Prevention of hypertension in DOCA-salt rats by an inhibitor of soluble epoxide hydrolase

Cyclooxygenase and lipoxygenase metabolism of arachidonic acid produces compounds important in cardiovascular control. Further, arachidonic acid can be metabolised by cytochrome p450 to produce epoxyeicosatrienoic acids (EETs). These derivatives are inactivated by soluble epoxide hydrolase (sEH). The potential role of these EETs in hypertension and cardiac remodelling has been determined using the selective sEH inhibitor, N-adamantyl-N'-dodecylurea (ADU), in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Experiments were performed on male Wistar rats following uninephrectomy alone (UNX rats) or uninephrectomy with administration of DOCA (25 mg every fourth day subcutaneously) and 1% NaCl in drinking water (DOCA-salt rats). ADU (10 mg/kg/d subcutaneously) was administered for 2 wk starting 2 wk after surgery. Cardiovascular structure and function were determined using organ wet weights, histological analysis of collagen and inflammation, isolated heart and thoracic aortic ring preparations, and electrophysiological measurements. DOCA-salt hypertensive rats developed hypertension, hypertrophy, perivascular and interstitial fibrosis, endothelial dysfunction, and prolongation of the cardiac action potential duration within 4 wk. Administration of ADU prevented the further increase in systolic blood pressure and left-ventricular wet weight and normalized endothelial function. ADU treatment did not change inflammatory cell infiltration, collagen deposition, or cardiac action potential duration. EETs may be involved in the development of hypertension and endothelial dysfunction in DOCA-salt rats, but not in excessive collagen deposition or electrophysiological abnormalities.     

Prevention of hypertension in DOCA-salt rats by an inhibitor of soluble expoxide hydrolase

Cyclooxygenase and lipoxygenase metabolism of arachidonic acid produces compounds important in cardiovascular diovascular control. Further, arachidonic acid can be metabolised by cytochrome p450 to produce epoxyeicosatrienoic acids (EETs). These derivatives are inactivated by soluble epoxide hydrolase (sEH). The potential role of these EETs in hypertension and cardiac remodelling has been determined using the selective sEH inhibitor, N-adamantyl-N′-dodecylurea (ADU), in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Experiments were performed on male Wistar rats following uninephrectomy alone (UNX rats) or uninephrectomy with administration of DOCA (25 mg every fourth day subcutaneously) and 1% NaCl in drinking water (DOCA-salt rats). ADU (10 mg/kg/d subcutaneously) was administered for 2wk starting 2wk after surgery. Cardiovascular structure and function were determined using organ wet weights, histological analysis of collagen and inflammation, isolated heart and thoracic aortic ring preparation, and electrophysiological measurements. DOCA-salt hypertensive rats developed hypertension, hypertrophy, perivascular and interstitial fibrosis, endothelial dysfunction, and prolongation of the cardiac action potential duration within 4 wk. Administration of ADU prevented the further increase in systolic blood pressure and left-ventricular wet weight and normalized endothelial function. ADU treatment did not change inflammatory cell infiltration, collagen deposition, or cardiac action potential duration. EETs may be involved in the development of hypertension and endothelial dysfunction in DOCA-salt rats, but not in excessive collagen deposition or electrophysiological abnormalities.     

Coronary artery remodeling in a model of left ventricular pressure overload is influenced by platelets and inflammatory cells

Left ventricular hypertrophy (LVH) is usually accompanied by intensive interstitial and perivascular fibrosis, which may contribute to arrhythmogenic sudden cardiac death. The mechanisms underlying the development of cardiac fibrosis are incompletely understood. To investigate the role of perivascular inflammation in coronary artery remodeling and cardiac fibrosis during hypertrophic ventricular remodeling, we used a well-established mouse model of LVH (transverse aortic constriction [TAC]). Three days after pressure overload, macrophages and T lymphocytes accumulated around and along left coronary arteries in association with luminal platelet deposition. Consistent with these histological findings, cardiac expression of IL-10 was upregulated and in the systemic circulation, platelet white blood cell aggregates tended to be higher in TAC animals compared to sham controls. Since platelets can dynamically modulate perivascular inflammation, we investigated the impact of thrombocytopenia on the response to TAC. Immunodepletion of platelets decreased early perivascular T lymphocytes' accumulation and altered subsequent coronary artery remodeling. The contribution of lymphocytes were examined in Rag1(-/-) mice, which displayed significantly more intimal hyperplasia and perivascular fibrosis compared to wild-type mice following TAC. Collectively, our studies support a role of early perivascular accumulation of platelets and T lymphocytes in pressure overload-induced inflammation.     

