Under pressure: the search for the essential mechanisms of hypertension

The accumulation of brain water-free sodium is associated with ischemic damage independent of the blood pressure in female rats

Estrogen deficiency worsens ischemic stroke outcomes. In ovariectomized (OVX(+)) rats fed a high-salt diet (HSD), an increase in the body Na(+)/water ratio, which characterizes water-free Na(+) accumulation, was associated with detrimental vascular effects independent of the blood pressure (BP). We hypothesized that an increase in brain water-free Na(+) accumulation is associated with ischemic brain damage in OVX(+)/HSD rats. To test our hypothesis we divided female Wistar rats into 4 groups, OVX(+) and OVX(-) rats fed HSD or a normal diet (ND), and subjected them to transient cerebral ischemia. The brain Na(+)/water ratio was increased even in OVX(+)/ND rats and augmented in OVX(+)/HSD rats. The increase in the brain Na(+)/water ratio was positively correlated with expansion of the cortical infarct volume without affecting the BP. Interestingly, OVX(+) was associated with the decreased expression of ATP1α3, a subtype of the Na(+) efflux pump. HSD increased the expression of brain Na(+) influx-related molecules and the mineralocorticoid receptor (MR). The pretreatment of OVX(+)/HSD rats with the MR antagonist eplerenone reduced brain water-free Na(+) accumulation, up-regulated ATP1α3, down-regulated MR, and reduced the cortical infarct volume. Our findings show that the increase in the brain Na(+)/water ratio elicited by estrogen deficiency or HSD is associated with ischemic brain damage BP-independently, suggesting the importance of regulating the accumulation of brain water-free Na(+). The up-regulation of ATP1α3 and the down-regulation of MR may provide a promising therapeutic strategy to attenuate ischemic brain damage in postmenopausal women.

Brain inflammation and hypertension: the chicken or the egg?

Inflammation of forebrain and hindbrain nuclei controlling the sympathetic nervous system (SNS) outflow from the brain to the periphery represents an emerging concept of the pathogenesis of neurogenic hypertension. Angiotensin II (Ang-II) and prorenin were shown to increase production of reactive oxygen species and pro-inflammatory cytokines (interleukin-1 beta (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α)) while simultaneously decreasing production of interleukin-10 (IL-10) in the paraventricular nucleus of the hypothalamus and the rostral ventral lateral medulla. Peripheral chronic inflammation and Ang-II activity seem to share a common central mechanism contributing to an increase in sympathetic neurogenic vasomotor tone and entailing neurogenic hypertension. Both hypertension and obesity facilitate the penetration of peripheral immune cells in the brain parenchyma. We suggest that renin-angiotensin-driven hypertension encompasses feedback and feedforward mechanisms in the development of neurogenic hypertension while low-intensity, chronic peripheral inflammation of any origin may serve as a model of a feedforward mechanism in this condition.

Immunity in arterial hypertension: associations or causalities?

Numerous studies describe associations between markers of inflammation and arterial hypertension (aHT), but does that imply causality? Interventional studies that reduce blood pressure reduced also markers of inflammation, but does immunosuppression improve hypertension? Here, we review the available mechanistic data. Aberrant immunity can trigger endothelial dysfunction but is hardly ever the primary cause of aHT. Innate and adaptive immunity get involved once hypertension has caused vascular wall injury as immunity is a modifier of endothelial dysfunction and vascular wall remodelling. As vascular remodelling progresses, immunity-related mechanisms can become significant cofactors for cardiovascular (CV) disease progression; vice versa, suppressing immunity can improve hypertension and CV outcomes. Innate and adaptive immunity both contribute to vascular wall remodelling. Innate immunity is driven by danger signals that activate Toll-like receptors and other pattern-recognition receptors. Adaptive immunity is based on loss of tolerance against vascular autoantigens and includes autoreactive T-cell immunity as well as non-HLA angiotensin II type 1 receptor-activating autoantibodies. Such processes involve numerous other modulators such as regulatory T cells. Together, immunity is not causal for hypertension but rather an important secondary pathomechanism and a potential therapeutic target in hypertension.

Systematic review and meta-analysis of the prevalence of resistant hypertension in treated hypertensive populations

BACKGROUND

Although treatment-resistant hypertension (RH) is a serious burden on population health, there exists uncertainty about its prevalence. Hence, the objectives of this work were to systematically review and critically appraise the literature and to conduct a meta-analysis on the prevalence of RH in treated hypertensive populations.

METHODS

PubMed, Cochrane Library, CRD York databases, and study bibliographies were systematically searched for observational and interventional studies that report disease frequency in adult populations. The pooled prevalence was obtained through random-effect modeling. Furthermore, quality assessment, publication bias diagnostics, meta-regression, subgroup analysis by sex, and sensitivity analysis were performed.

RESULTS

Out of 318 retrieved studies, 20 observational studies and 4 randomized control trials (RCTs) with a total population of 961,035 were included. The random-effect method for observational studies and RCTs yielded RH prevalence ratios of 13.72% (95% confidence interval (CI) = 11.19%-16.24%) and 16.32% (95% CI = 10.68%-21.95%), respectively. Yet, most studies were incapable of ruling out pseudo-resistance caused by white-coat effect, poor medication adherence, and suboptimal dosing. Differences in RH prevalence by sex were negligible. Meta-regression analysis showed that study-level characteristics had no statistically significant influence on RH prevalence. The inclusion of further studies in the sensitivity analysis concurred with the baseline results (13.19%; 95% CI = 10.89%-15.49%).

CONCLUSIONS

Researchers should enhance comparability of future empirical evidence through homogeneous methodologies and comparable baseline populations. This meta-analysis concludes that RH is a frequent phenomenon and further harmonization in terms of RH definition and measurement would be necessary to clearly distinguish true treatment resistance from pseudo-resistance.

Epithelial sodium transport and its control by aldosterone: the story of our internal environment revisited

Transcription and translation require a high concentration of potassium across the entire tree of life. The conservation of a high intracellular potassium was an absolute requirement for the evolution of life on Earth. This was achieved by the interplay of P- and V-ATPases that can set up electrochemical gradients across the cell membrane, an energetically costly process requiring the synthesis of ATP by F-ATPases. In animals, the control of an extracellular compartment was achieved by the emergence of multicellular organisms able to produce tight epithelial barriers creating a stable extracellular milieu. Finally, the adaptation to a terrestrian environment was achieved by the evolution of distinct regulatory pathways allowing salt and water conservation. In this review we emphasize the critical and dual role of Na(+)-K(+)-ATPase in the control of the ionic composition of the extracellular fluid and the renin-angiotensin-aldosterone system (RAAS) in salt and water conservation in vertebrates. The action of aldosterone on transepithelial sodium transport by activation of the epithelial sodium channel (ENaC) at the apical membrane and that of Na(+)-K(+)-ATPase at the basolateral membrane may have evolved in lungfish before the emergence of tetrapods. Finally, we discuss the implication of RAAS in the origin of the present pandemia of hypertension and its associated cardiovascular diseases.

