Isoproterenol-induced hypertrophied rat hearts: does short-term treatment correspond to long-term treatment?

Paricalcitol improved cardiac hypertrophy and fibrosis through upregulation of fibroblast growth factor-23 and downregulation of transforming growth factor-beta in a rat model of isoproterenol-induced cardiomyopathy

Acute cardiomyopathy is a significant global health concern and one of the leading causes of death in developed countries. Prior studies have shown an association between acute cardiomyopathy and low vitamin D levels. Although paricalcitol, a vitamin D receptor (VDR) activator, has demonstrated clinical benefits in patients with advanced kidney disease, its effect on cardiac remodeling in cardiomyopathy is unknown. This study aimed to investigate the relative effects of paricalcitol on cardiomyopathy in rats. Wistar-Kyoto rats were administered vehicle (sham control group) or isoproterenol to induce cardiomyopathy. Rats administered isoproterenol were subsequently treated with paricalcitol (experimental group) or vehicle (isoproterenol group). Picrosirius red and immunofluorescence staining were used to analyze cardiac fibrosis and hypertrophy. Immunohistochemistry staining was used to confirm the molecular mechanisms involved in isoproterenol-induced cardiomyopathy in rats. Injection of paricalcitol could reduce collagen and transforming growth factor-beta 1 (TGF-β1) levels while activating fibroblast growth factor receptor 1 (FGFR1) and fibroblast growth factor-23 (FGF23) without the help of Klotho, thereby reducing myocardial hypertrophy and fibrosis. As a VDR activator, paricalcitol reduces isoproterenol-induced cardiac fibrosis and hypertrophy by reducing the expression of TGF-β1 and enhancing the expression of VDR, FGFR1, and FGF23.

Experimental models of cardiac physiology and pathology

Experimental models of cardiac disease play a key role in understanding the pathophysiology of the disease and developing new therapies. The features of the experimental models should reflect the clinical phenotype, which can have a wide spectrum of underlying mechanisms. We review characteristics of commonly used experimental models of cardiac physiology and pathophysiology in all translational steps including in vitro, small animal, and large animal models. Understanding their characteristics and relevance to clinical disease is the key for successful translation to effective therapies.

Chikusetsu saponin IVa attenuates isoprenaline-induced myocardial fibrosis in mice through activation autophagy mediated by AMPK/mTOR/ULK1 signaling

BACKGROUND

Myocardial fibrosis is a common pathological manifestation of many cardiovascular diseases at the end stage. Autophagy has been demonstrated to play a protective role in the cardiac fibrosis. Our previous studies have demonstrated that the Saponins from Panax japonicus effectively ameliorated the degree of fibrosis in rat acute myocardial ischemia injury model though the mechanisms are not clear.

HYPOTHESIS

We hypothesized that Chikusetsusaponin IVa (CS), a major component of Saponins from Panaxjaponicus, may improve isoprenaline induced myocardial fibrosis via AMPK/mTOR/ULK1 mediated autophagy METHODS: Continuous subcutaneous injection of isoproterenol for 21 days was used to induce myocardial fibrosis in mice and high and low doses (15 mg/kg and 5 mg/kg) of CS was administered by oral gavage to observe the efficacy. Animals were sacrificed 12 h after the last administration and samples were collected. H&E staining, Masson staining and wheat germ agglutinin (WGA) staining were used to evaluate histopathological changes, collagen deposition and myocardial cell hypertrophy. Autophagy-related markers (LC3β, Beclin1 and p62) and AMPK/mTOR/ULK1 pathway-related markers were evaluated by western blot.

RESULTS

CS effectively attenuated isoprenaline-induced myocardial fibrosis in vivo, reduced the heart index, inhibited inflammatory infiltration, decreased collagen deposition and myocardial cell size. CS treatment rescued the expression of autophagy-related markers. CS activated autophagy through the activation of AMPK, which in turn inhibited the phosphorylation of mTOR and ULK1(Ser757), rather than directly phosphorylate ULK1(Ser555) by AMPK.

CONCLUSION

Our data demonstrated that CS attenuated isoprenaline-induced myocardial fibrosis by activating autophagy through AMPK/mTOR/ULK1 pathway. Our findings suggested that CS is a potential candidate drug against cardiac fibrosis and have identified potential drug targets for the treatment of heart diseases.