l-Arginine attenuates cardiovascular impairment in DOCA-salt hypertensive rats

Nitric oxide (NO) is essential for normal function of the cardiovascular system. This study has determined whether chronic administration of l-arginine, the biological precursor of NO, attenuates the development of structural and functional changes in hearts and blood vessels of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Uninephrectomized rats treated with DOCA (25 mg every 4th day sc) and 1% NaCl in the drinking water for 4 wk were treated with l-arginine (5% in food, 3.4 +/- 0.3 g x kg body wt(-1) x day(-1)). Changes in cardiovascular structure and function were determined by echocardiography, microelectrode studies, histology, and studies in isolated hearts and thoracic aortic rings. DOCA-salt hypertensive rats developed hypertension, left ventricular hypertrophy with increased left ventricular wall thickness and decreased ventricular internal diameter, increased inflammatory cell infiltration, increased ventricular interstitial and perivascular collagen deposition, increased passive diastolic stiffness, prolonged action potential duration, increased oxidative stress, and inability to increase purine efflux in response to an increased workload. l-Arginine markedly attenuated or prevented these changes and also normalized the reduced efficacy of norepinephrine and acetylcholine in isolated thoracic aortic rings of DOCA-salt hypertensive rats. This study suggests that a functional NO deficit in blood vessels and heart due to decreased NO synthase activity or increased release of reactive oxygen species such as superoxide may be a key change initiating many aspects of the cardiovascular impairment observed in DOCA-salt hypertensive rats. These changes can be prevented or attenuated by administration of l-arginine.     

Mechanism of the anti-hypertensive property of the naturally occurring phenolic,malabaricone C in DOCA-salt rats

In this study, we studied whether chronic oral administration of the natural antioxidant, malabaricone C (mal C) can reduce blood pressure (BP) and attenuate cardio-vascular remodeling in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The dose of mal C for its anti-hypertensive action was optimized by measuring the systolic BP (SBP). DOCA-salt rats showed very high SBP, associated with organ hypertrophy, collagen depositions, and inflammatory infiltrations in cardiac and aortic sections, reduced plasma total antioxidant status and NO level, and increased levels of TBARS, PGI2 as well as vasoconstrictors (AVP, Big ET, and ET-1). DOCA-salt also reduced smooth muscle- and endothelium-dependent vascular relaxation in rats. Mal C reversed all these changes of the DOCA-salt rats and improved their vascular reactivity. Mal C exerts anti-hypertensive property in DOCA-salt rats by reducing oxidative stress and organ hypertrophy, and improving endothelial and vascular functions. Given that mal C has appreciable natural abundance and is non-toxic to rodents, further studies would help in establishing its medicinal potential against hypertension.     

Chronic administration of hexarelin attenuates cardiac fibrosis in the spontaneously hypertensive rat

Cardiac fibrosis is a hallmark of heart disease and plays a vital role in cardiac remodeling during heart diseases, including hypertensive heart disease. Hexarelin is one of a series of synthetic growth hormone secretagogues (GHSs) possessing a variety of cardiovascular effects via action on GHS receptors (GHS-Rs). However, the role of hexarelin in cardiac fibrosis in vivo has not yet been investigated. In the present study, spontaneously hypertensive rats (SHRs) were treated with hexarelin alone or in combination with a GHS-R antagonist for 5 wk from an age of 16 wk. Hexarelin treatment significantly reduced cardiac fibrosis in SHRs by decreasing interstitial and perivascular myocardial collagen deposition and myocardial hydroxyproline content and reducing mRNA and protein expression of collagen I and III in SHR hearts. Hexarelin treatment also increased matrix metalloproteinase (MMP)-2 and MMP-9 activities and decreased myocardial mRNA expression of tissue inhibitor of metalloproteinase (TIMP)-1 in SHRs. In addition, hexarelin treatment significantly attenuated left ventricular (LV) hypertrophy, LV diastolic dysfunction, and high blood pressure in SHRs. The effect of hexarelin on cardiac fibrosis, blood pressure, and cardiac function was mediated by its receptor, GHS-R, since a selective GHS-R antagonist abolished these effects and expression of GHS-Rs was upregulated by hexarelin treatment. In summary, our data demonstrate that hexarelin reduces cardiac fibrosis in SHRs, perhaps by decreasing collagen synthesis and accelerating collagen degradation via regulation of MMPs/TIMP. Hexarelin-reduced systolic blood pressure may also contribute to this reduced cardiac fibrosis in SHRs. The present findings provided novel insights and underscore the therapeutic potential of hexarelin as an antifibrotic agent for the treatment of cardiac fibrosis.     

