Mast cells and epsilonPKC: a role in cardiac remodeling in hypertension-induced heart failure

Heart failure (HF) is a chronic syndrome in which pathological cardiac remodeling is an integral part of the disease and mast cell (MC) degranulation-derived mediators have been suggested to play a role in its progression. Protein kinase C (PKC) signaling is a key event in the signal transduction pathway of MC degranulation. We recently found that inhibition of epsilonPKC slows down the progression of hypertension-induced HF in salt-sensitive Dahl rats fed a high-salt diet. We therefore determined whether epsilonPKC inhibition affects MC degranulation in this model. Six week-old male Dahl rats were fed with a high-salt diet to induce systemic hypertension, which resulted in concentric left ventricular hypertrophy at the age of 11 weeks, followed by myocardial dilatation and HF at the age of 17 weeks. We administered epsilonV1-2, an epsilonPKC-selective inhibitor peptide (3 mg/kg/day), deltaV1-1, a deltaPKC-selective inhibitor peptide (3 mg/kg/day), TAT (negative control; at equimolar concentration; 1.6 mg/kg/day) or olmesartan (angiotensin receptor blocker [ARB] as a positive control; 3 mg/kg/day) between 11 weeks and 17 weeks. Treatment with epsilonV1-2 attenuated cardiac MC degranulation without affecting MC density, myocardial fibrosis, microvessel patency, vascular thickening and cardiac inflammation in comparison to TAT- or deltaV1-1-treatment. Treatment with ARB also attenuated MC degranulation and cardiac remodeling, but to a lesser extent when compared to epsilonV1-2. Finally, epsilonV1-2 treatment inhibited MC degranulation in isolated peritoneal MCs. Together, our data suggest that epsilonPKC inhibition attenuates pathological remodeling in hypertension-induced HF, at least in part, by preventing cardiac MC degranulation.     

Pharmacological inhibition of epsilon PKC suppresses chronic inflammation in murine cardiac transplantation model

Epsilon protein kinase C (epsilonPKC) plays pivotal roles in myocardial infarction and in heart failure. Although cardiac transplantation is a well-established therapy for severe heart failure, allograft rejection and host inflammatory responses limit graft function and reduce life expectancy. Here we determined whether sustained epsilonPKC inhibition beginning 3 days after transplantation suppress allograft rejection and improve cardiac transplantation using a murine heterotopic transplantation model. Hearts of FVB mice (H-2(q)) were transplanted into C57BL/6 mice (H-2(b)). Delivery of the epsilonPKC inhibitor, TAT(47-57)-epsilonV1-2 (epsilonV1-2, n=9, 20 mg/kg/day), or the carrier control peptide, TAT(47-57) (TAT, n=8), by osmotic pump began 3 days after transplantation and continued for the remaining 4 weeks. epsilonV1-2 treatment significantly improved the beating score throughout the treatment. Infiltration of macrophages and T cells into the cardiac grafts was significantly reduced and parenchymal fibrosis was decreased in animals treated with epsilonV1-2 as compared with control treatment. Finally, the rise in pro-fibrotic cytokine, TGF-beta and monocyte recruiting chemokine MCP-1 levels was almost abolished by epsilonV1-2 treatment, whereas the rise in PDGF-BB level was unaffected. These data suggest that epsilonPKC activity contributes to the chronic immune response in cardiac allograft and that an epsilonPKC-selective inhibitor, such as epsilonV1-2, could augment current therapeutic strategies to suppress inflammation and prolong graft survival in humans.     

Role of blood pressure reduction in prevention of cardiac and vascular hypertrophy

We investigated whether prevention of cardiac and vascular remodeling associated with inhibition of angiotensin II is independent of the blood pressure (BP)-lowering action of angiotensin II type 1 (AT1) receptor blockade. Spontaneously hypertensive rats, 8 weeks old, were treated with olmesartan, atenolol, or vehicle in their drinking water for 56 days. At the end of each treatment, arterial pressure and heart rate were measured, the ratio of heart weight to body weight was calculated, collagen deposition in the heart was determined histochemically using picrosirius red staining, and wall-to-lumen ratio in isolated mesenteric arteries was measured by a videographic approach. At 3 weeks after the initiation of treatment, rats medicated with olmesartan showed lower values of systolic BP compared with rats given atenolol or vehicle, whereas no difference in directly measured BP were observed at the end of study in anesthetized rats given olmesartan or atenolol. Rats given atenolol showed sustained bradycardia, whereas cardiac hypertrophy and collagen deposition was prevented only in spontaneously hypertensive rats given olmesartan. Olmesartan or atenolol reduced arteriolar wall-to-lumen ratio (olmesartan: 11.5+/-0.4%; atenolol: 13.3+/-0.6%; vehicle: 18.4%+/-1.1); however, this effect was greatest in rats medicated with the angiotensin II type 1 antagonist. Although control of BP is a factor in the prevention of cardiac and vascular hypertrophy, our studies suggest that blockade of angiotensin II receptors may attenuate the structural changes in the heart and blood vessels of hypertensive animals independent of a reduction in BP.     

