Cardiovascular effects of inhibition of renin-angiotensin-aldosterone system components in hypertensive rats given salt excess

Effect of Angiotensin receptor blockade on Plasma Osmolality and Neurohumoral Responses to High Environmental Temperature in Rats Fed a High Salt Diet

Plasma osmolality (pOsmol) and neurohumoral signals play important roles in the pathophysiology of cardiovascular diseases. Our study investigated the effect of high environmental temperature (HET) on neurohumoral responses and pOsmol in rats fed a high salt diet (HSD), with and without angiotensin II receptor blockade (ARB), using telmisartan.  Fifty-six male 8-week old Sprague-Dawley rats (95-110g) were randomly assigned into seven groups of 8 rats. These included control rats (I) fed with 0.3% NaCl diet (normal diet, ND); salt-loaded rats (II) fed with 8% NaCl (high salt) diet; ND rats (III) exposed to HET (38.5±0.5oC ) 4 hours daily per week; rats (IV) fed with 8% NaCl diet and exposed to HET daily. Others included rats (V) fed with 8% NaCl diet and treated with telmisartan (30mg/kg); ND rats (VI) exposed to HET and treated with telmisartan; rats (VI) fed with 8% NaCl diet, exposed to HET and treated with telmisartan. Plasma angiotensin II, aldosterone, vasopressin and norepinephrine (NE) concentrations were determined by ELISA technique; pOsmol from plasma K+, Na+ and Urea. HSD combined with HET in rats synergistically increased pOsmol (P<0.001) with an associated non-synergistic rise in fluid intake (P<0.001), fluid balance (P<0.001), plasma angiotensin II (P<0.01) and aldosterone (P<0.05), NE (P<0.001) and vasopressin (P<0.05) concentrations compared to control. Telmisartan did not alter pOsmol in all the treated-rats, but normalized fluid intake levels and plasma vasopressin in the rats exposed to either HSD or HEt alone. Prolonged exposure of rats to hot environment exacerbated the effect of excess dietary salt on pOsmol, with no effect on angiotensin II-mediated neurohumoral responses.

Elabela Protects Spontaneously Hypertensive Rats From Hypertension and Cardiorenal Dysfunctions Exacerbated by Dietary High-Salt Intake

Objectives: Arterial hypertension, when exacerbated by excessive dietary salt intake, worsens the morbidity and mortality rates associated with cardiovascular and renal diseases. Stimulation of the apelinergic system appears to protect against several circulatory system diseases, but it remains unknown if such beneficial effects are conserved in severe hypertension. Therefore, we aimed at determining whether continuous infusion of apelinergic ligands (i.e., Apelin-13 and Elabela) exerted cardiorenal protective effects in spontaneously hypertensive (SHR) rats receiving high-salt diet.

Methods: A combination of echocardiography, binding assay, histology, and biochemical approaches were used to investigate the cardiovascular and renal effects of Apelin-13 or Elabela infusion over 6 weeks in SHR fed with normal-salt or high-salt chow.

Results: High-salt intake upregulated the cardiac and renal expression of APJ receptor in SHR. Importantly, Elabela was more effective than Apelin-13 in reducing high blood pressure, cardiovascular and renal dysfunctions, fibrosis and hypertrophy in high-salt fed SHR. Unlike Apelin-13, the beneficial effects of Elabela were associated with a counter-regulatory role of the ACE/ACE2/neprilysin axis of the renin-angiotensin-aldosterone system (RAAS) in heart and kidneys of salt-loaded SHR. Interestingly, Elabela also displayed higher affinity for APJ in the presence of high salt concentration and better resistance to RAAS enzymes known to cleave Apelin-13.

Conclusion: These findings highlight the protective action of the apelinergic system against salt-induced severe hypertension and cardiorenal failure. As compared with Apelin-13, Elabela displays superior pharmacodynamic and pharmacokinetic properties that warrant further investigation of its therapeutic use in cardiovascular and kidney diseases.