Prevention of angiotensin II-induced cardiac remodeling by angiotensin-(1-7)

Cardiac remodeling, which typically results from chronic hypertension or following an acute myocardial infarction, is a major risk factor for the development of heart failure and, ultimately, death. The renin-angiotensin system (RAS) has previously been established to play an important role in the progression of cardiac remodeling, and inhibition of a hyperactive RAS provides protection from cardiac remodeling and subsequent heart failure. Our previous studies have demonstrated that overexpression of angiotensin-converting enzyme 2 (ACE2) prevents cardiac remodeling and hypertrophy during chronic infusion of angiotensin II (ANG II). This, coupled with the knowledge that ACE2 is a key enzyme in the formation of ANG-(1-7), led us to hypothesize that chronic infusion of ANG-(1-7) would prevent cardiac remodeling induced by chronic infusion of ANG II. Infusion of ANG II into adult Sprague-Dawley rats resulted in significantly increased blood pressure, myocyte hypertrophy, and midmyocardial interstitial fibrosis. Coinfusion of ANG-(1-7) resulted in significant attenuations of myocyte hypertrophy and interstitial fibrosis, without significant effects on blood pressure. In a subgroup of animals also administered [d-Ala(7)]-ANG-(1-7) (A779), an antagonist to the reported receptor for ANG-(1-7), there was a tendency to attenuate the antiremodeling effects of ANG-(1-7). Chronic infusion of ANG II, with or without coinfusion of ANG-(1-7), had no effect on ANG II type 1 or type 2 receptor binding in cardiac tissue. Together, these findings indicate an antiremodeling role for ANG-(1-7) in cardiac tissue, which is not mediated through modulation of blood pressure or altered cardiac angiotensin receptor populations and may be at least partially mediated through an ANG-(1-7) receptor.     

Exercise induces renin–angiotensin system unbalance and high collagen expression in the heart of Mas-deficient mice

The renin–angiotensin system (RAS) is involved in the cardiac and vascular remodeling associated with cardiovascular diseases. Angiotensin (Ang) II/AT₁ axis is known to promote cardiac hypertrophy and collagen deposition. In contrast, Ang-(1–7)/Mas axis opposes Ang II effects in the heart producing anti-trophic and anti-fibrotic effects. Exercise training is known to induce cardiac remodeling with physiological hypertrophy without fibrosis. We hypothesize that cardiac remodeling induced by chronic exercise depends on the action of Ang-(1–7)/Mas axis. Thus, we evaluated the effect of exercise training on collagen deposition and RAS components in the heart of FVB/N mice lacking Mas receptor (Mas-KO). Male wild-type and Mas-KO mice were subjected to a moderate-intense swimming exercise training for 6 weeks. The left ventricle (LV) of the animals was sectioned and submitted to qRT-PCR and histological analysis. Circulating and tissue angiotensin peptides were measured by RIA. Sedentary Mas-KO presented a higher circulating Ang II/Ang-(1–7) ratio and an increased ACE2 expression in the LV. Physical training induced in Mas-KO and WT a similar cardiac hypertrophy accompanied by a pronounced increase in collagen I and III mRNA expression. Trained Mas-KO and trained WT presented increased Ang-(1–7) in the blood. However, only in trained-WT there was an increase in Ang-(1–7) in the LV. In summary, we showed that deletion of Mas in FVB/N mice produced an unbalance in RAS equilibrium increasing Ang II/AT₁ arm and inducing deleterious cardiac effects as deposition of extracellular matrix proteins. These data indicate that Ang-(1–7)/Mas axis is an important counter-regulatory mechanism in physical training mediate cardiac adaptations.     