Mast cells and ?PKC: A role in cardiac remodeling in hypertension-induced heart failure

Heart failure (HF) is a chronic syndrome in which pathological cardiac remodeling is an integral part of the disease and mast cell (MC) degranulation-derived mediators have been suggested to play a role in its progression. Protein kinase C (PKC) signaling is a key event in the signal transduction pathway of MC degranulation. We recently found that inhibition of ɛPKC slows down the progression of hypertension-induced HF in salt-sensitive Dahl rats fed a high-salt diet. We therefore determined whether ɛPKC inhibition affects MC degranulation in this model. Six week-old male Dahl rats were fed with a high-salt diet to induce systemic hypertension, which resulted in concentric left ventricular hypertrophy at the age of 11 weeks, followed by myocardial dilatation and HF at the age of 17 weeks. We administered ɛV1-2_, an ɛPKC-selective inhibitor peptide (3 mg/kg/day), δV1-1_, a δPKC-selective inhibitor peptide (3 mg/kg/day), TAT (negative control; at equimolar concentration; 1.6 mg/kg/day) or olmesartan (angiotensin receptor blocker [ARB] as a positive control; 3 mg/kg/day) between 11 weeks and 17 weeks. Treatment with ɛV1-2 attenuated cardiac MC degranulation without affecting MC density, myocardial fibrosis, microvessel patency, vascular thickening and cardiac inflammation in comparison to TAT- or δV1-1-treatment. Treatment with ARB also attenuated MC degranulation and cardiac remodeling, but to a lesser extent when compared to ɛV1-2. Finally, ɛV1-2 treatment inhibited MC degranulation in isolated peritoneal MCs. Together, our data suggest that ɛPKC inhibition attenuates pathological remodeling in hypertension-induced HF, at least in part, by preventing cardiac MC degranulation.     

Additive beneficial effects of the combination of a calcium channel blocker and an angiotensin blocker on a hypertensive rat-heart failure model.

The present study was undertaken to examine the effects of a calcium channel blocker, azelnidipine (1 mg/kg/day), an angiotensin converting enzyme (ACE) inhibitor, temocapril (10 mg/kg/day), an angiotensin II type 1 (AT1) receptor blocker (ARB), olmesartan (5 mg/kg/day), and their combination on Dahl salt-sensitive rats (DS rats) developing heart failure with preserved systolic function. DS rats were fed a high-salt diet (8% NaCl) from 7 weeks of age and progressively developed hypertension. Although monotherapy with azelnidipine lowered the blood pressure of DS rats to a greater extent than monotherapy with temocapril or olmesartan, the three drugs had similar effects on cardiac hypertrophy, cardiac fibrosis, the expressions of brain natriuretic peptide, transforming growth factor-beta1, collagen I, collagen III and monocyte chemoattractant protein-1 mRNA (as estimated by Northern blot analysis), and cardiac diastolic dysfunction (as estimated by echocardiography). These results show that ACE and AT1 receptor, as well as hypertension, are involved in the development of heart failure with preserved systolic function in DS rats. The combination of azelnidipine with olmesartan or temocapril produced no additive hypotensive effect in DS rats and no additive effect on cardiac hypertrophy or gene expressions. However, the combination therapy prolonged the survival rate of DS rats more than azelnidipine (p <0.01) or temocapril alone (p <0.05), and this additive beneficial effect by the combination therapy was associated with a greater reduction of cardiac fibrosis, urinary albumin excretion and serum creatinine. Our results thus showed that the combination of a calcium channel blocker with an ARB or an ACE inhibitor had additive preventive effects on a rat model of hypertensive heart failure with preserved systolic function. Thus, combination therapy with these agents seems to be a useful therapeutic strategy for the prevention of hypertensive heart failure.     