CXL-1020, a Novel Nitroxyl (HNO) Prodrug, Is More Effective than Milrinone in Models of Diastolic Dysfunction-A Cardiovascular Therapeutic: An Efficacy and Safety Study in the Rat

The nitroxyl (HNO) prodrug, CXL-1020, induces vasorelaxation and improves cardiac function in canine models and patients with systolic heart failure (HF). HNO's unique mechanism of action may be applicable to a broader subset of cardiac patients. This study investigated the load-independent safety and efficacy of CXL-1020 in two rodent (rat) models of diastolic heart failure and explored potential drug interactions with common HF background therapies. In vivo left-ventricular hemodynamics/pressure-volume relationships assessed before/during a 30 min IV infusion of CXL-1020 demonstrated acute load-independent positive inotropic, lusitropic, and vasodilatory effects in normal rats. In rats with only diastolic dysfunction due to bilateral renal wrapping (RW) or pronounced diastolic and mild systolic dysfunction due to 4 weeks of chronic isoproterenol exposure (ISO), CXL-1020 attenuated the elevated LV filling pressures, improved the end diastolic pressure volume relationship, and accelerated relaxation. CXL-1020 facilitated Ca²⁺ re-uptake and enhanced myocyte relaxation in isolated cardiomyocytes from ISO rats. Compared to milrinone, CXL-1020 more effectively improved Ca²⁺ reuptake in ISO rats without concomitant chronotropy, and did not enhance Ca²⁺ entry via L-type Ca²⁺ channels nor increase myocardial arrhythmias/ectopic activity. Acute-therapy with CXL-1020 improved ventricular relaxation and Ca²⁺ cycling, in the setting of chronic induced diastolic dysfunction. CXL-1020's lusitropic effects were greater than those seen with the cAMP-dependent agent milrinone, and unlike milrinone it did not produce chronotropy or increased ectopy. HNO is a promising new potential therapy for both systolic and diastolic heart failure.

Paricalcitol Attenuates Cardiac Fibrosis and Expression of Endothelial Cell Transition Markers in Isoproterenol-Induced Cardiomyopathic Rats

OBJECTIVES

Acute cardiomyopathy is a health problem worldwide. Few studies have shown an association between acute cardiomyopathy and low vitamin D status. Paricalcitol, a vitamin D receptor activator, clinically benefits patients with advanced kidney disease. The effect of paricalcitol supplement on cardiac remodeling in cardiomyopathic rats is unknown. This experimental study investigated the effect of paricalcitol in rats with cardiomyopathy induced by isoproterenol.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

Hospital-affiliated animal research institution.

SUBJECTS

Eight-week-old male Wistar-Kyoto rats.

INTERVENTIONS

Male Wistar-Kyoto rats were first injected intraperitoneally with isoproterenol to create a rat model of acute cardiomyopathy. Then paricalcitol was administered intraperitoneally to isoproterenol-injected rats at a dosage of 200 ng three times a week for 3 weeks. Relevant cardiomyopathy-related variables were measured regularly in three groups of rats, controls, isoproterenol, and isoproterenol plus paricalcitol. Rat hearts were obtained for evaluation of cardiac fibrosis using Masson trichrome staining and commercially available software, and evaluation of cell transition using immunofluorescence staining analysis.

MEASUREMENTS AND MAIN RESULTS

Isoproterenol infusions generated significant cardiac fibrosis (p < 0.001). Subsequent paricalcitol treatment attenuated the isoproterenol-induced cardiac fibrosis (p = 0.006). Fluorescence showed colocalization of endothelial and fibroblast cell markers (cluster differentiation 31 and α-smooth muscle actin, respectively) in the isoproterenol-treated hearts. Paricalcitol injections attenuated the isoproterenol-induced fluorescence intensity of two cell markers (p < 0.01).

CONCLUSIONS

Paricalcitol injections may ameliorate isoproterenol-induced cardiac fibrosis possibly through regulating cell transition.

Insulin-like growth factor 1 prevents diastolic and systolic dysfunction associated with cardiomyopathy and preserves adrenergic sensitivity

AIMS

Insulin-like growth factor 1 (IGF-1)-dependent signalling promotes exercise-induced physiological cardiac hypertrophy. However, the in vivo therapeutic potential of IGF-1 for heart disease is not well established. Here, we test the potential therapeutic benefits of IGF-1 on cardiac function using an in vivo model of chronic catecholamine-induced cardiomyopathy.

