Endothelial dysfunction in salt-sensitive essential hypertension

Partial baroreceptor dysfunction and low plasma nitric oxide bioavailability as determinants of salt-sensitive hypertension: a reverse translational rat study

This study determined whether clinical salt-sensitive hypertension (cSSHT) results from the interaction between partial arterial baroreceptor impairment and a high-sodium (HNa) diet. In three series (S-I, S-II, S-III), mean arterial pressure (MAP) of conscious male Wistar ChR003 rats was measured once before (pdMAP) and twice after either sham (SHM) or bilateral aortic denervation (AD), following 7 days on a low-sodium (LNa) diet (LNaMAP) and then 21 days on a HNa diet (HNaMAP). The roles of plasma nitric oxide bioavailability (pNOB), renal medullary superoxide anion production (RMSAP), and mRNA expression of NAD(P)H oxidase and superoxide dismutase were also assessed. In SHM (n=11) and AD (n=15) groups of S-I, LNaMAP-pdMAP was 10.5±2.1 vs 23±2.1 mmHg (P<0.001), and the salt-sensitivity index (SSi; HNaMAP-LNaMAP) was 6.0±1.9 vs 12.7±1.9 mmHg (P=0.03), respectively. In the SHM group, all rats were normotensive, and 36% were salt sensitive (SSi≥10 mmHg), whereas in the AD group ∼50% showed cSSHT. A 45% reduction in pNOB (P≤0.004) was observed in both groups in dietary transit. RMSAP increased in the AD group on both diets but more so on the HNa diet (S-II, P<0.03) than on the LNa diet (S-III, P<0.04). MAP modeling in rats without a renal hypertensive genotype indicated that the AD*HNa diet interaction (P=0.008) increases the likelihood of developing cSSHT. Translationally, these findings help to explain why subjects with clinical salt-sensitive normotension may transition to cSSHT.

Salt loading and potassium supplementation: effects on ambulatory arterial stiffness index and endothelin-1 levels in normotensive and mild hypertensive patients

The authors investigated effects of excessive salt intake and potassium supplementation on ambulatory arterial stiffness index (AASI) and endothelin-1 (ET-1) in salt-sensitive and non-salt-sensitive individuals. AASI and symmetric AASI (s-AASI) were used as indicators of arterial stiffness. Plasma ET-1 levels were used as an index of endothelial function. Chronic salt-loading and potassium supplementation were studied in 155 normotensive to mild hypertensive patients from rural northern China. After 3 days of baseline investigation, participants were maintained sequentially for 7 days each on diets of low salt (51.3 mmol/d), high salt (307.7 mmol/d), and high salt+potassium (60 mmol/d). Ambulatory 24-hour blood pressure (BP) and plasma ET-1 were measured at baseline and on the last 2 days of each intervention. High-salt intervention significantly increased BP, AASI, s-AASI (all P<.001); potassium supplementation reversed increased plasma ET-1 levels. High-salt-induced changes in BP, s-AASI, and plasma ET-1 were greater in salt-sensitive individuals. Potassium supplementation decreased systolic BP and ET-1 to a significantly greater extent in salt-sensitive vs non-salt-sensitive individuals (P<.001). Significant correlations were identified between s-AASI and ET-1 change ratios in response to both high-salt intervention and potassium supplementation (P<.001). Reducing dietary salt and increasing daily potassium improves arterial compliance and ameliorates endothelial dysfunction.

Mechanisms of sporadic cerebral small vessel disease: insights from neuroimaging

The term cerebral small vessel disease (SVD) describes a range of neuroimaging, pathological, and associated clinical features. Clinical features range from none, to discrete focal neurological symptoms (eg, stroke), to insidious global neurological dysfunction and dementia. The burden on public health is substantial. The pathogenesis of SVD is largely unknown. Although the pathological processes leading to the arteriolar disease are associated with vascular risk factors and are believed to result from an intrinsic cerebral arteriolar occlusive disease, little is known about how these processes result in brain disease, how SVD lesions contribute to neurological or cognitive symptoms, and the association with risk factors. Pathology often shows end-stage disease, which makes identification of the earliest stages difficult. Neuroimaging provides considerable insights; although the small vessels are not easily seen themselves, the effects of their malfunction on the brain can be tracked with detailed brain imaging. We discuss potential mechanisms, detectable with neuroimaging, that might better fit the available evidence and provide testable hypotheses for future study.

Endothelium-dependent relaxations in the aorta from K(2p)6.1 knockout mice

K2P6.1 or TWIK-2, a two-pore domain K channel, is an important regulator of cardiovascular function. K2P6.1 is highly expressed in vascular smooth muscle and endothelium. Mice (8-12 wk) lacking functional K2P6.1 (K2P6.1(-/-)) are hypertensive and have enhanced vascular contractility. It is not known whether the lack of functional K2P6.1 in endothelium has a role in the vascular dysfunction in K2P6.1(-/-) mice. We tested the hypothesis: K2P6.1(-/-) mice have impaired endothelium-dependent relaxations. K2P6.1(-/-) mice were ∼35 mmHg more hypertensive than WT mice at both 8-12 wk (young adult) and 20-24 wk (mature mice, P < 0.01; n = 8-10). Endothelium-dependent relaxations of the thoracic aorta were evaluated by isometric myography after contraction with phenylephrine (10(-6) M). Maximal ACh-dependent relaxations were increased from 65 ± 1% to 73 ± 1% in the aorta from young adult (P < 0.01; n = 6) and from 45 ± 1% to 74 ± 1% in the aorta from mature (P < 0.001; n = 5) K2P6.1(-/-) mice compared with K2P6.1(+/+) littermates. However, in the aorta from young adult and mature K2P6.1(+/+) mice, 10(-5) M indomethacin, a cyclooxygenase inhibitor, increased maximal ACh relaxations to knockout levels. Enhanced relaxation was also seen with ATP, a P2Y purinergic agonist, and A23187, a nonreceptor-based agonist in mature K2P6.1(-/-) mice. Mature adult aorta from K2P6.1(-/-) showed an attenuated ACh-mediated contraction in the presence of nitro-l-arginine methyl ester (l-NAME) and without precontraction of 0.97 mN vs. 7.5 mN in K2P6.1(-/-) and K2P6.1(+/+) (P < 0.001; n = 5). In summary, K2P6.1(-/-) mice, which are hypertensive, have enhanced endothelium-dependent relaxations in the aorta due to the suppression of an indomethacin-sensitive constrictor component.

