Upregulation of renal and vascular nitric oxide synthase in young spontaneously hypertensive rats

Chronic hydrogen-rich saline treatment attenuates vascular dysfunction in spontaneous hypertensive rats

In hypertensive patients, increased oxidative stress is thought to be one important cause of vascular dysfunction. Recently, it has been suggested that hydrogen exerts a therapeutic antioxidant activity by selectively reducing hydroxyl radical and peroxynitrite, the most cytotoxic chemicals of reactive oxygen species (ROS). Herein, we investigated the protective effect of chronic treatment with hydrogen-rich saline (HRS) against vascular dysfunction in SHR and the underlying mechanism. The 8-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto rats (WKY) were randomized into HRS-treated (6ml/kg/day for 3 months, i.p.) and vehicle treated group. Treatment with HRS ameliorated vascular dysfunction including aortic hypertrophy and endothelial function in SHR. Treatment with HRS had no significant effect on blood pressure, but it significantly improved baroreflex function in SHR. Treatment with HRS abated oxidative stress, restored antioxidant enzymes including superoxide dismutase, glutathione peroxidase, and catalase, and suppressed NADPH oxidase. Furthermore, treatment with HRS depressed pro-inflammatory cytokines expression including IL-6 and IL-1β and suppressed NF-κB activation, restored mitochondrial function including ATP formation and membrane integrity. In addition, although treatment with HRS had no significant effect on nitric oxide amount in circulating or aorta, it suppressed endothelial nitric oxide synthase expression and upregulated dimethylarginine dimethylaminohydrolase 2 expression in SHR. In conclusion, treatment with HRS alleviates vascular dysfunction through abating oxidative stress, restoring baroreflex function, suppressing inflammation, preserving mitochondrial function, and enhancing nitric oxide bioavailability.

Neuronal and non-neuronal modulation of sympathetic neurovascular transmission

Noradrenaline, neuropeptide Y and adenosine triphosphate are co-stored in, and co-released from, sympathetic nerves. Each transmitter modulates its own release as well as the release of one another; thus, anything affecting the release of one of these transmitters has consequences for all. Neurotransmission at the sympathetic neurovascular junction is also modulated by non-sympathetic mediators such as angiotensin II, serotonin, histamine, endothelin and prostaglandins through the activation of specific pre-junctional receptors. In addition, nitric oxide (NO) has been identified as a modulator of sympathetic neuronal activity, both as a physiological antagonist against the vasoconstrictor actions of the sympathetic neurotransmitters, and also by directly affecting transmitter release. Here, we review the modulation of sympathetic neurovascular transmission by neuronal and non-neuronal mediators with an emphasis on the actions of NO. The consequences for co-transmission are also discussed, particularly in light of hypertensive states where NO availability is diminished.

Oxidative stress and endothelial dysfunction in hypertension

Systemic arterial hypertension is a highly prevalent cardiovascular risk factor that causes significant morbidity and mortality, and is becoming an increasingly common health problem because of the increasing longevity and prevalence of predisposing factors such as sedentary lifestyle, obesity and nutritional habits. Further complicating the impact of this disease, mild and moderate hypertension are usually asymptomatic, and their presence (and the subsequent increase in cardiovascular risk) is often unrecognized. The pathophysiology of hypertension involves a complex interaction of multiple vascular effectors including the activation of the sympathetic nervous system, of the renin-angiotensin-aldosterone system and of the inflammatory mediators. Subsequent vasoconstriction and inflammation ensue, leading to vessel wall remodeling and, finally, to the formation of atherosclerotic lesions as the hallmark of advanced disease. Oxidative stress and endothelial dysfunction are consistently observed in hypertensive subjects, but emerging evidence suggests that they also have a causal role in the molecular processes leading to hypertension. Reactive oxygen species (ROS) may directly alter vascular function or cause changes in vascular tone by several mechanisms including altered nitric oxide (NO) bioavailability or signaling. ROS-producing enzymes involved in the increased vascular oxidative stress observed during hypertension include the NADPH oxidase, xanthine oxidase, the mitochondrial respiratory chain and an uncoupled endothelial NO synthase. In the current review, we will summarize our current understanding of the molecular mechanisms in the development of hypertension with an emphasis on oxidative stress and endothelial dysfunction.

Platelet nitric oxide signalling in heart failure: role of oxidative stress

AIMS

Heart failure is associated with deficient endothelial nitric oxide (NO) production as well as increased oxidative stress and accelerated NO degradation. The aim of this study was to evaluate platelet NO biosynthesis and superoxide anion (O(2)(-)) production in patients with heart failure.

METHODS AND RESULTS

In platelets from patients with heart failure due to idiopathic dilated cardiomyopathy (n= 16) and healthy control subjects (n= 23), NO synthase (NOS) activity was evaluated by L-[(3)H]-arginine to l-[(3)H]-citrulline conversion, cGMP was determined by radioimmunoassay, vasodilator-stimulated phosphoprotein (VASP: total and serine-239-phosphorylated) was assessed by western blotting, and O(2)(-) production and O(2)(-) scavenging capacity were measured by pholasin-enhanced chemiluminescence. In platelets from patients with heart failure, basal NOS activity was higher than in those from controls; furthermore, whereas platelet NOS activity increased as expected in response to albuterol or collagen in controls, no increase occurred in platelets from heart failure subjects. Despite this, basal intraplatelet NO-attributable cGMP was lower in heart failure than in control subjects, as was serine-239 phosphorylation of VASP, suggesting a decrease in bioactive NO. Platelets from heart failure subjects exhibited higher basal and collagen-stimulated O(2)(-) production and impaired O(2)(-) scavenging capacity, resulting in higher oxidative stress, consistent with the observed decrease in bioactive NO.

CONCLUSION

In heart failure, despite activation of NOS, platelets produce less bioactive NO, probably as a result of NO scavenging due to increased O(2)(-) production. This functional defect in the platelet l-arginine/NO/guanylyl cyclase pathway could contribute to the platelet activation observed in heart failure.

Urinary nitric oxide metabolites and individual blood pressure progression to overt hypertension

Baseline blood pressure (BP) is the strongest known determinant of progression to hypertension, but for an individualized prediction of the incidence of hypertension, the identification of additional biomarkers is crucial. In animal models of hypertension, renal nitric oxide (NO) handling modifies the systemic BP responses prior to the development of hypertension. This study aimed to evaluate whether urinary NO metabolites (NOx) predict the progression of hypertension in normotensive subjects. Among 62 participants enrolled in the Flemish Study on Environment, Genes and Health Outcomes, we assessed progression to hypertension over 4.6 years. In a case-control design, 49 normotensive subjects including 10 subjects with high-normal blood pressure were enrolled of whom 25 remained normotensive (controls), whereas 24 'progressed' to hypertension (progressors). Thirteen hypertensive patients served as negative controls. Urinary NOx concentration, renal function and the urinary excretion of electrolytes were assessed at baseline and follow-up. At baseline, progressors showed higher BP values than controls and urinary NOx concentration was significantly lower in progressors as compared to the normotensive controls (p < 0.01). In all initially normotensive subjects baseline urinary NOx concentration was associated with follow-up BP (r = -0.55, p < 0.001) and the relative increase of BP over time (r = -0.47, p < 0.001). In progressors baseline urinary NOx was associated with follow-up BP (r = -0.52, p < 0.009) and the relative increase of BP over time (r = -0.44, p = 0.033). Baseline urinary NOx and BP were independent predictors for the relative BP increase. A urinary NOx threshold of <130.5 mg/L predicted 75% of all progressors. In context with high-normal baseline BP, 87.5% of all progressors were identified. These findings indicate that urinary NO metabolites are associated with BP development in normotensive subjects. Moreover, urinary NOx predicts the progression to hypertension independent of baseline BP suggesting urinary NOx as a biomarker for individual new-onset hypertension.

Effect of endurance exercise training on oxidative stress in spontaneously hypertensive rats (SHR) after emergence of hypertension

The purpose of this study is to elucidate the effect of wheel training on oxidative stress maker levels in spontaneous hypertensive rats (SHR). 4-hydroxynonenal and 3-nitrotyrosine levels in the aorta of SHRs were allowed to run for 10 weeks from the age of 15 weeks were measured and compared with those of nonexercised SHRs. The 4-hydroxynonenal and 3-nitrotyrosine levels in the exercised group were significantly lower than those in the nonexercised group. The exercised group showed a significant increase of manganese-containing superoxide dismutase. Endurance exercise showed a possible suppressing effect on the arteriosclerosis development by reducing oxidative stress, even after emergence of hypertension.

Prehypertensive African-American women have preserved nitric oxide and renal function but high cardiovascular risk

AIMS

African-Americans, in particular women, exhibit disproportionate levels of hypertension, inflammation, and oxidative stress compared to other ethnic groups. The relationship between prehypertension, renal function, inflammation, and oxidative stress was examined.