Resolvin-D1 attenuation of angiotensin II-induced cardiac inflammation in mice is associated with prevention of cardiac remodeling and hypertension

AimsDespite the broad pharmacological arsenal to treat hypertension, chronic patients may develop irreversible cardiac remodeling and fibrosis. Angiotensin II, the main peptide responsible for the Renin-Angiotensin-Aldosterone-System, has been closely linked to cardiac remodeling, hypertrophy, fibrosis, and hypertension, and some of these effects are induced by inflammatory mediators. Resolvin-D1 (RvD1) elicits potent anti-inflammatory and pro-resolving effects in various pathological models. In this study, we aimed to examine whether RvD1 ameliorates cardiac remodeling and hypertension triggered by angiotensin II.Methods and resultsAlzet® osmotic mini-pumps filled with angiotensin II (1.5 mg/kg/day) were implanted in male C57BL/6 J mice for 7 or 14 days. RvD1 (3 μg/kg/day, i.p) was administered one day after the surgery and during the complete infusion period. Blood pressure and myocardial functional parameters were assessed by echocardiography. At the end of the experimental procedure, blood and heart tissue were harvested, and plasma and histological parameters were studied. After 7 and 14 days, RvD1 reduced the increase of neutrophil and macrophage infiltration triggered by angiotensin II, and also reduced ICAM-1 and VCAM-1 expression levels. RvD1 also reduced cytokine plasma levels (IL-1β, TNF-α, IL-6, KC, MCP-1), cardiac hypertrophy, interstitial and perivascular fibrosis, and hypertension.ConclusionsThis study unveils novel cardioprotective effects of RvD1 in angiotensin II-induced hypertension and cardiac remodeling by attenuating inflammation and provides insights into a potential clinical application.     

Influence of enalapril on established pressure-overload cardiac hypertrophy in low and normal renin states in female rats

To determine whether effects of angiotensin converting enzyme (ACE) inhibitors on well-established pressure overload-induced cardiac hypertrophy and coronary remodeling depend upon normal plasma renin levels, the influence of enalapril on ventricular mass and coronary vascular resistance (CVR) was determined in a low-renin female rat model of chronic pressure overload, (deoxycorticosterone acetate hypertension, DOCA), and compared to its effect in a normal-renin model, (aortic construction, AC). Six weeks after experiment initiation, plasma renin activity of DOCA-treated rats was reduced to approximately 12% that of sham-treated and AC-treated groups. Enalapril was then added to the drinking water of half the animals in each group for two additional weeks. Comparing experimental groups to controls, this delayed enalapril treatment had 1) no effect on the elevated arterial pressures, 2) no effect on the elevated coronary resistance, and, in the DOCA group, 3) no effect on cardiac hypertrophy. However, this brief enalapril treatment reduced absolute and relative ventricular weights of AC rats. These data suggest that circulating renin is required for the anti-hypertrophic efficacy of late-onset brief treatment with enalapril. Since enalapril-induced reversal of cardiac hypertrophy in AC rats was not accompanied by reversal of coronary remodeling, growth signals other than angiotensin II may be involved in coronary remodeling.     

Antifibrotic activity of an inhibitor of group IIA secretory phospholipase A2 in young spontaneously hypertensive rats

The development of fibrosis in the chronically hypertensive heart is associated with infiltration of inflammatory cells and cardiac hypertrophy. In this study, an inhibitor of the proinflammatory enzyme, group IIA human secretory phospholipase A2 (sPLA2-IIA), has been found to prevent collagen deposition as an important component of cardiovascular remodeling in a rat model of developing chronic hypertension. Daily treatment of young male spontaneously hypertensive rats (SHR) with an sPLA2-IIA inhibitor (KH064, 5-(4-benzyloxyphenyl)-4S-(phenyl-heptanoylamino)-pentanoic acid, 5 mg/kg/day p.o.) prevented increases in the content of perivascular (SHR 20.6 +/- 0.9%, n = 5; SHR+KH064 14.0 +/- 1.2%, n = 5) and interstitial (SHR 7.9 +/- 0.3%, n = 6; SHR+KH064 5.4 +/- 0.7%, n = 6) collagen in the left ventricle of rat hearts, but did not affect numbers of infiltrating monocytes/macrophages, left ventricular hypertrophy (SHR 2.88 +/- 0.08, n = 12; SHR+KH064 3.09 +/- 0.08 mg/g body weight, n = 9), increased systolic blood pressure, or thoracic aortic responses. This selective antifibrotic activity suggests that sPLA2-IIA may have an important but specific role in cardiac fibrosis, and that its inhibitors could be useful in dissecting molecular pathways leading to fibrotic conditions.     

