Heart Failure In Cardiomyopathic Hamsters Research Articles

Alterations in adhesion junction precede gap junction remodelling during the development of heart failure in cardiomyopathic hamsters

The intercalated disc (ID) contains two complexes, the adhesion junction (AJ) and the gap junction (GJ). We studied ID remodelling and its potential role in arrhythmogenesis and investigated the effects of olmesartan on ID remodelling during development of heart failure (HF) in UM-X7.1 cardiomyopathic hamsters. The UM-X7.1 hamsters showed left ventricular (LV) hypertrophy by the age of 10-15 weeks and a moderate impairment in LV contractility at 20 weeks. At age 10-15 weeks, 10-20% of the hamsters died suddenly without HF, and ventricular tachycardia (VT)/ventricular fibrillation (VF) was induced in ∼30% of hamsters. Electron microscopy showed that density linking cell-to-cell adhesion was irregular and unclearly defined, and filamentous structures attached to electron-dense components were arranged in disorder. Western blotting showed that the total cellular expression level of β-catenin was decreased, and expression of nuclear β-catenin, which functions as a T-cell factor/lymphocyte enhancer binding factor transcriptional activator, was also remarkably decreased. At age 20 weeks, LV connexin43 expression showed a remarkable decrease, and the VT/VF induction rate was ∼90%. In UM-X7.1 hamsters, olmesartan improved abnormal ID ultrastructural changes, attenuated the decrease of total cellular and nuclear β-catenin expression, decreased VT/VF induction, and improved survival rate. These results suggest that changes in AJ protein precede connexin43 GJ alterations, and ID remodelling might contribute to arrhythmogenesis during the development of HF. Angiotensin receptor blockade might be a new therapy for lethal ventricular arrhythmia by modulating both AJ and GJ remodelling.

Altered expression of connexin43 contributes to the arrhythmogenic substrate during the development of heart failure in cardiomyopathic hamster

Heart failure is known to predispose to life-threatening ventricular tachyarrhythmias even before compromising the systemic circulation, but the underlying mechanism is not well understood. The aim of this study was to clarify the connexin43 (Cx43) gap junction remodeling and its potential role in the pathogenesis of arrhythmias during the development of heart failure. We investigated stage-dependent changes in Cx43 expression in UM-X7.1 cardiomyopathic hamster hearts and associated alterations in the electrophysiological properties using a high-resolution optical mapping system. UM-X7.1 hamsters developed left ventricular (LV) hypertrophy by ages 6 approximately 10 wk and showed a moderate reduction in LV contractility at age 20 wk. Appreciable interstitial fibrosis was recognized at these stages. LV mRNA and protein levels of Cx43 in UM-X7.1 were unaffected at age 10 wk but significantly reduced at 20 wk. The expression level of Ser255-phosphorylated Cx43 in UM-X7.1 at age 20 wk was significantly greater than that in control golden hamsters at the same age. In UM-X7.1 at age 10 wk, almost normal LV conduction was preserved, whereas the dispersion of action potential duration was significantly increased. UM-X7.1 at age 20 wk showed significant reduction of cardiac space constant, significant decrease in conduction velocity, marked distortion of activation fronts, and pronounced increase in action potential duration dispersion. Programmed stimulation resulted in sustained ventricular tachycardia or fibrillation in UM-X7.1. LV activation during polymorphic ventricular tachycardia was characterized by multiple phase singularities or wavebreaks. During the development of heart failure in the cardiomyopathic hamster, alterations of Cx43 expression and phosphorylation in concert with interstitial fibrosis may create serious arrhythmogenic substrate through an inhibition of cell-to-cell coupling.

The Role of Anserine During the Development of Heart Failure in Cardiomyopathic Hamster

The Role of Anserine During the Development of Heart Failure in Cardiomyopathic Hamster

Recombinant bovine growth hormone-induced reduction of atrial natriuretic peptide is associated with improved left ventricular contractility and reverse remodeling in cardiomyopathic UM-X7.1 hamsters with congestive heart failure