METHODS

Twenty-eight African-American women (53.5 +/- 1.1 years) followed an AHA diet and then underwent 24-hour ambulatory BP (ABP) monitoring. Urinary albumin (uAlb), serum and urinary creatinine, glomerular filtration rate (GFR), 24-hour urinary Na(+) excretion, plasma superoxide dismutase, total antioxidant capacity (TAC), urinary (uNOx) and plasma (pNOx) nitric oxide levels, and high-sensitivity C-reactive protein (hsCRP) were measured.

RESULTS

When the group was divided by average 24-hour ABP into optimal and nonoptimal groups, a significant difference existed between the groups for uNOx (p = 0.001; nonoptimal: 933.5 +/- 140.4, optimal: 425.0 +/- 52.6 mumol/gCr), and for hsCRP (p = 0.018, nonoptimal: 3.9 +/- 0.7, optimal: 1.9 +/- 0.6 mg/l). Significant inverse relationships existed between hsCRP and uNOx and between uAlb and pNOx in the non-optimal group, between GFR and pNOx in the entire group, and positive association existed between TAC and uNOx in the optimal group.

CONCLUSIONS

These results suggest that in African-American women as BP levels rise toward hypertension, the NO/NOS balance may be associated with renal function, and may have implications for CV risk based on their hsCRP levels.

C-type natriuretic peptide effects on cardiovascular nitric oxide system in spontaneously hypertensive rats

The aim was to study the effects of C-type natriuretic peptide (CNP) on mean arterial pressure (MAP) and the cardiovascular nitric oxide (NO) system in spontaneously hypertensive rats (SHR), and to investigate the signaling pathways involved in this interaction. SHR and WKY rats were infused with saline or CNP. MAP and nitrites and nitrates excretion (NO(x)) were determined. Catalytic NO synthase (NOS) activity and endothelial (eNOS), neuronal (nNOS) and inducible NOS (iNOS) were measured in the heart and aorta artery. NOS activity induced by CNP was determined in presence of: iNOS or nNOS inhibitors, NPR-A/B natriuretic peptide receptors blocker and Gi protein and calmodulin inhibitors. CNP diminished MAP and increased NO(x) in both groups. Cardiovascular NOS activity was higher in SHR than in WKY. CNP increased NOS activity, but this activation was lower in SHR. CNP had no effect on NOS isoforms expression. iNOS and nNOS inhibitors did not modify CNP-induced NOS activity. NPR-A/B blockade induced no changes in NOS stimulation via CNP in both tissues. Cardiovascular NOS response to CNP was reduced by Gi protein and calmodulin inhibitors in both groups. CNP interacts with NPR-C receptors, activating Ca-calmodulin eNOS via Gi protein. NOS response to CNP is impaired in the heart and aorta of SHR. Alterations in the interaction between CNP and NO would be involved in the maintenance of high blood pressure in this model of hypertension.

Nitric oxide and oxidative stress in vascular disease

Endothelium-derived nitric oxide (NO) is a paracrine factor that controls vascular tone, inhibits platelet function, prevents adhesion of leukocytes, and reduces proliferation of the intima. An enhanced inactivation and/or reduced synthesis of NO is seen in conjunction with risk factors for cardiovascular disease. This condition, referred to as endothelial dysfunction, can promote vasospasm, thrombosis, vascular inflammation, and proliferation of vascular smooth muscle cells. Vascular oxidative stress with an increased production of reactive oxygen species (ROS) contributes to mechanisms of vascular dysfunction. Oxidative stress is mainly caused by an imbalance between the activity of endogenous pro-oxidative enzymes (such as NADPH oxidase, xanthine oxidase, or the mitochondrial respiratory chain) and anti-oxidative enzymes (such as superoxide dismutase, glutathione peroxidase, heme oxygenase, thioredoxin peroxidase/peroxiredoxin, catalase, and paraoxonase) in favor of the former. Also, small molecular weight antioxidants may play a role in the defense against oxidative stress. Increased ROS concentrations reduce the amount of bioactive NO by chemical inactivation to form toxic peroxynitrite. Peroxynitrite-in turn-can "uncouple" endothelial NO synthase to become a dysfunctional superoxide-generating enzyme that contributes to vascular oxidative stress. Oxidative stress and endothelial dysfunction can promote atherogenesis. Therapeutically, drugs in clinical use such as ACE inhibitors, AT(1) receptor blockers, and statins have pleiotropic actions that can improve endothelial function. Also, dietary polyphenolic antioxidants can reduce oxidative stress, whereas clinical trials with antioxidant vitamins C and E failed to show an improved cardiovascular outcome.

Role of nitric oxide as a key mediator on cardiovascular actions of atrial natriuretic peptide in spontaneously hypertensive rats

The objective was to study atrial natriuretic peptide (ANP) effects on mean arterial pressure (MAP) and cardiovascular nitric oxide (NO) system in spontaneously hypertensive rats (SHRs), investigating the receptors and signaling pathways involved. In vivo, SHRs and Wistar-Kyoto (WKY) rats were infused with saline (0.05 ml/min) or ANP (0.2 μg·kg−1·min−1) for 1 h. MAP and nitrites and nitrates excretion (NOx) were determined. NO synthase (NOS) activity and endothelial (eNOS), neuronal (nNOS) and inducible (iNOS) NOS expression were measured in the heart and aorta. In vitro, heart and aortic NOS activity induced by ANP was determined in the presence of iNOS and nNOS inhibitors, natriuretic peptide receptor (NPR)-A/B blocker, Gi protein, and calmodulin inhibitors. As a result, ANP diminished MAP and increased NOx in both groups. Cardiovascular NOS activity was higher in SHRs than in WKY rats. ANP increased NOS activity, but the activation was lower in SHRs than in WKY rats. ANP had no effect on NOS isoform expression. NOS activity induced by ANP was not modified by iNOS and nNOS inhibitors. NPR-A/B blockade blunted NOS stimulation via ANP in ventricle and aorta but not in atria. Cardiovascular NOS response to ANP was reduced by Gi protein and calmodulin inhibitors in both groups. In conclusion, in atria, ventricle, and aorta, ANP interacts with NPR-C receptors, activating Ca2+-calmodulin eNOS through Gi protein. In ventricle and aorta, NOS activation also involves NPR-A/B. The NOS response to ANP was impaired in heart and aorta of SHRs. The impaired NO-system response to ANP in hypertensive animals, involving alterations in the signaling pathway, could participate in the maintenance of high blood pressure in this model of hypertension.

Effects of deep-frying oil on blood pressure and oxidative stress in spontaneously hypertensive and normotensive rats

OBJECTIVE

Ingestion of deep-frying oil has been reported to cause physiologic and histologic changes in experimental animals' tissue, increase the oxidative stress, and possibly lead to death. The purpose of this study was to investigate the effect of deep-frying oil on oxidative stress and blood pressure in spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats.

METHODS

Deep-frying oil was prepared by frying fresh soybean oil at 180 +/- 5 degrees C for 8 h each day, for 4 consecutive days. Male SHR and WKY rats were fed diets containing 15% fresh soybean oil or deep-frying oil (DO) for 10 wk.

RESULTS

Rats ingesting the DO diet had lower feed efficiency and higher relative liver and kidney weights but deep frying had no significant influence on blood pressure in WKY or SHR rats. The DO diet had no effect on plasma renin activity, aldosterone content, or tissue angiotension-I-converting enzyme activity. WKY rats fed the DO diet showed significantly increased urinary thromboxane B(2) and 8-iso-prostaglandin F(2alpha) excretion, but not urinary 6-keto-prostaglandin F(1alpha) excretion. Diets containing deep-frying oil resulted in increased plasma thiobarbituric acid-reactive substances and nitric oxide contents and decreased plasma total antioxidant capacity in SHR and WKY rats.

CONCLUSION

The ingestion of deep-frying oil seemed not to influence blood pressure or its related parameters, but altered eicosanoid metabolism and elevated oxidative stress in SHR and WKY rats.

