Cardiomyopathic Hamsters Research Articles

Effect of Waon Therapy on Oxidative Stress in Chronic Heart Failure

A previous report by our team showed that Waon therapy, using a far infrared-ray dry sauna at 60°C, improves cardiac and vascular function in patients with chronic heart failure (CHF). The purpose of the present study was to clarify the effect of Waon therapy on oxidative stress in CHF patients and investigate its mechanism by animal experiments. Forty patients with CHF were divided into control (n=20) and Waon therapy (n=20) groups. All patients received standard optimal medications for CHF. Waon therapy group was treated with Waon therapy daily for 4 weeks. After 4 weeks of Waon therapy, concentrations of hydroperoxide and brain natriuretic peptide (BNP) decreased significantly (hydroperoxide, 422±116 to 327±88U.CARR, P<0.001; BNP, 402±221 to 225±137pg/ml, P<0.001), and the nitric oxide metabolites increased (71.2±35.4 to 92.0±40.5mmol/L, P<0.05). In contrast, none of these variables changed over the 4-week interval in the control group. Furthermore, animal experiments were performed using TO-2 cardiomyopathic hamsters. On immunohistochemistry, cardiac expression of 4-hydroxy-2-nonenal, a marker of oxidative stress, was decreased in the 4-week Waon therapy compared to untreated hamsters. On Western blotting, cardiac expressions of heat shock protein (HSP) 27, manganese superoxide dismutase and HSP32, which reduce oxidative stress, were significantly upregulated in the 4-week Waon therapy compared to untreated hamsters. Waon therapy decreases oxidative stress in patients and hamsters with heart failure.

Chronic Treatment With N-acetylcysteine Improves Cardiac Function but Does Not Prevent Progression of Cardiomyopathy in Syrian Cardiomyopathic Hamsters

Oxidative stress has been postulated to contribute to the onset and development of heart failure (HF). The efficacy of antioxidant therapy in HF, however, remains controversial. This study evaluates the effect of the antioxidant N-acetylcysteine (NAC, 1 g/kg per day) on cardiovascular function in 2- and 6-month-old Bio-TO2 Syrian cardiomyopathic hamsters (SCH) after treatment for 1 month and 5 months with this drug. Endothelial function, systolic blood pressure (SBP), and echocardiographic parameters were evaluated. Age-matched F1-B golden hamsters were used as controls. One month of NAC administration significantly decreased SBP in 2-month-old SCH (n = 5, P < 0.001) without modifying echocardiographic values. Five-month treatment of cardiomyopathic animals with the antioxidant improved the acetylcholine-induced relaxation in aortic rings by 24% (E( Max) value from 45.8% ± 4% to 55.3% ± 2% n = 7, P < .05) but did not modify EC(50) values for the acetylcholine concentration-response curve. In addition, 5-month administration of NAC to SCH increased ejection fraction from 39% ± 4% to 57% ± 4% (n = 11, P < .001) and decreased left ventricular end-diastolic and end-systolic volumes (from 0.38 ± 0.04 mL/100 g body weight (BW) and 0.22 ± 0.03 mL/100 g BW, before, to 0.24 ± 0.04 mL/100 g BW and 0.12 ± 0.03 mL/100 g BW after treatment, P < .01). Cardiac output index also improved after 5 months of treatment, although it did not reach statistical significance. These results suggest that antioxidant therapy alone decreases ventricular dilatation and improves cardiovascular function in this animal model of dilated cardiomyopathy, but it does not prevent the appearance of HF.

Waon Therapy Decreases Oxidative Stress via Upregulation of Heat Shock Protein 27 and Mn-SOD in TO-2 Cardiomyopathic Hamsters

Background: We have reported that Waon therapy reduces oxidative stress and improves cardiac and vascular function in patients with chronic heart failure (CHF). The aim of this study is to clarify the mechanism by which Waon therapy reduces oxidative stress using TO-2 cardiomyopathic hamsters with CHF. Methods: 30-week old TO-2 hamsters with CHF were divided into Waon therapy or control group. In Waon therapy group, they were treated with Waon therapy daily for 4 weeks. In contrast, control group did not take any treatment.