Role of the CYP4A/20-HETE pathway in vascular dysfunction of the Dahl salt-sensitive rat

20-HETE (20-hydroxyeicosatetraenoic acid), a vasoconstrictor metabolite of arachidonic acid formed through the action of CYP4A (cytochrome P450-4A) in vascular smooth muscle cells, has been implicated in the development of hypertension and vascular dysfunction. There have been a number of reports in human subjects demonstrating an association between elevated urinary excretion of 20-HETE and hypertension, as well as increased 20-HETE production and vascular dysfunction. The Dahl SS (salt-sensitive) rat is a genetic model of salt-sensitive hypertension that exhibits vascular dysfunction, even when maintained on a normal-salt diet and before the development of hypertension. This mini-review highlights our current research on the role of CYP4A and 20-HETE in the vascular dysfunction of the Dahl SS rat. In our studies, the SS rat is compared with the consomic SS-5BN rat, having chromosome 5 from the salt-resistant Brown Norway rat (carrying all CYP4A genes) introgressed on to the SS genetic background. Our laboratory has demonstrated restoration of normal vascular function in the SS rat with inhibition of the CYP4A/20-HETE pathway, suggesting a direct role for this pathway in the vascular dysfunction in this animal model. Our studies have also shown that the SS rat has an up-regulated CYP4A/20-HETE pathway within their cerebral vasculature compared with the SS-5BN consomic rat, which causes endothelial dysfunction through the production of ROS (reactive oxygen species). Our data shows that ROS influences the expression of the CYP4A/20-HETE pathway in the SS rat in a feed-forward mechanism whereby elevated ROS stimulates production of 20-HETE. The presence of this vicious cycle offers a possible explanation for the spiralling effects of elevated 20-HETE on the development of vascular dysfunction in this animal model.

Dietary sodium restriction reverses vascular endothelial dysfunction in middle-aged/older adults with moderately elevated systolic blood pressure

OBJECTIVES

This study sought to determine the efficacy of dietary sodium restriction (DSR) for improving vascular endothelial dysfunction in middle-aged/older adults with moderately elevated systolic blood pressure (SBP) (130-159 mm Hg) and the associated physiological mechanisms.

BACKGROUND

Vascular endothelial dysfunction develops with advancing age and elevated SBP, contributing to increased cardiovascular risk. DSR lowers BP, but its effect on vascular endothelial function and mechanisms involved are unknown.

METHODS

Seventeen subjects (11 men and 6 women; mean age, 62 ± 7 years) completed a, randomized crossover study of 4 weeks of both low (DSR) and normal sodium intake. Vascular endothelial function (endothelium-dependent dilation; EDD), nitric oxide (NO)/tetrahydrobiopterin (BH(4)) bioavailability, and oxidative stress-associated mechanisms were assessed following each condition.

RESULTS

Urinary sodium excretion was reduced by ≈ 50% (to 70 ± 30 mmol/day), and conduit (brachial artery flow-mediated dilation [FMD(BA)]) and resistance (forearm blood flow responses to acetylcholine [FBF(ACh)]) artery EDD were 68% and 42% (peak FBF(ACh)) higher following DSR (p < 0.005). Low sodium markedly enhanced NO-mediated EDD (greater ΔFBF(ACh) with endothelial NO synthase inhibition) without changing endothelial NO synthase expression/activation (Ser 1177 phosphorylation), restored BH(4) bioactivity (less ΔFMD(BA) with acute BH(4)), abolished tonic superoxide suppression of EDD (less ΔFMD(BA) and ΔFBF(ACh) with ascorbic acid infusion), and increased circulating superoxide dismutase activity (all p < 0.05). These effects were independent of ΔSBP. Other subject characteristics/dietary factors and endothelium-independent dilation were unchanged.

CONCLUSIONS

DSR largely reversed both macro- and microvascular endothelial dysfunction by enhancing NO and BH(4) bioavailability and reducing oxidative stress. Our findings support the emerging concept that DSR induces "vascular protection" beyond that attributable to its BP-lowering effects.

Leptin and Nitric Oxide Production in Normotensive and Hypertensive Men

OBJECTIVE

Recent findings have shown that leptin, the product of the obesity gene, may actively participate in the regulation of blood pressure and other cardiovascular functions through the nitric oxide (NO)-dependent mechanism.

RESEARCH METHODS AND PROCEDURES

In this study, to test the hypothesis that leptin regulation of NO metabolism is impaired in hypertension, we examined the possible relationship between circulating leptin and plasma NO metabolite level in normotensive (NT) and hypertensive (HT) men.

RESULTS

There were significant correlations between circulating leptin and BMI in both the NT and HT groups (NT: r = 0.64, n = 26, p < 0.01; HT: r = 0.59, n = 22, p < 0.01). The concentration of circulating leptin was similar between the NT and HT men, although the plasma NO metabolite level (nitrite and nitrate) was significantly reduced in the HT men compared with the NT men (NT: 51.0 +/- 4.9 microM, n = 26; HT: 37.1 +/- 2.5 microM, n = 22, p < 0.05). The circulating leptin was significantly correlated with the plasma NO metabolite level in the overall analysis of the NT and HT men (r = 0.35, n = 48, p < 0.05). When the analysis of the correlation for the NT and HT men was performed separately, there was a significant correlation between circulating leptin and plasma NO metabolites in the NT men (r = 0.45, n = 26, p < 0.05) but not in the HT men (r = 0.15, n = 22). The results of this study are consistent with the hypothesis that leptin-related metabolism of NO might be altered in HT men.

The antihypertensive effect of arginine

Hypertension is a leading cause of morbidity and mortality worldwide. Individuals with hypertension are at increased risk of stroke, heart disease and kidney failure. Although the etiology of essential hypertension has a genetic component, lifestyle factors such as diet play an important role. Reducing dietary salt is effective in lowering blood pressure in salt-sensitive individuals. Insulin resistance and altered glucose metabolism are common features of hypertension in humans and animal models, with or without salt sensitivity. Altered glucose metabolism leads to increased formation of advanced glycation end products. Insulin resistance is also linked to oxidative stress, and alterations in the nitric oxide pathway and renin angiotensin system. A diet rich in protein containing the semiessential amino acid, arginine, and arginine treatment, lowers blood pressure in humans and in animal models. This may be due to the ability of arginine to improve insulin resistance, decrease advanced glycation end products formation, increase nitric oxide, and decrease levels of angiotensin II and oxidative stress, with improved endothelial cell function and decreased peripheral vascular resistance. The Dietary Approaches to Stop Hypertension (DASH) study demonstrated that the DASH diet, rich in vegetables, fruits and low-fat dairy products; low in fat; and including whole grains, poultry, fish and nuts, lowered blood pressures even more than a typical North American diet with similar reduced sodium content. The DASH diet is rich in protein; the blood pressure-lowering effect of the DASH diet may be due to its higher arginine-containing protein, higher antioxidants and low salt content.

Association between sodium intake and change in uric acid, urine albumin excretion, and the risk of developing hypertension

BACKGROUND

A high-sodium diet has little short-term effect on blood pressure in nonhypertensive individuals but, for unclear reasons, is associated with hypertension if consumed long term. We hypothesized that a chronically high sodium intake would be associated with increases in biomarkers of endothelial dysfunction, specifically serum uric acid (SUA) and urine albumin excretion (UAE), and that high sodium intake would be associated with incident hypertension among those with higher SUA and UAE.

METHODS AND RESULTS

We prospectively analyzed the associations between sodium intake and the change in SUA (n=4062) and UAE (n=4146) among participants of the Prevention of Renal and Vascular End Stage Disease (PREVEND) study who were not taking antihypertensive medications. We also examined the association of sodium intake with the incidence of hypertension (n=5556) among nonhypertensive participants. After adjustment for confounders, each 1-g-higher sodium intake was associated with a 1.2-μmol/L increase in SUA (P=0.01) and a 4.6-mg/d increase in UAE (P<0.001). The relation between sodium intake and incident hypertension varied according to SUA and UAE. For each 1-g-higher sodium intake, the adjusted hazard ratio for developing hypertension was 0.98 (95% confidence interval, 0.89-1.08) among those in the lowest tertile of SUA and 1.09 (1.02-1.16) among those in the highest tertile. Corresponding hazard ratios were 0.99 (confidence interval, 0.93-1.06) among participants whose UAE was <10 mg/d and 1.18 (confidence interval, 1.07-1.29) among those whose UAE was >15 mg/d.