Objective To assess the effect of short-term treatment with GH on left ventricular contractility and remodeling, after the development of heart failure in cardiomyopathic hamsters (CMH). Design Two groups of 200-day-old UM-X7.1 CMH received daily subcutaneous injections of recombinant bovine (rb) GH (1 mg/kg/day) or 0.9% NaCl for 40 days. Golden Syrian hamsters (GSH) were used as controls. At 240-day-old, the hamsters were randomly subjected to (i) assessment of left ventricular systolic function in a Langendorff perfused mode followed by the determination of the passive diastolic pressure–volume relationship and morphometric measurements; (ii) assessment of left ventricular mRNA expression of genes belonging to the fetal gene program including atrial (ANP) and brain (BNP) natriuretic peptides and cardiac myosin heavy chain isoforms and of the circulating levels of the natriuretic peptides. Results Hearts from CMH were hypertrophied and dilated ( p < 0.05) compared to hearts from GSH, along with a ∼10-fold increase in the circulating ANP and BNP levels. Left ventricular BNP and ANP mRNAs were elevated by 2- and 3-fold, respectively, compared to GSH. rbGH reduced both ANP mRNA and ANP circulating levels by 34% ( p < 0.01) but did not significantly modulate BNP levels. This effect was associated with a preserved systolic function and reverse remodeling as assessed by a leftward shift of the passive diastolic pressure–volume relationship indicating reduced ventricular dilatation. Conclusions The data show that a short-term administration of GH in the terminal phase of the disease confers cardioprotection by attenuating systolic dysfunction and by inducing beneficial reverse remodeling.

Gap Junction Remodeling is An Important Arrhythmogenic Substrate During the Development of Heart Failure in Cardiomyopathic Hamster

Lethal ventricular arrhythmias often occur during the development of heart failure. Differences in the distribution of gap junction are considered to be an important factor in the origin of reentrant arrhythmias. We investigated the alterations in connexin (Cx)43 during the development of heart failure in UM-X7.1 cardiomyopathic hamster (CM) hearts. We analyzed Cx43 expressions (protein and mRNA) of the left ventricular (LV) myocardium by western blotting and RT-PCR. Echocardiographic and electrophysiological data were obtained. In CM, LV hypertrophy had developed at 10w, and LV global hypokinesis at 20w. In CM of 20w, random reentry was easily induced by programmed pacing, and conduction velocity was remarkably decreased in CM. The interstitial fibrosis was significantly increased in CM compared with G at 20w. The relative expression level of Cx43 protein and mRNA were significantly lower in CM at 20w than in G (0.52±0.29 vs 1.20±0.12, 0.58±0.14 vs 0.87±0.12, p<0.05, respectively). The relative expression level of serine255-phosphorylated Cx43, which initiates the down-regulation of gap junctional intercellular communication, was markedly increased in CM (1.1±0.4) compared with G (0.4±0.4, p<0.01) at 20w. Conclusions: In cardiomyopathic hamster hearts, in addition to an increase of interstitial fibrosis, downregulation and abnormal serine-phosphorylation of Cx43 may result in abnormal cell-to-cell communication and alter the electrophysiologic properties of the ventricle, leading to the initiation and perpetuation of ventricular arrythmias.

Gap junction remodeling is an arrhythmogenic substrate during the development of heart failure in cardiomyopathic hamster

Differences in the distribution of gap junctions are considered to be an important factor in the origin of reentrant arrhythmias. We investigated the alterations in connexin (Cx)43 during development of heart failure in UM-X7.1 cardiomyopathic hamster (CM). We analyzed Cx43 expressions of the left ventricular (LV) myocardium at age of 6, 10, and 20w. Echocardiographic and ECG monitoring data were obtained. Results: In CM, LV hypertrophy had developed at 10w, and LV global hypokinesis at 20w. QRS interval was markedly prolonged compared with golden hamster (G), and polymorphic ventricular tachycardia was easily induced by burst pacing at 20w of CM. The interstitial fibrosis was significantly increased in CM (8.5 ± 2.6%) compared with G (1.9 ± 1.1%, p < 0.05) at 20w. The relative expression level of Cx43 protein and mRNA were significantly lower in CM at 20w than in G (0.52 ± 0.29 vs 1.20 ± 0.12, 0.58 ± 0.14 vs 0.87 ± 0.12, p < 0.05, respectively). The relative expression level of serine255-phosphorylated Cx43, which initiates the down-regulation of gap junctional intercellular communication, was markedly increased in CM (1.1 ± 0.4) compared with G (0.4 ± 0.4, p < 0.01) at 20w. Serine255-phosphorylated Cx43 was overexpressed at cytoplasmic area in CM. Conclusions: In cardiomyopathic hearts, in addition to interstitial fibrosis, downregulation and abnormal serine-phosphorylation of Cx43 may result in abnormal cell-to-cell communication and alter the electrophysiologic properties of the ventricle, leading to the initiation and perpetuation of ventricular arrythmias.

Simvastatin preserves cardiac function in genetically determined cardiomyopathy.