Further studies on the effects of intracrine and extracellular angiotensin II on the regulation of heart cell volume. On the influence of aldosterone and spironolactone

The influence of extracellular and intracellular angiotensin II (Ang II) on the cell volume in the failing heart of cardiomyopathic hamsters (TO2) was further investigated as well as the influence of aldosterone and spironolactone on the Ang II action on cell volume. Measurements of cell width and area of quiescent ventricular cardiomyocytes were performed using a video camera and computer analysis and the relative cell volume was calculated. All measurements of cell volume were performed in the same cell before and after the administration of Ang II (10 − 8 M). The results indicated that: a) the increase in cell volume caused by extracellular Ang II(10 − 8 M) was enhanced in cells incubated with aldosterone (100 nM) for 48 h; b) the effect of aldosterone was abolished by spironolactone (10 − 8 M); c) the decline in cell volume elicited by intracellular administration of Ang II (10 − 8 M) was increased by aldosterone and inhibited by spironolactone; d) the effects of aldosterone and spironolactone were related, in part, to a change in expression of AT1 receptors; and e) the intracellular administration of Ang II reduced the swelling-dependent chloride current (I Clswell). The implications of these findings to the failing heart and myocardial ischemia are discussed.

Thyroid Replacement Therapy and Heart Failure

Heart failure (HF) is a major public health and economic problem in Western countries and is one of the most common causes of hospitalization and death. Coronary artery disease is the underlying cause in more than two thirds of chronic HF patients. By 2020, the World Health Organization projects that ischemic heart disease alone will be the most important global cause of morbidity and mortality. The estimated increases in HF-related morbidity and mortality suggest that our understanding of the pathophysiological mechanisms of this syndrome is inadequate. Interest in the role of thyroid hormones (THs) in HF has increased in recent years. The driving considerations can be summarized as follows: (1) the known effects of THs on contractile and relaxation properties of the heart; (2) experimental findings offering strong support for the hypothesis that TH signaling is critical in preserving cardiac structure and performance under normal conditions and after cardiac injury; and (3) evidence that mildly altered TH function is strongly associated with a worsening prognosis in cardiac patients in general and in HF patients in particular. Diastolic function and systolic function are clearly influenced by THs.1 Ventricular contractile function is also influenced by changes in hemodynamic conditions secondary to TH effects on peripheral vascular tone.1 TH homeostasis preserves positive ventricular-arterial coupling, leading to a favorable balance for cardiac work. A study in rats demonstrated that chronic hypothyroidism alone can eventually lead to HF.2 Other studies suggest reduced cardiac tissue triiodothyronine (T3) levels after myocardial infarction (MI) or with development of hypertension by upregulating type 3 deiodinase (D3), which leads to deactivation of T3 and T4 (thyroxine).3–6 This review highlights a growing body of evidence from animal studies and small-scale clinical trials suggesting that low cellular thyroid activity at the cardiac tissue level may adversely affect HF …

Cardioprotection by a nonerythropoietic, tissue-protective peptide mimicking the 3D structure of erythropoietin

Erythropoietin (EPO), originally identified for its critical hormonal role in regulating production and survival of erythrocytes, is a member of the type 1 cytokine superfamily. Recent studies have shown that EPO has cytoprotective effects in a wide variety of tissues, including the heart, by preventing apoptosis. However, EPO also has undesirable effects, such as thrombogenesis. In the present study, we investigated whether a helix B-surface peptide (HBSP), a nonerythropoietic, tissue-protective peptide mimicking the 3D structure of erythropoietin, protects cardiomyocytes from apoptosis in vitro and in vivo. In cultured neonatal rat cardiomyocytes, HBSP clearly inhibited apoptosis (approximately 80%) induced by TNF-alpha, which was comparable with the effect of EPO, and activated critical signaling pathways of cell survival, including Akt, ERK1/2, and STAT3. Among these pathways, Akt was shown to play an essential role in HBSP-induced prevention of apoptosis, as assessed by using a small interfering RNA approach. In the dilated cardiomyopathic hamster (J2N-k), whose cardiac tissues diffusely expressed TNF-alpha, HBSP also inhibited apoptosis (approximately 70%) and activated Akt in cardiomyocytes. Furthermore, the levels of serum creatine kinase activity and of cardiac expression of atrial natriuretic peptide, a marker of chronic heart failure, were down-regulated in animals treated with HBSP. These data demonstrate that HBSP protects cardiomyocytes from apoptosis and leads to a favorable outcome in failing hearts through an Akt-dependent pathway. Because HBSP does not have the undesirable effects of EPO, it could be a promising alternative for EPO to treat cardiovascular diseases, such as myocardial infarction and heart failure.