CONCLUSIONS

Over time, higher sodium intake is associated with increases in SUA and UAE. Among individuals with higher SUA and urine UAE, a higher sodium intake is an independent risk factor for developing hypertension.

Sodium intake is associated with parasympathetic tone and metabolic parameters in mild hypertension

BACKGROUND

Although the impairment of parasympathetic cardiac control was described in hypertensives submitted to a high salt diet, the impact of this autonomic abnormality on metabolic and inflammation markers in patients with mild hypertension has not been explored.

METHODS

Four hundred and ninety mild essential hypertensive patients (144 ± 9/94 ± 9 mm Hg, 49.5 ± 13.9 years, 67.9 % male) were studied. Dietary sodium intake was estimated by measuring 24-h urinary sodium excretion (UNa), and the patients were classified according to UNa levels as follows: low (<50 mEq/l), medium (50-99 mEq/l), and high UNa (≥100 mEq/l). Parasympathetic tone was evaluated by assessing heart rate recovery (HRR) after an exercise stress test. HRR, plasma lipids, glucose metabolism, and inflammatory biomarkers were compared across UNa groups.

RESULTS

HRR and high-density lipoprotein (HDL)-cholesterol were progressively lower, and insulin (INS), homeostasis model assessment of insulin resistance (HOMAir), ultrasensitive-C-reactive protein (usCRP) were progressively higher across increasing UNa groups. In the low and medium UNa groups, HDL-cholesterol was higher and CRP was lower than that in high UNa (P < 0.01 and P < 0.05, respectively) (Dunnett post-hoc test). In the low UNa group, triglycerides (TGs), INS, and HOMAir were lower than that in high UNa (P < 0.05). Multiple linear regression analysis showed that UNa, HOMAir, and heart rate (HR) were negatively associated with HRR (P < 0.0001, P < 0.0001, and P = 0.001, respectively).

CONCLUSIONS

In the essential hypertensive patients studied high sodium intake is associated with parasympathetic inhibition, lipid disturbances, and inflammation. Studies designed to assess causality between sodium intake and metabolic and autonomic status are needed to evaluate the relevance of controlling sodium intake, especially in hypertensive patients.

Dietary salt influences postprandial plasma sodium concentration and systolic blood pressure

The plasma sodium concentration has a direct effect on blood pressure in addition to its effects on extracellular volume regulated through changes in the endothelium. The mechanism for elevated blood pressure seen with habitually increased salt intake is unclear, especially the effect of salt in a single meal on plasma sodium concentration and blood pressure. To resolve this we compared the effect of soup with or without 6 g of salt (an amount similar to that in a single meal) on the plasma sodium concentration and blood pressure in 10 normotensive volunteers using a randomized, crossover design. The plasma sodium concentration was significantly increased by 3.13±0.75 mmol/l with salted compared with unsalted soup. Blood pressure increased in volunteers ingesting soup with added salt, and there was a significant positive correlation between plasma sodium concentration and systolic blood pressure. A 1-mmol/l increase in plasma sodium was associated with a 1.91-mm Hg increase in systolic blood pressure by linear regression. Thus, changes in plasma sodium concentration occur each time a meal containing salt is consumed. A potential mechanism for the changes in blood pressure seen with salt intake may be through its effects on plasma sodium concentration.

Abnormalities of vascular function in resistant hypertension

We aimed to evaluate markers of vascular dysfunction in patients with resistant hypertension (RH). A group of 144 patients (61 years, 42% women) with essential RH were divided in two groups based on ambulatory blood pressure monitoring (ABPM). True RH (72%) was considered when 24-h blood pressure (BP) was ≥ 130 and/or 80 mmHg. Otherwise, patients were classified as white coat RH (28%). Hyperemia-induced forearm vasodilation (HIFV), serum inflammatory biomarkers (hs-CRP, s-ICAM-1, s-VCAM-1, e-selectin, p-selectin and MCP-1) and large (C1) and small arterial (C2) compliance (HDI/Pulse Wave CR 2000) were determined in all individuals. In comparison with patients with white coat RH, and after adjustment for age, office systolic BP and diabetes status, those with true RH had a more impaired HIFV (201 ± 159 vs 436 ± 157%; p < 0.001), increased e-selectin (53.1 ± 29.8 vs 40.7 ± 23.5 ng/ml; p = 0.035), and MCP-1 (445 ± 120 vs 386 ± 126 ng/ml; p = 0.027). No significant differences were observed in arterial compliance. Maximal HIFV inversely correlated with urinary albumin excretion (Rho: - 0.278; p = 0.004) and with some inflammatory biomarkers (MCP-1: - 0.441; p < 0.001, e-selectin: - 0.468; p < 0.001 and p-selectin: - 0.329; p = 0.001). We conclude that true RH, diagnosed by ABPM, is associated with a more severe degree of vascular dysfunction, as measured by HIFV and serum biomarkers, whereas other types of vascular alterations, such as compliance, are not directly linked with the level of BP.

High salt intake abolishes AT(2)-mediated vasodilation of pial arterioles in rats

BACKGROUND

Angiotensin II (Ang II) induces constriction (AT(1)) and dilation (AT(2) receptors) of cerebral arterioles. High sodium intake induces changes in receptors expression and loss of AT(2)-mediated vasodilation in extracerebral vessels. We investigated whether high salt modifies the AT(2)-mediated response of cerebral arterioles.

METHODS

Three-month-old male Wistar rats received drinking water supplemented or not with 1% NaCl. We measured at day 4 or 30 plasma aldosterone concentration, AT receptors expression (brain microvessels, western blot, RT-qPCR), internal diameter of pial arterioles (cranial window) following suffusion with Ang II (10(-6) mol/l, or 10(-8) mol/l + losartan 10(-5) mol/l), serotonin (5-HT, 10(-6) mol/l), sodium nitroprusside (10(-5) mol/l) and adenosine diphosphate (ADP, 10(-4) mol/l).

RESULTS

High salt did not modify arterial pressure, baseline arteriolar diameter, vasoconstriction to Ang II or 5-HT, nor vasodilation to SNP. High salt lowered plasma aldosterone concentration (d4 138 ± 71 not significant vs. control 338 ± 73; d30 150 ± 21 P < 0.05 vs. control 517 ± 79 μmol/l). AT receptors mRNA did not change while protein level of AT(2) receptors decreased at d4 (64 ± 9% of control, P < 0.05). AT(2)-mediated vasodilation (control d4; d30 8 ± 2; 5 ± 2%) was abolished at d4 (-2 ± 2%, P < 0.05) and reversed to vasoconstriction at d30 (-7 ± 2%, P < 0.05). ADP-induced vasodilation is abolished at d30 (2 ± 2, P < 0.05 vs. control 19 ± 4%).

CONCLUSION

High salt specifically abolishes AT(2)-mediated vasodilation, immediately, via decreased level of AT(2) receptor protein, and after 30 days, in association with abolition of endothelial vasodilation. Such loss of AT(2)-mediated vasodilation may be deleterious in case of stroke.