Lymphocyte adaptor protein LNK deficiency exacerbates hypertension and end-organ inflammation

The lymphocyte adaptor protein LNK (also known as SH2B3) is primarily expressed in hematopoietic and endothelial cells, where it functions as a negative regulator of cytokine signaling and cell proliferation. Single-nucleotide polymorphisms in the gene encoding LNK are associated with autoimmune and cardiovascular disorders; however, it is not known how LNK contributes to hypertension. Here, we determined that loss of LNK exacerbates angiotensin II-induced (Ang II-induced) hypertension and the associated renal and vascular dysfunction. At baseline, kidneys from Lnk-/- mice exhibited greater levels of inflammation, oxidative stress, and glomerular injury compared with WT animals, and these parameters were further exacerbated by Ang II infusion. Aortas from Lnk-/- mice exhibited enhanced inflammation, reduced nitric oxide levels, and impaired endothelial-dependent relaxation. Bone marrow transplantation studies demonstrated that loss of LNK in hematopoietic cells is primarily responsible for the observed renal and vascular inflammation and predisposition to hypertension. Ang II infusion increased IFN-γ-producing CD8+ T cells in the spleen and kidneys of Lnk-/- mice compared with WT mice. Moreover, IFN-γ deficiency resulted in blunted hypertension in response to Ang II infusion. Together, these results suggest that LNK is a potential therapeutic target for hypertension and its associated renal and vascular sequela.

A Salt-Induced Reno-Cerebral Reflex Activates Renin-Angiotensin Systems and Promotes CKD Progression

Salt intake promotes progression of CKD by uncertain mechanisms. We hypothesized that a salt-induced reno-cerebral reflex activates a renin-angiotensin axis to promote CKD. Sham-operated and 5/6-nephrectomized rats received a normal-salt (0.4%), low-salt (0.02%), or high-salt (4%) diet for 2 weeks. High salt in 5/6-nephrectomized rats increased renal NADPH oxidase, inflammation, BP, and albuminuria. Furthermore, high salt activated the intrarenal and cerebral, but not the systemic, renin-angiotensin axes and increased the activity of renal sympathetic nerves and neurons in the forebrain of these rats. Renal fibrosis was increased 2.2-fold by high versus low salt, but intracerebroventricular tempol, losartan, or clonidine reduced this fibrosis by 65%, 69%, or 59%, respectively, and renal denervation or deafferentation reduced this fibrosis by 43% or 38%, respectively (all P<0.05). Salt-induced fibrosis persisted after normalization of BP with hydralazine. These data suggest that the renal and cerebral renin-angiotensin axes are interlinked by a reno-cerebral reflex that is activated by salt and promotes oxidative stress, fibrosis, and progression of CKD independent of BP.

Epigenetics and arterial hypertension: the challenge of emerging evidence

Epigenetic phenomena include DNA methylation, post-translational histone modifications, and noncoding RNAs, as major marks. Although similar to genetic features of DNA for their heritability, epigenetic mechanisms differ for their potential reversibility by environmental and nutritional factors, which make them potentially crucial for their role in complex and multifactorial diseases. The function of these mechanisms is indeed gaining interest in relation to arterial hypertension (AH) with emerging evidence from cell culture and animal models as well as human studies showing that epigenetic modifications have major functions within pathways related to AH. Among epigenetic marks, the role of DNA methylation is mostly highlighted given the primary role of this epigenetic feature in mammalian cells. A lower global methylation was observed in DNA of peripheral blood mononuclear cells of hypertensive patients. Moreover, DNA hydroxymethylation appears modifiable by salt intake in a Dahl salt-sensitive rat model. The specific function of DNA methylation in regulating the expression of AH-related genes at promoter site was described for hydroxysteroid (11-beta) dehydrogenase 2 (HSD11B2), somatic angiotensin converting enzyme (sACE), Na+/K+/2Cl- cotransporter 1 (NKCC1), angiotensinogen (AGT), α-adducin (ADD1), and for other crucial genes in endocrine hypertension. Post-translational histone methylation at different histone 3 lysine residues was also observed to control the expression of genes related to AH as lysine-specific demethylase-1(LSD1), HSD11B2, and epithelial sodium channel subunit α (SCNN1A). Noncoding RNAs including several microRNAs influence genes involved in steroidogenesis and the renin-angiotensin-aldosterone pathway. In the present review, the current knowledge on the relationship between the main epigenetic marks and AH will be presented, considering the challenge of epigenetic patterns being modifiable by environmental factors that may lead toward novel implications in AH preventive and therapeutic strategies.

Genetic variant coding for iron regulatory protein HFE contributes to hypertension, the TAMRISK study

Iron is essential for body homeostasis, but iron overload may lead to metabolic abnormalities and thus increase the risk for atherosclerosis and many other diseases. Major histocompatibility complex class I-like transmembrane protein (HFE) is involved in body iron metabolism. The gene coding for HFE has 3 well-known polymorphic sites of which H63D (rs1799945, C > G) has recently been associated with hypertension in a genome-wide association study (GWAS) study. In the present study, we wanted to clarify whether the genetic variant associates with hypertension in a Finnish cohort consisting of 50-year-old men and women. The study included 399 hypertensive cases and 751 controls from the Tampere adult population cardiovascular risk study (TAMRISK) cohort. Genotyping of polymorphisms was done by polymerase chain reaction using DNAs extracted from buccal swabs. We found that individuals with the mutated form of the H63D polymorphic site (G-allele) had a 1.4-fold risk (P = 0.037, 95% confidence interval [CI] 1.02-1.89) for hypertension at the age of 50 years compared with the CC genotype carriers. When obese subjects (body mass index > 30 kg/m²) were analyzed in their own group, the risk for hypertension was even stronger (odds ratio 4.15, P < 0.001, 95% CI 1.98-8.68). We also noticed that the blood pressure (BP) readings were higher in those with the minor G-allele when compared to ones having a normal genotype already at the age of 35 years. Means of systolic/diastolic BPs were 127/81 mm Hg for CC and 131/83 mm Hg for CG + GG groups (P < 0.001 for systolic and P = 0.005 for diastolic pressure). In conclusion, HFE genetic variant H63D was associated with essential hypertension in Finnish subjects from the TAMRISK cohort confirming a previous GWAS study. The effect of this SNP on BP was also confirmed from a longitudinal study.