Role of AT1 receptor in isoproterenol-induced cardiac hypertrophy and oxidative stress in mice

Elevated activities of the sympathetic nerve and renin-angiotensin systems are common features of heart failure. This study was designed to investigate the roles of the AT1 receptor in cardiac hypertrophy and oxidative stress during excessive beta-adrenoceptor stimulation using an AT1 receptor antagonist (ARB) and AT1a receptor-deficient (AT1aR(-/-)) mice. Isoproterenol (ISO) was given to C57BL mice with or without ARB (olmesartan) treatment and to AT1aR(-/-) mice by a subcutaneously implanted osmotic mini-pump for 11 days at a rate of 15 mg/kg/day. Chronic ISO infusion to C57BL mice caused concentric cardiac hypertrophy (sham; 4.1+/-0.1, ISO; 5.2+/-0.2 mg/g heart to body weight ratio), accompanied by enhancement of cardiac collagen accumulation, lipid peroxidation, superoxide generation and NADPH oxidase activity. The AT1a and beta-1,2 receptor mRNA expressions were down-regulated in the heart of ISO-infused mice. Olmesartan markedly suppressed cardiac mass enlargement as well as increases of oxidative indicators without any effects on heart rate. Olmesartan did not affect the cardiac angiotensin and beta-adrenergic receptor mRNA expression patterns. The AT1a receptor contribution to ISO-induced cardiac hypertrophy was reproduced in AT1aR(-/-) mice. These data suggest that the AT1 receptor plays a crucial role in the development of cardiac hypertrophy and oxidative stress under excessive beta-adrenergic stimulation, and that ARB treatment is beneficial for sympatho-excitatory cardiac hypertrophy and failure in mice.     

Modulation of in vivo cardiac hypertrophy with insulin-like growth factor-1 and angiotensin-converting enzyme inhibitor: relationship between change in myosin isoform and progression of left ventricular dysfunction

OBJECTIVES: Supplemental myocardial hypertrophy induced by insulin-like growth factor (IGF)-1 may prevent transition from hypertrophy to heart failure under chronic mechanical overload. BACKGROUND: Several studies have suggested that IGF-1 treatment may be beneficial in chronic heart failure. In addition, recent studies indicated that the amount of alpha-myosin heavy chain (MHC) plays a significant hemodynamic role in large animals including humans. METHODS: We treated Dahl salt-sensitive hypertensive rats on a long-term basis with IGF-1. The effects were compared with those produced by treatment using a sub-antihypertensive dose of temocapril, an angiotensin-converting enzyme (ACE) inhibitor. At 11 weeks, when these rats displayed compensated left ventricular hypertrophy (LVH), they were randomized to three groups: 1) IGF group (3 mg/kg/day); 2) temocapril group (1 mg/kg/day); and 3) vehicle (control) group. RESULTS: After 15 weeks, the control rats showed left ventricular (LV) enlargement and severe LV dysfunction and rapidly died of pulmonary congestion (mean survival time: 16.8+/-0.5 weeks). The survival time was significantly shortened (15.6+/-0.3 weeks) in the IGF-1 group but significantly prolonged (19.5+/-0.6 weeks) in the temocapril group. The rats in the IGF-1 group showed accelerated LV dilation and dysfunction. Of the several parameters investigated, it was found that the relative amounts of MHC isoforms differed among the three groups. The alpha-MHC mRNA level was decreased by 52% (p<0.01) in the IGF group, while it increased by 58% (p<0.01) in the temocapril group compared with the control group. These changes were related to the progression of LV dysfunction. CONCLUSIONS: Supplemental myocardial hypertrophy with long-term IGF-1 treatment may not be beneficial if concentric LVH already exists. Our data suggest that IGF-1 may not protect myocardial performance when its hypertrophic effect aggravates the reduction of alpha-MHC. By contrast, the ACE inhibitor may improve myocardial function and prognosis by preventing the down-regulation of this isoform.     

