Rat Model Of Salt-sensitive Hypertension Research Articles

Hypoxia-inducible factor-prolyl hydroxylase inhibitor Roxadustat (FG-4592) reduces renal fibrosis in Dahl salt-sensitive rats.

Although hypoxia-inducible factor-prolyl hydroxylase (HIF-PH) inhibitors have been developed for the treatment of renal anemia, their effects on cardiac and renal dysfunction remain unknown. We previously reported on Dahl salt-sensitive rats, in a rat model of salt-sensitive hypertension, that exhibited anemia and impaired expression of duodenal iron transporters after the development of hypertensive cardiac and renal dysfunction. Therefore, we investigated the effects of Roxadustat (FG-4592), an HIF-PH inhibitor, on anemia, iron regulation, and cardiac and renal dysfunction in Dahl salt-sensitive rats. Six-week-old male Dahl salt-sensitive rats were fed a normal or high-salt diet for 8 weeks. A further subset of Dahl salt-sensitive rats, that were fed a high-salt diet, was administered Roxadustat for 8 weeks. Dahl salt-sensitive rats fed a high-salt diet developed hypertension, cardiac and renal dysfunction, and anemia after 8 weeks of feeding. Roxadustat increased hemoglobin and serum erythropoietin levels in Dahl salt-sensitive rats fed a high-salt diet. With regard to the iron-regulating system, Roxadustat lowered hepatic hepcidin gene expression and increased the gene expression of duodenal iron transporters, such as cytochrome b and divalent metal transporter 1 , in Dahl salt-sensitive rats fed a high-salt diet. Roxadustat did not affect the development of hypertension and cardiac hypertrophy in Dahl salt-sensitive rats with a high-salt diet; however, Roxadustat treatment attenuated renal fibrosis in these rats. Roxadustat ameliorated anemia with affecting the gene expression of the iron-regulating system, and did not affect cardiac hypertrophy but attenuated renal fibrosis in Dahl salt-sensitive rats fed a high-salt diet.

κ-Opioid Receptors Improve Vascular Endothelial Dysfunction in Salt-Sensitive Hypertension via PI3K/Akt/eNOS Signaling Pathway.

κ-Opioid receptors (κ-OR) are widely used to regulate the activity of the cardiovascular system. To explore the effect and mechanism of κ-OR on salt-sensitive hypertensive endothelial dysfunction, we used Dah1 rats to construct a rat model of salt-sensitive hypertension on a high-salt (HS) diet. Then, the rats were treated with κ-OR activators U50,488H (1.25 mg/kg) and inhibitor nor-BNI (2.0 mg/kg) for 4 weeks, respectively. The rat aortas were collected to detect the contents of NO, ET-1, AngII, NOS, T-AOC, SO, and NT. Protein expression was determined for NOS, Akt, and Caveolin-1. In addition, the vascular endothelial cells were extracted, and the levels of NO, TNF-α, IL-1, IL-6, IL-8, IL-10, p-Akt, and p-eNOS in cell supernatants were detected. In vivo results showed that compared with the HS group, treated with U50,488H promoted rats' vasodilation by increasing the NO content and decreasing ET-1 and AngII contents. U50,488H reduced endothelial cell apoptosis and attenuated vascular, smooth muscle cell and endothelial cell injury. U50,488H also enhanced the rats' response to oxidative stress by increasing the NOS and T-AOC contents. Moreover, U50,488H increased the eNOS, p-eNOS, Akt, and p-AKT expression and decreased the iNOS and Caveolin-1 expression. In vitro results showed that U50,488H promoted NO, IL-10, p-Akt, and p-eNOS levels in endothelial cell supernatants versus the HS group. And U50,488H reduced the adhesion of peripheral blood mononuclear cells and polymorphonuclear neutrophils to endothelial cells and the migration function of polymorphonuclear neutrophils. Our study suggested that κ-OR activation may improve vascular endothelial dysfunction in salt-sensitive hypertensive rats through the PI3K/Akt/eNOS signaling pathway. This may be a potential therapeutic approach in the treatment of hypertension.