Effects of direct high sodium exposure at endothelial cell migration

The present study aimed to test the hypothesis that high sodium affects the migratory phenotype of endothelial cells (EC) and investigates mechanisms involved independently of hemodynamic factors. Cell migration was evaluated by Wound-Healing at conditions: High Sodium (HS; 160 mM) and Control (CT; 140 mM). O₂^- production was evaluated by DHE. NADPH oxidase activity was determined by chemiluminescence assay. Expression of adhesion molecules was analyzed by RT-PCR. Shear Stress was performed using a rhythmic shake. Nitric oxide production was measured by Griess reaction. HS-induced impairment in EC migration while both Candesartan and DPI prevented it. HS increased NADPH oxidase activity, which was blocked by Candesartan. Also, HS increased O₂^- production that was inhibited by Candesartan. HS decreased adhesion molecules expression via ROS (Integrin Alpha 5, Integrin Beta 1, Integrin Beta 3, VE-Cadherin and PECAM) and via AT1R (PECAM). The nitric oxide production induced by shear stress was decreased after EC exposure to HS while both Candesartan and DPI prevented it. Conclusion: This study demonstrated that HS reduced EC migration by AT1R and ROS derived from NADPH Oxidase and mitochondria. The HS reduction in adhesion molecules expression modulated by ROS and AT1R may help to explain the impairment in migration capacity. Also, HS affected EC functionality by reducing their nitric oxide production in response to shear stress.

Blockade of AT1 receptor restore the migration of vascular smooth muscle cells in high sodium medium

The present study aimed to test the hypothesis that increased sodium concentration affects the migratory phenotype of vascular smooth muscle cells (VSMCs) independently of the haemodynamic factors. Cell migration was evaluated by wound-healing assay under the following conditions: high sodium (HS, 160 mM) and control (CT, 140 mM). Cell viability was assessed by annexin V and propidium iodide labeling. Cyclooxygenase-2 (COX-2) gene expression was analysed by reverse transcription polymerase chain reaction. ERK1/2 phosphorylation was assessed by western blot. Exposure of VSMCs to HS reduced migration, and AT1R blockade prevented this response. HS increased COX-2 gene expression, and COX-2 blockade prevented the reduction in VSMC migration induced by HS. HS also increased ERK1/2 phosphorylation, and ERK1/2 inhibition recovered VSMC migration as well as blocked COX-2 gene expression. The TXA₂ receptor blocker, but not the prostacyclin receptor blocker, prevented the HS-induced VSMCs migration decrease. HS reduces the migration of VSMCs by increasing COX-2 gene expression via AT1R-ERK1/2 phosphorylation. In addition, increased COX-2 by HS seems to modulate the reduction of VSMCs migration by the TXA₂ receptor.

Targeting multiple pathways reduces renal and cardiac fibrosis in rats with subtotal nephrectomy followed by coronary ligation

AIM

Multiple interacting pathways contribute to progression of renal and cardiac damage in chronic kidney disease followed by chronic heart failure (renocardiac syndrome). We hypothesized that simultaneous pharmacological modulation of critical pathways implicated in renocardiac syndrome would effectively reduce fibrosis in and preserve function of heart and kidney.

METHODS

Rats were subjected to subtotal nephrectomy followed 9 weeks later by coronary artery ligation. From week 11 until week 16, rats received vehicle or losartan, or a combination of the NF-kB inhibitor PDTC, the NO donor molsidomine and superoxide dismutase mimetic tempol, or a combination of all four of these plus metoprolol together. At week 16, renal and cardiac structure, function and gene expression were assessed.

RESULTS

Individual and combined treatments were similarly effective in limiting cardiac fibrosis and further decline in systolic function. Combined treatment with all five drugs reduced renal fibrosis and CTGF gene expression more effectively than other strategies. Combining all five drugs reduced heart rate, inotropy and mean arterial pressure (MAP).

CONCLUSION

Thus, in our model of chronic renocardiac syndrome, combined treatments similarly decreased cardiac fibrosis and stabilized systolic function as losartan alone, perhaps suggesting a dominant role for a single factor such as angiotensin II type 1 (AT1) receptor activation or inflammation in the network of aberrant systems in the heart. However, tubulointerstitial fibrosis was most effectively reduced by a five-drug regimen, pointing to additive effects of multiple pathophysiological pathways in the kidney.