A role for cardiotrophin-1 in myocardial remodeling induced by aldosterone

Hyperaldosteronim is associated with left ventricular (LV) hypertrophy (LVH) and fibrosis. Cardiotrophin (CT)-1 is a cytokine that induces myocardial remodeling. We investigated whether CT-1 mediates aldosterone (Aldo)-induced myocardial remodeling in two experimental models. Wistar rats were treated with Aldo-salt (1 mg·kg(-1)·day(-1)) with or without spironolactone (200 mg·kg(-1)·day(-1)) for 3 wk. Wild-type (WT) and CT-1-null mice were infused with Aldo (1 mg·kg(-1)·day(-1)) for 3 wk. Hemodynamic parameters were analyzed. LVH, fibrosis, inflammation, and CT-1 expression were evaluated in both experimental models by histopathological analysis, RT-PCR, Western blot analysis, and ELISA. Hypertensive Aldo-treated rats exhibited increased LV end-diastolic pressure and -dP/dt compared with controls. The cardiac index, LV cross-sectional area and wall thickness, cardiomyocyte size, collagen deposition, and inflammation were increased in Aldo-salt-treated rats. Myocardial expression of molecular markers assessing LVH and fibrosis as well as CT-l levels were also augmented by Aldo-salt. Spironolactone treatment reversed all the above effects. CT-1 correlated positively with hemodynamic, histological, and molecular parameters showing myocardial remodeling. In WT and CT-1-null mice, Aldo infusion did not modify blood pressure. Whereas Aldo treatment induced LVH, fibrosis, and inflammation in WT mice, the mineralocorticoid did not provoke cardiac remodeling in CT-1-null mice. In conclusion, in experimental hyperaldosteronism, the increase in CT-1 expression was associated with parameters showing LVH and fibrosis. CT-1-null mice were resistant to Aldo-induced LVH and fibrosis. These data suggest a key role for CT-1 in cardiac remodeling induced by Aldo independent of changes in blood pressure levels.     

Angiotensin-(1-7) abrogates mitogen-stimulated proliferation of cardiac fibroblasts

Previous studies showed that angiotensin-(1-7) [Ang-(1-7)] attenuates cardiac remodeling by reducing both interstitial and perivascular fibrosis. Although a high affinity binding site for Ang-(1-7) was identified on cardiac fibroblasts, the molecular mechanisms activated by the heptapeptide hormone were not identified. We isolated cardiac fibroblasts from neonatal rat hearts to investigate signaling pathways activated by Ang-(1-7) that participate in fibroblast proliferation. Ang-(1-7) reduced (3)H-thymidine, -leucine and -proline incorporation into cardiac fibroblasts stimulated with serum or the mitogen endothelin-1 (ET-1), demonstrating that the heptapeptide hormone decreases DNA, protein and collagen synthesis. The reduction in DNA synthesis by Ang-(1-7) was blocked by the AT((1-7)) receptor antagonist [d-Ala(7)]-Ang-(1-7), showing specificity of the response. Treatment of cardiac fibroblasts with Ang-(1-7) reduced the Ang II- or ET-1-stimulated increase in phospho-ERK1 and -ERK2. In contrast, Ang-(1-7) increased dual-specificity phosphatase DUSP1 immunoreactivity and mRNA, suggesting that the heptapeptide hormone increases DUSP1 to reduce MAP kinase phosphorylation and activity. Incubation of cardiac fibroblasts with ET-1 increased cyclooxygenase 2 (COX-2) and prostaglandin synthase (PGES) mRNAs, while Ang-(1-7) blocked the increase in both enzymes, suggesting that the heptapeptide hormone alters the concentration and the balance between the proliferative and anti-proliferative prostaglandins. Collectively, these results indicate that Ang-(1-7) participates in maintaining cardiac homeostasis by reducing proliferation and collagen production by cardiac fibroblasts in association with up-regulation of DUSP1 to reduce MAP kinase activities and attenuation of the synthesis of mitogenic prostaglandins. Increased Ang-(1-7) or agents that enhance production of the heptapeptide hormone may prevent abnormal fibrosis that occurs during cardiac pathologies.     