Renal NOS activity, expression, and localization in male and female spontaneously hypertensive rats

The goal of this study was to examine the status of the renal nitric oxide (NO) system by determining NO synthase (NOS) isoform activity and expression within the three regions of the kidney in 14-wk-old male and female spontaneously hypertensive rats (SHR). NOS activity, and NOS1 and NOS3 protein expressions and localization were comparable in the renal cortex and outer medulla of male and female SHR. In contrast, male SHR had significantly less NOS1 and NOS3 enzymatic activity (0 +/- 5 and 53 +/- 7 pmol.mg(-1).30 min(-1), respectively) compared with female SHR (37 +/- 16 and 172 +/- 40 pmol.mg(-1).30 min(-1), respectively). Lower levels of inner medullary NOS1 activity in male SHR were associated with less NOS1 protein expression [45 +/- 7 relative densitometric units (RDU)] and fewer NOS1-positive cells in the renal inner medulla compared with female SHR (79 +/- 12 RDU). Phosphorylation of NOS3 is an important determinant of NOS activity. Male SHR had significantly greater phosphorylation of NOS3 on threonine 495 in the renal cortex compared with females (0.25 +/- 0.05 vs. 0.15 +/- 0.06 RDU). NOS3 phosphorylation was comparable in males and females in the other regions of the kidney. cGMP levels were measured as an indirect index of NO production. cGMP levels were significantly lower in the renal cortex (0.08 +/- 0.01 pmol/mg) and inner medulla (0.43 +/- 0.02 pmol/mg) of male SHR compared with females (cortex: 0.14 +/- 0.02 pmol/mg; inner medulla: 0.56 +/- 0.02 pmol/mg). Our data suggest that the effect of the sex of the animal on NOS activity and expression is different in the three regions of the SHR kidney and supports the hypothesis that male SHR have lower NO bioavailability compared with females.

Polyphenol-containing azuki bean (Vigna angularis) extract attenuates blood pressure elevation and modulates nitric oxide synthase and caveolin-1 expressions in rats with hypertension

BACKGROUND AND AIMS

Azuki beans (Vigna angularis) contain polyphenols such as proanthocyanidins that exhibit potential radical scavenging activities. We herein investigated the effects of polyphenol-containing azuki bean extract (ABE) on elevated blood pressure, nitric oxide (NO) production, and expressions of endothelial NO synthase (eNOS), inducible NOS (iNOS), and caveolin-1 proteins in the aorta and kidney of chronically hypertensive rats.

METHODS AND RESULTS

Spontaneously hypertensive rats (SHRs/Izm) with approximately 200 mm Hg systolic blood pressure (SBP) were randomly divided into 2 groups fed either 0% or 0.9% ABE-containing diet. Age-matched normotensive Wistar-Kyoto rats were used as the control. The content of 24-h urinary nitrate/nitrite (NOx) excretion was measured to evaluate NO production. After 8 weeks of treatment, the eNOS, iNOS, and caveolin-1 protein expressions in the aorta and kidney were analyzed by western blotting. The SBP of the ABE-treated SHR was significantly lower than that of the untreated SHR. The level of 24-h urinary NOx excretion was significantly higher in the ABE-treated SHR than in the untreated SHR. The eNOS and iNOS expressions in the aorta and kidney were remarkably upregulated in the untreated SHR but suppressed in the ABE-treated SHR. The vascular and renal caveolin-1 expressions were upregulated in the ABE-treated SHR.

CONCLUSIONS

ABE reduced the elevated blood pressure and increased NO production in long-term treatment. It may be associated with the modulation of eNOS and iNOS protein expressions in the aorta and kidney during the development of hypertension.

The role of allopurinol on oxidative stress in experimental hyperthyroidism

AIM

During hyperthyroidism, production of free oxygen radicals derives, where xanthine oxidase may also play an important role. Allopurinol, a xanthine oxidase inhibitor, has a significant effect on thyrotoxicosis-related oxidative stress. However, the relationship between thyroid hormones, oxidative stress parameters and allopurinol remains to be explored.

METHODS

Forty-two Wistar albino rats were divided into three groups. Rats in group A served as negative controls, while group B had untreated thyrotoxicosis and group C received allopurinol. Hyperthyroidism was induced by daily 0.2 mg/kg L-thyroxine intraperitoneally in groups B and C; 40 mg/kg allopurinol were given daily intraperitoneally. Efficacy of the treatment was assessed after 72 h and 21 days, by measuring serum xanthine oxidase (XO), malondialdehyde (MDA), glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPx) and nitric oxide derivates (NO*x).

RESULTS

In both time periods, serum XO, MDA, GSH and NO*x levels were significantly increased after thyroid hormone induction (p<0.05). Levels of XO, MDA and NO*x decreased with allopurinol treatment (p<0.05). There was a remarkable decrease in triiodothyronine levels in group C after 72 h (p<0.05), and in both triiodothyronine and thyroxine levels in group C after 21 days (p<0.05). There was no difference between groups B and C in means of serum GSH, GR and GPx levels (p>0.05).

CONCLUSIONS

This study suggests an association between allopurinol and the biosynthesis of thyroid hormones. Allopurinol prevents the hyperthyroid state, which is mediated predominantly by triiodothyronine and not by XO. This issue has to be questioned in further studies where allopurinol is administered in control subjects.

Altered nitric oxide calcium responsiveness of aortic smooth muscle cells in spontaneously hypertensive rats depends on low expression of cyclic guanosine monophosphate-dependent protein kinase type I

OBJECTIVES

The nitric oxide/cyclic guanosine monophosphate (GMP)/cyclic GMP-dependent protein kinase type I (cGKI) pathway has been extensively investigated in the spontaneously hypertensive rat (SHR) as a possible pathogenetic factor. Therefore, we investigated the role of nitric oxide/cGKI on intracellular calcium dynamics ([Ca2+]i) of aortic smooth muscle cells isolated from control normotensive Wistar Kyoto rats (WKY) and SHR.

METHODS

Rat aortic smooth muscle cells (RASMCs) were obtained from 12 to 16-week-old WKY and SHR. [Ca2+]i dynamics were monitored by imaging analysis of fura-2-loaded RASMCs. cGKI mRNA and cGKI protein expression were evaluated by reverse transcription-PCR and western blot. Plasmids codifying for enhanced green fluorescent protein (EGFP) or cGKIalpha-EGFP were transfected on SHR RASMCs.

RESULTS

Angiotensin II similarly increased [Ca2+]i in WKY and SHR RASMCs. In WKY RASMCs, S-nitroso-N-acetyl-DL-penicillamine (SNAP, 1-100 micromol/l) reduced the decay time of angiotensin II-induced [Ca2+]i transient. On the contrary, in SHR cells, SNAP was ineffective. Dibutyryl cyclic GMP (1-100 nmol/l), a membrane-permeable cyclic GMP analogue, behaved similarly to SNAP. In naive SHR RASMCs, cGKI mRNA and cGKI protein were low or absent. After transfection of a plasmid encoding for cGKIalpha-EGFP, the [Ca2+]i dynamic of SHR-transfected cells regained sensitivity to the nitric oxide/cyclic GMP pathway.

CONCLUSION

The low expression of cGKI determines the lack of nitric oxide/cyclic GMP-dependent regulation on [Ca2+]i transient in SHR RASMCs. This alteration may contribute to the development of hypertension and explain suboptimal responses to nitroglycerin and other nitric oxide-releasing molecules in patients.

Effect of chronic apocynin treatment on nitric oxide and reactive oxygen species production in borderline and spontaneous hypertension

The purpose of this study was to investigate the effect of NAD(P)H oxidase inhibitor - apocynin (4-hydroxy-3-methoxyacetophenone) on the increase of systolic blood pressure (SBP) in borderline (BHR) and spontaneously hypertensive rats (SHR). Young 6-week-old male BHR (offspring of SHR dams and Wistar Kyoto sires) and SHR were treated with apocynin (30 mg/kg/day) for six weeks. SBP was measured by tail-cuff plethysmography. Nitric oxide synthase (NOS) activity was determined in the left ventricle and aorta. Protein expression of nuclear factor kappa B (NF-kappaB) and NAD(P)H oxidase subunits p67phox and p22phox as well as concentration of cGMP were determined for the left ventricle. Apocynin significantly decreased SBP in all groups investigated. Administration of apocynin had no effect on NOS activity in either tissue studied. However, apocynin decreased protein expression of NF-kappaB (p65) and NAD(P)H oxidase subunit p22phox in both hypertensive groups and p67phox subunit in the SHR group. Moreover, apocynin was able to prevent a decrease in cGMP concentration in the left ventricle of both hypertensive groups. In conclusion, our study demonstrated that apocynin treatment partially prevented SBP rise in borderline and spontaneously hypertensive rats, yet without increasing activity of NOS in the left ventricle and aorta. However, apocynin was able to decrease production of reactive oxygen species in hypertensive rats; thus preventing the decrease in cGMP formation.