Salt-induced hemodynamic regulation mediated by nitric oxide

Excess daily salt intake impairs vasodilatation and enhances vasoconstriction, resulting in reduction of regional blood flow and elevation of blood pressure in healthy individuals and hypertensive patients with either salt sensitivity or not tested for salt sensitivity or not evaluated for salt sensitivity. The mechanism may involve decreased production of nitric oxide via endothelial nitric oxide synthase (eNOS), impaired bioavailability of nitric oxide, and elevated plasma levels of asymmetric dimethylarginine (ADMA). Experimental animals, irrespective of salt sensitivity, although less extensive in those with salt-resistance, fed a high-salt diet have deteriorated endothelial functions; the mechanisms involved include an impairment of eNOS activation, a decrease in eNOS expression, and an increase in oxidative stress and ADMA. The imbalance of interactions between nitric oxide and angiotensin II is also involved in salt sensitivity. Deficiency of nitric oxide formed via neuronal NOS and inducible NOS may contribute to salt-induced hypertension. Reduced daily salt intake, therefore, would be the most rational prophylactic measure against the development of hypertension.

Endothelial function is impaired after a high-salt meal in healthy subjects

BACKGROUND

Dietary salt is related to blood pressure (BP), and cardiovascular disease and increased sodium intakes have been shown to impair vascular function. The effect of salt on endothelial function postprandially is unknown.

OBJECTIVE

The aim was to investigate the postprandial effect of dietary salt on endothelial function as measured by flow-mediated dilatation (FMD) and peripheral arterial tonometry in healthy subjects.

DESIGN

Sixteen healthy, normotensive subjects received a meal with added salt (HSM; 65 mmol Na) and a control low-salt meal (LSM; 5 mmol Na) on 2 separate occasions in a randomized order. Endothelial function was measured while fasting and postprandially at 30, 60, 90, and 120 min by using FMD and reactive hyperemia peripheral arterial tonometry. BP was also measured.

RESULTS

Baseline FMD, reactive hyperemia index (RHI), and BP values were similar across interventions. Overall FMD was reduced 2 h postprandially. FMD was significantly more impaired after the HSM than after the LSM at 30 min [HSM (mean ± SD): 3.39 ± 2.44%; LSM: 6.05 ± 3.21%; P < 0.01] and at 60 min (HSM: 2.20 ± 2.77%; LSM: 4.64 ± 2.48%; P < 0.01). No significant differences in BP or RHI were observed between meals.

CONCLUSIONS

An HSM, which reflects the typical amount of salt consumed in a commonly eaten meal, can significantly suppress brachial artery FMD within 30 min. These results suggest that high salt intakes have acute adverse effects on vascular dilatation in the postprandial state. This trial was registered at www.anzctr.org.au/trial_view.aspx?ID=335115 as ACTRN12610000124033.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

High-salt diet and hypertension: focus on the renin-angiotensin system

A high-salt diet is one of the major risk factors in the development and maintenance of hypertension. Numerous experimental and observational studies have confirmed the association of sodium intake with blood pressure levels. The effects of a high-salt diet are related to the function of the renin-angiotensin system, which is normally suppressed by a high-salt diet. Endothelial dysfunction probably plays an important role in the influence of high sodium intake on blood pressure, although the exact mechanisms remain elusive. Genetic factors are known to be very important, and various consomic and congenic rat strains as animal models have proven to be very useful in bringing us a step closer to understanding the interaction between salt intake and hypertension. In this article, experimental data obtained in studies on animals and humans, as well as epidemiological data are reviewed.

Impaired relaxation of cerebral arteries in the absence of elevated salt intake in normotensive congenic rats carrying the Dahl salt-sensitive renin gene

This study evaluated endothelium-dependent vascular relaxation in response to acetylcholine (ACh) in isolated middle cerebral arteries (MCA) from Dahl salt-sensitive (Dahl SS) rats and three different congenic strains that contain a portion of Brown Norway (BN) chromosome 13 introgressed onto the Dahl SS genetic background through marker-assisted breeding. Two of the congenic strains carry a 3.5-Mbp portion and a 2.6-Mbp portion of chromosome 13 that lie on opposite sides of the renin locus, while the third contains a 2.0-Mbp overlapping region that includes the BN renin allele. While maintained on a normal salt (0.4% NaCl) diet, MCAs from Dahl SS rats and the congenic strains retaining the Dahl SS renin allele failed to dilate in response to ACh, whereas MCAs from the congenic strain carrying the BN renin allele exhibited normal vascular relaxation. In congenic rats receiving the BN renin allele, vasodilator responses to ACh were eliminated by nitric oxide synthase inhibition with N(G)-nitro-l-arginine methyl ester, angiotensin-converting enzyme inhibition with captopril, and AT(1) receptor blockade with losartan. N(G)-nitro-l-arginine methyl ester-sensitive vasodilation in response to ACh was restored in MCAs of Dahl SS rats that received either a 3-day infusion of a subpressor dose of angiotensin II (3 ng·kg(-1)·min(-1) iv), or chronic treatment with the superoxide dismutase mimetic tempol (15 mg·kg(-1)·day(-1)). These findings indicate that the presence of the Dahl SS renin allele plays a crucial role in endothelial dysfunction present in the cerebral circulation of the Dahl SS rat, even in the absence of elevated dietary salt intake, and that introgression of the BN renin allele rescues endothelium-dependent vasodilator responses by restoring normal activation of the renin-angiotensin system.

Aerobic exercise acutely improves insulin- and insulin-like growth factor-1-mediated vasorelaxation in hypertensive rats

Limited information is available concerning the effects of aerobic exercise on vasorelaxation in hypertension. The aim of this study was to investigate the effects of a single bout of aerobic exercise on insulin- and insulin-like growth factor-1 (IGF-1)-induced vasorelaxation in hypertensive rats. Four-month-old spontaneously hypertensive rats were randomly divided into a sedentary group (SHR) and an exercise group (SHR+Ex) subjected to a single bout of aerobic exercise conducted by treadmill running at 21 m min(1) for 1 h. Age-matched Wistar-Kyoto rats were used as a normotensive control group (WKY). Insulin- and IGF-1-induced vasorelaxant responses in the three groups were evaluated by using isolated aortic rings, with or without endothelial denudation, in organ baths. Possible roles of phosphatidylinositol 3-kinase (PI3K) and nitric oxide synthase (NOS) involved in the NO-dependent vasorelaxation were examined by adding selective inhibitors. The role of superoxide was also clarified by adding superoxide dismutase (SOD). In addition, the endothelium-independent vascular responses to sodium nitroprusside (SNP), a NO donor, were examined. The insulin- and IGF-1-induced vasorelaxation was significantly (P < 0.05) decreased in the SHR group compared with the WKY group. This decreased response in SHR was improved by exercise. These vasorelaxant responses among the three groups became similar after endothelial denudation and pretreatment with the PI3K inhibitor, NOS inhibitor or SOD. Also, no difference among groups was found in the SNP-induced vasorelaxation. We concluded that a single bout of aerobic exercise acutely improves insulin- and IGF-1-mediated vasorelaxation in an endothelium-dependent manner in hypertensive rats.