Glucagon-like peptide-1 and blood pressure in young and healthy adults from the general population

Hypertension and diabetes mellitus are highly correlated, but the underlying mechanisms are only partly understood. Therefore, the aim of our study was to investigate the relationships between plasma levels of glucagon-like peptide-1, a key factor in the regulation of glucose homeostasis, and various blood pressure indices. Healthy adults aged 25 to 41 years were enrolled in a population-based study. Established cardiovascular disease, diabetes mellitus, or a body mass index >35 kg/m(2) were exclusion criteria. Fasting plasma glucagon-like peptide-1 levels as determined with a novel high-sensitive assay and ambulatory blood pressure data were available in 1479 participants not using antihypertensive treatment. Median age of our population was 38 years. Mean systolic and diastolic blood pressure across increasing glucagon-like peptide-1 quartiles were 120.6, 122.8, 123.2, and 124.9 mm Hg and 77.1, 78.7, 78.9, and 79.9 mm Hg, respectively. We found a linear relationship of glucagon-like peptide-1 with 24-hour ambulatory blood pressure after multivariable adjustment (β per 1 log-unit increase 2.01; 95% confidence interval, 1.02-3.00; P<0.0001 for systolic and 1.22; 0.47-1.97; P=0.002 for diastolic blood pressure). In separate analyses, glucagon-like peptide-1 was significantly related to both awake (β per 1 log-unit increase 2.05; 1.02-3.09; P=0.0001 for systolic and 1.15; 0.35-1.96; P=0.005 for diastolic blood pressure) and asleep blood pressure (β per 1 log-unit increase 1.34; 0.26-2.42; P=0.01 for systolic and 1.05; 0.26-1.84; P=0.009 for diastolic blood pressure). In conclusion, plasma levels of glucagon-like peptide-1 are significantly associated with both systolic and diastolic blood pressure levels.

The angiogenic factor PlGF mediates a neuroimmune interaction in the spleen to allow the onset of hypertension

Hypertension is a health problem affecting over 1 billion people worldwide. How the immune system gets activated under hypertensive stimuli to contribute to blood pressure elevation is a fascinating enigma. Here we showed a splenic role for placental growth factor (PlGF), which accounts for the onset of hypertension, through immune system modulation. PlGF repressed the expression of the protein Timp3 (tissue inhibitor of metalloproteinases 3), through the transcriptional Sirt1-p53 axis. Timp3 repression allowed costimulation of T cells and their deployment toward classical organs involved in hypertension. We showed that the spleen is an essential organ for the development of hypertension through a noradrenergic drive mediated by the celiac ganglion efferent. Overall, we demonstrate that PlGF mediates the neuroimmune interaction in the spleen, organizing a unique and nonredundant response that allows the onset of hypertension.

Human aldosterone synthase gene polymorphism promotes miRNA binding and regulates gene expression

Hypertension is a serious risk factor for myocardial infarction, heart failure, vascular disease, stroke, and renal failure. Like other complex diseases, hypertension is caused by a combination of genetic and environmental factors. The renin-angiotensin-aldosterone system plays an important role in the regulation of blood pressure. The octapeptide angiotensin II (ANG II) is one of the most active vasopressor agents and is obtained from the precursor molecule, angiotensinogen, by the combined proteolytic action of renin and angiotensin-converting enzyme. ANG II increases the expression of aldosterone synthase (coded by Cyp11B2 gene), which is the rate-limiting enzyme in the biosynthesis of aldosterone. Previous studies have shown that increased expression of aldosterone synthase increases blood pressure and cardiac hypertrophy in transgenic mice. Human Cyp11B2 gene has a T/C polymorphism at -344 positions in its 5'-untranslated region (UTR), and the -344T allele is associated with hypertension. Human Cyp11B2 gene also has an A/G polymorphism at 735 position in its 3'-UTR (rs28491316) that is in linkage disequilibrium with single nucleotide polymorphism at -344. We show here that 1) microRNA (miR)-766 binds to the 735G-allele and not the 735A-allele of the hCyp11B2 gene and 2) transfection of miR-766 reduces the human aldosterone synthase mRNA and protein level in human adrenocortical cells H295R. These studies suggest that miR-766 may downregulate the expression of human aldosterone synthase gene and reduce blood pressure in human subjects containing -344T allele.

DC isoketal-modified proteins activate T cells and promote hypertension

Oxidative damage and inflammation are both implicated in the genesis of hypertension; however, the mechanisms by which these stimuli promote hypertension are not fully understood. Here, we have described a pathway in which hypertensive stimuli promote dendritic cell (DC) activation of T cells, ultimately leading to hypertension. Using multiple murine models of hypertension, we determined that proteins oxidatively modified by highly reactive γ-ketoaldehydes (isoketals) are formed in hypertension and accumulate in DCs. Isoketal accumulation was associated with DC production of IL-6, IL-1β, and IL-23 and an increase in costimulatory proteins CD80 and CD86. These activated DCs promoted T cell, particularly CD8+ T cell, proliferation; production of IFN-γ and IL-17A; and hypertension. Moreover, isoketal scavengers prevented these hypertension-associated events. Plasma F2-isoprostanes, which are formed in concert with isoketals, were found to be elevated in humans with treated hypertension and were markedly elevated in patients with resistant hypertension. Isoketal-modified proteins were also markedly elevated in circulating monocytes and DCs from humans with hypertension. Our data reveal that hypertension activates DCs, in large part by promoting the formation of isoketals, and suggest that reducing isoketals has potential as a treatment strategy for this disease.

Arterial Innervation in Development and Disease

Innervation of arteries by sympathetic nerves is well known to control blood supply to organs. Recent studies have elucidated the mechanisms that regulate the development of arterial innervation and show that in addition to vascular tone, sympathetic nerves may also influence arterial maturation and growth. Understanding sympathetic arterial innervation may lead to new approaches to treat peripheral arterial disease and hypertension.

Mutation of Plekha7 attenuates salt-sensitive hypertension in the rat

PLEKHA7 (pleckstrin homology domain containing family A member 7) has been found in multiple studies as a candidate gene for human hypertension, yet functional data supporting this association are lacking. We investigated the contribution of this gene to the pathogenesis of salt-sensitive hypertension by mutating Plekha7 in the Dahl salt-sensitive (SS/JrHsdMcwi) rat using zinc-finger nuclease technology. After four weeks on an 8% NaCl diet, homozygous mutant rats had lower mean arterial (149 ± 9 mmHg vs. 178 ± 7 mmHg; P < 0.05) and systolic (180 ± 7 mmHg vs. 213 ± 8 mmHg; P < 0.05) blood pressure compared with WT littermates. Albumin and protein excretion rates were also significantly lower in mutant rats, demonstrating a renoprotective effect of the mutation. Total peripheral resistance and perivascular fibrosis in the heart and kidney were significantly reduced in Plekha7 mutant animals, suggesting a potential role of the vasculature in the attenuation of hypertension. Indeed, both flow-mediated dilation and endothelium-dependent vasodilation in response to acetylcholine were improved in isolated mesenteric resistance arteries of Plekha7 mutant rats compared with WT. These vascular improvements were correlated with changes in intracellular calcium handling, resulting in increased nitric oxide bioavailability in mutant vessels. Collectively, these data provide the first functional evidence that Plekha7 may contribute to blood pressure regulation and cardiovascular function through its effects on the vasculature.