METHODS

Rats were perfused with isoproterenol via osmotic pump (1 mg kg(-1) per day) and treated with 2 mg kg(-1) IGF-1 (2 mg kg(-1) per day, 6 days a week) for 2 or 4 weeks. Echocardiography, ECG, and blood pressure were assessed. In vivo pressure-volume loop studies were conducted at 4 weeks. Heart sections were analysed for fibrosis and apoptosis, and relevant biochemical signalling cascades were assessed.

RESULTS

After 4 weeks, diastolic function (EDPVR, EDP, tau, E/A ratio), systolic function (PRSW, ESPVR, dP/dtmax) and structural remodelling (LV chamber diameter, wall thickness) were all adversely affected in isoproterenol-treated rats. All these detrimental effects were attenuated in rats treated with Iso+IGF-1. Isoproterenol-dependent effects on BP were attenuated by IGF-1 treatment. Adrenergic sensitivity was blunted in isoproterenol-treated rats but was preserved by IGF-1 treatment. Immunoblots indicate that cardioprotective p110α signalling and activated Akt are selectively upregulated in Iso+IGF-1-treated hearts. Expression of iNOS was significantly increased in both the Iso and Iso+IGF-1 groups; however, tetrahydrobiopterin (BH4) levels were decreased in the Iso group and maintained by IGF-1 treatment.

CONCLUSION

IGF-1 treatment attenuates diastolic and systolic dysfunction associated with chronic catecholamine-induced cardiomyopathy while preserving adrenergic sensitivity and promoting BH4 production. These data support the potential use of IGF-1 therapy for clinical applications for cardiomyopathies.

Cardiomyopathy confers susceptibility to particulate matter-induced oxidative stress, vagal dominance, arrhythmia and pulmonary inflammation in heart failure-prone rats

Acute exposure to ambient fine particulate matter (PM2.5) is tied to cardiovascular morbidity and mortality, especially among those with prior cardiac injury. The mechanisms and pathophysiological events precipitating these outcomes remain poorly understood but may involve inflammation, oxidative stress, arrhythmia and autonomic nervous system imbalance. Cardiomyopathy results from cardiac injury, is the leading cause of heart failure, and can be induced in heart failure-prone rats through sub-chronic infusion of isoproterenol (ISO). To test whether cardiomyopathy confers susceptibility to inhaled PM2.5 and can elucidate potential mechanisms, we investigated the cardiophysiologic, ventilatory, inflammatory and oxidative effects of a single nose-only inhalation of a metal-rich PM2.5 (580 µg/m(3), 4 h) in ISO-pretreated (35 days × 1.0 mg/kg/day sc) rats. During the 5 days post-treatment, ISO-treated rats had decreased HR and BP and increased pre-ejection period (PEP, an inverse correlate of contractility) relative to saline-treated rats. Before inhalation exposure, ISO-pretreated rats had increased PR and ventricular repolarization time (QT) and heterogeneity (Tp-Te). Relative to clean air, PM2.5 further prolonged PR-interval and decreased systolic BP during inhalation exposure; increased tidal volume, expiratory time, heart rate variability (HRV) parameters of parasympathetic tone and atrioventricular block arrhythmias over the hours post-exposure; increased pulmonary neutrophils, macrophages and total antioxidant status one day post-exposure; and decreased pulmonary glutathione peroxidase 8 weeks after exposure, with all effects occurring exclusively in ISO-pretreated rats but not saline-pretreated rats. Ultimately, our findings indicate that cardiomyopathy confers susceptibility to the oxidative, inflammatory, ventilatory, autonomic and arrhythmogenic effects of acute PM2.5 inhalation.

Effects of acute and chronic sunitinib treatment on cardiac function and calcium/calmodulin-dependent protein kinase II

BACKGROUND AND PURPOSE

Calcium/calmodulin-dependent protein kinase IIδ (CaMKIIδ) is an important regulator of cardiac contractile function and dysfunction and may be an unwanted secondary target for anti-cancer drugs such as sunitinib and imatinib that have been reported to alter cardiac performance. This study aimed to determine whether anti-cancer kinase inhibitors may affect CaMKII activity and expression when administered in vivo.