Effect of Angiotensin 1-7 on Myocardial Calcium Pump in Salt-Sensitive Hypertensive Rats

Objective — To investigate the effects of angiotensin 1-7 (Ang1-7) on plasma membrane ATPase isoform 1 (PMCA1) in salt-sensitive hypertensive rats. Methods — Thirty newborn male Wistar rats were selected to establish the salt-sensitive hypertensive rat model with sensory nerve injury, which were then randomly divided into 5 groups (n=5), including model group, Telmisartan group, Ramipril group, Ang1-7 group, and A-779 group. Another normal control group was established (n=5). After 4 weeks of intervention, the tail blood pressure of rats in each group was measured, and then the apical tissue of left ventricle was cut. The contents of AngⅡ and Ang1-7 in cardiomyocytes were detected by enzyme-linked immunosorbent assay. The expression of PMCA1 mRNA and protein in heart of salt-sensitive hypertensive rats were detected by RT-PCR and immunohistochemistry. Results — (1) Compared with the normal control group, the concentration of AngⅡ in the myocardium of salt-sensitive hypertensive rats increased (P < 0.05), which decreased after the intervention of Telmisartan and Ramipril (P < 0.05), and no change occurred after the intervention of Ang1-7 in concentration (P＞0.05). (2) Compared with the normal control group, the concentration of myocardial Ang1-7 in salt-sensitive hypertensive rats decreased (P < 0.05), and increased after the intervention of telmisartan and ramipril (P < 0.05), and increased after the intervention of A-779 (P < 0.05). (3) The expression of PMCA1 mRNA and protein in salt-sensitive hypertensive rats was increased compared with the normal control group (P < 0.05), and the expression of Ang-(1-7), telmisartan and ramipril was decreased compared with the model group (P < 0.05). The expression of p38MAPK mRNA and p-p38MAPK protein in the myocardium of salt-sensitive hypertensive rats was increased compared with that in the normal control group (P < 0.05), and the expression of Ang-(1-7), Telmisartan and Ramipril was decreased compared with that in the model group (P < 0.05). Conclusion — Ang-(1-7) may be involved in the regulation of cardiac calcium pump, inhibiting its overcompensation and delaying the occurrence of calcium pump inhibition in the early stage of salt-sensitive hypertension. Ang-(1-7) can inhibit the activity of p38MAPK and protect the heart, and its regulation on PMCA1 may be mediated by the expression of p38MAPK pathway.

Cannabinoid Administration Does Not Affect Mean Arterial Pressure or Glomerular Filtration Rate in DOCA‐Salt Hypertensive Rats

Hypertension remains the leading cause of cardiovascular disease – the leading cause of morbidity and mortality worldwide, and effective pharmacological options remain limited. Recent studies have shown HTN may result from increased renal inflammation and elevated renal sensory nerve activity, particularly in the deoxycorticosterone acetate (DOCA)-salt rat model of salt-sensitive hypertension. Cannabinoid administration is demonstrated to mitigate peripheral inflammation as well as sensory nerve activation in models of rheumatoid arthritis and cancer-related pain through cannabinoid receptor type 2 (CB2). Therefore, we hypothesized CB2 activation through either endogenous cannabinoid accumulation with a fatty acid amide hydrolase inhibitor (URB-597) or selective CB2 agonist (JWH-015) would attenuate DOCA-salt HTN and improve renal function and inflammation. To test this hypothesis, uninephrectomized male Sprague Dawley rats (300-400 g) received DOCA (100 mg, SC), 0.9% NaCl drinking water, and one of the following drug treatments administered by osmotic mini-pump for 21 days: JWH-015 (JWH; 1mg/kg/day; n=5), URB-597 (URB; 1mg/kg/day; n=5), or vehicle (VEH; 10% DMSO, 10% Tween 80, 80% PBS; n=10). 24-hour mean arterial pressure (MAP) was measured by implanted telemeters. Final glomerular filtration rate (GFR) and renal inflammation were assessed by transcutaneous FITC-sinistrin clearance and histological analysis, respectively. Data presented as mean ±SEM. Following the 21-day DOCA-salt treatment, MAP increased in VEH animals (∆62.6 ± 4.2 mmHg), and no differences in URB (∆74.4 ± 7.5 mmHg) or JWH (∆51.1 ± 6.0 mmHg) were detected vs. VEH. Regarding renal function, no improvements in GFR were detected in URB (0.81 ± 0.09 mL/min/100mg bodyweight) nor JWH (0.78 ± 0.06 mL/min/100mg bodyweight) treatments vs. VEH (0.73 ± 0.07 mL/min/100 mg bodyweight). Finally, no differences in bodyweight, kidney, or heart weights were detected between any treatment groups. Renal inflammation analysis and final serum cannabinoid concentration measurements are currently underway. Collectively, these data did not support our initial hypothesis, as no mitigating effects of either URB or JWH on MAP or renal function were detected in this model of hypertension. Though similar doses reportedly mitigate inflammation and pain in other preclinical models disease including rheumatoid arthritis and cancer-related pain, we conclude peripheral CB2 activation through exogenous or endogenous cannabinoid therapies (JWH-015 and URB-597) do not prevent the renal or cardiovascular pathophysiology in this preclinical model of salt-sensitive hypertension. Future dose-response studies are required to evaluate any potential effect beneficial effect of cannabinoid treatment in this model.