Low-salt diet increases NO bioavailability and COX-2 vasoconstrictor prostanoid production in spontaneously hypertensive rats

AIMS

The ability of dietary sodium restriction to reduce the incidence of cardiovascular mortality and improve vascular function in hypertension still remains poorly understood. The aim of this study was to observe the effects of a long period of salt restriction on the vascular reactivity of mesenteric resistance arteries of SHRs.

METHODS

Male SHRs received either standard-salt diet (0.3% NaCl) or low-salt diet (0.03% NaCl) for 28weeks. Vascular reactivity was studied in mesenteric artery segments and the influence of cyclooxygenase-2 (COX-2), reactive oxygen species (ROS) and participation of the renin-angiotensin system were analyzed.

KEY FINDINGS

Decreased salt intake did not affect phenylephrine-induced vasoconstriction but increased acetylcholine-induced vasodilatation and also increased the response to phenylephrine after inhibition of NO synthase by L-NAME (100μM) and iNOS protein expression was elevated. Cyclooxygenase inhibitor indomethacin (10μM) and COX-2 inhibitor NS 398 (1μM) decreased the reactivity to phenylephrine in low-salt-treated group, and COX-2 protein expression was elevated in low-salt group. The effects of apocynin (10μM); superoxide anion scavenger, tiron (1mM); hydrogen peroxide scavenger, catalase (1000UmL(-1)); and ACE and AT1 receptor blockers, enalapril (10μM) and losartan (10μM) on vascular reactivity were not different between two groups. The levels of AT1 protein expression were similar in both groups.

SIGNIFICANCE

Low-salt diet modulates mesenteric vascular responses via increased NO bioavailability suggested by increased iNOS protein expression and vasoconstrictor prostanoid production via COX-2 pathway, in SHRs. Neither ROS nor the local renin-angiotensin system is involved in these responses.

Effects of Valsartan vs Amlodipin on renal function in salt loaded spontaneously hypertensive rats

The goal of this study was to compare the effects of valsartan and amlodipin on the systolic blood pressure and parameters specific to the renal function in salt loaded spontaneously hypertensive rats (SHR). 32 male SHR were used at age of 20 weeks and body weight ranging between 265-300 g. From 8 weeks of age tab water was replaced with a solution of NaCl (1%) given ad libitum. Rats were divided into 2 groups: valsartan treated group SHRVAL (n=16) in which valsartan was given at a dose of 10 mg/kg b. w. and amlodipine treated group SHRAMLO (n=16) in which amlodipine was given at a dose of 5 mg/kg b. w. For a period of 12 weeks we have evaluated the effect of the investigated drugs on systolic blood pressure, body weight and renal function tests. In salt loaded rats amlodipine was more effective in reducing the systolic blood pressure in contrast to valsartan who had more pronounced effect on renal parameters most evident in proteinuria. Since both treatment groups have different mechanism of action a combination therapy may be beneficial in improving renal function in SHR rats.

High salt intake does not produce additional impairment in the coronary artery relaxation of spontaneously hypertensive aged rats

The effect of a salt-based diet on the coronary responsiveness in aged hypertensive rats (SHR) still is unclear. We investigated the effects of high salt intake on the relaxation properties of coronary arteries of aged SHRs. Male SHR (32 week-old) received drinking water (SHR) or 1% NaCl solution (SHR-Salt) for 8 weeks. Isolated coronary segments were subjected to concentration-response curves to acetylcholine (ACh) in the presence or absence of L-NAME (100 μM), enalaprilate (10 μM), losartan (10 μM), and spironolactone (100 μM). Salt intake did not increase blood pressure in old SHRs, but caused ventricular hypertrophy. The endothelium-dependent relaxation in SHRs was lower than in Wistar rats. However, salt intake did not add further impairment. Both enalaprilate and losartan reduced the vasodilator response in coronary arteries from Wistar, but did not affect SHR-salt rats. Conversely, losartan attenuated the impaired ACh relaxation observed in SHR. Spironolactone reduced the relaxation induced by ACh in coronary arteries from Wistar rats but not in SHR. The renin-angiotensin-aldosterone system participates in the impaired coronary relaxation in aged SHR, but does not partake in this deleterious effect under increased salt intake, indicating that age could differentiate the effects of high sodium intake in coronary arteries of SHR.