Endothelial dysfunction characterizes heart failure (HF). Simvastatin (Sim) increases endothelial nitric oxide (NO) independent of lipid-lowering. We evaluated the effect of Sim on cardiac function, apoptosis, and NO availability in HF. Five-month-old cardiomyopathic (CM) hamsters were divided into 2 groups: Sim (20 mg/kg, 6 weeks, n = 6) and Untreated (n = 6). Age-matched normal hamsters served as controls (n = 6). Serial echocardiograms were performed to measure LV function. Myocardial apoptosis, eNOS, and capillary density were measured at 6 weeks. Cardiomyopathic hamsters had lower LV shortening fraction (SF) compared with controls (17 +/- 3% vs 59 +/- 2%), higher LV end-diastolic volume (30 +/- 3 vs 6 +/- 2 mL/m2), and lower LV mass/volume ratio (0.5 +/- 0.04 vs 0.72 +/- 0.02 mg/ml, P < 0.001). During follow-up, SF decreased (9 +/- 2%) and LV volume increased (38 +/- 1 mL/m2) in untreated hamsters (P < 0.05 from baseline) but did not change significantly in the Sim group (P < 0.05 vs untreated). Myocardial caspase-3 activity was higher and apoptotic nuclear density was lower in Sim compared with untreated CM hamsters (0.072 +/- 0.02% vs 0.107 +/- 0.03%, P < 0.01). Myocardial capillary density was highest in the Sim group (P < 0.05). eNOS expression was not different between groups. Sim retards the progression of HF in CM hamsters. This may be related to an increase in coronary microvasculature, increase in NO availability, and decreased apoptosis.

Chronic phospholamban inhibition prevents progressive cardiac dysfunction and pathological remodeling after infarction in rats.

Ablation or inhibition of phospholamban (PLN) has favorable effects in several genetic murine dilated cardiomyopathies, and we showed previously that a pseudophosphorylated form of PLN mutant (S16EPLN) successfully prevented progressive heart failure in cardiomyopathic hamsters. In this study, the effects of PLN inhibition were examined in rats with heart failure after myocardial infarction (MI), a model of acquired disease. S16EPLN was delivered into failing hearts 5 weeks after MI by transcoronary gene transfer using a recombinant adeno-associated virus (rAAV) vector. In treated (MI-S16EPLN, n = 16) and control (MI-saline, n = 18) groups, infarct sizes were closely matched and the left ventricle was similarly depressed and dilated before gene transfer. At 2 and 6 months after gene transfer, MI-S16EPLN rats showed an increase in left ventricular (LV) ejection fraction and a much smaller rise in LV end-diastolic volume, compared with progressive deterioration of LV size and function in MI-saline rats. Hemodynamic measurements at 6 months showed lower LV end-diastolic pressures, with enhanced LV function (contractility and relaxation), lowered LV mass and myocyte size, and less fibrosis in MI-S16EPLN rats. Thus, PLN inhibition by in vivo rAAV gene transfer is an effective strategy for the chronic treatment of an acquired form of established heart failure.

Effects of mibefradil, a T- and L-type calcium channel blocker, on cardiac remodeling in the UM-X7.1 cardiomyopathic hamster.

Abnormalities of T-type calcium channel function reported to occur in the transition phase to heart failure in the hamster cardiomyopathy may contribute to progression of the disease. We tested the hypothesis that chronic exposure to mibefradil, a selective T-type calcium channel blocker, improves the deleterious cardiac remodeling observed in this condition. In the present study, 40 normal (N) and 40 UM-X7.1 cardiomyopathic hamsters (CMH), aged 180 days, were treated daily by gavage for 21 days with mibefradil (30 mg/Kg). Eight to 10 animals from each group were sacrificed at the end of the treatment period while the remainder were followed for an additional 30 days without treatment (washout period). Hearts were harvested, fixed with 10%-buffered paraformaldehyde and then cut in half down the middle. Several slices were dehydrated, embedded in paraffin and stained with Masson Trichrome. Wall thickness and dilatation index of the left ventricle were estimated by planimetry. Myocardial capillary density was also computed. The greater heart weight/body weight ratio seen in untreated CMH (7.7 +/- 0.4 vs 5.5 +/- 0.2 in N, p < 0.05) was improved with mibefradil. The dilatation index averaged 0.504 +/- 0.04 in N was increased in untreated CMH (0.566 +/- 0.03) and ameliorated in mibefradil-treated CMH. The 1-month washout period led to further deterioration of the dilatation index in untreated and mibefradil-treated CMH. Capillary density averaged 10,000 +/- 781 per mm2 in hearts from untreated N hamsters and 8,830 +/- 795 per mm2 in untreated CMH (p = NS). Chronic exposure to mibefradil resulted in a significant reduction of capillary density in both N and CMH hearts. Following the 1-month washout period, the change in myocardial capillary density associated with mibefradil was no longer detectable. In conclusion, chronic exposure to mibefradil, a T- and L-type calcium channel blocker, exerts opposite effects during the transition phase to heart failure in CMH, improving the deleterious left ventricular remodeling in UM-X7.1 hamsters and reducting myocardial capillary density independently of the disease process.