Exercise training delays renal disorders with decreasing oxidative stress and increasing production of 20-hydroxyeicosatetraenoic acid in Dahl salt-sensitive rats

Exercise training has antihypertensive and renoprotective effects in humans and rats. However, the effects of exercise training on renal disorders that occur with salt-sensitive hypertension remains unclear. The study aim was to investigate the effects and mechanisms of exercise training on renal function in a rat model of salt-sensitive hypertension. Six-week-old male Dahl salt-sensitive rats were divided into normal-salt (0.6% NaCl) diet, high-salt (8% NaCl) diet, and high-salt diet with exercise training groups. The high-salt diet with exercise training group underwent daily treadmill running for 8 weeks. The high-salt diet induced severe hypertension and renal dysfunction. Exercise training significantly improved high-salt diet-induced urinary protein, albumin, and L-type fatty acid-binding protein excretion, and glomerulosclerosis but not renal interstitial fibrosis without changing blood pressure. Exercise training significantly attenuated high-salt diet-induced oxidative stress in the kidneys and decreased high-salt diet-stimulated xanthine oxidoreductase activity but not nicotinamide adenine dinucleotide phosphate oxidase activity. The high-salt diet did not change urinary excretion of 20-hydroxyeicosatetraenoic acid and decreased cytochrome P450 4A protein expression in the kidneys. Exercise training increased urinary 20-hydoroxyeicosatetraenoic acid excretion and renal cytochrome P450 4A protein expression. Exercise training improved renal disorders without lowering blood pressure in Dahl salt-sensitive rats. Exercise training also decreased oxidative stress and increased 20-hydroxyeicosatetraenoic acid production in the kidneys. These results suggest that improvements in oxidative stress and 20-hydroxyeicosatetraenoic acid production may be potential mechanisms by which exercise training improved renal disorders in Dahl salt-sensitive rats.

Intravital imaging of the kidney in a rat model of salt-sensitive hypertension.

Hypertension is one of the most prevalent diseases worldwide and a major risk factor for renal failure and cardiovascular disease. The role of albuminuria, a common feature of hypertension and robust predictor of cardiorenal disorders, remains incompletely understood. The goal of this study was to investigate the mechanisms leading to albuminuria in the kidney of a rat model of hypertension, the Dahl salt-sensitive (SS) rat. To determine the relative contributions of the glomerulus and proximal tubule (PT) to albuminuria, we applied intravital two-photon-based imaging to investigate the complex renal physiological changes that occur during salt-induced hypertension. Following a high-salt diet, SS rats exhibited elevated blood pressure, increased glomerular sieving of albumin (GSCalb = 0.0686), relative permeability to albumin (+Δ16%), and impaired volume hemodynamics (-Δ14%). Serum albumin but not serum globulins or creatinine concentration was decreased (-0.54 g/dl), which was concomitant with increased filtration of albumin (3.7 vs. 0.8 g/day normal diet). Pathologically, hypertensive animals had significant tubular damage, as indicated by increased prevalence of granular casts, expansion and necrosis of PT epithelial cells (+Δ2.20 score/image), progressive augmentation of red blood cell velocity (+Δ269 µm/s) and micro vessel diameter (+Δ4.3 µm), and increased vascular injury (+Δ0.61 leakage/image). Therefore, development of salt-induced hypertension can be triggered by fast and progressive pathogenic remodeling of PT epithelia, which can be associated with changes in albumin handling. Collectively, these results indicate that both the glomerulus and the PT contribute to albuminuria, and dual treatment of glomerular filtration and albumin reabsorption may represent an effective treatment of salt-sensitive hypertension.

A two-for-one bargain: using cilnidipine to treat hypertension and its comorbidities.

A two-for-one bargain: using cilnidipine to treat hypertension and its comorbidities.