Telmisartan Prevents Excess-Salt-Induced Exacerbated (Malignant) Hypertension in Spontaneously Hypertensive Rats

The effects of angiotensin receptor blocker, diuretic, a calcium antagonist, and their combination were evaluated on the progression of cardiovascular and renal damage in spontaneously hypertensive rats (SHRs) given excess salt. To this end, 8-week male SHRs were divided into 7 groups. The control group (C) received normal NaCl (0.6%) diet. All other groups were given 8% NaCl rat chow. In addition, group 2 was given placebo (tap water alone), group 3 the angiotensin receptor antagonist telmisartan (10 mg/kg per d), group 4 received the diuretic chlorothiazide (80 mg/kg per d), group 5 was given telmisartan plus the diuretic, group 6 was given the calcium antagonist amlodipine (10 mg/kg per d), and group 7 was given telmisartan plus amlodipine. All treatments lasted for 8 weeks. Compared with controls, mean arterial pressure (MAP), renal blood flow, coronary flow reserve, minimal coronary vascular resistance, diastolic time constant, and maximal rate of ventricular pressure fall were all adversely affected by salt loading. Increased left ventricular mass with marked cardiac fibrosis was also found in the salt-overloaded SHR group. Telmisartan normalized all indices except MAP, whereas diuretic and amlodipine only partially restored cardiac functional and mass indexes. Combination therapy with telmisartan and either diuretic or amlodipine also normalized all indices including arterial pressure. These data suggest that (1) cardiovascular  damage induced by excess salt in the SHRs was not pressure dependent; (2) compared with the calcium antagonist and diuretic, blockade of angiotensin receptors  was extremely effective in this model.

Mapping genetic determinants of coronary microvascular remodeling in the spontaneously hypertensive rat

The mechanisms underlying coronary microvascular remodeling and dysfunction, which are critical determinants of abnormal myocardial blood flow regulation in human hypertension, are poorly understood. The spontaneously hypertensive rat (SHR) exhibits many features of human hypertensive cardiomyopathy. We demonstrate that remodeling of intramural coronary arterioles is apparent in the SHR already at 4 weeks of age, i.e. before the onset of systemic hypertension. To uncover possible genetic determinants of coronary microvascular remodeling, we carried out detailed histological and histomorphometric analysis of the heart and coronary vasculature in 30 weeks old SHR, age-matched Brown Norway (BN-Lx) parentals and BXH/HXB recombinant inbred (RI) strains. Using previously mapped expression quantitative trait loci (eQTLs), we carried out a genome-wide association analysis between genetic determinants of cardiac gene expression and histomorphometric traits. This identified 36 robustly mapped eQTLs in the heart which were associated with medial area of intramural coronary arterioles [false discovery rate (FDR) ~5%]. Transcripts, which were both under cis-acting genetic regulation and significantly correlated with medial area (FDR <5%), but not with blood pressure indices, were prioritized and four candidate genes were identified (Rtel1, Pla2g5, Dnaja4 and Rcn2) according to their expression levels and biological functions. Our results demonstrate that genetic factors play a role in the development of coronary microvascular remodeling and suggest blood pressure independent candidate genes for further functional experiments.