Low-Sodium DASH reduces oxidative stress and improves vascular function in salt-sensitive humans

Salt induces oxidative stress in salt-sensitive (SS) animals and man. It is not known whether in SS subjects the low-sodium dietary approaches to stop hypertension (LS-DASH) reduces oxidative stress more than DASH, which is high in antioxidants. To assess the effects of DASH and LS-DASH on oxidative stress, 19 volunteers were studied after 3 weeks of a standardized usual low fruits and vegetables diet (ULFV), followed by 3 weeks on DASH (both diets approximately 120 mmol Na(+) per day), then 3 weeks on LS-DASH (60 mmol Na(+) per day). SS was defined as systolic blood pressure >or=5 mm Hg lower on LS-DASH than DASH. In SS subjects (N=9), systolic blood pressure was lower on LS-DASH (111.0+/-2.0 mm Hg) than DASH (118.0+/-2.2, P<0.01) and ULFV (122.3+/-2.7, P=0.002). In salt-resistant (SR) volunteers (N=10), systolic blood pressure was lower on DASH (113.0+/-1.6) than ULFV (119.0+/-1.8, P<0.05) but not LS-DASH (115.7+/-1.8). Urine F2-isoprostanes, a marker of oxidative stress, were lower in SS subjects on LS-DASH (1.69+/-0.24) than ULFV (3.09+/-0.50, P<0.05) and marginally lower than DASH (2.46+/-0.44, P<0.20). F2-isoprostanes were not different among the three diets in SR volunteers (2.18+/-0.29, 2.06+/-0.29, 2.27+/-0.53, respectively). Aortic augmentation index, a measure of vascular stiffness, was lower in SS subjects on LS-DASH than either DASH or ULFV, and lower on DASH than ULFV in SR volunteers. In SS but not SR subjects, LS-DASH is associated with lower values for F2-isoprostanes and the aortic augmentation index. The results suggest that LS-DASH decreases oxidative stress, improves vascular function and lowers blood pressure in SS but not SR volunteers.

Endothelial dysfunction is associated with increased levels of biomarkers in essential hypertension

To assess the correlation between endothelial dysfunction and the serum levels of biomarkers of inflammation, remodelling and oxidative stress in essential hypertension, 78 treatment-naïve essential hypertensives (mean age 43 years) underwent measurement of endothelial dysfunction, using the maximal acetylcholine-induced forearm vasodilation and serum levels of adhesion molecules, selectins, chemokines, metalloproteinases, copper, zinc, selenium, vitamins, homocysteine, malondialdehyde, erythrocyte glutathione peroxidase and erythrocyte superoxide dismutase. Mean (+/-s.e.m.) maximal acetylcholine-induced vasodilation was 367+/-20%. Patients with a more impaired acetylcholine-dependent vasodilation (first tertile) had increased levels of e-selectin (P=0.009), p-selectin (P<0.001), monocyte chemotactic protein type 1 (MCP-1; P=0.012) and the tissue inhibitor of metalloproteinases type 1 (TIMP-1; P=0.044), which in turn showed significant inverse correlations with maximal endothelium-dependent vasodilation. Serum levels of selenium (P=0.012), vitamin C (P=0.038), erythrocyte glutathione peroxidase (P<0.001) and superoxide dismutase (P=0.022) activities were reduced in patients with a more impaired endothelium-dependent vasodilation. Recently diagnosed treatment-naïve essential hypertensives showed a relationship between the endothelial dysfunction, serum markers of inflammation and remodelling and levels of antioxidant substances. These could be potentially helpful markers of high risk in hypertensive patients.

Fructose and moderately high dietary salt-induced hypertension: prevention by a combination of N-acetylcysteine and L-arginine

Diets containing 8% salt or 4% fructose (FR) cause insulin resistance and increase tissue methylglyoxal and advanced glycation end products (AGEs), platelet cytosolic-free calcium, and systolic blood pressure (SBP) in rats. In WKY rats, we have shown that moderately high salt, 4% NaCl (MHS) alone in diet does not cause hypertension, and when given along with 4% FR it does not have an additive effect. N-acetylcysteine (NAC) or L-arginine (ARG), treatment alone does not prevent hypertension in this model. The objectives of this study were to investigate the effect of NAC plus ARG in diet on SBP, platelet cytosolic-free calcium in a MHS + FR model, and to measure the plasma levels of methylglyoxal and the AGE, methylglyoxal-derived hydroimidazolone (MGH). At 7 weeks of age, WKY rats were divided into three groups: control group was given regular rat chow (0.7% NaCl) and water; MHS + FR group, diet containing 4% NaCl and 4% FR in drinking water; and MHS + FR + NAC + ARG group, MHS diet supplemented with 1.5% N-acetylcysteine (NAC) and 1.5% L-arginine (ARG), and 4% FR in drinking water, and followed for 6 weeks. NAC + ARG prevented the increase in platelet cytosolic-free calcium and SBP in MHS + FR treated rats. There was no difference in mean values of plasma methylglyoxal and MGH among the groups. In conclusion, NAC + ARG treatment is effective in preventing hypertension in a moderately high salt + FR-induced animal model. Plasma methylglyoxal and MGH may not represent tissue modification or, alternatively, other tissue AGEs, derived from methylglyoxal or other aldehydes, may be involved in hypertension in this model.

Low dietary sodium intake is associated with enhanced vascular endothelial function in middle-aged and older adults with elevated systolic blood pressure

BACKGROUND

Age and increasing systolic blood pressure (BP) are associated with vascular endothelial dysfunction, but the factors involved are incompletely understood. We tested the hypothesis that vascular endothelial function is related to dietary sodium intake among middle-aged and older adults (MA and O) with elevated systolic BP.

METHODS

Data were analyzed on 25 otherwise healthy adults aged 48-73 years with high normal systolic BP or stage I systolic hypertension (130-159 mmHg). Self-reported sodium intake was <100 mmol/d in 12 (7 M) subjects (low sodium, 73+/-6 mmol/d) and between 100 and 200 mmol/d in 13 (9 M) subjects (normal sodium, 144+/-6 mmol/d).

RESULTS

Groups did not differ in other dietary factors, age, body weight and composition, BP, metabolic risk factors, physical activity and maximal aerobic capacity. Plasma concentrations of norepinephrine, endothelin-1, oxidized low-density lipoproteins (LDL), antioxidant status and inflammatory markers did not differ between groups. Brachial artery flow-mediated dilation (FMD) was 42% (mm Delta) to 52% (% Delta) higher in the low versus normal sodium group (p < 0.05). In all subjects, brachial artery FMD was inversely related to dietary sodium intake (FMD mm Delta r =-0.40, p < 0.05; %Delta r =-0.53, p < 0.01). Brachial artery FMD was not related to any other variable. In contrast, endothelium-independent dilation did not differ between groups (p >or= 0.24) and was not related to sodium intake in the overall group (p >or= 0.29).

CONCLUSIONS

Low sodium intake is associated with enhanced brachial artery FMD in MA and O with elevated systolic BP. These results suggest that dietary sodium restriction may be an effective intervention for improving vascular endothelial function in this high-risk group.