FXR Agonist INT-747 Upregulates DDAH Expression and Enhances Insulin Sensitivity in High-Salt Fed Dahl Rats

AimsGenetic and pharmacological studies have shown that impairment of the nitric oxide (NO) synthase (NOS) pathway is associated with hypertension and insulin-resistance (IR). In addition, inhibition of NOS by the endogenous inhibitor, asymmetric dimethylarginine (ADMA), may also result in hypertension and IR. On the other hand, overexpression of dimethylarginine dimethylaminohydrolase (DDAH), an enzyme that metabolizes ADMA, in mice is associated with lower ADMA, increased NO and enhanced insulin sensitivity. Since DDAH carries a farnesoid X receptor (FXR)-responsive element, we aimed to upregulate its expression by an FXR-agonist, INT-747, and evaluate its effect on blood pressure and insulin sensitivity.Methods and ResultsIn this study, we evaluated the in vivo effect of INT-747 on tissue DDAH expression and insulin sensitivity in the Dahl rat model of salt-sensitive hypertension and IR (Dahl-SS). Our data indicates that high salt (HS) diet significantly increased systemic blood pressure. In addition, HS diet downregulated tissue DDAH expression while INT-747 protected the loss in DDAH expression and enhanced insulin sensitivity compared to vehicle controls.ConclusionOur study may provide the basis for a new therapeutic approach for IR by modulating DDAH expression and/or activity using small molecules.

Reply to “Letter to the Editor: ‘How does potassium supplementation lower blood pressure?’”

to the editor: We appreciate Dr. McDonough's and Dr. Nguyen's valuable comments and interest (6a) in our study. They raised several interesting issues regarding our recent paper ([4][1]), which explored the molecular mechanisms responsible for the blood pressure-lowering effect of potassium

Predictive response-relevant clustering of expression data provides insights into disease processes

This article describes and illustrates a novel method of microarray data analysis that couples model-based clustering and binary classification to form clusters of `response-relevant' genes; that is, genes that are informative when discriminating between the different values of the response. Predictions are subsequently made using an appropriate statistical summary of each gene cluster, which we call the `meta-covariate' representation of the cluster, in a probit regression model. We first illustrate this method by analysing a leukaemia expression dataset, before focusing closely on the meta-covariate analysis of a renal gene expression dataset in a rat model of salt-sensitive hypertension. We explore the biological insights provided by our analysis of these data. In particular, we identify a highly influential cluster of 13 genes—including three transcription factors (Arntl, Bhlhe41 and Npas2)—that is implicated as being protective against hypertension in response to increased dietary sodium. Functional and canonical pathway analysis of this cluster using Ingenuity Pathway Analysis implicated transcriptional activation and circadian rhythm signalling, respectively. Although we illustrate our method using only expression data, the method is applicable to any high-dimensional datasets. Expression data are available at ArrayExpress (accession number E-MEXP-2514) and code is available at http://www.dcs.gla.ac.uk/inference/metacovariateanalysis/.

Early-life sodium exposure unmasks susceptibility to stroke in hyperlipidemic, hypertensive heterozygous Tg25 rats transgenic for human cholesteryl ester transfer protein.

Early-life risk factor exposure increases aortic atherosclerosis and blood pressure in humans and animal models; however, limited insight has been gained as to end-organ complications. We investigated the effects of early-life Na exposure (0.23% versus 0.4% NaCl regular rat chow) on vascular disease outcomes using the inbred, transgenic [hCETP](25) Dahl salt-sensitive hypertensive rat model of male-predominant coronary atherosclerosis, Tg25. Rather than the expected increase in coronary heart disease, fetal 0.4% Na exposure (< or =2 g of Na per 2-kcal/d diet) induced adult-onset stroke in both sexes (ANOVA P<0.0001), with earlier stroke onset in Tg25 females. Analysis of later onset of 0.4% Na exposure resulted in decreased stroke risk and later stroke onset despite longer 0.4% Na exposure durations, which indicates increasing risk with earlier onset of 0.4% Na exposure. Histological analysis of stroke-positive rat brains revealed cerebral cortical hemorrhagic infarctions, microhemorrhages, neuronal ischemia, and microvascular injury. Ex vivo MRI of stroke-positive rat brains detected cerebral hemorrhages, microhemorrhages, and ischemia with middle cerebral artery distribution and cerebellar noninvolvement. Ultrasound microimaging detected carotid artery disease. Prestroke analysis detected neuronal ischemia and decreased mass of isolated cerebral but not cerebellar microvessels. Early-life Na exposure exacerbated hypertension and unmasked stroke susceptibility, with greater female vulnerability in hypertensive, hyperlipidemic Tg25 rats. The reproducible modeling in stroke-prone Tg25 rats of carotid artery disease, cerebral hemorrhagic infarctions, neuronal ischemia, microhemorrhages, and microvascular alterations suggests a pathogenic spectrum with causal interrelationships. This "mixed-stroke" spectrum could represent paradigms of ischemic-hemorrhagic transformation and/or a microangiopathic basis for the association of ischemic lesions, microhemorrhages, and strokes in humans. Together, the data reveal early-life Na exposure to be a significant modifier of hypertension and stroke disease course and hence a potentially modifiable prevention target that deserves systematic study.