Chronic ouabain treatment increases the contribution of nitric oxide to endothelium-dependent relaxation

The aim of this study was to analyze the contribution of nitric oxide, prostacyclin and endothelium-dependent hyperpolarizing factor to endothelium-dependent vasodilation induced by acetylcholine in rat aorta from control and ouabain-induced hypertensive rats. Preincubation with the nitric oxide synthase inhibitor N-omega-nitro-L-arginine methyl esther (L-NAME) inhibited the vasodilator response to acetylcholine in segments from both groups but to a greater extent in segments from ouabain-treated rats. Basal and acetylcholine-induced nitric oxide release were higher in segments from ouabain-treated rats. Preincubation with the prostacyclin synthesis inhibitor tranylcypromine or with the cyclooxygenase inhibitor indomethacin inhibited the vasodilator response to acetylcholine in aortic segments from both groups. The Ca2+-dependent potassium channel blocker charybdotoxin inhibited the vasodilator response to acetylcholine only in segments from control rats. These results indicate that hypertension induced by chronic ouabain treatment is accompanied by increased endothelial nitric oxide participation and impaired endothelium-dependent hyperpolarizing factor contribution in acetylcholine-induced relaxation. These effects might explain the lack of effect of ouabain treatment on acetylcholine responses in rat aorta.

Defective phosphatidylinositol 3-kinase signaling in central control of cardiovascular effects in the nucleus tractus solitarii of spontaneously hypertensive rats

Recently we have shown functional involvement of the phosphatidylinositol 3-kinase (PI3K)-Akt-nitric oxide synthase (NOS) signaling pathway in central control of cardiovascular effects in the nucleus tractus solitarii (NTS) of normotensive Wistar-Kyoto (WKY) rats. In this study we determined whether PI3K/Akt signaling was defective in spontaneously hypertensive rats (SHR). WKY rats and SHR were anesthetized with urethane. Mean blood pressure (MBP) and heart rate (HR) were monitored intra-arterially. Unilateral microinjection (60 nL) of insulin (100 IU/mL) into the NTS produced prominent depressor and bradycardic effects in 8- and 16-week-old normotensive WKY and 8-week-old SHR. However, no significant cardiovascular effects were found in 16-week-old SHR after insulin injection. Furthermore, pretreatment with PI3K inhibitor LY294002 and NOS inhibitor L-NAME into the NTS attenuated the cardiovascular response evoked by insulin in WKY and 8-week-old SHR but not in 16-week-old SHR. Unilateral microinjection of 1 mmol/L of PI(3,4,5)P(3) (phosphatidylinositol 3,4,5-triphosphate), a phospholipids second messenger produced by PI3K, into the NTS produced prominent depressor and bradycardic effects in 8- or 16-week-old WKY rats as well as 8-week-old SHR but not in 16-week-old SHR. Western blot analysis showed no significant increase in Akt phosphorylation in 8-week-old pre-hypertensive SHR after insulin injection. Similar results were also found in hypertensive 16-week-old SHR. Our results indicate that the Akt-independent signaling pathway is involved in NOS activation to regulate cardiovascular effects in the NTS of 8-week-old pre-hypertensive SHR. Both Akt-dependent and Akt-independent signaling pathways are defective in hypertensive 16-week-old SHR.

Nitric oxide, tetrahydrobiopterin, oxidative stress, and endothelial dysfunction in hypertension

Endothelial dysfunction in the setting of cardiovascular risk factors such as hypercholesterolemia, diabetes mellitus, chronic smoking, as well hypertension, is, at least in part, dependent of the production of reactive oxygen species (ROS) and the subsequent decrease in vascular bioavailability of nitric oxide (NO). ROS-producing enzymes involved in increased oxidative stress within vascular tissue include NADPH oxidase, xanthine oxidase, and mitochondrial superoxide producing enzymes. Superoxide produced by the NADPH oxidase may react with NO, thereby stimulating the production of the NO/superoxide reaction product peroxynitrite. Peroxynitrite in turn has been shown to uncouple eNOS, therefore switching an antiatherosclerotic NO producing enzyme to an enzyme that may accelerate the atherosclerotic process by producing superoxide. Increased oxidative stress in the vasculature, however, is not restricted to the endothelium and also occurs within the smooth muscle cell layer. Increased superoxide production has important consequences with respect to signaling by the soluble guanylate cyclase and the cGMP-dependent kinase I, which activity and expression is regulated in a redox-sensitive fashion. The present review will summarize current concepts concerning eNOS uncoupling, with special focus on the role of tetrahydrobiopterin in mediating eNOS uncoupling.

Fosinopril prevents the pulmonary arterial remodeling in sinoaortic-denervated rats by regulating phosphodiesterase

AIM

To study the effects of fosinopril on sinoaortic denervation (SAD)-induced pulmonary vascular remodeling and on phosphodiesterases (PDE) 1 in rats.

METHODS

SAD was performed in male Sprague-Dawley rats at the age of 10 weeks. The experiment included sham-operated (Sham), SAD, and fosinopril-treated SAD groups. Fosinopril (15 mg/kg/d) was given in rat chow. After 16 weeks of treatment, the pulmonary arteries were taken for investigations, including pharmacological study, measurement of cGMP, light microscopy, immunohistochemistry, Western blotting, and quantitative real-time RT-PCR.

RESULTS

Compared with Sham rats, blood pressure variability (BPV) was significantly increased in the SAD group. However, the mean pulmonary artery pressure (mPAP) was not significant change among 3 groups. After SAD, maximal contraction of pulmonary artery rings to phenylephrine was markedly decreased; the most prominent morphological change in the lung included thickening vascular walls, increasing number of smooth muscle cells, and greater wall-to-lumen ratio; the tissue concentrations of cGMP was reduced significantly; PDE1A or PDE1C expression was upregulated significantly, and endothelial nitric oxide synthase (eNOS) expression was downregulated significantly. Fosinopril treatment prevented these changes induced by SAD.

CONCLUSION

Pulmonary artery remodeling (structural and functional abnormalities) was induced by SAD. Fosinopril, an angiotensin-converting enzyme inhibitor, mainly via potentiating eNOS pathway and inhibiting AngII formation, effectively prevented increased blood pressure variability and vascular remodeling of the pulmonary artery after SAD by regulating the activity levels or expression of eNOS, cGMP, and PDE1s.

Hydroxyhydroquinone interferes with the chlorogenic acid-induced restoration of endothelial function in spontaneously hypertensive rats

BACKGROUND

Coffee is a rich source of antioxidative polyphenols, but epidemiological studies and interventional trials have failed to demonstrate any clear beneficial effects of coffee consumption on hypertension. The interaction between hydroxyhydroquinone (HHQ) and 5-caffeoylquinic acid (CQA) was examined, in an attempt to understand the controversial effects of coffee on hypertension.

METHODS

Male Wistar Kyoto (WKY) rats or spontaneously hypertensive rats (SHRs, 14 weeks old) were divided into the following four groups; those on a control diet, 0.005% HHQ diet, 0.5% CQA diet, and HHQ plus CQA diet. The rats were fed the above diets for 8 weeks, and the tail arterial blood pressure was monitored in conscious rats at 2-week intervals. Urinary nitric oxide (NO) metabolites and hydrogen peroxide (H(2)O(2)) excretion were measured 8 weeks after the start of the experiment. Endothelium-dependent and -independent vasorelaxant responses and immunohistochemical staining for nitrotyrosine were examined in aortas.

RESULTS

HHQ inhibited the CQA-induced improvement in hypertension, urinary NO metabolites or H(2)O(2) excretion, endothelial dysfunction, and nitrotyrosine deposits in aortas in SHR. However, the administration of HHQ alone had little effect on either strain.

CONCLUSIONS

Based on the content ratio of HHQ and chlorogenic acids in coffee, HHQ interfered with the CQA-induced improvement in blood pressure and endothelial function in SHR. The results explain, at least in part, the conflicting action of coffee drinking on hypertension and vascular reactivity.

Oxidative stress attenuates NO-induced modulation of sympathetic neurotransmission in the mesenteric arterial bed of spontaneously hypertensive rats

Current evidence suggests that hyperactivity of the sympathetic nervous system and endothelial dysfunction are important factors in the development and maintenance of hypertension. Under normal conditions the endothelial mediator nitric oxide (NO) negatively modulates the activity of the norepinephrine portion of sympathetic neurotransmission, thereby placing a “brake” on the vasoconstrictor ability of this transmitter. This property of NO is diminished in the isolated, perfused mesenteric arterial bed taken from the spontaneously hypertensive rat (SHR), resulting in greater nerve-stimulated norepinephrine and lower neuropeptide Y (NPY) overflow from this mesenteric preparation compared with that of the normotensive Wistar-Kyoto rat (WKY). We hypothesized that increased oxidative stress in the SHR contributes to the dysfunction in the NO modulation of sympathetic neurotransmission. Here we demonstrate that the antioxidant N-acetylcysteine reduced nerve-stimulated norepinephrine and increased NPY overflow in the mesenteric arterial bed taken from the SHR. Furthermore, this property of N-acetylcysteine was prevented by inhibiting nitric oxide synthase with Nω-nitro-l-arginine methyl ester, demonstrating that the effect of N-acetylcysteine was due to the preservation of NO from oxidation. Despite a reduction in norepinephrine overflow, the nerve-stimulated perfusion pressure response in the SHR mesenteric bed was not altered by the inclusion of N-acetylcysteine. Studies including the Y1 antagonist BIBO 3304 with N-acetylcysteine demonstrated that this preservation of the perfusion pressure response was due to elevated NPY overflow. These results demonstrate that the reduction in the bioavailability of NO as a result of elevated oxidative stress contributes to the increase in norepinephrine overflow from the SHR mesenteric sympathetic neuroeffector junction.