TNF-alpha-mediated signal transduction pathway is a major determinant of apoptosis in dilated cardiomyopathy.

Although J2N-k strain of cardiomyopathic hamsters is an excellent model of dilated cardiomyopathy, the presence and mechanisms of apoptosis in the hearts of these genetically modified animals have not been investigated. This study examined the hypothesis that cardiac dysfunction and apoptosis in the cardiomyopathic hamsters were associated with tumour necrosis factor-alpha (TNF-α)-mediated signalling pathway involving the activation of some pro-apoptotic proteins and/or deactivation of some antiapoptotic proteins. Echocardiographic assessment of 31-week-old hamsters indicated an increase in the internal dimension of the left ventricle as well as decreases in the ejection fraction, fractional shortening and cardiac output without any evidence of cardiac hypertrophy. Increased level of TNF-α and apoptosis in cardiomyopathic hearts were accompanied by increased protein content for protein kinase C (PKC) -α and -ɛ isozymes as well as caspases 3 and 9. Phosphorylated protein content for p38 MAPK and NFκB was increased whereas that for Erk1/2, BAD and Bcl-2 was decreased in cardiomyopathic hearts. These results support the view that TNF-α and PKC isozymes may promote apoptosis due to the activation of p38 MAPK and deactivation of Erk1/2 pathways, and these changes may contribute toward the development of cardiac dysfunction in dilated cardiomyopathy.

Vascular ACE and eNOS Expression in Syrian Cardiomyopathic Hamsters

Angiotensin Converting Enzyme (ACE) and endothelial Nitric Oxide Synthase (eNOS) have been implicated in the pathophysiology of heart failure. We evaluated the time‐course expression of ACE and eNOS in aortic tissue from 1‐ to 4‐month‐old Syrian cardiomyopathic hamsters (SCH) to correlate these variables with vascular status. The expression of both genes in 2‐month‐old SCH after one month of treatment with the antioxidant N‐acetylcysteine (NAC, 1g/kg/d) and the β‐blocker‐antioxidant carvedilol (1mg/kg/d) was also evaluated. Age‐matched golden hamsters were used as controls (CT). Total RNA was extracted and gene expression was quantified by Real‐Time RT‐PCR. Our results showed up‐regulation in ACE (1.5 fold) and eNOS (4‐fold) expression in 2‐month‐old SCH when compared to 1‐, 3‐ and 4‐month‐old SCH and to CT. In 2‐month‐old SCH, carvedilol down‐regulated eNOS and ACE gene expressions, whereas NAC down‐regulated eNOS expression without modifying ACE expression. These results suggest that the improvements in CV function observed previously in SCH after early administration of NAC or carvedilol may involve modifications in the expression of ACE and eNOS genes. Supported by NIH‐SCORE S06‐RR 08224.