High sodium intake increases vascular superoxide formation and promotes atherosclerosis in apolipoprotein E‐deficient mice

Hypertension is a major risk factor for atherosclerosis. We tested the hypothesis whether high salt intake aggravates endothelial dysfunction and promotes atherosclerosis in apolipoprotein E-deficient mice (ApoE(-)/(-) mice) and their littermate controls (C57Bl/6 mice). The role of increased oxidative stress was also examined. A high-salt diet (NaCl 7%) for 12 weeks increased blood pressure and induced cardiac hypertrophy and albuminuria more pronouncedly in ApoE(-)/(-) mice compared with C57Bl/6. Endothelium-dependent vascular relaxation in response to acetylcholine was almost maximally impaired in ApoE(-)/(-) mice during a normal sodium diet. A high-salt diet did not further impair NO-mediated vascular relaxation. A high-salt diet also markedly attenuated endothelium-dependent relaxation in C57Bl/6 mice. Preincubation with the superoxide scavenger Tiron normalized endothelial function almost completely in both mice strains indicating the central role of increased oxidative stress in the pathogenesis. Aortic superoxide production and the extent of atherosclerotic lesions were greater in ApoE(-)/(-) mice on a normal-salt diet compared with C57Bl/6. The high-salt diet increased vascular superoxide formation and promoted atherosclerosis in ApoE(-)/(-) mice. Changes in dietary salt intake did not influence serum lipids in either mouse strains. Our findings suggest a detrimental role for high salt intake in the development of atherosclerosis and underscore the importance of increased oxidative stress in the pathogenesis salt-induced vascular damage.

Arterial stiffness: methods of measurement, physiologic determinants and prediction of cardiovascular outcomes

Arterial stiffness has been shown to be a potent and independent predictor of cardiovascular risk. In this review, we outline methods for the measurement of arterial stiffness, describe the physiological mechanisms that underpin the utility of arterial stiffness as an integrative marker of cardiovascular disease, and detail the evidence examining the value of arterial stiffness for prediction of adverse cardiovascular events and mortality. The extent to which arterial stiffness may be modified by medical and lifestyle therapy is reviewed.

Endothelial dysfunction and cardiovascular risk factors

The endothelium plays an integral role in the regulation of vascular tone, platelet activity, leukocyte adhesion, and thrombosis and is intimately involved in the development of atherosclerosis. Endothelial dysfunction has been observed in patients with established coronary artery disease or coronary risk factors, both in the coronary and peripheral vasculature. Therapeutic interventions with lipid-lowering drugs, ACE inhibitors, physical activity, and antioxidant agents have been shown to improve endothelial function in coronary and peripheral vessels. This systemic manifestation and improvement of endothelial function suggests that a common mechanism may contribute to endothelial dysfunction in the coronary and peripheral circulation.

TARGET AUDIENCE

Internist, Cardiologists, Family physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to define the participation of cardiovascular risk factors in the various complications associated with endothelial dysfunction.

Salt inactivates endothelial nitric oxide synthase in endothelial cells

There is a 1-4 mmol/L rise in plasma sodium concentrations in individuals with high salt intake and in patients with essential hypertension. In this study, we used 3 independent assays to determine whether such a small increase in sodium concentrations per se alters endothelial nitric oxide synthase (eNOS) function and contributes to hypertension. By directly measuring NOS activity in living bovine aortic endothelial cells, we demonstrated that a 5-mmol/L increase in salt concentration (from 137 to 142 mmol/L) caused a 25% decrease in NOS activity. Importantly, the decrease in NOS activity was in a salt concentration-dependent manner. The NOS activity was decreased by 25, 45, and 70%, with the increase of 5, 10, and 20 mmol/L of NaCl, respectively. Using Chinese hamster ovary cells stably expressing eNOS, we confirmed the inhibitory effects of salt on eNOS activity. The eNOS activity was unaffected in the presence of equal milliosmol of mannitol, which excludes an osmotic effect. Using an ex vivo aortic angiogenesis assay, we demonstrated that salt attenuated the nitric oxide (NO)-dependent proliferation of endothelial cells. By directly monitoring blood pressure changes in response to salt infusion, we found that in vivo infusion of salt induced an acute increase in blood pressure in a salt concentration-dependent manner. In conclusion, our findings demonstrated that eNOS is sensitive to changes in salt concentration. A 5-mmol/L rise in salt concentration, within the range observed in essential hypertension patients or in individuals with high salt intake, could significantly suppress eNOS activity. This salt-induced reduction in NO generation in endothelial cells may contribute to the development of hypertension.

Endothelial function and oxidative stress in cardiovascular diseases

The vascular endothelium is involved in the release of various vasodilators, including nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor, as well as vasoconstrictors. NO plays an important role in the regulation of vascular tone, inhibition of platelet aggregation, and suppression of smooth muscle cell proliferation. Endothelial dysfunction is the initial step in the pathogenesis of atherosclerosis. Cardiovascular diseases are associated with endothelial dysfunction. It is well known that the grade of endothelial function is a predictor of cardiovascular outcomes. Oxidative stress plays an important role in the pathogenesis and development of cardiovascular diseases. Several mechanisms contribute to impairment of endothelial function. An imbalance of reduced production of NO or increased production of reactive oxygen species, mainly superoxide, may promote endothelial dysfunction. One mechanism by which endothelium-dependent vasodilation is impaired is an increase in oxidative stress that inactivates NO. This review focuses on recent findings and interaction between endothelial function and oxidative stress in cardiovascular diseases.

Endothelial dysfunction in African-Americans

The journey of atherosclerosis begins with endothelial dysfunction and culminates into its most fearful destination producing ischemia, myocardial infarction and death. The excess cardiovascular disease morbidity and mortality in African-Americans is one of the major public health problems. In this review, we discuss vascular endothelial dysfunction as a key element for excess cardiovascular disease burden in this target population. It can be logical window of future atherosclerotic outcomes, and further efforts should be made to detect it at the earliest in African American individuals even if they are appearing healthy as the therapeutic interventions if instituted early, might prevent the subsequent cardiac events.

Hemodynamic parameters during normal and hypertensive pregnancy in rats: evaluation of renal salt and water transporters

OBJECTIVE

To determine whether alterations in extracellular volume expansion observed during normal and hypertensive pregnancy run in parallel to changes in the mRNA expression of renal transporters.

METHODS

Wistar rats were divided into four groups: control (C, n = 5); pregnancy (P, n = 5); N(omega)-nitro-l-arginine methyl ester (L-NAME; 50 mg/kg/d)-treated control (H, n = 6); and pregnant rats (HP, n = 6). Hemodynamic studies were performed on day 14 of pregnancy, at which time we also analyzed of the sodium transporters (NHE3, Na/K/2Cl and Na/Cl), potassium channel (ROMK2) and water channel (AQP2).

RESULTS

As expected, P rats presented high cardiac output (CO) and normal blood pressure (BP), whereas H rats presented lower CO and elevated BP. A significant (threefold) increase in total vascular resistance and a decrease in stroke volume were observed in the HP group. Hypertension resulting from nitric oxide (NO) synthesis inhibition blunted systemic hemodynamic adaptations during pregnancy. Compared with C rats, mRNA expression of ROMK2 in P rats was lower, whereas that of AQP2 was higher. Expression of AQP2 was significantly higher in H than in C or HP groups. Expression of BSC and NHE3 was lower in the HP than in the P group. The NO inhibition also provoked renal transporter alterations in HP.

CONCLUSIONS

Our results suggest that tubule transporter variants may mediate the hemodynamic adaptations seen during pregnancy, although we cannot rule out the hypothesis that other factors are also mediating hemodynamic changes.