Role of NADPH oxidase and iNOS in vasoconstrictor responses of vessels from hypertensive and normotensive rats

BACKGROUND AND PURPOSE

To analyse the influence of hypertension in the modulation induced by inducible NOS (iNOS)-derived NO and superoxide anion (O(2) (*-)) of vasoconstrictor responses and the sources of O(2) (*-) implicated.

EXPERIMENTAL APPROACH

Vascular reactivity experiments were performed in segments of aorta from normotensive, Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR); protein and mRNA expressions were respectively measured by western blot and quantitative reverse transcription-polymerase chain reaction and O(2) (*-) production was evaluated by ethidium fluorescence.

KEY RESULTS

The contractile responses to phenylephrine (1 nM-30 microM) and 5-hydroxytryptamine (0.1-100 microM) were greater in aortic segments from SHR than WKY. The selective iNOS inhibitor, 1400W (10 microM), increased the phenylephrine contraction only in WKY segments; however, iNOS protein and mRNA expressions were greater in aorta from SHR than WKY. Superoxide dismutase (SOD, 150 U ml(-1)) reduced phenylephrine and 5-hydroxytryptamine responses only in aorta from SHR; the NAD(P)H oxidase inhibitor apocynin (0.3 mM) decreased phenylephrine and 5-hydroxytryptamine responses more in vessels from SHR than WKY. Co-incubation with SOD plus 1400W potentiated the phenylephrine and 5-hydroxytryptamine responses more in segments from SHR than WKY. O(2) (*-) production was greater in aorta from SHR than WKY; apocynin abolished this difference.

CONCLUSIONS AND IMPLICATIONS

Increased O(2) (*-) formation from NADP(H) oxidase in vessels from hypertensive rats contributes to the vasoconstrictor responses and counteract the increase of NO from iNOS and the consequent modulation of these responses.

Renoprotective effects of neuronal NOS-derived nitric oxide and cyclooxygenase-2 metabolites in transgenic rats with inducible malignant hypertension

The present study was performed to determine the effects of neuronal nitric oxide synthase (nNOS) and cyclooxygenase-2 (COX-2) inhibition on blood pressure and renal hemodynamics in transgenic rats with inducible ANG II-dependent malignant hypertension [strain name: TGR(Cyp1a1Ren2)]. Male Cyp1a1-Ren2 rats (n = 7) were fed a normal diet containing indole-3-carbinol (I3C; 0.3%) for 6-9 days to induce malignant hypertension. Mean arterial pressure (MAP) and renal hemodynamics were assessed in pentobarbital sodium-anesthetized Cyp1a1-Ren2 rats before and during intravenous infusion of the nNOS inhibitor S-methyl-l-thiocitrulline (l-SMTC; 1 mg/h). In hypertensive Cyp1a1-Ren2 rats, l-SMTC increased MAP from 169 +/- 3 to 188 +/- 4 mmHg (P < 0.01), which was a smaller increase than in noninduced rats (124 +/- 9 to 149 +/- 9 mmHg, P < 0.01, n = 5). Additionally, l-SMTC decreased renal plasma flow (RPF) to a similar extent (-34 +/- 13 vs. -35 +/- 12%) in the hypertensive and normotensive rats (4.1 +/- 0.2 to 2.7 +/- 0.5 and 3.1 +/- 0.3 to 2.0 +/- 0.3 ml x min(-1) x g(-1), respectively, P < 0.01) but did not alter glomerular filtration rate (GFR) in either group. In additional experiments, administration of the COX-2 inhibitor, nimesulide (3 mg/kg i.v.), during simultaneous infusion of l-SMTC decreased MAP in both hypertensive and noninduced rats (182 +/- 2 to 170 +/- 3 mmHg and 153 +/- 3 to 140 +/- 3 mmHg, respectively, P < 0.01). Nimesulide also decreased RPF (1.9 +/- 0.2 to 0.8 +/- 0.1 ml x min(-1) x g(-1), P < 0.01) and GFR (0.9 +/- 0.1 to 0.4 +/- 0.1 ml x min(-1) x g(-1), P < 0.01) in hypertensive rats but did not alter RPF or GFR in noninduced rats. The present findings demonstrate that both nNOS-derived NO and COX-2 metabolites exert pronounced renal vasodilator influences in hypertensive Cyp1a1-Ren2 rats. The data also indicate that the renal vasodilator effects of COX-2-derived prostanoids in hypertensive Cyp1a1-Ren2 rats are not dependent on nNOS activity.

Characterization of myocardial hypertrophy in prehypertensive spontaneously hypertensive rats: interaction between adrenergic and nitrosative pathways

OBJECTIVE AND METHODS

Left ventricular hypertrophy in human and experimental hypertension is not always associated with pressure overload but seems to precede an increase in blood pressure. In this study, performed in male 5-week-old prehypertensive spontaneously hypertensive rats (SHR; n = 65) and age-matched Wistar-Kyoto rats (n = 56), the relationship between myocardial structure and activation of the adrenergic and nitric oxide systems was evaluated.

RESULTS

Body weight, blood pressure and heart rate were similar in both groups. A higher left ventricle/body weight ratio was found in SHR, as a result of greater mononuclear (+47%) and binuclear (+43%) myocyte volumes, without changes in interstitial collagen. Both adrenergic and nitric oxide pathways were activated in SHR, as expressed by higher myocardial norepinephrine content, tyrosine hydroxylase activity, myocardial nitric oxide synthase 3 expression and protein nitration, indicating greater peroxynitrite (ONOO) generation from nitric oxide and superoxide. No difference was measured in nitric oxide synthase 1 expression, whereas nitric oxide synthase 2 was undetectable. A positive correlation between myocardial tyrosine hydroxylase activity and protein nitration was observed in SHR (r = 0.328; P < 0.01). Early treatment with a superoxide dismutase mimetic, 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl, from the third to the fifth week of age, reduced ONOO generation, protein nitration and sympathetic activation in SHR without changes in myocardial structure.

CONCLUSION

In prehypertensive SHR, left ventricular hypertrophy is associated with adrenergic and nitrosative imbalance. Early superoxide dismutase mimetic treatment in SHR effectively reduces higher myocardial ONOO generation, sympathetic activation, and heart rate without affecting the development of myocardial hypertrophy.

Nitric oxide and superoxide interactions in the kidney and their implication in the development of salt-sensitive hypertension

1. Enhanced superoxide (O2(-)) activity as a result of the inhibition of the superoxide dismutase (SOD) enzyme results in vasoconstrictor and antinatriuretic responses in the canine kidney; these responses were shown to be greatly enhanced during inhibition of nitric oxide synthase (NOS). Glomerular filtration rate remained mostly unchanged during SOD inhibition in the intact nitric oxide (NO) condition, but was markedly reduced during NOS inhibition. These findings indicate that endogenous NO has a major renoprotective effect against O2(-) by acting as an anti-oxidant. Nitric oxide synthase inhibition was also shown to enhance endogenous O2(-) activity. 2. Experiments in our laboratory using dogs, rats and gene knockout mice have shown that renal vasoconstrictor and antinatriuretic responses to acute or chronic angiotensin (Ang) II administration are mediated, in part, by O2(-) generation. In the absence of NO, enhanced O2(-) activity largely contributes to AngII-induced renal tubular sodium reabsorption. Acute or chronic treatment with the O2(-) scavenger tempol in experimental models of hypertension (induced by chronic low-dose treatment with AngII and NO inhibitors) causes an improvement in renal haemodynamics and in excretory function, abolishes salt sensitivity and reduces blood pressure. 3. The present mini review also discusses related studies from many other laboratories implicating a role for O2(-) and its interaction with NO in the development of salt-sensitive hypertension. 4. Overall, the collective data support the hypothesis that an imbalance between the production of NO and O2(-) in the kidney primarily determines the condition of oxidative stress that alters renal haemodynamics and excretory function leading to sodium retention and, thus, contributes to the development of salt-sensitive hypertension.

Nitric oxide, superoxide and renal blood flow autoregulation in SHR after perinatal L-arginine and antioxidants

AIM

Nitric oxide (NO) and superoxide are considered to be regulatory in renal blood flow (RBF) autoregulation, and hence may contribute to development of hypertension. To extend our previous observations that dynamic NO release is impaired in the spontaneously hypertensive rat (SHR) we investigated, firstly, if superoxide dependency of RBF autoregulation is increased in SHR and, secondly, if the beneficial effect of perinatal supplementation in SHR is partly as a result of early correction of RBF autoregulation. We hypothesized that perinatal supplementation by restoring dynamic NO release and/or decreasing superoxide dependency and would improve life-long blood pressure regulation.