Sequence analysis of type VI collagen subunits in cardiomyopathic hamster hearts

At the AALAS 2009 meeting, we reported an accumulation of collagen type VI (COL6) in the hearts of cardiomyopathic hamsters (J2N‐k) in comparison with normal controls (J2N‐n). In this study, we determined the cDNA sequences of three subunits of COL6 in the cardiomyopathic hearts of J2N‐k hamsters using a SMARTer RACE cDNA amplification kit (Clontech) with total RNA extracted from a 6‐month‐old J2N‐k male hamster heart and subsequent direct sequencing of the PCR products. Primers were designed from the corresponding mouse and rat sequences. The sequences have been deposited in DDBJ with the accession numbers AB529512, AB529513, and AB530134 for COL6A1, COL6A2, and COL6A3, respectively. NCBI conserved domain searches indicated that all three subunits contained the same vWFA domain structures as their mouse counterparts. In particular, hamster heart COL6A3 lacks three domains in the N‐terminus, as in normal mouse and human hearts. These results suggest that the accumulation of COL6 in J2N‐k hearts is caused by altered expression and/or degradation of COL6, not by its structural abnormality. This work was supported by a grant from the Ministry of Health, Labor, and Welfare of Japan.

Cerebral Malaria: A Vasculopathy

Cerebral Malaria: A Vasculopathy

Targeting Sarcoplasmic Reticulum Ca 2+ Uptake to Improve Heart Failure

The association between disturbed Ca2+ handling within cardiac myocytes and heart failure has been established in many studies of human myocardium from patients with end-stage heart failure undergoing heart transplantation.1–3 The causality is more difficult to prove at this late time point.4 Yet, the observed reduction in the Ca2+ available for myofilament activation and reduced Ca2+ reuptake in the sarcoplasmic reticulum (SR) are obvious targets to improve myocyte contraction and relaxation and, thus, cardiac pump function. Early pharmacotherapy mimicked adrenergic stimulation, the physiological boost of contraction and relaxation, by raising cAMP. Although this worked well, and still does, for acute treatment, the long-term results showed an increase in mortality. Alternative therapy to enhance myofilament sensitivity seems a safer alternative.5,6 Many animal models have been designed to reproduce heart failure in humans allowing study of myocyte remodeling at different stages of disease. The most extensively studied are genetic predisposition (the cardiomyopathic hamster), pressure overload (hypertensive models, aortic banding), myocardial infarction (MI), and tachycardia pacing (in dog or rabbit). Except for genetic model, obvious discrepancies with human disease are the fast time course of the disease and the relative lack of complexity, as, for example, the absence of atherosclerosis in most models of MI. Nevertheless these models have been very useful to demonstrate that very often in vivo cardiac dysfunction paralleled changes in Ca2+ handling, suggesting causality. It should be pointed out that disturbed Ca2+ handling is not always the one or only cause of in vivo heart failure. Loss of myocardium in MI, increased loading on healthy myocardium by the scar tissue, reduced perfusion distal to coronary stenosis, suboptimal preload because of stiffness of the ventricle with hypertrophy, and matrix remodeling are but a few factors that can contribute to global cardiac dysfunction …

Circadian Body Temperature Variability is an Indicator of Poor Prognosis in Cardiomyopathic Hamsters

BackgroundLow body temperature is an independent predictor of poor prognosis in patients with congestive heart failure. The cardiomyopathic hamster develops progressive biventricular dysfunction, resulting in heart failure death at 9 months to 1 year of life. Our goal was to use cardiomyopathic hamsters to examine the relationship between body temperature and heart failure decompensation and death. Methods and ResultsTo this end, we implanted temperature and activity transducers with telemetry into the peritoneal space of 46 male Bio-TO-2 Syrian cardiomyopathic hamsters. Multiple techniques, including computing mean temperature, frequency domain analysis, and nonlinear analysis, were used to determine the most useful method for predicting poor prognosis. Data from 44 hamsters were included in our final analysis. We detected a decline in core body temperature in 98% of the hamsters 8±4 days before death (P < .001). We examined the dominant frequency of temperature variation (ie, the circadian rhythm) by using cosinor analysis, which revealed a significant decrease in the amplitude of the body temperature circadian rhythm 8 weeks before death (0.28°C; 95% CI, 0.26-0.31) compared to baseline (0.36°C; 95% CI, 0.34-0.39; P=.005). The decline in the circadian temperature variation preceded all other evidence of decompensation. ConclusionsWe conclude that a decrease in the amplitude of the body temperature circadian rhythm precedes fatal decompensation in cardiomyopathic hamsters. Continuous temperature monitoring may be useful in predicting preclinical decompensation in patients with heart failure and in identifying opportunities for therapeutic intervention.