High fructose diet increases mortality in hypertensive rats compared to a complex carbohydrate or high fat diet

BACKGROUND: Chronic hypertension leads to cardiac hypertrophy, heart failure, and premature death. Little is known about the impact of dietary macronutrient composition on hypertension-induced cardiac hypertrophy and mortality. We investigated the effects of consuming either a high complex carbohydrate diet, a high simple sugar diet, or a high fat diet on cardiac hypertrophy and mortality in hypertensive Dahl salt-sensitive (DSS) rats. METHODS: Rats were assigned to four diets: complex carbohydrate (CC; 70% starch, 10% fat, 20% protein by energy), high fat (FAT; 20% carbohydrates, 60% fat, 20% protein), high fructose (FRU; 70% fructose, 10% fat, 20% protein), and "western" (WES; 35% fructose, 45% fat, 20% protein). Hypertension was initiated by adding 6% NaCl (+S) to the chow of half the animals within each diet (n = 10 to 13/group). Tail cuff blood pressure measurements were assessed after 5 and 11 weeks of treatment, and echocardiography were assessed after 12 weeks of treatment. RESULTS: All rats fed a high salt diet had similar levels of hypertension (CC+S 220 +/-2 mm Hg, FAT+S 221 +/- 3 mm Hg, FRU+S 221 +/- 1 mm Hg, WES+S 226 +/- 3 mm Hg). Echocardiography results show that the addition of salt to FRU resulted in increased regional wall thickness that was not observed in other dietary groups. All rats fed a low salt diet (CC, FAT, FRU, WES) and the FAT+S group survived 90 days. On the other hand, there was 90-day mortality in the WES+S group (18% mortality) and the CC+S group (30% mortality). In addition, FRU+S rats started dying after 45 days of salt feeding, and only 15% survived the full 90 days. CONCLUSIONS: These results demonstrate that a high fructose diet consumed during hypertension increases mortality and left ventricular (LV) wall thickness compared to either a high fat, high starch, or a "western" diet.     

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors prevent the development of cardiac hypertrophy and heart failure in rats

OBJECTIVES: The aim of the present study was to determine whether 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have preventive effects on the development of cardiac hypertrophy and heart failure. BACKGROUND: Statins have been reported to have various pleiotropic effects, such as inhibition of inflammation and cell proliferation. METHODS: Dahl rats were divided into three groups: LS, the rats fed the low-salt diet (0.3% NaCl); HS, the rats fed the high-salt diet (8% NaCl) from the age of 6 weeks; and CERI, the rats fed the high-salt diet with cerivastatin 1 mg/kg/d by gavage from the age of 6 weeks. RESULTS: In HS rats, cardiac function was markedly impaired and all rats showed the signs of heart failure within 17 weeks of age. In CERI rats, cardiac function was better than that of HS and no rats were dead up to 17 weeks of age. The development of cardiac hypertrophy and fibrosis was attenuated, and the number of apoptotic cells and expression of proinflammatory cytokine interleukin (IL)-1beta gene were less as compared with HS rats. Pretreatment of cerivastatin suppressed the adriamycin-induced apoptosis of cultured cardiomyocytes of neonatal rats. CONCLUSIONS: These results suggest that statins have a protective effect on cardiac myocytes and may be useful to prevent the development of hypertensive heart failure.     

DeltaPKC-mediated activation of epsilonPKC in ethanol-induced cardiac protection from ischemia

Previous studies have demonstrated that acute ethanol exposure induces activation of delta protein kinase C (deltaPKC) and epsilonPKC, and mimics ischemic preconditioning via epsilonPKC activation. However, the role of deltaPKC isozyme in ischemia and reperfusion is still controversial. Here, we investigated the role of deltaPKC in ethanol-induced cardioprotection using a selective deltaPKC activator (psideltaRACK), or inhibitor (deltaV1-1), and a selective epsilonPKC inhibitor (epsilonV1-2) in isolated mouse hearts. Mice were injected intraperitoneally or by gavage with ethanol, regulators of delta and epsilonPKC or an adenosine A1 receptor blocker (DPCPX). Isolated perfused mouse hearts were subjected to a 30-min global ischemia and a 120-min reperfusion, ex vivo. Injection of 0.5 g/kg ethanol 1 h, but not 10 min, before ischemia reduced infarct size and CPK release. Pretreatment with epsilonV1-2 abolished this ethanol-induced cardioprotection. Pretreatment with deltaV1-1 induced cardioprotection when injected with ethanol (0.5 g/kg) 10 min before ischemia, but deltaV1-1 partly inhibited ethanol-induced cardioprotection when injected with ethanol 1-h before the onset of ischemia. psideltaRACK injection 1 h, but not 10 min, before ischemia induced cardioprotection and translocation of epsilonPKC from the cytosol to the particulate fraction. Pretreatment with DPCPX or epsilonV1-2 inhibited psideltaRACK-induced cardioprotection and translocation of epsilonPKC. Therefore, activation of deltaPKC-induced by ethanol or by the deltaPKC activator is cardioprotective, provided that sufficient time passes to allow deltaPKC-induced activation of epsilonPKC, an A1 adenosine receptor-dependent process.     