A proton-activated, outwardly rectifying chloride channel in human umbilical vein endothelial cells

Extracellular acidic pH-activated chloride channel I(Cl, acid), has been characterized in HEK 293 cells and mammalian cardiac myocytes. This study was designed to characterize I(Cl,acid) in human umbilical vein endothelial cells(HUVECs). The activation and deactivation of the current rapidly and repeatedly follows the change of the extracellular solution at pH 4.3, with the threshold pH 5.3. In addition, at very positive potentials, the current displays a time-dependent facilitation. pH-response relationship for I(Cl,acid) revealed that EC(50) is pH 4.764 with a threshold pH value of pH 5.3 and nH of 14.545. The current can be blocked by the Cl(-) channel inhibitor DIDS (100 microM). In summary, for the first time we report the presence of proton-activated, outwardly rectifying chloride channel in HUVECs. Because an acidic environment can develop in local myocardium under pathological conditions such as myocardial ischemia, I(Cl,acid) would play a role in regulation of EC function under these pathological conditions.

Racial differences in nitric oxide-dependent vasorelaxation

Along with the growing heterogeneity of the American population, ethnic/racial disparity is becoming a clear health issue in the United States. The awareness of ethnic/racial disparities has been growing because of considerable data gathered from recent clinical and epidemiological studies. These studies have highlighted the importance of addressing these differences in the diagnosis and treatment of various diseases potentially according to race. It is becoming particularly clear that there is a 2- to 3-fold racial difference in certain cardiovascular diseases (eg, preeclampsia) associated with dysfunctional nitric oxide-mediated vasodilation. In this review, the authors summarize the current literature on racial disparities in nitric oxide-mediated vasodilation in relation to cardiovascular health with an emphasis on vascular nitric oxide bioavailability as a balance between production via endothelial nitric oxide synthase and degradation through reactive oxygen species. The major hypotheses postulated on the biological basis of these differences are also highlighted.

Antihypertensive agents and arterial stiffness: relevance to reducing cardiovascular risk in the chronic kidney disease patient

PURPOSE OF REVIEW

Arterial stiffness is a sign of diffuse adventitial macrovascular disease. The purpose of the present review is to discuss, in patients with chronic kidney disease, the pathophysiology of increased arterial stiffness, the role of antihypertensive therapy on reduction of arterial stiffness, and the clinical ways by which the prognostication of cardiovascular disease in patients with chronic kidney disease can be refined using arterial stiffness monitoring.

RECENT FINDINGS

Arterial stiffness is increased with increasing prevalence of traditional cardiovascular risk factors. In patients with chronic kidney disease some unique factors further increase the risk of arterial stiffness, and include volume overload, activation of the renin-angiotensin system, anemia, and dysregulated mineral metabolism. Arterial stiffness is increased even in patients with early-stage chronic kidney disease. Blood pressure reduction when accompanied by a reduction in arterial stiffness is associated with improved prognosis. Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers can preferentially improve arterial stiffness, which may be an additional mechanism of cardiovascular protection with these agents.

SUMMARY

The impact of improvement in arterial stiffness with antihypertensive agents on cardiovascular outcomes needs well designed clinical trials.

Common genetic variants and haplotypes in renal CLCNKA gene are associated to salt-sensitive hypertension

Abnormal renal reabsorption of sodium (Na(+)) is likely to play a role in the pathogenesis of salt-sensitivity. In the kidney, chloride channels CLC-Ka (gene CLCNKA) and CLC-Kb (gene CLCNKB) and their subunit Barttin (gene BSND) have important effects on the control of Na(+) and water homeostasis. We investigated if single nucleotide polymorphisms (SNPs) or haplotypes within CLCNKA, CLCNKB and BSND loci affect salt-sensitivity in hypertensive subjects. Associations between blood pressure (BP) change after Na(+)-load and 15 SNPs spanning the length of CLCNKA and CLCNKB and six SNPs spanning the length of BSND were studied in 314 never treated essential hypertensives who underwent an i.v. infusion of saline (300 mm NaCl in 2 l H(2)O in 120 min). Four SNPs were significantly associated with BP change after Na-load. Rs848307 (P = 0.0026) and rs1739843 (P = 0.0023) map upstream the 5' of CLCNKA. Non-coding Rs1010069 (P = 0.0006) and non-synonymous rs1805152 (Thr447Ala; P = 0.0078) map within CLCNKA. Moreover, basal plasma renin activity and heart rate (measured before Na-load) were significantly lower in patients carrying the alleles associated with the larger mean BP increase after Na-load, indicating that such alleles are associated with chronic volume expansion. This study supports the candidacy of CLCNKA as a new susceptibility gene for salt-sensitivity.

The effect of hypertension on serum nitric oxide and vascular endothelial growth factor concentrations. A study in DOCA-Salt hypertensive ovariectomized rats

CardioVascular Disease (CVD) accounts for considerable mortality and morbidity in developed countries. Most of the common forms of CVD, such as hypertension, are caused by functional and structural changes in endothelial function. This study was designed to study the effect of hypertension on serum Nitric Oxide (NO) and Vascular Endothelial Growth Factor (VEGF) concentrations in DOCA-Salt hypertensive ovariectomized rats. Thirty female rats were ovariectomized. Blood samples were taken and the animals were divided into hypertensive and control groups. Hypertension was induced by DOCA-Salt method. DOCA was injected 30 mg/kg of body weight subcutaneously, twice a week with NaCl 1% instead of tap water for drinking throughout the experiment. The control group received normal saline injection with usual drinking water. Results showed that serum NO concentration in DOCA-Salt hypertensive rats was lower than the control group (18.35 +/- 5.31, 45.01 +/- 12.54 micromol/l, respectively) (p < 0.05). Also, the mean serum VEGF concentration was raised after induced hypertension (120.55 +/- 8.11 vs. 88.58 +/- 2.24 pg/ml) (p < 0.05). In conclusion, reduced serum NO and increased serum VEGF concentrations in hypertensive animals support the concept of endothelial dysfunction in hypertensive subjects.

Low-renin (volume dependent) mild-hypertensive patients have impaired flow-mediated and glyceryl-trinitrate stimulated vascular reactivity

BACKGROUND

Low-renin (volume-dependent) hypertension represents 25-30% of all cases of primary hypertension. Endothelial dysfunction and vascular remodeling are associated with hypertension but their relevance to volume-dependent hypertension (VDH) is not yet known. To evaluate this, flow-mediated dilation (FMD) of the brachial artery and the carotid intima-media thickness in the distal common carotid artery were measured and compared between renin-dependent mild-hypertensive patients (RDH) and controls.

METHOD AND RESULTS

The study group comprised 40 mild-hypertensive patients and 25 controls. Plasma renin activity (PRA), plasma aldosterone concentration, angiotensin II and nitrite/nitrate plasma levels were measured. According to PRA, subjects were classified as VDH (<0.6 ng . ml (-1) . h(-1)), or RDH (>0.6 ng . ml(-1) . h (-1)). Vascular function was evaluated by FMD before and after reactive hyperemia (RH) and glyceryl-trinitrate (GTN) administration. FMD in response to RH and GTN in the VDH group when compared with RDH group was 10.2+/-2.8% vs 13.3+/-3.6% (p=0.01); and 16.0+/-3.5% vs 19.9+/-4.5% (p=0.01), respectively.