Passive Stress in Myofibrils from Cardiomyopathic Hamsters

Dilated cardiomyopahty (DCM) is a frequent heart disease characterized by cardiac dilation and contractile dysfunction. The Bio TO-2 hamster is a genetic animal model of human DCM. The purpose of this research is to study the progression of DCM by comparing over time the passive mechanical properties of left ventricular wall myofibrils from TO-2 hamsters to those from F1B control hamsters. To date, we measured the passive stress-sarcomere length relations for two myofibrils each from experimental and control animals aged 36 weeks. Myofibrils were attached at one end to a glass needle controlled by a motor for stretching, and at the other end to a silicon-nitride nanolever of known stiffness for force measurements. Sarcomere lengths were measured from the myofibrillar striation patterns. Passive stresses in the experimental and control myofibrils were comparable. More passive mechanical experiments will be performed to confirm this result. In a single myofibril, titin is thought to be responsible for essentially all of the passive stress response to stretch (Linke et al., 1994; Bartoo et al., 1997). Titin depletion experiments and titin molecular weight determination will therefore also be performed to detect changes in titin isoform.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Influence of Enalapril Therapy Schedule on the Progression of the Disease in Dilated Cardiomyopathic Syrian Hamsters (Bio TO-2 strain)

The influence of enalapril therapy schedule on the progression of the disease in terms of hemodynamics, cardiac remodeling and survival was assessed in cardiomyopathic Syrian hamsters (CMHs). CMHs (Bio TO-2 dilated strain) were treated orally with enalapril at 20 mg/kg/day from 60 to 200 (early treatment), from 120 to 200 (late treatment) or 120 to 250 (prolonged treatment) days of age. In survival studies, CMHs were treated until 90% of controls are death. Early, late and prolonged treatments significantly decreased mean arterial blood pressure (-23%, -27% and -22%, respectively), but had no effects on cardiac output and stroke volume. Late and prolonged treatments significantly decreased total peripheral resistance (-38% and -24%, respectively), but not early treatment. Only, prolonged treatment significantly decreased left ventricle (LV) end diastolic blood pressure (-60%). Early, late and prolonged treatments significantly decreased LV collagen density (-44%, -31% and -54%, respectively) and LV cavity area (-26%, -21% and -29%, respectively). Survival was significantly improved when enalapril was administered from 120 days of age, but not significantly when administered earlier. In conclusion, enalapril exerted beneficial effects (improvement of cardiac function and prolonged survival) more marked when the treatment was begun late in the evolution of congestive heart failure.

Beneficial Effects of Growth Hormone-Releasing Peptide on Myocardial Oxidative Stress and Left Ventricular Dysfunction in Dilated Cardiomyopathic Hamsters

Growth hormone-releasing peptide (GHRP) may act directly on the myocardium and improve left ventricular (LV) function, suggesting a potential new approach to the treatment of cardiomyopathic hearts. The present study tested the hypothesis that the beneficial cardiac effects of GHRP might include attenuation of myocardial oxidative stress. Dilated cardiomyopathic TO-2 hamsters were injected with GHRP-2 (1 mg/kg) or saline from 6 to 12 weeks of age. F1B hamsters served as controls. Untreated TO-2 hamsters progressively developed LV dilation, wall thinning, and systolic dysfunction between 6 and 12 weeks of age. Marked myocardial fibrosis was apparent in untreated hamsters at 12 weeks of age in comparison with F1B controls. The ratio of reduced to oxidized glutathione (GSH/GSSG) was decreased and the concentration of 4-hydroxynonenal (4-HNE) was increased in the hearts of untreated TO-2 hamsters. Treatment with GHRP-2 attenuated the progression of LV remodeling and dysfunction, as well as myocardial fibrosis, in TO-2 hamsters. GHRP-2 also inhibited both the decrease in the GSH/GSSG ratio and the increase in the concentration of 4-HNE in the hearts of TO-2 hamsters. GHRP-2 can suppress the increase in the level of myocardial oxidative stress, leading to attenuation of progressive LV remodeling and dysfunction in dilated cardiomyopathic hamsters. (Circ J 2010; 74: 163 - 170).