METHODS

Autoregulation was studied using stepwise reductions in renal perfusion pressure in anaesthetized male SHR, SHR perinatally supplemented with arginine and antioxidants (SHRsuppl) and Wistar-Kyoto (WKY), prior to and during i.v. Nomega-nitro-l-arginine (NO synthase inhibitor) or tempol (superoxide dismutase mimetic).

RESULTS

Spontaneously hypertensive rat displayed a wider operating range of RBF autoregulation as compared with WKY (59 +/- 4 vs. 33 +/- 2 mmHg, respectively; P < 0.01). Perinatal supplementation in SHR decreased mean arterial pressure, renal vascular resistance and the operating range of RBF autoregulation (43 +/- 3 mmHg; P < 0.01). In addition autoregulation efficiency decreased. RBF autoregulation characteristics shifted towards those of normotensive WKY. However, dynamic NO release was still impaired and no clear differences in superoxide dependency in RBF autoregulation between groups was observed.

CONCLUSION

Perinatal supplements shifted RBF autoregulation characteristics of SHR towards WKY, although capacity of the SHRsuppl kidney to modulate NO production to shear stress still seems impaired. The less strictly controlled RBF as observed in perinatally supplemented SHR could result in an improved long-term blood pressure control. This might partly underlie the beneficial effects of perinatal supplementation.

Effect of L-Carnitine and Propionyl-L-Carnitine on Endothelial Function of Small Mesenteric Arteries from SHR

BACKGROUND

The effect of treatment with either 200 mg x kg(-1) of L-carnitine (LC) or propionyl-L-carnitine (PLC) was studied on endothelial dysfunction of small mesenteric arteries (SMA) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.

METHODS

Systolic blood pressure (SBP) was measured and endothelial and vascular functions were assessed by the effect of carbachol (CCh) and phenylephrine (Phe). O2- produced by SMA and eNOS expression were evaluated by chemiluminescence and Western blot, respectively.

RESULTS

Although SBP was not affected, endothelial relaxation increased in both LC- and PLC-treated SHR. Nevertheless, the CCh-induced contraction remained sensitive to indomethacin in these rats. On the contrary, NO participation was increased in all the groups except for LC-treated WKY. Furthermore, high concentrations of Phe produced NO-dependent relaxation of SMA from PLC-treated rats. Both compounds decreased basal and NADPH-stimulated O2- in SHR toward values observed in WKY. Only PLC increased eNOS protein expression in SHR. Neither LC nor PLC affected endothelium-derived hyperpolarizing factor-induced relaxation.

CONCLUSIONS

LC and its propionate improved endothelial responses of SMA from SHR by decreasing O2- production and thus increasing NO availability. PLC also increased NO synthesis by enhancing eNOS expression.

The effect of N-acetylcysteine and melatonin in adult spontaneously hypertensive rats with established hypertension

The attenuated nitric oxide (NO) formation and/or elevated production of reactive oxygen species are often found in experimental and human hypertension. We aimed to determine possible effects of N-acetylcysteine (1.5 g/kg/day) and N-acetyl-5-methoxytryptamine (melatonin, 10 mg/kg/day) in adult spontaneously hypertensive rats (SHR) with established hypertension. After a six-week-treatment, blood pressure was measured and NO synthase (NOS) activity, concentration of conjugated dienes, protein expression of endothelial NOS, inducible NOS and nuclear factor-kappaB (NF-kappaB) in the left ventricle were determined. Both treatments improved the NO pathway by means of enhanced NOS activity and reduced reactive oxygen species level as indicated by decreased conjugated diene concentrations and lowered NF-kappaB expression. N-acetylcysteine (but not melatonin) also increased the endothelial NOS protein expression. However, only melatonin was able to reduce blood pressure significantly. Subsequent in vitro study revealed that both N-acetylcysteine and melatonin lowered the tone of phenylephrine-precontracted femoral artery via NO-dependent relaxation. Nevertheless, melatonin-induced relaxation also involved NO-independent component which was preserved even after the blockade of soluble guanylate cyclase by oxadiazolo[4,3-a]quinoxalin-1-one. In conclusion, both N-acetylcysteine and melatonin were able to improve the NO/reactive oxygen species balance in adult SHR, but blood pressure was significantly lowered by melatonin only. This implies that a partial restoration of NO/reactive oxygen species balance achieved by the antioxidants such as N-acetylcysteine has no therapeutic effect in adult rats with established hypertension. The observed antihypertensive effect of melatonin is thus mediated by additional mechanisms independent of NO pathway.

Janus-faced role of endothelial NO synthase in vascular disease: uncoupling of oxygen reduction from NO synthesis and its pharmacological reversal

Endothelial NO synthase (eNOS) is the predominant enzyme responsible for vascular NO synthesis. A functional eNOS transfers electrons from NADPH to its heme center, where L-arginine is oxidized to L-citrulline and NO. Common conditions predisposing to atherosclerosis, such as hypertension, hypercholesterolemia, diabetes mellitus and smoking, are associated with enhanced production of reactive oxygen species (ROS) and reduced amounts of bioactive NO in the vessel wall. NADPH oxidases represent major sources of ROS in cardiovascular pathophysiology. NADPH oxidase-derived superoxide avidly interacts with eNOS-derived NO to form peroxynitrite (ONOO(-)), which oxidizes the essential NOS cofactor (6R-)5,6,7,8-tetrahydrobiopterin (BH(4)). As a consequence, oxygen reduction uncouples from NO synthesis, thereby rendering NOS to a superoxide-producing pro-atherosclerotic enzyme. Supplementation with BH(4) corrects eNOS dysfunction in several animal models and in patients. Administration of high local doses of the antioxidant L-ascorbic acid (vitamin C) improves endothelial function, whereas large-scale clinical trials do not support a strong role for oral vitamin C and/or E in reducing cardiovascular disease. Statins, angiotensin-converting enzyme inhibitors and AT1 receptor blockers have the potential of reducing vascular oxidative stress. Finally, novel approaches are being tested to block pathways leading to oxidative stress (e.g. protein kinase C) or to upregulate antioxidant enzymes.

Time course of vascular arginase expression and activity in spontaneously hypertensive rats

There is growing evidence that vascular arginase plays a role in pathophysiology of vascular diseases. We recently reported high arginase activity/expression in young adult hypertensive spontaneously hypertensive rats (SHR). The aim of the present study was to characterize the time course of arginase pathway abnormalities in SHR and to explore the contributing role of hemodynamics and inflammation. Experiments were conducted on 5, 10, 19 and 26-week-old SHR and their age-matched control Wistar Kyoto (WKY) rats. Arginase activity as well as expression of arginase I, arginase II, endothelial and inducible NOS were determined in aortic tissue extracts. Levels of L-arginine, NO catabolites and IL-6 (a marker of inflammation) were measured in plasma. Arginase activity/expression was also measured in 10-week-old SHR previously treated with hydralazine (20 mg/kg/day, per os, for 5 weeks). As compared to WKY, SHR exhibited high vascular arginase I and II expression from prehypertensive to established stages of hypertension. However, a mismatch between expression and activity was observed at the prehypertensive stage. Arginase expression was not related either to plasma IL-6 levels or to expression of NOS. Prevention of hypertension by hydralazine significantly blunted arginase upregulation and restored arginase activity. Importantly, arginase activity and blood pressure (BP) correlated in SHR. In conclusion, our results demonstrate that arginase upregulation precedes blood pressure rising and identify elevated blood pressure as a contributing factor of arginase dysregulation in genetic hypertension. They also demonstrated a close relationship between arginase activity and BP, thus making arginase a promising target for antihypertensive therapy.