ACE2 expression and activity are enhanced during pregnancy

In the current study, we investigated the expression and activity of ACE2 during pregnancy in normotensive and hypertensive rats, focusing on the relative contribution of the uterus and the placentas, the kidney serving as a reference. We used the Sabra rat model of salt-sensitive hypertension. We confirmed a systemic vasodilatory state during the third trimester of pregnancy, as evidenced by a reduction in blood pressure, both in normotensive and hypertensive rats. At the time that blood pressure was reduced, ACE2 was expressed abundantly in the reproductive organs. The relative levels of ACE2 mRNA in the pregnant animal were placenta > kidneys > or = uterus and of ACE2 activity kidney > placenta > uterus. In the uterus and the placenta, ACE2 expression was unaffected by strain, salt-loading, or the level of blood pressure. ACE2 activity in the uterus of the nonpregnant rat was not affected by any of these variables either, but during pregnancy increased in salt-loaded animals. When estimating the total contribution of the uterus to ACE2 mRNA and activity during pregnancy, we found that the amount of ACE2 mRNA increased in both strains irrespective of diet, but that ACE2 activity increased only in salt-loaded animals. We further estimated the relative total contribution of the uterus, placentas, and kidneys to ACE2 expression and activity during pregnancy by adjusting for mass and number of organs and found that the placentas were the major contributors, followed by the kidney and the uterus. We conclude that during pregnancy, the placentas, in particular, but also the uterus, constitute important sources of ACE2, in addition to its normal production in the kidney, leading to an estimated twofold increase in total ACE2 activity. These data are consistent the hypothesis that transient ACE2 overexpression and increased activity during pregnancy may be important in modulating systemic, as well as local hemodynamics in the uteroplacental unit.

Chronic Intake of a Phytochemical-Enriched Diet Reduces Cardiac Fibrosis and Diastolic Dysfunction Caused by Prolonged Salt-Sensitive Hypertension

Salt-sensitive hypertension is common in the aged population. Increased fruit and vegetable intake reduces hypertension, but its effect on eventual diastolic dysfunction is unknown. This relationship is tested in the Dahl Salt-Sensitive (Dahl-SS) rat model of salt-sensitive hypertension and diastolic dysfunction. Table grape powder contains phytochemicals that are relevant to human diets. For 18 weeks, male Dahl-SS rats were fed one of five diets: low salt (LS), a low salt + grape powder (LSG), high salt (HS), a high salt + grape powder (HSG), or high salt + vasodilator hydralazine (HSH). Compared to the HS diet, the HSG diet lowered blood pressure and improved cardiac function; reduced systemic inflammation; reduced cardiac hypertrophy, fibrosis, and oxidative damage; and increased cardiac glutathione. The HSH diet similarly reduced blood pressure but did not reduce cardiac pathogenesis. The LSG diet reduced cardiac oxidative damage and increased cardiac glutathione. In conclusion, physiologically relevant phytochemical intake reduced salt-sensitive hypertension and diastolic dysfunction.