Quinapril: Overview of preclinical data

Quinapril hydrochloride, a new, orally active, nonpeptide, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor, has been studied extensively in a variety of in vitro and in vivo animal models. Quinapril inhibits the contractile and pressor effects of angiotensin I in rabbit aorta and in rats, respectively, and lowers blood pressure in both high- and normal-renin rodent and diuretic-treated dog models of hypertension. No tolerance to the antihypertensive effects of quinapril was noted in spontaneously hypertensive rats treated with quinapril for up to 14 consecutive days. As with other ACE inhibitors, quinapril had virtually no effect on the development of hypertension in the renin-independent one-kidney deoxycorticosterone (DOCA)-salt hypertensive rat. Antihypertensive activity best correlates with the inhibition of tissue (vascular) ACE, and thus the reduction in peripheral vascular resistance associated with plasma and tissue ACE most likely accounts for the therapeutic benefit of quinapril. Preliminary data from a trial of quinapril in cardiomyopathic hamsters show that the drug prevents the anticipated decline in left ventricular contractile function and retards the temporal progression of left ventricular failure. ACE inhibitors have been found to have a lipid-neutral profile, unlike some other classes of antihypertensives. Quinapril is rapidly absorbed and extensively distributed to all tissues except brain. It is rapidly hydrolyzed to quinaprilat, its pharmacologically active diacid form. Metabolism to other compounds is not extensive. Quinapril's preclinical toxicologic profile is similar to that of other ACE inhibitors. Long-term toxicology studies show that quinapril is not teratogenic, carcinogenic, or mutagenic.

Characterization of Morphological, Biochemical and Electrocardiological Assessments in Young Cardiomyopathic Hamsters

Characterization of Morphological, Biochemical and Electrocardiological Assessments in Young Cardiomyopathic Hamsters

Intramuscular VEGF repairs the failing heart: role of host-derived growth factors and mobilization of progenitor cells

Skeletal muscle produces a myriad of mitogenic factors possessing cardiovascular regulatory effects that can be explored for cardiac repair. Given the reported findings that VEGF may modulate muscle regeneration, we investigated the therapeutic effects of chronic injections of low doses of human recombinant VEGF-A(165) (0.1-1 microg/kg) into the dystrophic hamstring muscle in a hereditary hamster model of heart failure and muscular dystrophy. In vitro, VEGF stimulated proliferation, migration, and growth factor production of cultured C2C12 skeletal myocytes. VEGF also induced production of HGF, IGF2, and VEGF by skeletal muscle. Analysis of skeletal muscle revealed an increase in myocyte nuclear [531 +/- 12 VEGF 1 microg/kg vs. 364 +/- 19 for saline (number/mm(2)) saline] and capillary [591 +/- 80 VEGF 1 microg/kg vs. 342 +/- 21 for saline (number/mm(2))] densities. Skeletal muscle analysis revealed an increase in Ki67(+) nuclei in the VEGF 1 microg/kg group compared with saline. In addition, VEGF mobilized c-kit(+), CD31(+), and CXCR4(+) progenitor cells. Mobilization of progenitor cells was consistent with higher SDF-1 concentrations found in hamstring, plasma, and heart in the VEGF group. Echocardiogram analysis demonstrated improvement in left ventricular ejection fraction (0.60 +/- 0.02 VEGF 1 microg/kg vs. 0.45 +/- 0.01 mm for saline) and an attenuation in ventricular dilation [5.59 +/- 0.12 VEGF 1 microg/kg vs. 6.03 +/- 0.09 for saline (mm)] 5 wk after initiating therapy. Hearts exhibited higher cardiomyocyte nuclear [845 +/- 22 VEGF 1 microg/kg vs. 519 +/- 40 for saline (number/mm(2))] and capillary [2,159 +/- 119 VEGF 1 microg/kg vs. 1,590 +/- 66 for saline (number/mm(2))] densities. Myocardial analysis revealed approximately 2.5 fold increase in Ki67+ cells and approximately 2.8-fold increase in c-kit(+) cells in the VEGF group, which provides evidence for cardiomyocyte regeneration and progenitor cell expansion. This study provides novel evidence of a salutary effect of VEGF in the cardiomyopathic hamster via induction of myogenic growth factor production by skeletal muscle and mobilization of progenitor cells, which resulted in attenuation of cardiomyopathy and repair of the heart.