Reduced hyperpolarization of endothelial cells following high dietary Na+: effects of enalapril and tempol

1. High dietary Na(+) is associated with impaired vascular endothelial function. However, the underlying mechanisms are not completely understood. In the present study, we investigated whether the endothelial hyperpolarization response to acetylcholine (ACh) exhibited any abnormalities in Wistar rats fed a high-salt diet (HSD) for 1 month and, if so, whether chronic treatment with the angiotensin-converting enzyme inhibitor enalapril or the anti-oxidant tempol could normalize the response. Membrane potential was recorded using the perforated patch-clamp technique on the endothelium of rat aorta. 2. Acetylcholine (2 μmol/L) produced a hyperpolarization sensitive to TRAM-34, a blocker of intermediate-conductance Ca(2+) -sensitive K(+) channels (IK(Ca)), but not to apamin, a blocker of small-conductance Ca(2+)-sensitive K(+) channels (SK(Ca)). NS309 (3 μmol/L), an activator of SK(Ca) and IK(Ca) channels, produced a hyperpolarization of similar magnitude as ACh. 3. In the HSD group, the ACh-evoked hyperpolarization was significantly attenuated compared with that in the control group, which was fed normal chow rather than an HSD. Similarly, the hyperpolarization produced by NS309 was weaker in tissues from HSD-fed rats. 4. Combination of HSD with chronic enalapril treatment (20 mg/kg per day for 1 month) normalized endothelial hyperpolarizing responses to ACh. Chronic tempol treatment (1 mmol/L in tap water for 1 month) prevented the reduced hyperpolarization to ACh. 5. The results of the present study indicate that excess in dietary Na(+) results in a failure of endothelial cells to generate normal IK(Ca) channel-mediated hyperpolarizing responses. Our observations implicate oxidative stress mediated by increased angiotensin II signalling as a mechanism underlying altered endothelial hyperpolarization during dietary salt loading.

Sodium, blood pressure, and cardiovascular disease: further evidence supporting the American Heart Association sodium reduction recommendations

Recent reports of selected observational studies and a meta-analysis have stirred controversy and have become the impetus for calls to abandon recommendations for reduced sodium intake by the US general population. A detailed review of these studies documents substantial methodological concerns that limit the usefulness of these studies in setting, much less reversing, dietary recommendations. Indeed, the evidence base supporting recommendations for reduced sodium intake in the general population remains robust and persuasive. The American Heart Association is committed to improving the health of all Americans through implementation of national goals for health promotion and disease prevention, including its recommendation to reduce dietary sodium intake to <1500 mg/d.

Effect of amiloride and spironolactone on renal tubular function and central blood pressure in patients with arterial hypertension during baseline conditions and after furosemide: a double-blinded, randomized, placebo-controlled crossover trial

This study demonstrates that the increased potassium content in the body seems to change both the blood pressure and renal tubular function. We wanted to test the hypotheses that amiloride and spironolactone induced potassium retention reduces ambulatory blood pressure (ABP) and central blood pressure (CBP) during baseline conditions and after furosemide and that the tubular transport via the epithelial sodium channels (ENaCs) and aquaporin-2 (AQP2) water channels was increased by furosemide in arterial hypertension. Each of three 28-day treatment periods (placebo, amiloride, and spironolactone) was completed by a 4-day period with standardized diet regarding calories and sodium and water intake. At the end of each period, we measured pulse wave velocity (PWV), central systolic blood pressure (CSBP), central diastolic blood pressure (CDBP), glomerular filtration rate (GFR), free water clearance (CH2O), fractional excretion of sodium (FENa) and potassium (FEK), urinary excretion of AQP2 (u-AQP2), urinary excretion of γ-fraction of the ENaC (u-ENaCγ), and plasma concentrations of renin (PRC), angiotensin II (p-Ang II), and aldosterone (p-Aldo) at baseline conditions and after furosemide bolus. Ambulatory blood pressure and CBP were significantly lowered by amiloride and spironolactone. During 24-hour urine collection and at baseline, GFR, CH2O, FENa, FEK, u-AQP2 and u-ENaCγ were the same. After furosemide, CH2O, FENa, FEK, u-AQP2, u-ENaCγ, PRC, p-Ang II, p-Aldo, PWV and CDBP increased after all treatments. However, during amiloride treatment, FEK increased to a larger extent than after spironolactone and during placebo after furosemide, and CSBP was not significantly reduced. The increases in water and sodium absorption via AQP2 and ENaC after furosemide most likely are compensatory phenomena to antagonize water and sodium depletion. Amiloride is less effective than spironolactone to reduce renal potassium excretion.

