in vivo vascular response to H₂O₂ from in vitro experiments; however, our data suggests that whereas veins contract more robustly to H₂O₂, in hypertension, arterial but not venous reactivity to H₂O₂ is altered such that elevated plasma H₂O₂ will lead to increases in arterial but not venous tone. This work highlights the complex functions of reactive oxygen species in vascular tissue and continues to a support a profound difference in arterial versus venous function both in normal and high blood pressure.

	Acknowledgments

 
This work was supported by National Heart, Lung, and Blood Institute Grant PO1 HL-70687 and a Ford Foundation Diversity Fellowship.

Received November 28, 2005; first decision December 12, 2005; accepted December 16, 2005.

	References

Top Abstract Introduction Methods Results Discussion References

 
1. Jin N, Rhoades RA. Activation of tyrosine kinases in H₂O₂-induced contraction in pulmonary artery. Am J Physiol. 1997; 272: H2686–H2692.[Medline] [Order article via Infotrieve]

2. Pelaez NJ, Braun TR, Paul RJ, Meiss RA, Packer S. H₂O₂ mediates Ca²⁺- and MLC₂₀ phosphorylation-independent contraction in intact and permeabilized vascular muscle. Am J Physiol. 2000; 279: H1185–H1193.

3. Rodriguez-Martinez MA, Garcia-Cohen EC, Baena AB, Gonzalez R, Salaices M, Marin J. Contractile responses elicited by hydrogen peroxide in aorta from normotensive and hypertensive rats. Endothelial modulation and mechanism involved. Br J Pharmacol. 1998; 125: 1329–1335.[CrossRef][Medline] [Order article via Infotrieve]

4. Sheehan DW, Giese EC, Gugino SF, Russell JA. Characterization and mechanisms of H₂O₂-induced contractions of pulmonary arteries. Am J Physiol. 1993; 264: H1542–H1547.[Medline] [Order article via Infotrieve]

5. Sotnikova R. Investigation of the mechanisms underlying H₂O₂-evoked contraction in the isolated rat aorta. Gen Pharmacol. 1998; 31: 115–119.[Medline] [Order article via Infotrieve]

6. Wei EP, Kontos HA, Beckman JS. Mechanisms of cerebral vasodilation by superoxide, hydrogen peroxide, and peroxynitrite. Am J Physiol. 1996; 271: H1262–H1266.[Medline] [Order article via Infotrieve]

7. Gil-Longo J, Gonzalez-Vazquez C. Characterization of four different effects elicited by H₂O₂ in rat aorta. Vascul Pharmacol. 2005; 43: 128–138.[CrossRef][Medline] [Order article via Infotrieve]

8. Barlow RS, White RE. Hydrogen peroxide relaxes porcine coronary arteries by stimulating BKCa channel activity. Am J Physiol. 1998; 275: H1283–H1289.[Medline] [Order article via Infotrieve]

9. Lucchesi PA, Belmadani S, Matrougui K. Hydrogen peroxide acts as both vasodilator and vasoconstrictor in the control of perfused mouse mesenteric resistance arteries. J Hypertens. 2005; 23: 571–579.[Medline] [Order article via Infotrieve]

10. Iesaki T, Okada T, Shimada I, Yamaguchi H, Ochi R. Decrease in Ca²⁺ sensitivity as a mechanism of hydrogen peroxide-induced relaxation of rabbit aorta. Cardiovasc Res. 1996; 31: 820–825.[CrossRef][Medline] [Order article via Infotrieve]

11. Thakali K, Demel SL, Fink GD, Watts SW. Endothelin-1-induced contraction in veins is independent of hydrogen peroxide. Am J Physiol Heart Circ Physiol. 2005; 289: H1115–H11122.[Abstract/Free Full Text]

12. Watts SW. Serotonin-induced contraction in mesenteric resistance arteries: signaling and changes in deoxycorticosterone acetate-salt hypertension. Hypertension. 2002; 39: 825–829.[Abstract/Free Full Text]

13. Lee DL, Webb RC, Jin L. Hypertension and RhoA/Rho-kinase signaling in the vasculature: highlights from the recent literature. Hypertension. 2004; 44: 796–799.[Abstract/Free Full Text]

14. Gao YJ, Lee RM. Hydrogen peroxide induces a greater contraction in mesenteric arteries of spontaneously hypertensive rats through thromboxane A(2) production. Br J Pharmacol. 2001; 134: 1639–1646.[CrossRef][Medline] [Order article via Infotrieve]

15. Silva EG, Frediani-Neto E, Ferreira AT, Paiva AC, Paiva TB. Role of Ca(+)-dependent K-channels in the membrane potential and contractility of aorta from spontaneously hypertensive rats. Br J Pharmacol. 1994; 113: 1022–1028.[Medline] [Order article via Infotrieve]

16. Cox RH, Lozinskaya I, Dietz NJ. Calcium exerts a larger regulatory effect on potassium+ channels in small mesenteric artery myocytes from spontaneously hypertensive rats compared to Wistar-Kyoto rats. Am J Hypertens. 2003; 16: 21–27.[CrossRef][Medline] [Order article via Infotrieve]

17. Safar ME, London GM, Weiss YA, Milliez PL. Altered blood volume regulation in sustained essential hypertension: a hemodynamic study. Kidney Int. 1975; 8: 42–47.[CrossRef][Medline] [Order article via Infotrieve]

18. Johnson RJ, Galligan JJ, Fink GD. Effect of an ET(B)-selective and a mixed ET(A/B) endothelin receptor antagonist on venomotor tone in deoxycorticosterone-salt hypertension. J Hypertens. 2001; 19: 431–440.[CrossRef][Medline] [Order article via Infotrieve]