Rap1b in smooth muscle and endothelium is required for maintenance of vascular tone and normal blood pressure

OBJECTIVE

Small GTPase Ras-related protein 1 (Rap1b) controls several basic cellular phenomena, and its deletion in mice leads to several cardiovascular defects, including impaired adhesion of blood cells and defective angiogenesis. We found that Rap1b(-/-) mice develop cardiac hypertrophy and hypertension. Therefore, we examined the function of Rap1b in regulation of blood pressure.

APPROACH AND RESULTS

Rap1b(-/-) mice developed cardiac hypertrophy and elevated blood pressure, but maintained a normal heart rate. Correcting elevated blood pressure with losartan, an angiotensin II type 1 receptor antagonist, alleviated cardiac hypertrophy in Rap1b(-/-) mice, suggesting a possibility that cardiac hypertrophy develops secondary to hypertension. The indices of renal function and plasma renin activity were normal in Rap1b(-/-) mice. Ex vivo, we examined whether the effect of Rap1b deletion on smooth muscle-mediated vessel contraction and endothelium-dependent vessel dilation, 2 major mechanisms controlling basal vascular tone, was the basis for the hypertension. We found increased contractility on stimulation with a thromboxane analog or angiotensin II or phenylephrine along with increased inhibitory phosphorylation of myosin phosphatase under basal conditions consistent with elevated basal tone and the observed hypertension. Cyclic adenosine monophosphate-dependent relaxation in response to Rap1 activator, Epac, was decreased in vessels from Rap1b(-/-) mice. Defective endothelial release of dilatory nitric oxide in response to elevated blood flow leads to hypertension. We found that nitric oxide-dependent vasodilation was significantly inhibited in Rap1b-deficient vessels.

CONCLUSIONS

This is the first report to indicate that Rap1b in both smooth muscle and endothelium plays a key role in maintaining blood pressure by controlling normal vascular tone.

Mechanisms of AT1a receptor-mediated uptake of angiotensin II by proximal tubule cells: a novel role of the multiligand endocytic receptor megalin

The present study tested the hypothesis that the multiligand endocytic receptor megalin is partially involved in the uptake of ANG II and downstream signaling responses in mouse proximal tubule cells (mPCT) by interacting with AT1a receptors. mPCT cells of wild-type (WT) and AT1a receptor-deficient (AT1a-KO) mice were treated with vehicle, the AT1 receptor blocker losartan (10 μM), or a selective megalin small interfering (si) RNA for 48 h. The uptake of fluorescein (FITC)-labeled ANG II (10 nM, 37°C) and downstream signaling responses were analyzed by fluorescence imaging and Western blotting. AT1a receptors and megalin were abundantly expressed in mPCT cells, whereas AT1a receptors were absent in AT1a-KO mPCT cells (P < 0.01). In WT mPCT cells, FITC-ANG II uptake was visualized at 30 min in the cytoplasm and in the nuclei 1 h after exposure. Losartan alone completely blocked the uptake of FITC-ANG II, whereas megalin siRNA inhibited only 30% of the response (P < 0.01). The remaining FITC-ANG II uptake in the presence of megalin siRNA was completely abolished by losartan. ANG II induced threefold increases in phosphorylated MAP kinases ERK1/2 and a onefold increase in phosphorylated sodium and hydrogen exchanger 3 (NHE3) proteins, which were also blocked by losartan and megalin-siRNA. By contrast, losartan and megalin siRNA had no effects on these signaling proteins in AT1a-KO mPCT cells. We conclude that the uptake of ANG II and downstream MAP kinases ERK1/2 and NHE3 signaling responses in mPCT cells are mediated primarily by AT1a receptors. However, megalin may also play a partial role in these responses to ANG II.

Hypertension and sleep: overview of a tight relationship

Autonomic cardiovascular control changes across sleep stages. Thus, blood pressure (BP), heart rate and peripheral vascular resistance progressively decrease in non-rapid eye movement sleep. Any deterioration in sleep quality or quantity may be associated with an increase in nocturnal BP which could participate in the development or poor control of hypertension. In the present report, sleep problems/disorders, which impact either the quality or quantity of sleep, are reviewed for their interaction with BP regulation and their potential association with prevalent or incident hypertension. Obstructive sleep apnea syndrome, sleep duration/deprivation, insomnia, restless legs syndrome and narcolepsy are successively reviewed. Obstructive sleep apnea is clearly associated with the development of hypertension that is only slightly reduced by continuous positive airway pressure treatment. Shorter and longer sleep durations are associated with prevalent or incident hypertension but age, gender, environmental exposures and ethnic differences are clear confounders. Insomnia with objective short sleep duration, restless legs syndrome and narcolepsy may impact BP control, needing additional studies to establish their impact in the development of permanent hypertension. Addressing sleep disorders or sleep habits seems a relevant issue when considering the risk of developing hypertension or the control of pre-existent hypertension. Combined sleep problems may have potential synergistic deleterious effects.

Sodium balance is not just a renal affair

PURPOSE OF REVIEW

The equilibration theory of extracellular body fluids is tightly linked to sodium (Na) metabolism. It is accepted that with changes in salt intake, renal sodium elimination will prevent any change in interstitial Na content and concentration. This review summarizes recent anomalous findings regarding salt and water homeostasis that are inconsistent with current assumptions.

RECENT FINDINGS

Recent findings from chemical analysis studies of laboratory animals, as well as noninvasive quantitative Na MRI (Na-MRI) studies in patients, have shown that remarkable amounts of Na are stored in muscle and in skin without commensurate water retention. Furthermore, an ultra-long Na balance study in humans suggests the presence of endogenous clocks that generate weekly and monthly infradian rhythmicity of Na storage independent of salt intake. Animal experiments suggest that fluids in the skin interstitium are hypertonic compared with plasma, and that interstitial osmotic stress induces local extrarenal immune cell and lymph-capillary driven mechanisms for electrolyte clearance and maintenance of the internal environment.

SUMMARY

Recent quantitative evidence challenges current ideas on salt and water homeostasis, and suggests that Na homeostasis cannot be maintained without additional previously unappreciated extrarenal regulatory mechanisms.