Hemodynamic Alterations in the Coronary Circulation of Cardiomyopathic Hamsters: Age and Ang II–dependent Mechanisms

Background Coronary vasospasms have been reported in the early stages of cardiomyopathy in the Syrian cardiomyopathic hamster (CM; BIO-TO2 strain). It has been proposed these alterations could lead to ischemic heart disease and heart failure. However, the cause of these coronary abnormalities has not been established. In this study, we evaluated coronary hemodynamic to assess the role of Ang-II, reactive oxygen species, and nitric oxide (NO) in the development of these alterations in CM of 1, 2, and 6 months of age. Methods and Results Excised hearts from control (CT) and CM were retroperfused with Krebs-Ringer bicarbonate solution (KRB), and coronary resistance (CR) was determined. The experimental protocol involved sequential infusions of the thromboxane analog U46619 (THX, 0.1 μmol/L), bradykinin (BKN, 10 μmol/L), and sodium nitroprusside (SNP, 10 μmol/L). Similar experiments were conducted after treatment of hearts with N ω -nitro-L-arginine methyl ester (L-NAME, 10 μmol/L). Basal CR increased with age, but no significant differences were observed between CT and CM. Reactivity to THX was increased (69%, P < .05) in 2-month-old CM when compared with CT. This effect was observed concomitantly with a significant reduction (53%, P < .05) in BKN-induced relaxation. The reduction in BKN-dependent relaxation was prevented by treatment for 1 month with the antioxidant N-acetylcysteine (1 g·kg·day), or losartan, an Ang II type 1 receptor blocker (10 mg·kg·day). Losartan also prevented the THX-induced increased reactivity in 2-month-old CM. The BKN-induced relaxation occurred through an L-NAME–sensitive pathway that was impaired with age. SNP dilation was preserved in all animal groups. Conclusions Our results strongly implicate vascular renin-angiotensin-system (RAS) and oxidative stress in endothelial dysfunction and increased reactivity in the early stages of cardiomyopathy in CM. These findings could be relevant to understand the etiology of cardiovascular disorders, in particular, in patients with sarcoglycanopathies.

Cell swelling, impulse conduction, and cardiac arrhythmias in the failing heart. Opposite effects of angiotensin II and angiotensin (1–7) on cell volume regulation

The influence of hypotonic solution on cell volume and electrophysiology properties of the failing heart of cardiomyopathic hamsters (TO-2) was investigated. The results showed an increase in cell volume of quiescent isolated ventricular myocytes by 66% within 30 min. Angiotensin (1-7) [Ang (1-7)] (10(-8) M) administered to isotonic solution, elicited a gradual decline in cell volume and a significant decrease of the swelling-activated chloride current (I (Clswell)). The effect of Ang (1-7) on cell volume was inhibited by ouabain (10(-7) M). Angiotensin II (10(-8) M) caused cell swelling and increased I (Clswell). Experiments performed on isolated left ventricles of cardiomyopathic hamsters at an advanced stage of the disease, indicated that hypotonic solution prepared by diluting the normal Krebs solution by 25%, showed a gradual decrease of conduction velocity, generation of early after depolarizations and block of impulse conduction within 10 min. Implications to myocardial ischemia are discussed.