Beta-1 adrenergic receptor antisense-oligodeoxynucleotides ameliorates left ventricular remodeling in 2-Kidney, 1-Clip rats

Gene therapy has been applied to reduce blood pressure in rats. However, little is known about the effects of gene therapy on both blood pressure and left ventricular (LV) remodeling. This study was designed to compare the antihypertensive effect of ss(1) adrenergic receptor antisense oligodeoxynucleotides (ss(1)- AS-ODN) by delivery with the different charge ratios cationic liposomes DOTAP/DOPE and its impact on the LV remodeling in rats with 2-Kidney, 1-Clip (2K1C) Hypertension. Five charge ratios of liposome/ODN were tested in 2K1C rats. There was hypertension, cardiac dysfunction, LV hypertrophy and LV collagen deposition in 2K1C rats. On the basis of the magnitude and duration of hypotension, 2.0 was determined to be the optimal charge ratio, which decreased blood pressure by up to 39 mm Hg for 27 days. ss(1)-AS-ODN preserved cardiac function and inhibited LV mass and LV interstitial collagen deposition. In conclusion, cationic liposomes DOTAP/DOPE improve the antihypertensive effects of ss(1)-AS-ODN in renovascular hypertension and 2.0 were determined to be the optimal charge ratio. This study demonstrated that cardiac ss(1)-AR played a key role in LV remodeling and ss1-AS-ODN ameliorates cardiac dysfunction and LV remodeling.     

Chronic infusion of angiotensin-(1-7) into the lateral ventricle of the brain attenuates hypertension in DOCA-salt rats

Angiotensin-(ANG)-(1-7) is known by its central and peripheral actions, which mainly oppose the deleterious effects induced by accumulation of ANG II during pathophysiological conditions. In the present study we evaluated whether a chronic increase in ANG-(1-7) levels in the brain would modify the progression of hypertension. After DOCA-salt hypertension was induced for seven days, Sprague-Dawley rats were subjected to 14 days of intracerebroventricular (ICV) infusion of ANG-(1-7) (200 ng/h, DOCA-A7) or 0.9% sterile saline. As expected, on the 21st day, DOCA rats presented increased mean arterial pressure (MAP) (≈40%), and impaired baroreflex control of heart rate (HR) and baroreflex renal sympathetic nerve activity (RSNA) in comparison with that in normotensive control rats (CTL). These changes were followed by an overactivity of the cardiac sympathetic tone and reduction of the cardiac parasympathetic tone, and exaggerated mRNA expression of collagen type I (≈9-fold) in the left ventricle. In contrast, DOCA rats treated with ANG-(1-7) ICV had an improvement of baroreflex control of HR, which was even higher than that in CTL, and a restoration of the baroreflex control of RSNA, the balance of cardiac autonomic tone, and normalized mRNA expression of collagen type I in the left ventricle. Furthermore, DOCA-A7 had MAP lowered significantly. These effects were not accompanied by significant circulating or cardiac changes in angiotensin levels. Taken together, our data show that chronic increase in ANG-(1-7) in the brain attenuates the development of DOCA-salt hypertension, highlighting the importance of this peptide in the brain for the treatment of cardiovascular diseases.     

Angiotensin II-induced sudden arrhythmic death and electrical remodeling

Rats harboring the human renin and angiotensinogen genes (dTGR) feature angiotensin (ANG) II/hypertension-induced cardiac damage and die suddenly between wk 7 and 8. We observed by electrocardiogram (ECG) telemetry that ventricular tachycardia (VT) is a common terminal event in these animals. Our aim was to investigate electrical remodeling. We used ECG telemetry, noninvasive cardiac magnetic field mapping (CMFM) at wk 5 and 7, and performed in vivo programmed electrical stimulation at wk 7. We also investigated whether or not losartan (Los; 30 mg x kg(-1) x day(-1)) would prevent electrical remodeling. Cardiac hypertrophy and systolic blood pressure progressively increased in dTGR compared with Sprague-Dawley (SD) controls. Already by wk 5, untreated dTGR showed increased perivascular and interstitial fibrosis, connective tissue growth factor expression, and monocyte infiltration compared with SD rats, differences that progressed through time. Left-ventricular mRNA expression of potassium channel subunit Kv4.3 and gap-junction protein connexin 43 were significantly reduced in dTGR compared with Los-treated dTGR and SD. CMFM showed that depolarization and repolarization were prolonged and inhomogeneous. Los ameliorated all disturbances. VT could be induced in 88% of dTGR but only in 33% of Los-treated dTGR and could not be induced in SD. Untreated dTGR show electrical remodeling and probably die from VT. Los treatment reduces myocardial remodeling and predisposition to arrhythmias. ANG II target organ damage induces VT.     