Renal angiotensin-converting enzyme and blood pressure control

PURPOSE OF REVIEW

This review presents novel findings regarding the renal angiotensin-converting enzyme (ACE) and its role in blood pressure (BP) control.

RECENT FINDINGS

The textbook flow diagram of the renin-angiotensin system (RAS) shows the pulmonary endothelium as the main source of the ACE that converts angiotensin I to angiotensin II. However, ACE is made in large quantities by the kidneys, which raises the important question of what precisely is the function of renal ACE? Recent studies in gene-targeted mice indicates that renal ACE plays a dominant role in regulating the response of the kidney to experimental hypertension. In particular, renal ACE and locally generated angiotensin II affect the activity of several key sodium transporters and the induction of sodium and water retention resulting in the elevation of BP.

SUMMARY

New experimental data link the renal ACE/angiotensin II pathway and the local regulation of sodium transport as key elements in the development of hypertension.

Mechanism of salt-sensitive hypertension: focus on adrenal and sympathetic nervous systems

A central role for the kidney among the systems contributing to BP regulation and the development of hypertension has been proposed. Both the aldosterone/mineralocorticoid receptor pathway and the renal sympathetic nervous system have important roles in the regulation of renal excretory function and BP control, but the mechanisms underlying these processes have remained unclear. However, recent studies revealed the activation of two pathways in salt-sensitive hypertension. Notably, Rac1, a member of the Rho-family of small GTP binding proteins, was identified as a novel ligand-independent modulator of mineralocorticoid receptor activity. Furthermore, these studies point to crucial roles for the Rac1-mineralocorticoid receptor-NCC/ENaC and the renal β-adrenergic stimulant-glucocorticoid receptor-WNK4-NCC pathways in certain rodent models of salt-sensitive hypertension. The nuclear mineralocorticoid and glucocorticoid receptors may contribute to impaired renal excretory function and the resulting salt-sensitive hypertension by increasing sodium reabsorption at different tubular segments. This review provides an in-depth discussion of the evidence supporting these conclusions and considers the significance with regard to treating salt-sensitive hypertension and salt-induced cardiorenal injury.

Identifying common genetic variants in blood pressure due to polygenic pleiotropy with associated phenotypes

Blood pressure is a critical determinant of cardiovascular morbidity and mortality. It is affected by environmental factors, but has a strong heritable component. Despite recent large genome-wide association studies, few genetic risk factors for blood pressure have been identified. Epidemiological studies suggest associations between blood pressure and several diseases and traits, which may partly arise from a shared genetic basis (genetic pleiotropy). Using genome-wide association studies summary statistics and a genetic pleiotropy-informed conditional false discovery rate method, we systematically investigated genetic overlap between systolic blood pressure (SBP) and 12 comorbid traits and diseases. We found significant enrichment of single nucleotide polymorphisms associated with SBP as a function of their association with body mass index, low-density lipoprotein, waist/hip ratio, schizophrenia, bone mineral density, type 1 diabetes mellitus, and celiac disease. In contrast, the magnitude of enrichment due to shared polygenic effects was smaller with the other phenotypes (triglycerides, high-density lipoproteins, type 2 diabetes mellitus, rheumatoid arthritis, and height). Applying the conditional false discovery rate method to the enriched phenotypes, we identified 62 loci associated with SBP (false discovery rate <0.01), including 42 novel loci. The observed polygenic overlap between SBP and several related disorders indicates that the epidemiological associations are not mediated solely via lifestyle factors but also reflect an etiologic relation that warrants further investigation. The new gene loci identified implicate novel genetic mechanisms related to lipid biology and the immune system in SBP.

Reactive oxygen species, vascular Noxs, and hypertension: focus on translational and clinical research

SIGNIFICANCE

Reactive oxygen species (ROS) are signaling molecules that are important in physiological processes, including host defense, aging, and cellular homeostasis. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in the onset and/or progression of chronic diseases, including hypertension.

RECENT ADVANCES

Although oxidative stress may not be the only cause of hypertension, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors, such as salt loading, activation of the renin-angiotensin-aldosterone system, and sympathetic hyperactivity, at least in experimental models. A major source for ROS in the cardiovascular-renal system is a family of nicotinamide adenine dinucleotide phosphate oxidases (Noxs), including the prototypic Nox2-based Nox, and Nox family members: Nox1, Nox4, and Nox5.

CRITICAL ISSUES

Although extensive experimental data support a role for increased ROS levels and altered redox signaling in the pathogenesis of hypertension, the role in clinical hypertension is unclear, as a direct causative role of ROS in blood pressure elevation has yet to be demonstrated in humans. Nevertheless, what is becoming increasingly evident is that abnormal ROS regulation and aberrant signaling through redox-sensitive pathways are important in the pathophysiological processes which is associated with vascular injury and target-organ damage in hypertension.

FUTURE DIRECTIONS

There is a paucity of clinical information related to the mechanisms of oxidative stress and blood pressure elevation, and a few assays accurately measure ROS directly in patients. Such further ROS research is needed in humans and in the development of adequately validated analytical methods to accurately assess oxidative stress in the clinic.

Hypertension: what's sex got to do with it?

Hypertension is a complex and multifaceted disease, and there are well established sex differences in many aspects of blood pressure (BP) control. The intent of this review is to highlight recent work examining sex differences in the molecular mechanisms of BP control in hypertension to assess whether the "one-size-fits-all" approach to BP control is appropriate with regard to sex.

New frontiers in the intrarenal Renin-Angiotensin system: a critical review of classical and new paradigms

The renin-angiotensin system (RAS) is well-recognized as one of the oldest and most important regulators of arterial blood pressure, cardiovascular, and renal function. New frontiers have recently emerged in the RAS research well beyond its classic paradigm as a potent vasoconstrictor, an aldosterone release stimulator, or a sodium-retaining hormone. First, two new members of the RAS have been uncovered, which include the renin/(Pro)renin receptor (PRR) and angiotensin-converting enzyme 2 (ACE2). Recent studies suggest that prorenin may act on the PRR independent of the classical ACE/ANG II/AT1 receptor axis, whereas ACE2 may degrade ANG II to generate ANG (1-7), which activates the Mas receptor. Second, there is increasing evidence that ANG II may function as an intracellular peptide to activate intracellular and/or nuclear receptors. Third, currently there is a debate on the relative contribution of systemic versus intrarenal RAS to the physiological regulation of blood pressure and the development of hypertension. The objectives of this article are to review and discuss the new insights and perspectives derived from recent studies using novel transgenic mice that either overexpress or are deficient of one key enzyme, ANG peptide, or receptor of the RAS. This information may help us better understand how ANG II acts, both independently or through interactions with other members of the system, to regulate the kidney function and blood pressure in health and disease.