Anti-fibrotic effect of Aliskiren in rats with deoxycorticosterone induced myocardial fibrosis and its potential mechanism

The objective of our study was to investigate the effect of Aliskiren, a renin inhibitor, on the deoxycorticosterone (DOCA) induced myocardial fibrosis in a rat model and its underlying mechanism. A total of 45 Sprague-Dawley (SD) rats underwent right nephrectomy and were randomly assigned into 3 groups: control group (CON group: silicone tube was embedded subcutaneously); DOCA treated group (DOC group: 200 mg of DOCA was subcutaneously administered); DOCA and Aliskiren (ALI) treated group (ALI group: 200 mg of DOCA and 50 mg/kg/d ALI were subcutaneously and intragastrically given, respectively). Treatment was done for 4 weeks. Sirius red staining was employed to detect the expression of myocardial collagen, and the myocardial collagen volume fraction (CVF) and perivascular collagen volume area (PVCA) were calculated. Radioimmunoassay was carried out to measure the renin activity (RA) and content of angiotensin II (Ang II) in the plasma and ventricle. Western blot assay was done to detect the expressions of extracellular signal-regulated kinase 1/2 (ERK1/2), phosphorylated ERK1/2 (PERK1/2) and matrix metalloproteinase 9 (MMP-9). In the DOC group and ALI group, the CVF and PVCA were significantly increased; the RA and Ang II levels in the plasma and ventricle were remarkably lowered when compared with the CON group. The RA and Ang II levels in the ventricle of the ALI group were significantly lower than those in the DOC group. Moreover, the expressions of ERK1/2, PERK1/2 and MMP9 were the lowest in the CON group, but those in the ALI group were significantly reduced as compared to the DOC group. ALI can inhibit the DOCA induced myocardial fibrosis independent of its pressure-lowing effect, which may be related to the suppression of RA and Ang II production, inhibition of ERK1/2 phosphorylation and MMP9 expression in the heart.

Pressure overload

This review discusses cardiac consequences of pressure overload. In response to elevated pressure, the ventricular hypertrophy compensates for the increased wall stress. However, the ventricular hypertrophy involves numerous structural adaptations that may lead to ventricular dysfunction and, eventually, heart failure. Particular emphasis is placed on molecular mechanisms that govern the development of hypertrophy and that may lead to maladaptive structural changes resulting in adverse cardiac events.

Ramipril and telmisartan exhibit differential effects in cardiac pressure overload-induced hypertrophy without an additional benefit of the combination of both drugs

OBJECTIVES

We aimed to characterize different cellular effects of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin 1 (AT1) receptor blockers (ARBs) as mono- or combination therapy in cardiac pressure overload. Methods and

RESULTS

C57B1/6 mice received either the ACEI ramipril (2.5 mg/kg body weight), the ARB telmisartan (20 mg/kg body weight), or the combination. In all groups, pressure overload was induced by transverse aortic constriction (TAC). Cardiac hypertrophy (heart weight/tibia length) induced by TAC was reduced in all 3 treatment groups, with the most pronounced effect in the telmisartan group. The cardiomyocyte short-axis diameter and cardiac fibrosis were increased by TAC and similarly reduced by ACEI, ARB, and the combination therapy. The TAC-induced increase in the number of proliferating Ki67(pos) cardiomyocytes and noncardiomyocytes was reduced more potently by ACEI than by ARB. Four days of drug treatment induced a significant increase in Scal(pos)/VEGFR1(pos) endothelial progenitor cells (EPCs) in all animals in the treated SHAM groups. After 1 day of aortic constriction, only ramipril increased EPC numbers; after 5 weeks, telmisartan monotherapy did not change the EPC levels compared to vehicle or the combination therapy but raised it compared to ramipril. Neither TAC nor one of the therapies changed the number of cardiac capillaries per cardiomyocytes.