Increased calcium influx mediates increased cardiac stiffness in hyperthyroid rats

Cardiac remodeling (hypertrophy and fibrosis) and an increased left ventricular diastolic stiffness characterize models of hypertension such as the SHR and DOCA-salt hypertensive rats. By contrast, hyperthyroidism induces hypertrophy and hypertension, yet collagen expression and deposition is unchanged or decreased, whereas diastolic stiffness is increased. We determined the possible role of increased calcium influx in the development of increased diastolic stiffness in hyperthyroidism by administering verapamil (15 mg/[kg x d] orally) to rats given triiodothyronine (T3) (0.5 mg/[kg x d] subcutaneously for 14 d). Administration of T3 significantly increased body temperature (control: 36.7 +/- 0.2 degrees C; T3: 39.6 +/- 0.2 degrees C), left ventricular wet weight (control: 2.09 +/- 0.02 mg/kg; T3 3.07 +/- 0.07 mg/kg), systolic blood pressure (control: 128 +/- 5 mmHg; T3: 156 +/- 4 mmHg), and left ventricular diastolic stiffness (control: 20.6 +/- 2.0; T3: 28.8 +/- 1.4). Collagen content of the left ventricle was unchanged. Contractile response to noradrenaline in thoracic aortic rings was reduced. Relaxation in response to acetylcholine (ACh) was also reduced in T3-treated rats, whereas sodium nitroprusside response was unchanged. Verapamil treatment of hyperthyroid rats completely prevented the increased diastolic stiffness and systolic blood pressure while attenuating the increased body temperature and left ventricular weight; collagen content remained unchanged. ACh response in thoracic aortic rings was restored by verapamil. Thus, in hyperthyroid rats, an increased calcium influx is a potential mediator of the increased diastolic stiffness independent of changes in collagen.     

Paeoniflorin attenuates pressure overload-induced cardiac remodeling via inhibition of TGFβ/Smads and NF-κB pathways

Cardiac remodeling is a key determinant in the clinical course and outcome of heart failure and characterized by cardiac hypertrophy, fibrosis, cardiomyocyte apoptosis and inflammation. The anti-inflammatory, anti-apoptotic and anti-fibrotic effects of paeoniflorin have been identified in various types of tissue and cells. However, the role of paeoniflorin in cardiac remodeling remains unclear. We performed aortic banding (AB) in mice to induce a cardiac remodeling model in response to pressure overload. Paeoniflorin (20 mg/kg) was administered by daily intraperitoneal (i.p.) injection. Paeoniflorin treatment promoted the survival rate and improved cardiac function of mice at 8 weeks post surgery. AB-induced cardiac hypertrophy, as assessed by heart weight, gross heart, HE and WGA staining, cross-sectional area of cardiomyocyte and mRNA expresssion of hypertrophic makers, was attenuated by paeoniflorin. Paeoniflorin also inhibited collagen deposition, expression of TGFβ, CTGF, collagen Iα and collagen IIIα, and phosphorylation of Smad2 and Smad3 in the heart exposed to pressure overload. Cardiomyocyte apoptosis and induction of Bax and cleaved caspase3 in response to AB were suppressed by paeoniflorin. Furthermore, paeoniflorin decreased the quantity of CD68+ cells, protein levels of TNF-α and IL-1β, and phosphorylation of IκBα and NFκB-p65 in the heart after AB. In conclusion, paeoniflorin attenuated cardiac hypertrophy, fibrosis, apoptosis and inflammation, and improved left ventricular function in pressure overloaded mice. The cardioprotective effect of paeoniflorin is associated with the inhibition of TGFβ/Smads and NF-κB pathways.