Rediscovering ACE: novel insights into the many roles of the angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is best known for the catalytic conversion of angiotensin I to angiotensin II. However, the use of gene-targeting techniques has led to mouse models highlighting many other biochemical properties and actions of this enzyme. This review discusses recent studies examining the functional significance of ACE tissue-specific expression and the presence in ACE of two independent catalytic sites with distinct substrates and biological effects. It is these features which explain why ACE makes important contributions to many different physiological processes including renal development, blood pressure control, inflammation, and immunity.

Excess maternal salt intake produces sex-specific hypertension in offspring: putative roles for kidney and gastrointestinal sodium handling

Hypertension is common and contributes, via cardiovascular disease, towards a large proportion of adult deaths in the Western World. High salt intake leads to high blood pressure, even when occurring prior to birth – a mechanism purported to reside in altered kidney development and later function. Using a combination of in vitro and in vivo approaches we tested whether increased maternal salt intake influences fetal kidney development to render the adult individual more susceptible to salt retention and hypertension. We found that salt-loaded pregnant rat dams were hypernatraemic at day 20 gestation (147±5 vs. 128±5 mmoles/L). Increased extracellular salt impeded murine kidney development in vitro, but had little effect in vivo. Kidneys of the adult offspring had few structural or functional abnormalities, but male and female offspring were hypernatraemic (166±4 vs. 149±2 mmoles/L), with a marked increase in plasma corticosterone (e.g. male offspring; 11.9 [9.3–14.8] vs. 2.8 [2.0–8.3] nmol/L median [IQR]). Furthermore, adult male, but not female, offspring had higher mean arterial blood pressure (effect size, +16 [9–21] mm Hg; mean [95% C.I.]. With no clear indication that the kidneys of salt-exposed offspring retained more sodium per se, we conducted a preliminary investigation of their gastrointestinal electrolyte handling and found increased expression of proximal colon solute carrier family 9 (sodium/hydrogen exchanger), member 3 (SLC9A3) together with altered faecal characteristics and electrolyte handling, relative to control offspring. On the basis of these data we suggest that excess salt exposure, via maternal diet, at a vulnerable period of brain and gut development in the rat neonate lays the foundation for sustained increases in blood pressure later in life. Hence, our evidence further supports the argument that excess dietary salt should be avoided per se, particularly in the range of foods consumed by physiologically immature young.

Heterozygous disruption of renal outer medullary potassium channel in rats is associated with reduced blood pressure

The renal outer medullary potassium channel (ROMK, KCNJ1) mediates potassium recycling and facilitates sodium reabsorption through the Na(+)/K(+)/2Cl(-) cotransporter in the loop of Henle and potassium secretion at the cortical collecting duct. Human genetic studies indicate that ROMK homozygous loss-of-function mutations cause type II Bartter syndrome, featuring polyuria, renal salt wasting, and hypotension; humans heterozygous for ROMK mutations identified in the Framingham Heart Study have reduced blood pressure. ROMK null mice recapitulate many of the features of type II Bartter syndrome. We have generated an ROMK knockout rat model in Dahl salt-sensitive background by using zinc finger nuclease technology and investigated the effects of knocking out ROMK on systemic and renal hemodynamics and kidney histology in the Dahl salt-sensitive rats. The ROMK(-/-) pups recapitulated features identified in the ROMK null mice. The ROMK(+/-) rats, when challenged with a 4% salt diet, exhibited a reduced blood pressure compared with their ROMK(+/+) littermates. More importantly, when challenged with an 8% salt diet, the Dahl salt-sensitive rats with 50% less ROMK expression showed increased protection from salt-induced blood pressure elevation and signs of protection from renal injury. Our findings in ROMK knockout Dahl salt-sensitive rats, together with the previous reports in humans and mice, underscore a critical role of ROMK in blood pressure regulation.

Angiotensin II regulates microRNA-132/-212 in hypertensive rats and humans

MicroRNAs (miRNAs), a group of small non-coding RNAs that fine tune translation of multiple target mRNAs, are emerging as key regulators in cardiovascular development and disease. MiRNAs are involved in cardiac hypertrophy, heart failure and remodeling following cardiac infarction; however, miRNAs involved in hypertension have not been thoroughly investigated. We have recently reported that specific miRNAs play an integral role in Angiotensin II receptor (AT₁R) signaling, especially after activation of the Gαq signaling pathway. Since AT₁R blockers are widely used to treat hypertension, we undertook a detailed analysis of potential miRNAs involved in Angiotensin II (AngII) mediated hypertension in rats and hypertensive patients, using miRNA microarray and qPCR analysis. The miR-132 and miR-212 are highly increased in the heart, aortic wall and kidney of rats with hypertension (159 ± 12 mm Hg) and cardiac hypertrophy following chronic AngII infusion. In addition, activation of the endothelin receptor, another Gαq coupled receptor, also increased miR-132 and miR-212. We sought to extend these observations using human samples by reasoning that AT₁R blockers may decrease miR-132 and miR-212. We analyzed tissue samples of mammary artery obtained from surplus arterial tissue after coronary bypass operations. Indeed, we found a decrease in expression levels of miR-132 and miR-212 in human arteries from bypass-operated patients treated with AT₁R blockers, whereas treatment with β-blockers had no effect. Taken together, these data suggest that miR-132 and miR-212 are involved in AngII induced hypertension, providing a new perspective in hypertensive disease mechanisms.

Neurogenic hypertension: revelations from genome-wide gene expression profiling

There is now good evidence for a role of the sympathetic nervous system in the etiology of essential hypertension in humans. Although genetic variation is expected to underlie the elevated sympathetic outflow in this complex polygenic condition, only limited information has emerged from classic molecular genetic studies. Recently, progress has been made in understanding neurogenic aspects by determination of global alterations in gene expression in key brain regions of animal models of neurogenic hypertension. Such genome-wide expression studies in the hypothalamus and brainstem support roles for factors such as neuronal nitric oxide synthase, inflammation and reactive oxygen species. A role for non-coding RNAs such as microRNAs, and epigenetic alterations await exploration. Ongoing novel approaches should provide a better understanding of the processes responsible for the increased sympathetic outflow in animal models, as well as essential hypertension in humans. Such information may lead to better therapies for neurogenic hypertension in humans.

Birth weight and childhood blood pressure

A large body of literature suggests an inverse relationship between birth weight and blood pressure in children, adolescents and adults. The most persistent findings have been observed in children with a history of low birth weight or intrauterine growth restriction, while a large number of studies carried out in populations with normally distributed birth weight have shown conflicting results. A recently reported strong direct association between high birth weight and blood pressure, and the significant positive effect of postnatal growth on blood pressure suggests that the fetal origins of adult disease hypothesis should be expanded to include the role of excessive fetal and postnatal growth. In this paper, we review recent studies on the relationship between birth weight and blood pressure in childhood, with a focus on confounding variables that may explain the conflicting results of published work in this field.