Signaling pathways modulated by fish oil in salt-sensitive hypertension

Although many studies have indicated that fish oil (FO) improves cardiovascular risk factors and reduces histopathological manifestations of injury in experimental renal injury models, potential mechanisms underlying this protective effect have not been adequately defined. The objective of this study was to identify potential signaling pathways that confer protection in the Dahl rat model of salt-sensitive hypertension. Male Dahl salt-sensitive rats (n = 10/group) were provided with formulated diets containing 8% NaCl, 20% protein, and 25% FO or 25% corn oil (CO) for 28 days. FO reduced blood pressure (-11% at 4 wk; P < 0.05), urine protein excretion (-45% at 4 wk; P < 0.05), plasma cholesterol and triglyceride levels (-54%, P < 0.001; and -58%, P < 0.05), and histopathological manifestations of renal injury, including vascular hypertrophy, segmental and global glomerular sclerosis, interstitial fibrosis, and tubular atrophy. Interstitial inflammation was significantly reduced by FO (-32%; P < 0.001), as assessed by quantitative analysis of ED1-positive cells in sections of the renal cortex. FO reduced tubulointerstitial proliferative activity, as assessed by Western blot analysis of cortical homogenates for PCNA (-51%; P < 0.01) and quantitative analysis of Mib-1-stained sections of the renal cortex (-42%; P < 0.001). Decreased proliferative activity was associated with reduced phospho-ERK expression (-37%; P < 0.005) and NF-kappaB activation (-42%; P < 0.05). FO reduced cyclooxygenase (COX)-2 expression (-63%; P < 0.01) and membrane translocation of the NADPH oxidase subunits p47(phox) and p67(phox) (-26 and -34%; P < 0.05). We propose that FO ameliorates renal injury in Dahl salt-sensitive rats through the inhibition of ERK, decreased NF-kappaB activation, inhibition of COX-2 expression, and decreased NADPH oxidase activation.

Function and regulation of epithelial sodium transporters in the kidney of a salt-sensitive hypertensive rat model

To determine the function and regulation of thiazide-sensitive NaCl co-transporters (NCC), NaK2Cl co-transporters (NKCC2), and epithelial sodium channels (ENaC) in the kidneys of a salt-sensitive hypertensive model. Neonatal Wistar rats were treated with capsaicin or vehicle. Seven-week-old male rats were treated for 2 weeks with: vehicle plus a normal (Con-NS) or high (Con-HS) sodium diet, and capsaicin pretreatment plus a normal (Cap-NS) or high (Cap-HS) sodium diet. Mean arterial pressure (MAP), renal excretory function, and protein expression determined by western blot were performed. MAP was increased in Cap-HS compared with other groups. Trichlormethiazide increased urine sodium excretion (UNaV) and urine flow rate (UFR) and decreased MAP in Cap-HS rats only. Furosemide increased UNaV and UFR in Cap-NS, Con-HS and Cap-HS, and decreased MAP in Cap-HS rats only. Amiloride had no effect on UNaV, UFR and MAP in any group. Renal NCC contents were increased in Cap-HS compared with Con-NS, Con-HS and Cap-NS rats, and NKCC2 expression was increased in Cap-NS, Con-HS and Cap-HS compared with Con-NS rats. No change was found in ENaC alpha subunit expression. The capsaicin-induced release of calcitonin gene-related peptide from renal tissues was decreased in Cap-HS and Cap-NS compared with Con-HS and Con-NS rats. NCC and possibly NKCC2, but not ENaC, were functionally upregulated in the kidneys of rats subjected to sensory nerve degeneration plus high salt intake, suggesting that sensory neurotransmitters may regulate the expression of the former but not the latter, which may underlie the development of salt-sensitive hypertension in this model.

Primed polymorphonuclear leukocytes, oxidative stress, and inflammation antecede hypertension in the Sabra rat.

Hypertension is accompanied by systemic oxidative stress, inflammation, and priming of peripheral polymorphonuclear leukocytes (PMNLs), yet the involvement of these factors in the pathophysiology of hypertension is incompletely understood. We investigated the relationship between oxidative stress, primed PMNLs, and inflammation and the development of hypertension in the Sabra rat model of salt-sensitive hypertension. Sabra hypertension-resistant rats (SBN/y) (salt-resistant) and Sabra hypertension-prone rats (SBH/y) (salt-sensitive) were studied under normal conditions or during salt loading. Systolic blood pressure (BP) was measured by the tail-cuff method. The extent of oxidative stress was evaluated by the rate of superoxide release from PMNLs, plasma-reduced glutathione (GSH) levels, malondialdehyde (MDA) levels (estimated by thiobarbituric acid-reacting substances), and plasma-carbonylated fibrinogen (Western blotting). Plasma fibrinogen levels and the peripheral PMNL count served as indices of inflammation. In SBH/y and SBN/y provided regular chow without salt loading, BP did not rise above baseline values, yet superoxide release, plasma MDA, carbonylated fibrinogen, and PMNL count were higher in SBH/y than in SBN/y, whereas GSH levels were lower in SBH/y. Four weeks of salt loading resulted in a gradual increase in systolic BP in SBH/y to 205+/-3 mm Hg, whereas BP remained in SBN/y at baseline normotensive levels. All the parameters reflecting oxidative stress and inflammation were further aggravated with the development of hypertension in salt-loaded SBH/y. We conclude that primed PMNLs, oxidative stress, and inflammation antecede the development of hypertension in this experimental model of hypertension.