Coordinated shifts in Na/K-ATPase isoforms and their endogenous ligands during cardiac hypertrophy and failure in NaCl-sensitive hypertension

OBJECTIVES: NaCl loading of Dahl salt-sensitive rats (DS) stimulates marinobufagenin (MBG), an alpha1 Na/K-ATPase (NKA) isoform ligand. Cardiac function depends on NKA, which is regulated in part by endogenous digitalis-like ligands. Our goal was to study whether changes occur in MBG and endogenous ouabain (EO) production during cardiac remodelling in hypertensive DS, and whether these are associated with changes in myocardial NKA isoforms and sensitivity to MBG and ouabain. METHODS: Changes in MBG and EO levels, changes in myocardial NKA isoform composition, and sensitivity to endogenous ligands during development of cardiac hypertrophy and the transition to heart failure were studied in DS rats with an 8% NaCl intake. RESULTS: The animals developed compensated left ventricular hypertrophy after 4 weeks, which progressed to heart failure at 9-12 weeks. The hypertrophic stage was associated with increased plasma MBG levels (mean +/- SEM of 1.22 +/- 0.22 versus 0.31 +/- 0.03 nmol/l; P < 0.01), increased sensitivity of NKA to MBG, and an increased abundance of alpha1 NKA. Plasma levels of EO did not change, and the sensitivity of NKA to ouabain decreased. The transition to heart failure was accompanied by a decrease in alpha1 NKA, a reduction in plasma MBG, and decreased sensitivity of NKA to MBG. In addition, an increased abundance of ouabain-sensitive alpha3 NKA, a three-fold rise in plasma EO (1.01 +/- 0.13 versus 0.27 +/- 0.06 nmol/l), and a seven-fold increase in the ouabain sensitivity of NKA compared with controls were observed. CONCLUSIONS: During cardiac hypertrophy and the transition to heart failure, a shift in endogenous NKA ligands production is linked to a shift in myocardial NKA isoforms.     

Amelioration of hypertensive heart failure by amlodipine may occur via antioxidative effects.

Although recent clinical studies have suggested that long-acting calcium channel blockers (CCBs) have beneficial effects on heart failure, the precise mechanism is unknown. In this study, Dahl salt-sensitive rats fed a high salt diet were treated with the long-acting CCB amlodipine, the low-molecular-weight membrane permeable superoxide dismutase mimetic 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (Tempol), or saline from 11 weeks after birth. The cardiac geometry and function, and gene expression profiles were determined at 17 weeks. Dahl salt-sensitive rats fed a high salt diet followed by saline as a non-treatment control (HS group) showed a marked increase in blood pressure and developed concentric hypertrophy at 11 weeks, followed by left ventricular (LV) dilation and congestive heart failure by 17 weeks. The treatment with amlodipine (AMLO group) or Tempol (TEMP group) significantly inhibited the development of LV hypertrophy and cardiac dysfunction. Analysis using an Affymetrix GeneChip U34 revealed that the expression levels of 195 genes were changed by the treatment with amlodipine. Among these 195 genes, 110 genes were increased in HS rats and decreased in AMLO rats. And of these 110 genes, 54 genes were also decreased in TEMP rats. In contrast, 85 genes were decreased in HS rats and increased in AMLO rats. Of these 85 genes, 38 genes were also increased in TEMP rats. Approximately 48% of the genes were changed in similar fashion in AMLO and TEMP rats, suggesting that amlodipine shows beneficial effects on heart failure mainly via antioxidative mechanisms.     

Temporal regulation of extracellular matrix components in transition from compensatory hypertrophy to decompensatory heart failure