Proximal tubule-dominant transfer of AT(1a) receptors induces blood pressure responses to intracellular angiotensin II in AT(1a) receptor-deficient mice

The role of intracellular ANG II in proximal tubules of the kidney remains poorly understood. We tested the hypothesis that proximal tubule-dominant transfer of AT(1a) receptors in the cortex mediates intracellular ANG II-induced blood pressure responses in AT(1a) receptor-deficient (Agtr1a-/-) mice. A GFP-tagged AT(1a) receptor, AT(1a)R/GFP, and an enhanced cyan fluorescent intracellular ANG II fusion protein, ECFP/ANG II, were expressed in proximal tubules of Agtr1a-/- mouse kidneys via the adenoviral transfer using a sodium and glucose cotransporter 2 promoter. Transfer of AT(1a)R/GFP alone or with ECFP/ANG II induced proximal tubule-dominant expression of AT(1a)R/GFP and/or ECFP/ANG II with a peak response at 2 wk. No significant AT(1a)R/GFP and/or ECFP/ANG II expression was observed in the glomeruli, medulla, or extrarenal tissues. Transfer of AT(1a)R/GFP alone, but not ECFP/ANG II, increased systolic blood pressure by 12 ± 2 mmHg by day 14 (n = 9, P < 0.01). However, cotransfer of AT(1a)R/GFP with ECFP/ANG II increased blood pressure by 18 ± 2 mmHg (n = 12, P < 0.01). Twenty-four hour urinary sodium excretion was decreased by day 7 with proximal tubule-dominant transfer of AT(1a)R/GFP alone (P < 0.01) or with AT(1a)R/GFP and ECFP/ANG II cotransfer (P < 0.01). These responses were associated with twofold increases in phosphorylated ERK1/2, lysate, and membrane NHE-3 proteins in freshly isolated proximal tubules (P < 0.01). By contrast, transfer of control CMV-GFP (a recombinant human adenovirus type 5 expresses enhanced green fluorescent protein under the control of a cytomegalovirus (CMV) promoter), ECFP/ANG II, or a scrambled control ECFP/ANG IIc alone in proximal tubules had no effect on all indices. These results suggest that AT(1a) receptors and intracellular ANG II in proximal tubules of the kidney play an important physiological role in blood pressure regulation.

Variation in dietary salt intake induces coordinated dynamics of monocyte subsets and monocyte-platelet aggregates in humans: implications in end organ inflammation

BACKGROUND

Monocyte activation and tissue infiltration are quantitatively associated with high-salt intake induced target organ inflammation. We hypothesized that high-salt challenge would induce the expansion of CD14++CD16+ monocytes, one of the three monocyte subsets with a pro-inflammatory phenotype, that is associated with target organ inflammation in humans.

METHODOLOGY/PRINCIPAL FINDINGS

A dietary intervention study was performed in 20 healthy volunteers, starting with a 3-day usual diet and followed with a 7-day high-salt diet (≥15 g NaCl/day), and a 7-day low-salt diet (≤5 g NaCl/day). The amounts of three monocyte subsets ("classical" CD14++CD16-, "intermediate" CD14++CD16+ and "non-classical" CD14+CD16++) and their associations with monocyte-platelet aggregates (MPAs) were measured by flow cytometry. Blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) was used to evaluate renal hypoxia. Switching to a high-salt diet resulted in CD14++ monocyte activation and a rapid expansion of CD14++CD16+ subset and MPAs, with a reciprocal decrease in the percentages of CD14++CD16- and CD14+CD16++ subsets. In vitro study using purified CD14++ monocytes revealed that elevation in extracellular [Na(+)] could lead to CD14++CD16+ expansion via a ROS dependent manner. In addition, high-salt intake was associated with progressive hypoxia in the renal medulla (increased R2* signal) and enhanced urinary monocyte chemoattractant protein-1 (MCP-1) excretion, indicating a temporal and spatial correlation between CD14++CD16+ subset and renal inflammation. The above changes could be completely reversed by a low-salt diet, whereas blood pressure levels remained unchanged during dietary intervention.

CONCLUSIONS/SIGNIFICANCE

The present work demonstrates that short-term increases in dietary salt intake could induce the expansion of CD14++CD16+ monocytes, as well as an elevation of MPAs, which might be the underlying cellular basis of high-salt induced end organ inflammation and potential thromboembolic risk. In addition, this process seems largely unrelated to changes in blood pressure levels. This finding provides novel links between dietary salt intake, innate immunity and end organ inflammation.

Natriuretic peptide receptor-3 gene (NPR3): nonsynonymous polymorphism results in significant reduction in protein expression because of accelerated degradation

BACKGROUND- The primary role of natriuretic peptide receptor-3 (NPR3) or NPR-C is in the clearance of natriuretic peptides that play an important role in modulating intravascular volume and vascular tone. Genetic variation in NPR3 has been associated with variation in blood pressure and obesity. Despite the importance of NPR3, sequence variation in the gene has not been addressed using DNA from different ethnic populations. We set out to identify and functionally characterize genetic variation in NPR3 in 3 ethnic groups. METHODS AND RESULTS- DNA samples from 96 European American, 96 African American, and 96 Han Chinese American healthy subjects were used to resequence NPR3 exons, splice junctions, and flanking regions. We identified 105 polymorphisms, 50 of which were novel, including 8 nonsynonymous single-nucleotide polymorphisms, 7 were novel. Expression constructs were created for the nonsynonymous single-nucleotide polymorphisms. HEK293 cells were transfected with constructs for wild type and variant allozymes; and recombinant proteins were measured by quantitative Western blot analysis. The most significant change in NPR3 protein was observed for the Arg146 variant allozyme, with 20% of wild-type protein, primarily because of autophagy-dependent degradation. NPR3 structural modeling confirmed that the Arg146 variant protein was not compatible with wild-type conformation and could result in protein misfolding or instability. CONCLUSIONS- Multiple novel NPR3 genetic polymorphisms were identified in 3 ethnic groups. The Arg146 allozyme displayed a significant decrease in protein quantity because of degradation mediated predominantly by autophagy. This genetic variation could have a significant effect on the metabolism of natriuretic peptides with potential clinical implications.