Alterations in cardiac SR Ca(2+)-release channels during development of heart failure in cardiomyopathic hamsters.

The cardiomyopathic Syrian hamster develops a progressive cardiomyopathy characterized by cellular necrosis, hypertrophy, cardiac dilatation, and congestive heart failure. This study aimed to identify alterations in cardiac mechanical function and in the cellular content of sarcoplasmic reticulum (SR) Ca(2+)-release channels (ryanodine receptors, RyR) in the heart of the UM-X7.1 cardiomyopathic hamster during the development of heart failure. Experimental and healthy control hamsters were examined at 8, 18, and 28 wk of age. The UM-X7.1 hamsters had developed left ventricular (LV) hypertrophy at 8 wk and a marked LV dilatation at 18-28 wk. During the latter stage, the UM-X7.1 hamster hearts showed global hypokinesis. Equilibrium binding assays of high-affinity sites for [3H]ryanodine were performed in ventricular homogenate preparations. There was no significant difference between the two groups in the maximum number of [3H]ryanodine binding sites (Bmax) at either 8 or 18 wk of age, although the cardiac pump function was impaired in UM-X7.1 hamsters at 18 wk of age. By 28 wk, Bmax was significantly lower in the UM-X7.1 hamsters. Quantitative immunoblot assay revealed that the content of RyR protein in cardiomyopathic hearts, which was increased at the early stage, declined to below normal as heart failure advanced. These results suggest that the number of RyR in the UM-X7.1 cardiomyopathic hamsters was preserved at both the hypertrophic and early stages of heart failure with a possibly compensatory increase in the level of protein expression, although the cardiac function already showed a tendency to be impaired.

Assessment of compensatory mechanism at the late stage of congestive heart failure in cardiomyopathic hamster: T.Ryoke, S.Fukuta, T.Itagaki, T.Yoshinaga, K.Matsuo, R.Kusukawa. Department of Internal Med. Yamaguchi Univ., Ube, Japan

Assessment of compensatory mechanism at the late stage of congestive heart failure in cardiomyopathic hamster: T.Ryoke, S.Fukuta, T.Itagaki, T.Yoshinaga, K.Matsuo, R.Kusukawa. Department of Internal Med. Yamaguchi Univ., Ube, Japan

Interactions among the Effects of Aging, Chronic Disease, and Stress on Adrenocortical Function in Syrian Hamsters*

This study examined the effects of aging and chronic congestive heart failure on plasma corticosterone and cortisol levels in hamsters. It also assessed the effects of aging and heart failure on glucocorticoid responses to acute and chronic stress. Aging in healthy hamsters increased plasma cortisol levels, decreased corticosterone levels, and did not change total glucocorticoid levels. A similar pattern occurred as cardiomyopathic (CM) hamsters aged, until they developed severe heart failure. Plasma cortisol levels fell in CM hamsters with severe heart failure, and corticosterone levels remained low, so total glucocorticoid levels fell. Adrenocortical function similarly declined in very old healthy hamsters near the ends of their lives. Adrenocortical responses to acute and chronic stress were diminished in old healthy hamsters, and heart failure in CM hamsters also reduced the glucocorticoid responses to chronic stress. However, heart failure greatly enhanced the cortisol and total glucocorticoid responses to acute stress, but not that of corticosterone. These data suggest a number of conclusions. First, aging clearly changes the the ratio of corticosterone to cortisol in hamster plasma without changing total glucocorticoid levels and blunts adrenocortical responses to acute and chronic stress. Second, ill health, in the form of severe heart failure in CM hamsters and very old age in health hamsters, decreases adrenocortical function. At the same time, heart failure greatly enhances cortisol responses to acute stress. These results indicate that aging and chronic disease in hamsters have many similar effects on adrenocortical function, but that disease alone sensitizes them to the effects of acute stress.