OBJECTIVE: Extracellular matrix, particularly type I fibrillar collagen, provides tensile strength that allows cardiac muscle to perform systolic and diastolic functions. Collagen is induced during the transition from compensatory hypertrophy to heart failure. We hypothesized that cardiac stiffness during decompensatory hypertrophy is partly due to a decreased elastin:collagen ratio. MATERIALS AND METHODS: We prepared left ventricular tissue homogenates from spontaneously hypertensive rats (SHR) aged 30-36 weeks, which had compensatory hypertrophy with no heart failure, and from SHR aged 70-92 weeks, which had decompensatory hypertrophy with heart failure. Age- and sex-matched Wistar-Kyoto (WKY) rats were used as normotensive controls. In both SHR groups, increased levels of collagen were detected by immuno-blot analysis using type I collagen antibody. Elastin and collagen were quantitated by measuring desmosine/isodesmosine and hydroxyproline spectrophometrically, respectively. To determine whether the decrease in elastin content was due to increased elastinolytic activity of matrix metalloproteinase-2, we performed gelatin and elastin zymography on left ventricular tissue homogenates from control rats, SHR with compensatory hypertrophy and SHR with heart failure. RESULTS: The elastin:collagen ratio was 0.242 +/- 0.008 in hearts from WKY rats. In SHR without heart failure, the ratio was decreased to 0.073 +/- 0.003 and in decompensatory hypertrophy with heart failure, the ratio decreased to 0.012 +/- 0.005. Matrix metalloproteinase-2 activity was increased significantly in SHR with heart failure compared with controls (P < 0.001). The level of tissue inhibitor of metalloproteinase-4 was increased in compensatory hypertrophy and markedly reduced in heart failure. Decorin was strongly reduced in decompensatory heart failure compared with control hearts. CONCLUSIONS: Since collagen was induced in SHR with heart failure, decorin and elastin were decreased and the ratios of gelatinase A and elastase to tissue inhibitor of metalloproteinase-4 were increased, we conclude that heart failure is associated with adverse extracellular matrix remodeling.     

AT1 receptor blocker added to ACE inhibitor provides benefits at advanced stage of hypertensive diastolic heart failure

Diastolic heart failure (DHF) has become a social burden; however, evidences leading to its therapeutic strategy are lacking. This study investigated effects of addition of angiotensin II type 1 receptor blocker (ARB) to angiotensin-converting enzyme inhibitor (ACEI) at advanced stage of DHF in hypertensive rats. Dahl salt-sensitive rats fed 8% NaCl diet from age 7 weeks served as DHF model, and those fed a normal chow served as control. The DHF model rats were arbitrarily assigned to 3 treatment regimens at age 17 weeks: ACEI (temocapril 0.4 mg/kg per day), combination of ACEI (temocapril 0.2 mg/kg per day) with ARB (olmesartan 0.3 mg/kg per day), or placebo. At age 17 weeks, this model represents progressive ventricular hypertrophy and fibrosis, relaxation abnormality, and myocardial stiffening. Data were collected at age 20 weeks. As compared with the monotherapy with ACEI, the addition of ARB induced more prominent suppression of ventricular hypertrophy and fibrosis, leading to suppression of myocardial stiffening, improvement of relaxation, and inhibition of hemodynamic deterioration. Such benefits were associated with greater decreases in reactive oxygen species (ROS) generation, macrophage infiltration, and gene expression of transforming growth factor (TGF)-beta(1) and interleukin (IL)-1beta, but not with changes in gene expression of monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-alpha. Thus, ARB added to ACEI provides more benefits as compared with ACEI alone in DHF when initiated at an advanced stage. The additive effects are likely provided through more prominent suppression of ROS generation and inflammatory changes without effects on expression of MCP-1 and TNF-alpha.     

Effects of aldosterone and angiotensin II receptor blockade on cardiac angiotensinogen and angiotensin-converting enzyme 2 expression in Dahl salt-sensitive hypertensive rats

BACKGROUND: We previously reported that a high-sodium diet activates the local renin-angiotensin-aldosterone system (RAAS) in cardiovascular tissues of Dahl salt-sensitive hypertensive (DS) rats. Angiotensin-converting enzyme 2 (ACE2) is a novel regulator of blood pressure (BP) and cardiac function. The effect of blockade of aldosterone or angiotensin II (Ang II) on cardiac angiotensinogen and ACE2 in DS rats is unknown. METHODS: The BP, plasma renin activity (PRA), plasma aldosterone concentration (PAC), heart weight, endothelium-dependent relaxation (EDR), and messenger RNA (mRNA) levels of collagen III, angiotensinogen, ACE, and ACE2 in the heart were measured in DS rats and in Dahl salt-resistant (DR) rats fed high or low salt diets. The rats were treated orally with or without eplerenone (100 mg/kg/d), candesartan (10 mg/kg/d), or both drugs combined for 8 weeks. RESULTS: A high salt diet increased BP (140%), heart/body weight (132%), and collagen III mRNA levels (146%) and decreased PRA and PAC concomitant with increased expression of cardiac angiotensinogen mRNA and decreased mRNA levels of ACE2 in DS rats. Eplerenone or candesartan significantly decreased the systolic BP from 240 +/- 5 mm Hg to 164 +/- 4 mm Hg or to 172 +/- 10 mm Hg, respectively (P < .05). Eplerenone or candesartan partially improved heart/body weight and cardiac fibrosis, improved EDR and decreased cardiac ACE and angiotensinogen mRNA levels in DS rats. Candesartan increased ACE2 mRNA levels in the heart. Combination therapy normalized BP and further improved cardiac hypertrophy, fibrosis, and EDR. CONCLUSIONS: In DS rats, blockade of aldosterone or Ang II protects cardiac hypertrophy and fibrosis by inactivation of the local RAAS in the heart.     