CONCLUSIONS

ACE inhibition and AT1 receptor blockade have beneficial effects in remodeling processes during cardiac pressure overload. There are small differences between the 2 therapeutical approaches, but the combination therapy has no additional benefit.

Salt-induced renal injury in SHRs is mediated by AT1 receptor activation

OBJECTIVE

This study aimed to examine the effects of salt loading, with or without simultaneous angiotensin receptor blocker (ARB) treatment, on the systemic and tissue renin-angiotensin system (RAS) in spontaneously hypertensive rats (SHRs).

METHOD

Evaluation was performed early (4 weeks) in the course of salt loading in order to examine initial mediating events of cardiovascular and renal damage produced by salt excess. Four groups of rats were studied. Group 1 received regular rat chow (normal-salt diet); group 2 received normal-salt diet and an ARB (losartan, 30 mg/kg per day); group 3 received high-salt (8%) chow; and group 4 received high-salt diet and losartan.

RESULTS

High-salt diet increased systolic pressure to 193±1 mmHg compared to 180±2 in normal-salt diet group. Losartan reduced SBP in SHRs fed normal-salt diet but did not reduce SBP in the SHRs fed high-salt diet (192±2 mmHg). High-salt diet markedly increased urinary protein excretion from 27±4 to 64±13 mg/day and this increase was ameliorated by losartan (40±9 mg/day). In SHRs on high-salt diet, plasma angiotensin II concentration increased three to four-fold, whereas urinary angiotensinogen excretion increased 10-fold; and these changes were significantly reduced by losartan. High-salt diet accelerated glomerular injury and interstitial fibrosis in SHRs which were reduced by losartan.

CONCLUSION

These results demonstrate that the activity of RAS was either not suppressed or, even augmented, after 4 weeks of salt loading despite high salt intake and increased SBP. The data suggest that an augmented intrarenal RAS during high-salt diet may contribute to the development of renal injury in this experimental model.

CXCR4 antagonism attenuates the cardiorenal consequences of mineralocorticoid excess

BACKGROUND

Extensive evidence implicates aldosterone excess in the development and progression of cardiovascular disease states including hypertension, metabolic syndrome, cardiac hypertrophy, heart failure, and cardiorenal fibrosis. Recent studies show that activation of inflammatory cascade may play a specific role in the sequelae of mineralocorticoid activation, although the linking mechanism remains unclear. We tested the possibility that secondary stimulation of the stromal-derived factor 1/CXC chemokine receptor 4 (SDF-1/CXCR4) pathway plays a contributory role.

METHODS AND RESULTS

We investigated the effect of the highly selective CXCR4 antagonist AMD3465 (6 mg/kg per day for 6 weeks through minipump) in dexoycorticosterone acetate (DOCA)-treated, uninephrectomized mice. CXCR4 antagonism significantly attenuated the induction of cardiac fibrosis, renal fibrosis, hypertension, and left ventricular hypertrophy by DOCA. Mineralocorticoid excess also stimulated the accumulation of T-lymphocytes in the heart and kidney and this was significantly blunted by CXCR4 inhibition.

CONCLUSIONS

Taken together, these data strongly implicate the SDF-1/CXCR4 axis in the pathogenesis of mineralocorticoid excess induced hypertension, inflammation, and cardiorenal fibrosis. This insight provides a new potential therapeutic approach for the treatment of specific aspects of mineralocorticoid mediated cardiovascular disease.

Effects of spironolactone in spontaneously hypertensive adult rats subjected to high salt intake

OBJECTIVE

To evaluate the effect of spironolactone on ventricular stiffness in spontaneously hypertensive adult rats subjected to high salt intake.

INTRODUCTION

High salt intake leads to cardiac hypertrophy, collagen accumulation and diastolic dysfunction. These effects are partially mediated by cardiac activation of the renin-angiotensin-aldosterone system.

METHODS

Male spontaneously hypertensive rats (SHRs, 32 weeks) received drinking water (SHR), a 1% NaCl solution (SHR-Salt), or a 1% NaCl solution with a daily subcutaneous injection of spironolactone (80 mg.kg⁻¹) (SHRSalt- S). Age-matched normotensive Wistar rats were used as a control. Eight weeks later, the animals were anesthetized and catheterized to evaluate left ventricular and arterial blood pressure. After cardiac arrest, a double-lumen catheter was inserted into the left ventricle through the aorta to obtain in situ left ventricular pressure-volume curves.