The effect of dobutamine on myocardial performance and high-energy phosphate metabolism at different stages of heart failure in cardiomyopathic hamsters: A 31P MRS study

Dobutamine has been shown to exert disparate clinical effects in patients with cardiomyopathy and heart failure. This study evaluated the effects of dobutamine on hemodynamics and energetics in isolated, perfused myopathic hamster hearts at a moderate and advanced stage of heart failure. Biochemical changes were correlated with left ventricular developed pressure, coronary flow, and myocardial oxygen consumption. During dobutamine treatment left ventricular developed pressure increased in the control and moderate heart failure group 28.0 ± 1.0% and 114.2 ± 11.6%, respectively. Myocardial oxygen consumption increased 50.1 ± 9.1% and 45.5 ± 16.0%, respectively. There were no significant changes of left ventricular developed pressure and myocardial oxygen consumption in the advanced heart failure group. Inorganic phosphate (P i) increased in the control group from 6.8 ± 0.5 to 11.4 ± 1.2 mmol ( p < 0.005) and in the advanced heart failure group from 10.4 ± 1.1 to 15.3 ± 1.2 mmol ( p < 0.01). Phosphocreatine (PCr) and β-ATP (adenosine triphosphate) decreased in the control group from 12.2 ± 0.4 to 8.7 ± 0.7 mmol ( p < 0.001) and 10.4 ± 0.8 to 7.7 ± 0.7 mmol ( p < 0.02), respectively. PCr P i ratio, reflecting mitochondrial function, fell in the control and advanced heart failure group from 1.84 ± 0.14 to 0.84 ± 0.14 ( p < 0.02) and 0.81 ± 0.16 to 0.37 ± 0.08 ( p < 0.03), respectively. Thus in cardiomyopathic hamsters dobutamine improved mechanical performance and thermodynamic efficiency in moderate stages of heart failure by improving mitochondrial activity, but did not improve mechanical performance in an advanced stage of heart failure. These experiments provide insight into the disparate clinical effects of dobutamine at various stages of heart failure.

Pimobendan Increases Survival of Cardiomyopathic Hamsters

We investigated the effect of the new cardiotonic drug pimobendan on survival of hereditary cardiomyopathic hamsters. Untreated cardiomyopathic hamsters served as controls. A 50% mortality was observed after 280 days for the control group and after 318 days for the pimobendan-treated animals. After 340 days, survival was 0% for the untreated cardiomyopathic hamsters and 27% in the pimobendan-treated group. We conclude that pimobendan slows the progression of heart failure in cardiomyopathic hamsters.

Stress-induced heart failure.

Stress produced heart failure in cardiomyopathic hamsters (CMHs) with subclinical heart disease. CMHs exhibited a variety of peripheral manifestations of heart failure including subcutaneous edema, fluid in the abdominal and thoracic cavities, and increased organ weight. In contrast, stress did not produce heart failure in healthy hamsters. These data indicate that the presence of covert heart disease can dramatically alter the pathogenic consequences of stress.

Membrane changes in the development of heart failure in cardiomyopathic hamsters: N.S. Dhalla. Department of Physiology, University of Manitoba, Winnipeg, Canada R3E OW3

Membrane changes in the development of heart failure in cardiomyopathic hamsters: N.S. Dhalla. Department of Physiology, University of Manitoba, Winnipeg, Canada R3E OW3

Renin and aldosterone in the cardiomyopathic hamster in congestive heart failure.

The renin-aldosterone system was studied in cardiomyopathic hamsters (CMH) before and after the onset of untreated clinical congestive heart failure. Age-matched random-bred hamsters (RB) served as controls. Before heart failure, there were no differences in body weight accretion, sodium balance, plasma renin activity or in vitro aldosterone production. After the onset of heart failure in CMH, body weight increased at a greater rate than in RB and positive sodium balance was nearly twice control levels. Although plasma renin activity was greater (P less than 0.005) in CMH than in RB (23.4+/-4.2 (mean+/-SEM) vs. 3.8+/-1.8 ng/ml/h), aldosterone production (101+/-15 vs. 95+/-16 ng/h) did not differ. Plasma aldosterone was low or undetectable in RB and in CMH in heart failure. In response to angiotensin stimulation, aldosterone production increased in both strains and did not differ. No difference in muscle potassium content, potassium balance or excretion was detected. Thus, in CMH, congestive heart failure is attended by increased plasma renin activity without a significant increase in aldosterone production, a dissociation which does not appear to be due to adrenal unresponsiveness to angiotensin II or to potassium depletion.