Cardioprotective effects of the Na(+)/H(+)-exchange inhibitor cariporide in infarct-induced heart failure

OBJECTIVE: We investigated the effect of chronic treatment with the new Na(+)/H(+)-exchange inhibitor, cariporide, on cardiac function and remodelling 6 weeks after myocardial infarction (MI) in rats. METHODS: Treatment with cariporide was commenced either 1 week pre or 30 min, 3 h, 24 h or 7 days after ligation of the left ventricular artery and was continued until haemodynamic parameters were obtained 6 weeks after MI in conscious rats. RESULTS: Compared to sham animals, untreated MI-controls developed pronounced heart failure after 6 weeks. Basal left ventricular end-diastolic pressure (in mmHg) was reduced in the groups in which cariporide was started 1 week pre (16.0+/-1.7) or 30 min (12.5+/-1.1), 3 h (11.8+/-1.0) and 24 h (13.0+/-2.5) after MI compared to untreated MI-controls (22. 4+/-1.5; P<0.01). Basal myocardial contractility (in 1000 mmHg/s) was only increased when treatment was initiated after 30 min (9. 0+/-0.7), 3 h (8.5+/-0.3) and 24 h (8.0+/-0.7) compared to untreated MI-controls (5.8+/-0.7; P<0.05-0.01). Infarct size (in % of left ventricular circumference) was 40.0+/-2.1 in MI-controls and was decreased when treatment was begun after 30 min (32.6+/-2.7) or 3 h (32.4+/-2.3) (P<0.05). In animals, in which cariporide was started 3 h after induction of MI, heart weight/body weight ratio was significantly decreased, indicating reduced cardiac hypertrophy. When treatment started 7 days after MI, cariporide did not exert any beneficial actions on structural and functional cardiac parameters. CONCLUSION: Our results show for the first time that chronic treatment with the Na(+)/H(+)-exchange inhibitor cariporide engendered marked cardioprotective effects when commenced before and up to 24 h after MI. The optimal time for the start of treatment was between 30 min and 3 h post MI.     

Pharmacological inhibition of βIIPKC is cardioprotective in late-stage hypertrophy

We previously found that in the hearts of hypertensive Dahl salt-sensitive rats, βIIPKC levels increase during the transition from compensated cardiac hypertrophy to cardiac dysfunction. Here we showed that a six-week treatment of these hypertensive rats with a βIIPKC-specific inhibitor, βIIV5-3, prolonged their survival by at least 6 weeks, suppressed myocardial fibrosis and inflammation, and delayed the transition from compensated hypertrophy to cardiac dysfunction. In addition, changes in the levels of the Ca²⁺-handling proteins, SERCA2 and the Na⁺/Ca²⁺ exchanger, as well as troponin I phosphorylation, seen in the control-treated hypertensive rats were not observed in the βΙΙPKC-treated rats, suggesting that βΙΙPKC contributes to the regulation of calcium levels in the myocardium. In contrast, treatment with the selective inhibitor of βIPKC, an alternative spliced form of βIIPKC, had no beneficial effects in these rats. We also found that βIIV5-3, but not βIV5-3, improved calcium handling in isolated rat cardiomyocytes and enhanced contractility in isolated rat hearts. In conclusion, our data using an in vivo model of cardiac dysfunction (late-phase hypertrophy), suggest that βIIPKC contributes to the pathology associated with heart failure and thus an inhibitor of βIIPKC may be a potential treatment for this disease.     