CONCLUSION

This study showed impaired FMD and reduced GTN response in mildly hypertensive patients with low-renin plasma levels.

Endothelial nitric oxide synthase Glu298Asp gene polymorphism, blood pressure and hypertension in a general population sample

OBJECTIVE

The Glu298Asp (E/D) polymorphism of the endothelial nitric oxide synthase (eNOS) gene has been related to hypertension. Since several studies have produced contradictory results, this issue is still subject to ongoing debate. We investigated the association of the eNOS E298D polymorphism with hypertension and with blood pressure (BP) in a large population-based sample of Caucasian ethnicity.

DESIGN

Cross-sectional study in a random sample of the general population.

METHODS

The eNOS E298D polymorphism was determined by 5'-exonuclease assay among 4219 participants aged 20-79 years of the Study of Health in Pomerania (SHIP).

RESULTS

The percentages of the EE298, ED298 and DD298 genotypes were 49.2, 42.0 and 8.8%, respectively. The D allele frequencies did not differ between the groups of normotensive and hypertensive subjects (29.7 versus 29.9%, P = 0.812). Similarly, no association could be established between E298D genotype and prevalent hypertension, neither for D allele carriership (multivariate odds ratio 0.97, 95% confidence interval 0.83-1.12) nor for DD homozygosity (multivariate odds ratio 1.10, 95% confidence interval 0.84-1.43). Likewise, genotype groups did not differ as to the distribution of systolic (ANCOVA P = 0.917) or diastolic BP values (ANCOVA P = 0.657). Nearly identical results were obtained if the analyses were repeated sex-specifically or if subjects on antihypertensive medication were excluded.

CONCLUSION

In a population-based cohort of Caucasians covering a broad age range, the eNOS E298D polymorphism is neither associated with prevalent hypertension nor with systolic or diastolic BP. These results do not support the hypothesis that the E298D polymorphism contributes to the genetic susceptibility to hypertension.

Low-renin hypertension with relative aldosterone excess is associated with impaired NO-mediated vasodilation

Recent studies suggest that hypertension associated with low renin status and hyperaldosteronism is associated with increased risk for end-organ damage and cardiovascular events compared with other forms of hypertension. Additionally, experimental studies have demonstrated impaired nitric oxide-mediated bioactivity in these states. To investigate the relation between renin/aldosterone status and resistance vessel function, we examined plasma renin activity, serum aldosterone level, and forearm blood flow responses to the endothelium-dependent vasodilator methacholine and the endothelium-independent vasodilators sodium nitroprusside and verapamil using venous occlusion plethysmography in 130 volunteers (43 hypertensive, 87 normotensive). Low renin status was associated with impaired responses to methacholine and nitroprusside in patients with hypertension. Peak methacholine response was 8.7+/-5.6 mL/min per dL in the lowest renin quartile (0.1 to 0.3 ng/mL per hour) versus 14.3+/-7.3 mL/min per dL in the highest 3 renin quartiles combined (0.4 to 4.6 ng/mL per hour; P<0.001). Peak nitroprusside response was 5.6+/-2.3 mL/min per dL in the lowest renin quartile versus 13.3+/-4.1 mL/min per dL in the highest 3 renin quartiles combined (P<0.001). Blood pressure and other clinical characteristics were similar in all 4 quartiles. Vasodilator responses to verapamil did not relate to renin activity. Methacholine and nitroprusside responses did not relate to renin status in normotensive controls (P=0.34). Importantly, hypertensive patients with a high aldosterone/renin ratio also had impaired responses to methacholine. This study demonstrates that low-renin hypertension is associated with marked impairment of nitric oxide-mediated vasodilation of resistance vessels in the forearm vasculature of humans. This impairment could contribute to adverse outcomes in patients with low-renin hypertension and relative aldosterone excess.

Epoxide hydrolase and epoxygenase metabolites as therapeutic targets for renal diseases

Renal epoxygenase metabolites are involved in blood flow regulation and long-term blood pressure control. One feature of renal and cardiovascular diseases is the inability of the kidney to properly increase epoxyeicosatrienoic acid (EET) levels. Others (Busse R, Edwards G, Félétou M, Fleming I, Vanhoutte PM, and Weston AH. Trends Phamacol Sci 23: 374–380, 2002; Campbell WB, Gebremedhin D, Pratt PF, and Harder DR. Circ Res 78: 415–423, 1996; Capdevila JH and Falck JR. Biochem Biophys Res Commun 285: 571–576, 2001; Roman RJ. Physiol Rev 82: 131–185, 2002; Zeldin DC. J Biol Chem 276: 36059–36062, 2001) and we (Imig JD, Falck JR, Wei S, and Capdevila JH. J Vasc Res 38: 247–255, 2001; Imig JD, Zhao X, Capdevila JH, Morisseau C, and Hammock BD. Hypertension 39: 690–694, 2002; Zhao X, Pollock DM, Inscho EW, Zeldin DC, and Imig JD. Hypertension 41: 709–714, 2003; Zhao X, Pollock DM, Zeldin DC, and Imig JD. Hypertension 42: 775–780, 2003) have provided compelling evidence that cytochrome P-450-derived EETs have antihypertensive properties and are endothelially derived hyperpolarizing factors (EDHFs) in the kidney. EETs also possess anti-inflammatory actions that could protect the kidney vasculature from injury during renal and cardiovascular diseases. A tactic that has been used to increase EET levels has been inhibition of the soluble epoxide hydrolase enzyme. Epoxide hydrolase inhibitors have been demonstrated to be antihypertensive and renal protective. Thus the renal and cardiovascular protective actions of increasing epoxygenase levels could be translated to therapies for preventing end-organ damage.

Restoration of normal vascular relaxation mechanisms in cerebral arteries by chromosomal substitution in consomic SS.13BN rats

This study sought to identify the mechanisms of vascular relaxation that are rescued in middle cerebral arteries (MCA) of SS.13BN consomic rats by substituting chromosome 13 containing the renin gene from Brown Norway (BN) rats into the Dahl salt-sensitive (SS) genetic background. Isolated MCA from SS rats exhibited an indomethacin-sensitive constriction in response to acetylcholine (ACh) and hypoxia. ACh-induced dilation was NO dependent and hypoxic dilations were cyclooxygenase (COX) dependent in BN and SS.13BN rats. In SS rats, hypoxic dilation was restored by indomethacin and abolished by inhibiting cytochrome P-450 epoxygenases, suggesting a role for epoxyeicosatrienoic acids. MCA from SS and SS.13BN rats constricted and MCA from BN rats dilated in response to the stable prostacyclin analog iloprost. MCA from SS.13BN and BN rats (but not SS rats) dilated in response to the prostaglandin E2 receptor agonist butaprost. Hypoxia increased prostacyclin release in cerebral arteries from all the strains, whereas thromboxane A2 production was reduced in BN rat vessels only. These data suggest that SS rats may be less sensitive to vasodilator prostaglandins and that normalization of renin-angiotensin system regulation causes a switch from production of COX-derived vasoconstrictor metabolites (in SS rats) toward NO-dependent relaxation in response to ACh- and prostaglandin-dependent dilation in response to hypoxia in SS.13(BN) rats.