19. Martin DS, Rodrigo MC, Appelt CW. Venous tone in the developmental stages of spontaneous hypertension. Hypertension. 1998; 31: 139–144.[Abstract/Free Full Text]

20. Gao YJ, Zhang Y, Hirota S, Janssen LJ, Lee RM. Vascular relaxation response to hydrogen peroxide is impaired in hypertension. Br J Pharmacol. 2004; 142: 143–149.[CrossRef][Medline] [Order article via Infotrieve]

21. Jiang J, Backx PH, Teoh H, Ward ME. Role of Cl- currents in rat aortic smooth muscle activation by prostaglandin F2 alpha. Eur J Pharmacol. 2003; 481: 133–140.[Medline] [Order article via Infotrieve]

22. Li L, Wu J, Jiang C. Differential expression of Kir6.1 and SUR2B mRNAs in the vasculature of various tissues in rats. J Membr Biol. 2003; 196: 61–69.[CrossRef][Medline] [Order article via Infotrieve]

23. Kreulen DL. Activation of mesenteric arteries and veins by preganglionic and postganglionic nerves. Am J Physiol. 1986; 251: H1267–H1275.[Medline] [Order article via Infotrieve]

24. Yang ZW, Zheng T, Wang J, Zhang A, Altura BT, Altura BM. Hydrogen peroxide induces contraction and raises [Ca2+]i in canine cerebral arterial smooth muscle: participation of cellular signaling pathways. Naunyn Schmiedebergs Arch Pharmacol. 1999; 360: 646–653.[CrossRef][Medline] [Order article via Infotrieve]

25. Pesic A, Madden JA, Pesic M, Rusch NJ. High blood pressure upregulates arterial L-type Ca²⁺ channels: is membrane depolarization the signal? Circ Res. 2004; 94: 97–104.

26. Zhang Y, Gao YJ, Zuo J, Lee RM, Janssen LJ. Alteration of arterial smooth muscle potassium channel composition and BKCa current modulation in hypertension. Eur J Pharmacol. 2005; 514: 111–119.[Medline] [Order article via Infotrieve]

27. Sadanaga T, Ohya Y, Ohtsubo T, Goto K, Fujii K, Abe I. Decreased 4-aminopyridine sensitive K+ currents in endothelial cells from hypertensive rats. Hypertens Res. 2002; 25: 589–596.[CrossRef][Medline] [Order article via Infotrieve]

28. Sakurada S, Takuwa N, Sugimoto N, Wang Y, Seto M, Sasaki Y, Takuwa Y. Ca2+-dependent activation of Rho and Rho kinase in membrane depolarization-induced and receptor stimulation-induced vascular smooth muscle contraction. Circ Res. 2003; 93: 548–556.[Abstract/Free Full Text]

29. Cai H, Harrison DG. Endothelial dysfunction in cardiovascular diseases: the role of oxidant stress. Circ Res. 2000; 87: 840–844.[Abstract/Free Full Text]

30. Liu Y, Pleyte K, Knaus HG, Rusch NJ. Increased expression of Ca²⁺-sensitive K⁺ channels in aorta of hypertensive rats. Hypertension. 1997; 30: 1403–1409.[Abstract/Free Full Text]

31. Xu H, Bian X, Watts SW, Hlavacova A. Activation of vascular BK channel by tempol in DOCA-salt hypertensive rats. Hypertension. 2005; 46: 1154–1162.[Abstract/Free Full Text]

This article has been cited by other articles:

				T. Szasz, J. M. Thompson, and S. W. Watts A comparison of reactive oxygen species metabolism in the rat aorta and vena cava: focus on xanthine oxidase Am J Physiol Heart Circ Physiol, September 1, 2008; 295(3): H1341 - H1350. [Abstract] [Full Text] [PDF]

				A. Just, C. L. Whitten, and W. J. Arendshorst Reactive oxygen species participate in acute renal vasoconstrictor responses induced by ETA and ETB receptors Am J Physiol Renal Physiol, April 1, 2008; 294(4): F719 - F728. [Abstract] [Full Text] [PDF]

				T. Szasz, K. Thakali, G. D. Fink, and S. W. Watts A Comparison of Arteries and Veins in Oxidative Stress: Producers, Destroyers, Function, and Disease Experimental Biology and Medicine, January 1, 2007; 232(1): 27 - 37. [Abstract] [Full Text] [PDF]

				K. Thakali, L. Davenport, G. D. Fink, and S. W. Watts Cyclooxygenase, p38 Mitogen-Activated Protein Kinase (MAPK), Extracellular Signal-Regulated Kinase MAPK, Rho Kinase, and Src Mediate Hydrogen Peroxide-Induced Contraction of Rat Thoracic Aorta and Vena Cava J. Pharmacol. Exp. Ther., January 1, 2007; 320(1): 236 - 243. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) All Versions of this Article: 47/3/482    most recent 01.HYP.0000201540.91234.8fv1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Thakali, K. Articles by Watts, S. W. Search for Related Content PubMed PubMed Citation Articles by Thakali, K. Articles by Watts, S. W. Pubmed/NCBI databases Compound via MeSH Substance via MeSH Hazardous Substances DB CALCIUM COMPOUNDS CALCIUM, ELEMENTAL HYDROGEN PEROXIDE OUABAIN SODIUM CHLORIDE Medline Plus Health Information High Blood Pressure Related Collections Other Vascular biology