Effect of renal injury-induced neurogenic hypertension on NO synthase, caveolin-1, AKt, calmodulin and soluble guanylate cyclase expressions in the kidney

Single injection of a small quantity of phenol into the cortex of one kidney in rats results in development of persistent hypertension (HTN) which is thought to be mediated by activation of renal afferent and efferent sympathetic pathways and sodium retention. Nitric oxide (NO) plays a major role in regulation of renal vascular resistance, tubular Na(+) reabsorption, pressure natriuresis, and thereby systemic arterial pressure. The present study was performed to test the hypothesis that chronic renal injury-induced HTN may be associated with dysregulation of NO system in the kidney. Accordingly, urinary NO metabolite (NO(x)) and cGMP excretions as well as renal cortical tissue (right kidney) expressions of NO synthase (NOS) isoforms [endothelial, neuronal, and inducible NOS, respectively (eNOS, nNOS, and iNOS)], NOS-regulatory factors (Caveolin-1, phospho-AKt, and calmodulin), and second-messenger system (soluble guanylate cyclase [sGC] and phosphodiesterase-5 [PDE-5]) were determined in male Sprague-Dawley rats 4 wk after injection of phenol (50 mul of 10% phenol) or saline into the lower pole of left kidney. The phenol-injected group exhibited a significant elevation of arterial pressure, marked reductions of urinary NO(x) and cGMP excretions, downregulations of renal tissue nNOS, eNOS, Phospho-eNOS, iNOS, and alpha chain of sGC. However, renal tissue AKt, phospho-AKT, Calmodulin, and PDE-5 proteins were unchanged in the phenol-injected animals. In conclusion, renal injury in this model results in significant downregulations of NOS isoforms and sGC and consequent reductions of NO production and cGMP generation by the kidney, events that may contribute to maintenance of HTN in this model.

Allopurinol and enalapril failed to conserve urinary NOx and sodium in ischemic acute renal failure in spontaneously hypertensive rats

BACKGROUND

Ischemia-reperfusion-induced acute renal failure (ARF) is associated with a high mortality in patients with hypertension and with an unfavorable outcome of kidney transplants from marginal donors.

AIM

The influence of allopurinol and enalapril on urinary nitrate/nitrite (UNOx), glomerular filtration rate, plasma and urinary sodium, and hemodynamic parameters was examined in spontaneously hypertensive rats (SHR) with ARF.

METHODS

ARF was induced by right-kidney removal and clamping the left renal artery for 40 min in 50 male 26-week-old SHR weighing 300 +/- 23 g. The rats were randomly allocated to five groups: (1) sham operated; (2) ARF; (3) ARF after pretreatment with 40 mg/kg allopurinol; (4) ARF after pretreatment with 40 mg/kg enalapril, and (5) ARF after pretreatment with 40 mg/kg allopurinol and 40 mg/kg enalapril. Creatinine clearance, UNOx (Griess reaction), cardiac output (dye dilution technique), mean arterial blood pressure, and renal blood flow were measured 24 h after reperfusion. Total vascular resistance and renal vascular resistance were calculated and compared between the groups.

RESULTS

A nonsignificant decrease was found in both daily UNOx excretion and creatinine clearance when pretreated ARF groups and the ARF group without pretreatment were compared (p > 0.05). Significantly lower plasma sodium values (139.5 +/- 4.86 mmol/l) in the allopurinol-pretreated ARF group were found than in the ARF group without pretreatment, in the ARF group pretreated with enalapril, and in the sham SHR group (p = 0.029). The urinary sodium loss was greater in the enalapril-pretreated than in the allopurinol-pretreated ARF group (p = 0.047). Allopurinol and/or enalapril pretreatment decreased total vascular resistance (p = 0.003) in comparison with the sham SHR group.

CONCLUSION

Neither allopurinol nor enalapril nor both were protective against ischemia-reperfusion injury in SHR, nor altered glomerular filtration rate and UNOx in a favorable direction.

Chlorogenic acid attenuates hypertension and improves endothelial function in spontaneously hypertensive rats

BACKGROUND AND OBJECTIVES

Epidemiologic studies indicate that ingestion of vegetables and fruit inhibits the development of cardiovascular disease. Chlorogenic acids are abundant phenolic compounds contained in vegetables and fruits, but the impact of dietary chlorogenic acids on vascular function in hypertension is not known. We therefore examined the effects of 5-caffeoylquinic acid (CQA), a representative chlorogenic acid, on blood pressure and vascular function in age-matched normotensive Wistar-Kyoto rats and spontaneously hypertensive rats.

METHODS AND RESULTS

A single ingestion of CQA (30-600 mg/kg) reduced blood pressure in spontaneously hypertensive rats, an effect that was blocked by administration of a nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester. When spontaneously hypertensive rats were fed diets containing 0.5% CQA for 8 weeks (approximately 300 mg/kg per day), the development of hypertension was inhibited compared with the control diet group. CQA ingestion increased urinary excretion of nitric oxide metabolites and decreased urinary excretion of hydrogen peroxide; decreased NADPH-dependent superoxide anion production in the aorta, suggesting that dietary CQA inhibited vascular NADPH oxidase activity; significantly improved acetylcholine-induced endothelium-dependent vasodilation in the aorta; and markedly reduced the degree of immunohistochemical staining for nitrotyrosine and media hypertrophy in aorta sections. In contrast, CQA had no effects in Wistar-Kyoto rats.

CONCLUSIONS

Dietary CQA reduces oxidative stress and improves nitric oxide bioavailability by inhibiting excessive production of reactive oxygen species in the vasculature, and leads to the attenuation of endothelial dysfunction, vascular hypertrophy, and hypertension in spontaneously hypertensive rats.

Exposure to stress

Stress-induced vascular adaptive response in SHR was investigated, focusing on the endothelium. Noradrenaline responses were studied in intact and denuded aortas from 6-week-old (prehypertensive) and 14-week-old (hypertensive) SHR and age-matched Wistar rats submitted or not to acute stress (20-min swimming and 1-h immobilization 25 min apart), preceded or not by chronic stress (2 sessions 2 days apart of 1-h day immobilization for 5-consecutive days). Stress did not alter the reactivity of denuded aorta. Moreover, no alteration in the EC50 values was observed after stress exposure. In intact aortas, acute stress-induced hyporeactivity to noradrenaline similar between strains at both age. Chronic stress potentiated this adaptive response in 6- and 14-week-old Wistar but not in 6-week-old SHR, and did not alter the reactivity of 14-week-old SHR. Maximum response (g) in intact aortas [6-week-old: Wistar 3.25+/-0.12, Wistar/acute 1.95+/-0.12*, Wistar/chronic 1.36+/-0.21*(+), SHR 1.75+/-0.11, SHR/acute 0.88+/-0.08*, SHR/chronic 0.85+/-0.05*; 14-week-old: Wistar 3.83+/-0.13, Wistar/acute 2.72+/-0.13*, Wistar/chronic 1.91+/-0.19*(+), SHR 4.03+/-0.17, SHR/acute 2.26+/-0.12*, SHR/chronic 4.10+/-0.23; inside the same strain: *P < 0.05 relate to non-stressed rat, +P < 0.05 related to acute stressed rat; n = 6-18]. Independent of age and strain, L-NAME and endothelium removal abolished the stress-induced aorta hyporeactivity.

CONCLUSION

The vascular adaptive response to stress is impaired in SHR, independently of the hypertensive state. Moreover, this vascular adaptive response is characterized by endothelial nitric oxide-system hyperactivity in both strains.

Effect of chronic N-acetylcysteine treatment on the development of spontaneous hypertension

The imbalance between NO (nitric oxide) and ROS (reactive oxygen species) is an important factor in the development of hypertension. The aim of the present study was to determine the preventive and therapeutic effects of NAC (N-acetylcysteine) in SHRs (spontaneously hypertensive rats). Young and adult SHRs and WKY (Wistar-Kyoto) rats were treated with NAC (20 g/l in the drinking water). After 8 weeks of treatment, BP (blood pressure) and NOS (NO synthase) activity, conjugated dienes and GSH (reduced glutathione) in the kidney and left ventricle were determined. Protein expression of eNOS (endothelial NOS), inducible NOS and NF-kappaB (nuclear factor kappaB) were also determined in the left ventricle and kidney. Chronic NAC treatment partially attenuated the rise in BP in young SHRs (179+/-6 compared with 210+/-8 mmHg in untreated animals), but it had no significant effect on BP in adult SHRs. The antioxidant action of NAC, measured as a decrease of the concentration of conjugated dienes or inhibition of NF-kappaB expression, was greater in young than in adult SHRs. Similarly, eNOS protein expression was attenuated more in young than in adult SHRs, although NAC treatment increased NOS activity to a similar extent in both young and adult rats. In conclusion, both decreased ROS production and increased NOS activity appear to participate in the BP changes after NAC treatment in young SHRs. In adult SHRs with established hypertension, however, the secondary alterations (such as pronounced structural remodelling of resistance vessels) might attenuate the therapeutic effect of NAC.

The vasodilator potency of the endothelium-derived relaxing factor, L-S-nitrosocysteine, is impaired in conscious spontaneously hypertensive rats

OBJECTIVE

This study compared the hemodynamic responses elicited by the endothelium-derived relaxing factor (EDRF), L-S-nitrosocysteine (L-SNC), the non-prostanoid EDRF released by acetylcholine (ACh) and nitric oxide (NO)-donors such as MAHMA NONOate, in conscious spontaneously hypertensive (SH) and normotensive Wistar-Kyoto (WKY) rats.