EXPERIMENTAL APPROACH

Cardiovascular haemodynamics in response to acute and chronic sunitinib treatment, and chronic imatinib treatment, were assessed in guinea pigs and the effects compared with those of the known positive and negative inotropes, isoprenaline and verapamil. Parallel studies from the same animals assessed CaMKIIδ expression and CaMKII activity following drug treatments.

KEY RESULTS

Acute administration of sunitinib decreased left ventricular (LV) dP/dtmax. Acute administration of isoprenaline increased LVdP/dtmax dose-dependently, while LVdP/dtmax was decreased by verapamil. CaMKII activity was decreased by acute administration of sunitinib and was increased by acute administration of isoprenaline, and decreased by acute administration of verapamil. CaMKIIδ expression following all acute treatments remained unchanged. Chronic imatinib and sunitinib treatments did not alter fractional shortening; however, both CaMKIIδ expression and CaMKII activity were significantly increased. Chronic administration of isoprenaline and verapamil decreased LV fractional shortening with parallel increases in CaMKIIδ expression and CaMKII activity.

CONCLUSIONS AND IMPLICATIONS

Chronic sunitinib and imatinib treatment increased CaMKIIδ expression and CaMKII activity. As these compounds are associated with cardiac dysfunction, increased CaMKII expression could be an early indication of cellular cardiotoxicity marking potential progression of cardiac contractile dysfunction.

Changes in cardiac aldosterone and its synthase in rats with chronic heart failure: an intervention study of long-term treatment with recombinant human brain natriuretic peptide

The physiological mechanisms involved in isoproterenol (ISO)-induced chronic heart failure (CHF) are not fully understood. In this study, we investigated local changes in cardiac aldosterone and its synthase in rats with ISO-induced CHF, and evaluated the effects of treatment with recombinant human brain natriuretic peptide (rhBNP). Sprague-Dawley rats were divided into 4 different groups. Fifty rats received subcutaneous ISO injections to induce CHF and the control group (n=10) received equal volumes of saline. After establishing the rat model, 9 CHF rats received no further treatment, rats in the low-dose group (n=8) received 22.5 μg/kg rhBNP and those in the high-dose group (n=8) received 45 μg/kg rhBNP daily for 1 month. Cardiac function was assessed by echocardiographic and hemodynamic analysis. Collagen volume fraction (CVF) was determined. Plasma and myocardial aldosterone concentrations were determined using radioimmunoassay. Myocardial aldosterone synthase (CYP11B2) was detected by quantitative real-time PCR. Cardiac function was significantly lower in the CHF group than in the control group (P<0.01), whereas CVF, plasma and myocardial aldosterone, and CYP11B2 transcription were significantly higher than in the control group (P<0.05). Low and high doses of rhBNP significantly improved hemodynamics (P<0.01) and cardiac function (P<0.05) and reduced CVF, plasma and myocardial aldosterone, and CYP11B2 transcription (P<0.05). There were no significant differences between the rhBNP dose groups (P>0.05). Elevated cardiac aldosterone and upregulation of aldosterone synthase expression were detected in rats with ISO-induced CHF. Administration of rhBNP improved hemodynamics and ventricular remodeling and reduced myocardial fibrosis, possibly by downregulating CYP11B2 transcription and reducing myocardial aldosterone synthesis.

A new calpain inhibitor protects left ventricular dysfunction induced by mild ischemia-reperfusion in in situ rat hearts

We have previously indicated that a new soluble calpain inhibitor, SNJ-1945 (SNJ), attenuates cardiac dysfunction after cardioplegia arrest-reperfusion by inhibiting the proteolysis of α-fodrin in in vitro study. Nevertheless, the in vivo study design is indispensable to explore realistic therapeutic approaches for clinical use. The aim of the present in situ study was to investigate whether SNJ attenuated left ventricular (LV) dysfunction (stunning) after mild ischemic-reperfusion (mI-R) in rat hearts. SNJ (60 μmol/l, 5 ml i.p.) was injected 30 min before gradual and partial coronary occlusion at proximal left anterior descending artery. To investigate LV function, we obtained curvilinear end-systolic pressure-volume relationship by increasing afterload 60 min after reperfusion. In the mI-R group, specific LV functional indices at midrange LV volume (mLVV), end-systolic pressure (ESP(mLVV)), and pressure-volume area (PVA(mLVV): a total mechanical energy per beat, linearly related to oxygen consumption) significantly decreased, but SNJ reversed these decreases to time control level. Furthermore, SNJ prevented the α-fodrin degradation and attenuated degradation of Ca(2+) handling proteins after mI-R. Our results indicate that improvements in LV function following mI-R injury are associated with inhibition of the proteolysis of α-fodrin in in situ rat hearts. In conclusion, SNJ should be a promising tool to protect the heart from the stunning.