RESULTS

The blood pressures of all the SHR groups were similar to each other but were different from the normotensive controls (Wistar = 109 ± 2; SHR = 118 ± 2; SHR-Salt = 117 ± 2; SHR-Salt-S = 116 ± 2 mmHg; P < 0.05). The cardiac hypertrophy observed in the SHR was enhanced by salt overload and abated by spironolactone (Wistar = 2.90 ± 0.06; SHR = 3.44 ± 0.07; SHR-Salt = 3.68 ± 0.07; SHR-Salt-S = 3.46 ± 0.05 mg/g; P < 0.05). Myocardial relaxation, as evaluated by left ventricular dP/dt, was impaired by salt overload and improved by spironolactone (Wistar = -3698 ± 92; SHR = -3729 ± 125; SHR-Salt = -3342 ± 80; SHR-Salt-S = -3647 ± 104 mmHg/s; P < 0.05). Ventricular stiffness was not altered by salt overload, but spironolactone treatment reduced the ventricular stiffness to levels observed in the normotensive controls (Wistar = 1.40 ± 0.04; SHR = 1.60 ± 0.05; SHR-Salt = 1.67 ± 0.12; SHR-Salt- S = 1.45 ± 0.03 mmHg/ml; P < 0.05).

CONCLUSION

Spironolactone reduces left ventricular hypertrophy secondary to high salt intake and ventricular stiffness in adult SHRs.

Vascular structure and oxidative stress in salt-loaded spontaneously hypertensive rats: effects of losartan and atenolol

BACKGROUND

Renin-angiotensin system (RAS) modulation by high dietary sodium may contribute to salt-induced hypertension, oxidative stress, and target organ damage. We investigated whether angiotensin II (Ang-II) type 1 (AT1)-receptor blockade (losartan) could protect the aorta and renal arteries from combined hypertension- and high dietary salt-related oxidative stress.

METHODS

Spontaneously hypertensive rats (3-month-old, n = 10/group) received tap water (SHR), water containing 1.5% NaCl (SHR+S), 1.5% NaCl and 30 mg losartan/kg/day (SHR+S+L), or 50 mg atenolol/kg/day (SHR+S+A). Atenolol was used for comparison. Ten Wistar-Kyoto rats (WKY) were controls. Systolic blood pressure (SBP) was determined by tail plethysmography. After 5 months of treatment, vascular remodeling and oxidative stress (superoxide production and NAD(P)H-oxidase activity (chemiluminescence), malondialdehyde (MDA) content (high-performance liquid chromatography), endothelial nitric oxide synthase (eNOS) activity [(14)C-arginine to (14)C citrulline], CuZn-SOD activity (spectrophotometry)) were studied.

RESULTS

In SHR, salt-loading significantly aggravated hypertension, urinary protein excretion, intraparenchymal renal artery (IPRArt) perivascular fibrosis, aortic and renal artery oxidative stress, and induced endothelial cell loss in IPRArts. In salt-loaded SHR, 5-month losartan and atenolol treatments similarly reduced SBP, but only losartan significantly prevented (i) urinary protein excretion increase, (ii) or attenuated hypertension-related vascular remodeling, (iii) aortic MDA accumulation, (iv) renal artery eNOS activity lowering, and (v) aortic and renal artery superoxide dismutase (SOD) activity reduction. In SHR+S, the contributions to aortic superoxide production were as follows: uncoupled eNOS > xanthine oxidase (XO) > NAD(P)H oxidase.

CONCLUSIONS

In this salt-sensitive genetic hypertension model, losartan protects from hypertension- and high dietary salt-related vascular oxidative stress, exceeding the benefits of BP reduction. Also, during salt overload, BP-independent factors contribute to vascular remodeling, at least part of which derive from AT1-receptor activation.