Endothelin-A receptor blockade prevents left ventricular hypertrophy and dysfunction in salt-sensitive experimental hypertension.

Salt-sensitive hypertension represents a major cause of left ventricular (LV) dysfunction. We therefore explored the potential effects of the selective endothelin-A (ETA) receptor antagonist darusentan on the development of hypertension, LV hypertrophy (LVH), and dysfunction in a genetic rat model of salt-sensitive hypertension. Animals from the salt-sensitive Sabra rat strain (SBH/y) and the salt-resistant strain (SBN/y) were treated with either normal diet (SBH/y and SBN/y) or with deoxycorticosterone-acetate (DOCA) and salt (SBN/y-DOCA and SBH/y-DOCA). Additional groups were treated with 50 mg x kg(-1) x d(-1) of darusentan (SBH/y-DOCA-DA and SBN/y-DOCA-DA). Systolic blood pressure and LV weight increased in response to DOCA only in the SBH/y strain (+75 mm Hg and +30%; P<0.05). LV end-diastolic pressure increased and -dP/dtmax decreased in SBH/y-DOCA compared with SBH/y (P<0.05). This was paralleled by a 5-fold upregulation of LV mRNA expression of atrial natriuretic factor (ANF) and a significant reduction of sarcoplasmic reticulum (SR) Ca2+-reuptake and the SR Ca2+-ATPase to phospholamban protein ratio (-30%). Whereas treatment with darusentan in SBH/y-DOCA-DA reduced the SBP increase by 50%, LVH elevation of ANF mRNA and LV dysfunction were completely prevented (P<0.05); this was associated with a normalization of SR Ca2+-reuptake and SR Ca2+-ATPase to phospholamban ratio by darusentan (P<0.05). A moderate elevation of interstitial fibrosis in SBH/y-DOCA (P<0.05) remained unaffected by darusentan treatment. In the Sabra model of salt-sensitive hypertension, ETA-receptor blockade demonstrated striking effects on the prevention of LVH and LV dysfunction beyond its considerable antihypertensive effect.

The Dual AngII/AVP Receptor Gene N119S/C163R Variant Exhibits Sodium-Induced Dysfunction and Cosegregates With Salt-Sensitive Hypertension in the Dahl Salt-Sensitive Hypertensive Rat Model

Essential hypertension is a prevalent complex polygenic disease and a major risk factor for cardiovascular disease, the leading cause of death in developed countries. Because of its complex and multifactorial nature, its genetic determinants still remain largely unknown. The Dahl salt-sensitive hypertensive rat model exhibits impaired sodium handling, which is hypothesized to play a key role in the pathophysiology of polygenic hypertension. Thus, genes associated with renal regulation of salt and water balance are a priori likely candidates for a causative role in hypertension pathogenesis. The functional properties and renal-specific expression of the recently characterized AngII/AVP receptor suggest a putative modulator role in tubular sodium and fluid reabsorption. Based on these observations, we investigated the potential involvement of the AngII/AVP receptor in salt-sensitive hypertension. We performed cosegregation analysis of the AngII/AVP receptor locus with salt-sensitive hypertension in an F2 (Dahl S X Dahl salt-resistant [R]) hybrid male cohort characterized for blood pressure by radiotelemetry after 8 weeks of high salt challenge. Further molecular analysis was done to identify putative AngII/AVP receptor molecular variants that could account for the AngII/ AVP receptor involvement in salt-sensitive hypertension pathogenesis. The AngII/AVP receptor was mapped to rat chromosome 1, 1.7 cM centromeric to the D1Rat188 marker by radiation hybrid mapping analysis. Quantitative trait locus (QTL) analysis detected a highly significant linkage of the AngII/AVP receptor locus with high blood pressure (LRS = 13.8, p= 0.0002). Molecular characterization of the Dahl S and Dahl R AngII/AVP receptor cDNAs revealed two amino acid substitutions in the Dahl S AngII/AVP receptor (N119S, C163R) when compared to the Dahl R AngII/AVP receptor. These mutations are associated with an increased receptor affinity for both ligands (AVP and AngII) and an enhanced G(s)-coupling by the receptor resulting in increased activation of adenylate cyclase with concomitant increase in cAMP production. The observed molecular dysfunction in the Dahl S AngII/AVP receptor is consistent with increased tubular sodium and fluid reabsorption observed in Dahl S rats. Interestingly, the AngII/AVPr locus is within the narrowed chromosome 1 QTL region for blood pressure detected in different rat intercross linkage analyses. Altogether, the data strongly suggest that the AngII/AVP receptor is a hypertension susceptibility gene in the Dahl S rat model, as well as raises the hypothesis that it too underlies the chromosome 1 blood pressure QTL identified in other hypertension rat models.