METHODS

The depressor and/or vasodilator responses elicited by intravenous injections of ACh, L-SNC and MAHMA NONOate were determined in adult WKY and SH rats before and after intravenous injection of the NO synthesis inhibitor, N(G)-nitro-L-arginine methylester (L-NAME), or the cyclooxygenase inhibitor, indomethacin.

RESULTS

The responses elicited by ACh and L-SNC were smaller in SH than in WKY rats whereas the responses elicited by MAHMA NONOate were augmented in SH rats. The ACh-induced responses were not diminished after injection of L-NAME in WKY or SH rats. Indomethacin did not affect the responses to any of the vasodilator agents in WKY or SH rats. Addition of L-SNC to whole blood or thoracic aortae from SH rats yielded similar amounts of NO to those of WKY rats.

CONCLUSIONS

The vasodilator potencies of ACh and L-SNC were diminished whereas that of NO was augmented in SH rats. The loss of potency of L-SNC in SH rats was not obviously due to differences in decomposition to NO or the overactivity of cyclooxygenase factors. This study provides the first evidence that diminished endothelium-dependent vasodilation in SH rats may involve a loss of vasodilator potency of endogenous L-SNC.

Endothelium-Dependent Inhibition of the Contractile Response Is Decreased in Aorta from Aged and Spontaneously Hypertensive Rats

BACKGROUND

Stimulation of vascular 5-hydroxytryptamine-2C (5-HT(2c)) receptors produces contraction in rat aorta. We investigated the effect of aging on endothelium-dependent inhibition of contractile responses in thoracic aorta from normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR).

METHODS

Endothelium-intact and denuded aortic rings were prepared from young (7-9 weeks old) and senescent (65-70 weeks old) WKY and SHR rats. Changes in isometric tension elicited by 5-HT, in the absence or in the presence of N(G)-nitro-L-arginine methyl ester (L-NAME) or indomethacin were recorded.

RESULTS

In aorta from WKY and SHR, 5-HT elicited concentration-dependent contractions, which were increased by endothelium removal. The ability of endothelium to depress contractile response to 5-HT was found to be reduced in vessels from senescent animals, mainly in SHR. L-NAME increased the sensitivity and maximal effect to 5-HT in endothelium-intact but not in denuded aortic rings from young WKY rats. The effect of L-NAME was lower in young SHR compared with age-matched WKY rats, but it did not modify the response to 5-HT in senescent rats. Indomethacin did not affect contraction in arteries from young WKY or in denuded aortic rings from young SHR and aged WKY. In contrast, the inhibitor attenuated the response in endothelium-intact vessels from young SHR and aged WKY, and this effect was more marked in arteries with and without endothelium from senescent SHR. Thus, inhibition of cyclooxygenases by indomethacin revealed an enhanced endothelium-dependent modulation of contraction in senescent and hypertensive rats.

CONCLUSIONS

Results indicate that hypertension and aging decrease the negative modulator role of endothelium, in 5-HT-induced vasoconstriction in aorta from WKY and SHR. Data also point out that endothelial dysfunction involves an increased formation of vasoconstrictor prostanoids, which counteract nitric oxide effects. In addition, SHR endothelium releases contractile prostanoids at an early stage of hypertension, whereas in old SHR vascular smooth muscle also releases prostanoids, which contribute to 5-HT-induced contraction.

Blockade of angiotensin II provides additional benefits in hypertension- and ageing-related cardiac and vascular dysfunctions beyond its blood pressure-lowering effects

OBJECTIVES

To assess the blockade of the renin-angiotensin system (RAS) or blood pressure-lowering on cardiovascular functions in hypertensive and ageing animals.

METHODS

Male spontaneously hypertensive rats (SHR) and their normotensive counterparts, Wistar-Kyoto rats (WKY), at the ages of 3-4 (young), 34-35 (adult) and 74-75 (old) weeks were treated with an angiotensin II type 1 receptor antagonist, losartan (25 mg/kg) or a combination of a smooth muscle relaxant and a diuretic [H/H, hydralazine (50 mg/kg) plus hydrochlorothiazide (7.5 mg/kg), respectively] for 8 weeks. Each experimental group contained 10 SHR and 10 WKY, where equal numbers of untreated animals served as controls.

RESULTS

Compared to age-matched WKY groups, SHR groups possessed, on average, 48 +/- 7 mmHg and 57 +/- 16 mmHg (P < 0.05) higher systolic blood pressure and left ventricular developed pressures, respectively. The values of these parameters were significantly lowered in both strains by both treatment regimens. SHR had higher heart rates, which were increased by H/H treatment selectively in adult and old animal groups of both strains. Both treatment regimens enhanced KCl-mediated, that is, receptor-independent, aortic contractile responses and bradykinin-mediated coronary vasodilatation in adult and old WKY and SHR age-groups. Although both therapies augmented endothelium-dependent and endothelium-independent relaxant responses in young and adult, but not in old, SHR aortas to the levels observed in age-matched WKY, these beneficial effects were more prominent with losartan. Moreover, losartan reduced heart to body weight ratio in all SHR age groups, and selectively in the old WKY group.

CONCLUSIONS

Blockade of RAS provides a better protective effect on cardiovascular function compared to sole reduction of blood pressure, and the efficacy of antihypertensive treatment is dictated by age and the hypertensive stage of the animals.

Garlic supplementation prevents oxidative DNA damage in essential hypertension

Oxygen-free radicals and other oxygen/nitrogen species are constantly generated in the human body. Most are intercepted by antioxidant defences and perform useful metabolic roles, whereas others escape to damage biomolecules like DNA, lipids and proteins. Garlic has been shown to contain antioxidant phytochemicals that prevent oxidative damage. These include unique water-soluble organosulphur compounds, lipid-soluble organosulphur compounds and flavonoids. Therefore, in the present study, we have tried to explore the antioxidant effect of garlic supplementation on oxidative stress-induced DNA damage, nitric oxide (NO) and superoxide generation and on the total antioxidant status (TAS) in patients of essential hypertension (EH). Twenty patients of EH as diagnosed by JNC VI criteria (Group I) and 20 age and sex-matched normotensive controls (Group II) were enrolled in the study. Both groups were given garlic pearls (GP) in a dose of 250 mg per day for 2 months. Baseline samples were taken at the start of the study, i.e. 0 day, and thereafter 2 months follow-up. 8-Hydroxy-2'-deoxyguanosine (8-OHdG), lipids, lipid peroxidation (MDA), NO and antioxidant vitamins A, E and C were determined. A moderate decline in blood pressure (BP) and a significant reduction in 8-OHdG, NO levels and lipid peroxidation were observed in Group I subjects with GP supplementation. Further, a significant increase in vitamin levels and TAS was also observed in this group as compared to the control subjects. These findings point out the beneficial effects of garlic supplementation in reducing blood pressure and counteracting oxidative stress, and thereby, offering cardioprotection in essential hypertensives.

Quercetin downregulates NADPH oxidase, increases eNOS activity and prevents endothelial dysfunction in spontaneously hypertensive rats

BACKGROUND AND OBJECTIVE

Several studies have found that chronic treatment with the dietary flavonoid quercetin lowers blood pressure and restores endothelial dysfunction in hypertensive animal models. We hypothesized that increased endothelial nitric oxide synthase (eNOS) and/or decreased nicotinamide adenine dinucleotide phosphate (NADPH) oxidase protein expression and activity, and reduced reactive oxygen species might be involved in the improvement of endothelial function induced by quercetin in spontaneously hypertensive rats (SHR).

DESIGN AND METHODS

Male SHR and Wistar-Kyoto (WKY) rats (5 weeks old) were treated with quercetin (10 mg/kg) or vehicle for 13 weeks. Changes in vascular expression of eNOS, caveolin-1 and p47 were analysed by Western blot, eNOS activity by conversion of [H]arginine to L-[H]citrulline, and NADPH oxidase activity by NADPH-enhanced chemoluminescence of lucigenin.

RESULTS

In SHR, quercetin reduced the increase in blood pressure and heart rate and enhanced the endothelium-dependent aortic vasodilation induced by acetylcholine, but had no effect on the endothelium-independent response induced by nitroprusside. However, quercetin had no effect on endothelium-dependent vasoconstriction and aortic thromboxane B2 production. Compared to WKY, SHR showed upregulated eNOS and p47 protein expression, downregulated caveolin-1 expression, increased NADPH-induced superoxide production but, paradoxically, eNOS activity was reduced. Chronic quercetin treatment prevented all these changes in SHR. In WKY, quercetin had no effect on blood pressure, endothelial function or the expression or activity of the proteins analysed.

CONCLUSIONS

Enhanced eNOS activity and decreased NADPH oxidase-mediated superoxide anion (O2) generation associated with reduced p47 expression appear to be essential mechanisms for the improvement of endothelial function and the antihypertensive effects of chronic quercetin.