The molecular basis of blood pressure variation

Advances in genetic mapping and sequencing techniques have led to substantial progress in the study of rare monogenic (Mendelian) forms of abnormal blood pressure. Many disease-defining pathways for hypertension have been identified in the past two decades. Perturbations in renal salt handling appear to be a common mechanism underlying these rare syndromes of hypertension. Excess activation at various points in the mineralocorticoid signaling pathway and malfunctioning of the autonomic (specifically sympathetic) nervous system have both been implicated in inducing hypertension, while complementary studies examining low blood pressure phenotypes have identified novel pathways exclusively linked to renal salt wasting in either the thick ascending limb or the distal nephron. The genetic defects and the physiological and cellular pathways affected in these various disorders are reviewed here. Importantly, studies have suggested that genetic variation affecting these same genes and pathways may play an important role in explaining the variation of blood pressure levels in the general population. The investigation of rare syndromes of human blood pressure variation has important implications for improving the diagnosis and treatment of hypertension.

Discovery and characterization of alamandine: a novel component of the renin-angiotensin system

RATIONALE

The renin-angiotensin system (RAS) is a key regulator of the cardiovascular system, electrolyte, and water balance. Here, we report identification and characterization of alamandine, a new heptapeptide generated by catalytic action of angiotensin-converting enzyme-2 angiotensin A or directly from angiotensin-(1-7).

OBJECTIVE

To characterize a novel component of the RAS, alamandine.

METHODS AND RESULTS

Using mass spectrometry we observed that alamandine circulates in human blood and can be formed from angiotensin-(1-7) in the heart. Alamandine produces several physiological actions that resemble those produced by angiotensin-(1-7), including vasodilation, antifibrosis, antihypertensive, and central effects. Interestingly, our data reveal that its actions are independent of the known vasodilator receptors of the RAS, Mas, and angiotensin II type 2 receptor. Rather, we demonstrate that alamandine acts through the Mas-related G-protein-coupled receptor, member D. Binding of alamandine to Mas-related G-protein-coupled receptor, member D is blocked by D-Pro(7)-angiotensin-(1-7), the Mas-related G-protein-coupled receptor, member D ligand β-alanine and PD123319, but not by the Mas antagonist A-779. In addition, oral administration of an inclusion compound of alamandine/β-hydroxypropyl cyclodextrin produced a long-term antihypertensive effect in spontaneously hypertensive rats and antifibrotic effects in isoproterenol-treated rats. Alamandine had no noticeable proliferative or antiproliferative effect in human tumoral cell lines.

CONCLUSIONS

The identification of these 2 novel components of the RAS, alamandine and its receptor, provides new insights for the understanding of the physiological and pathophysiological role of the RAS and may help to develop new therapeutic strategies for treating human cardiovascular diseases and other related disorders.

Lipoprotein (a): More than a bystander in the etiology of hypertension? A study on essential hypertensive patients not yet on treatment

BACKGROUND

Hypertension (HTN) is a very common disorder with a substantial impact on public health because of its complications.

OBJECTIVES

To study the association of serum lipoprotein(a) [Lp(a)] elevation with essential hypertension (eHTN).

PATIENTS AND METHODS

This study was conducted on a group of essential hypertensive patients. Laboratory exams consisting of serum creatinine and Lp(a) were measured.

RESULTS

Ninety five essential hypertensive patients were enrolled to the study. Serum LP (a) in patients was 46.5±20. In patients an inverse correlation between serum Lp(a) andcreatinine clearance was seen (r = -0.175 p<0.05). There was a significant correlation between serum Lp(a) and age (r =0.191 p<0.05) or duration of HTN (known duration of hypertension period) (r =0.362 p<0.05).

CONCLUSIONS

Our data suggest that Lp(a) may be involved as a cofactor in essential hypertension, with a mechanism that remains to be elucidated.

Increase in body Na+/water ratio is associated with cerebral aneurysm formation in oophorectomized rats

The incidence of cerebral aneurysms is higher in women than in men, especially postmenopause. Although hypertension is thought to be associated with a high incidence of stroke, not all patients with unruptured cerebral aneurysms are hypertensive. The possibility of water-free Na(+) storage associated with hypertension has been raised. However, whether the increase in the body Na(+)/water ratio that characterizes water-free Na(+) accumulation is associated with the formation of cerebral aneurysms remains obscure. To examine this relationship, Sprague-Dawley female rats subjected to carotid artery ligation were divided into 3 groups: a high-salt diet group (HSD) without and another with bilateral oophorectomy (HSD/OVX) and a third group that underwent additional renal artery ligation (HSD/OVX/RL). Compared with rats receiving a normal diet (shams), water retention was increased in HSD rats but not in HSD/OVX rats. Interestingly, compared with HSD rats, the incidence of cerebral aneurysms and the body Na(+)/water ratio were significantly higher in HSD/OVX and HSD/OVX/RL rats, independent of hypertension. In their aneurysmal wall, ATP1α2, a subtype of Na(+)/K(+)-ATPase, was downregulated, whereas inflammatory-related molecules were upregulated. Treatment with low-dose olmesartan that did not affect the blood pressure in hypertensive HSD/OVX/RL rats reduced the rate of cerebral aneurysm formation, body Na(+) retention, and the Na(+)/water ratio and upregulated ATP1α2. These results suggest that the increase in the Na(+)/water ratio and a reduction in ATP1α2 may be associated with cerebral aneurysm formation. We provide the new insight that the management of water-free Na(+) is important to prevent their development.

T lymphocytes and vascular inflammation contribute to stress-dependent hypertension

BACKGROUND

Psychological stress is a significant risk factor for hypertension and also directly affects the immune system. We have previously reported that T lymphocytes are essential for development of hypertension and that the central nervous system contributes to peripheral T-lymphocyte activation and vascular inflammation in this disease; however, the role of T-cell activation in stress-related hypertension remains unclear.

METHODS

Wild-type and T-cell-deficient (RAG-1(-/-)) mice were subjected to daily episodes of stress and blood pressure was measured. Circulating T-cell activation markers and vascular infiltration of immune cells were analyzed, as were stress hormone levels and gene expression changes in the brain. The effects angiotensin II infusion in the presence of chronic stress was also studied.

RESULTS

Repeated daily stress contributed to acute elevations in blood pressure that were associated with increased activation of circulating T cells and increased vascular infiltration of T cells. Repeated stress increased blood pressure in wild-type but not RAG-1(-/-) mice. Adoptive transfer of T cells to RAG-1(-/-) mice restored blood pressure elevation in response to stress. Stress-related hypertension and vascular infiltration of T cells was markedly enhanced by angiotensin II. Moreover, angiotensin II-infused mice exposed to chronic stress exhibited greater blood pressure reactivity to an episode of acute stress.

CONCLUSIONS

These data demonstrate that stress-dependent hypertension triggers an inflammatory response that raises blood pressure at baseline and augments the hypertension caused by angiotensin II. These data provide insight as to how psychological stress contributes to hypertension.