An experimental rat model of salt-sensitive hypertension; biochemical and morphological parameters and sympathetic nervous system.

The objective of the study was to outline the characteristics of the development of hypertension and some neurohumoral, haematological and morphological factors contributing to development of high blood pressure in a genetic model of salt-sensitive rat. Characteristics of Dahl salt-sensitive (DS) rats, as compared to their Dahl salt-resistant (DR) controls were as follows: 1) DS rats display higher blood pressure and lower heart rate compared to DR rats as early as 1 month of age at weaning). They gradually develop hypertension at 2 months of age, irrespective of diet. Low-Na diet (0.5% NaCl) does not prevent hypertension but delays its development and ameliorates it. High Na-diet (8% NaCl) exacerbates hypertension. 2) DS rats have retardation in body weight gain. They develop mild hypochromic anaemia. 3) After 2 months of Na loading (3 months of age), DS rats express significantly increased Na and water retention and increased plasma volume by 15% compared to 2.8% increase in DR rats on high-Na diet. 4) DS rats showed renal parenchymal lesions, more pronounced after Na-loading, focal atrophy of cortical tubules, mesangial matrix expansion and glomerulosclerosis. Consistent with high blood pressure were changes in renal arterioles, fibromuscular proliferation, deposition of fibrinoid material in intima. 5) Sodium loading produced increased activity of the sympathetic nervous system (SNS), and sodium restriction reduced SNS responsiveness.

Role of chromosome X in the Sabra rat model of salt-sensitive hypertension.

We carried out a total genome screen in the Sabra rat model of hypertension to detect salt-susceptibility genes. We previously reported in male animals the presence of 2 major quantitative trait loci (QTLs) on chromosome 1 that together accounted for most of the difference in the blood pressure (BP) response to salt loading between Sabra hypertension-prone rats (SBH/y) and Sabra hypertension-resistant rats (SBN/y). In females, we reported on 2 major QTLs on chromosomes 1 and 17 that together accounted for only two thirds of the difference in the BP response between the strains. On the basis of phenotypic patterns of inheritance in reciprocal F2 crosses, we proposed a role of the X chromosome. We therefore continued the search for the missing QTL in females that would account for the remaining difference in the BP response between the 2 strains using newly developed microsatellite markers and focusing on chromosome X. We screened an F2 cross, consisting of 371 females and 336 males, using 19 polymorphic chromosome X microsatellite markers. We analyzed the averages of BP by genotype using ANOVA and the individual data using MAPMAKER/QTL. In female F2 progeny, we identified a segment on chromosome X that spans over 33.4 cM and shows significant cosegregation (P<0.001) of 14 microsatellite markers (demarcated by DXRat4 and DXMgh10) with systolic BP after salt loading. This segment has 2 apparent peaks at DXRat4 and DXRat13, with a BP effect of 14 mm Hg for each. Multipoint linkage analysis with a free model detected 3 peaks (logarithm of the odds ratio [LOD] score >4.3) within the same chromosomal segment: One between DXMgh9 and DXMit4 (LOD 4.9; 6.1% of variance), a second between DXMgh12 and DXRat8 (LOD 5.2; 7.2% of variance), and a third between DXRat2 and DXRat4 (LOD 5.8; 7.5% of variance). On the basis of these findings and until congenic strains become available, our working assumption is that within chromosome X, 1 to 3 genetic loci contribute importantly to the BP response of female Sabra rats to salt. In male F2 progeny, we detected no significant cosegregation of any region on chromosome X with the BP response to salt loading. We conclude that in the female rat, salt susceptibility is mediated by 3 to 5 gene loci on chromosomes 1, 17, and X, whereas in the male rat, the X chromosome does not affect the BP response to salt.