Pharmacological inhibition of βIIPKC is cardioprotective in late-stage hypertrophy

We previously found that in the hearts of hypertensive Dahl salt-sensitive rats, βIIPKC levels increase during the transition from compensated cardiac hypertrophy to cardiac dysfunction. Here we showed that a six-week treatment of these hypertensive rats with a βIIPKC-specific inhibitor, βIIV5-3, prolonged their survival by at least 6 weeks, suppressed myocardial fibrosis and inflammation, and delayed the transition from compensated hypertrophy to cardiac dysfunction. In addition, changes in the levels of the Ca²⁺-handling proteins, SERCA2 and the Na⁺/Ca²⁺ exchanger, as well as troponin I phosphorylation, seen in the control-treated hypertensive rats were not observed in the βΙΙPKC-treated rats, suggesting that βΙΙPKC contributes to the regulation of calcium levels in the myocardium. In contrast, treatment with the selective inhibitor of βIPKC, an alternative spliced form of βIIPKC, had no beneficial effects in these rats. We also found that βIIV5-3, but not βIV5-3, improved calcium handling in isolated rat cardiomyocytes and enhanced contractility in isolated rat hearts. In conclusion, our data using an in vivo model of cardiac dysfunction (late-phase hypertrophy), suggest that βIIPKC contributes to the pathology associated with heart failure and thus an inhibitor of βIIPKC may be a potential treatment for this disease.     

Experimental model for heart failure in rats--induction and diagnosis

BACKGROUND: Clinical heart failure is generally preceded by hypertrophy. Many animal models (e. g. toxic heart failure models) do not consider this hypertrophy. We set out to develop a heart failure model in rats by inducing pressure-overload hypertrophy. METHODS: We induced coarctation of the aortic arch with a tantalum clip (0.35 mm internal diameter) In 3-week-old rats (n=17). Starting at seven weeks postoperatively, we measured ejection fraction (EF), fractional shortening (FS), end-systolic (LVESD) and end-diastolic (LVEDD) left ventricular dimensions by echocardiography each week. Heart, lung, and liver specimens were analyzed histopathologically at least eleven weeks after the operation. RESULTS: Contractile function was significantly decreased in hearts from animals with aortic banding (EF: 45+/-5% vs. 73+/-5%, p<0.01; FS: 20+/-3% vs. 35+/-5%, p<0.01). At the same time, left ventricles were dilated (LVEDD: 9.1+/-0.6 mm vs. 7.4+/-0.5 mm; LVESD: 7.3+/-0.6 mm vs. 4.8+/-0.4 mm, p<0.01). These observations were associated with clinical and histopathological changes characteristic for chronic left heart failure. CONCLUSION: Placing a tantalum clip around the aortic arch in 3-week-old rats consistently induces left ventricular decrease in contractile function and dilatation after eleven weeks.     

Therapeutic effects of angiotensin II type 1 receptor blocker at an advanced stage of hypertensive diastolic heart failure

OBJECTIVE: Angiotensin II type 1 receptor blocker (ARB) is increasingly prescribed for the treatment of systolic heart failure with a growing body of clinical evidence. The roles of ARB, however, remain to be clarified in the treatment of diastolic heart failure (DHF), particularly at its advanced stage. This experimental study investigated the effects of ARB administered at an advanced stage of hypertensive DHF. METHODS: Dahl salt-sensitive rats fed an 8% NaCl diet from age 7 weeks represent overt DHF at age 20 weeks, as noted in previous studies (hypertensive DHF model). The DHF model rats were randomly divided into two groups at age 17 weeks when left ventricular diastolic dysfunction, hypertrophy, fibrosis, macrophage infiltration and reactive oxygen species generation were already augmented; six rats treated for 3 weeks with a subdepressor dose of ARB (olmesartan 0.6 mg/kg per day), and six untreated rats. RESULTS: The 3-week administration of ARB significantly decreased the left ventricular end-diastolic pressure in association with attenuation of left ventricular hypertrophy, fibrosis and diastolic dysfunction. Macrophage infiltration was attenuated with decreased gene expression of transforming growth factor-beta1 and monocyte chemoattractant protein-1 in the left ventricular myocardium of the ARB-treated rats. The production of reactive oxygen species also decreased with NADPH oxidase activity. CONCLUSIONS: ARB provides beneficial effects in hypertensive DHF independent of its antihypertensive effects even if initiated at an advanced stage. The beneficial effects are at least partly attributed to the attenuation of inflammatory changes and oxidative stress through the suppression of cytokine and chemokine production and of NADPH oxidase activity.