Pathophysiological model of chronic heart failure complicated with renal failure caused by three-quarter nephrectomy and subcutaneous injection of isoprenaline

This study aimed to investigate the pathophysiological changes in a rat chronic heart failure complicated with renal failure model, caused by three-quarters nephrectomy and subcutaneous injection of isoproterenol (ISO). Sprague-Dawley (SD) rats in the model group received three-quarters nephrectomy after twice undergoing surgical resections and subcutaneous injection of ISO (100 mg/kg body weight, injected twice, with a 24 h interval) after one week, while rats in the control group received sham surgery and injection of normal saline. Survival rate, heart failure and renal failure were compared between the two groups after 4 weeks. Serum creatinine (Cr), blood urea nitrogen (BUN), B-type natriuretic protein (BNP), aldolase (ALD), angiotensin II (Ang II) and C-reactive protein (CRP) were determined by kit assay. Urine protein at 24 h was determined by the Bradford method and left ventricular systolic pressure (LVSP), left ventricular diastolic pressure (LVDP) and left ventricular end-diastolic pressure (LVEDP), as well as the maximum rates of increased and decreased left ventricular pressure (±dP/dt_max) were determined by left ventricular intubation. Heart weight indices were determined and the myocardial pathological conditions were observed by hematoxylin and eosin (HE) staining. There was no death in the control group, while the survival rate of the model group was 73%. Compared with the control group, each index of serum and urine protein in the model group was significantly increased. Additionally, LVSP was decreased, LVDP and LVEDP were increased and heart weight index was increased, with a significant difference. The serum Cr was positively correlated to BNP levels in the model group. Three-quarters nephrectomy and subcutaneous injection of ISO induces left ventricular heart failure and renal failure at the same time, which is characterized in pathophysiology by left ventricular diastolic and systolic function failure, left ventricular myocardial hypertrophy and reconstruction complicated with renal insufficiency.

[Effects of a compound Chinese medicine Xinji' erkang on isoproterenol-induced ventricular remodeling in mice]

OBJECTIVE

To investigate the effects of Xinji' erkang (XJEK), a compound Chinese herbal medicine, on isoproterenol-induced ventricular remodeling in mice.

METHODS

Isoproterenol was given subcutaneously (1 mg/kg, twice per day for 7 d) to induce ventricular remodeling in mice. Mice were divided into normal control group, model group, XJEK low-, medium- and high- dose groups, XJEK water layer group, XJEK n-butanol layer group and metoprolol group. All drugs were given by intragastric administration. At the end of the 7th day, the hearts of the rats were weighted, and myocardial hypertrophy index was expressed as heart weight/body weight (HW/BW). The histological changes were observed by hemotoxylin-eosin and Van Gieson staining. Colorimetric method was used to determine the content of hydroxyproline in heart, and the activity of superoxide dismutase (SOD) and the content of malondialdehyde (MDA) in serum.

RESULTS

Compared with the isoproterenol injection only, XJEK potently inhibited cardiomyocyte hypertrophy and the increase of hydroxyproline content in heart (P<0.01), improved cardiac pathology change, inhibited the decrease of SOD activity and the increase of MDA content in serum (P<0.01). XJEK water layer also inhibited the increase of cardiomyocyte hypertrophy (P<0.01) while XJEK n-butanol layer inhibited cardiomyocyte hypertrophy and fibrosis (P<0.01).

CONCLUSION

XJEK possesses protective effects against isoproterenol-induced ventricular remodeling in mice, which may be related to its actions in reducing the oxidative stress and improving the antioxidant activity of the body. XJEK water layer and XJEK n-butanol layer attenuated ventricular remodeling without significant oxidative stress state changing, which indicates that a non-antioxidative stress mechanism may exist.

Cardiac mechanoenergetics for understanding isoproterenol-induced rat heart failure

Considering from clinical implication, it is often complained that short-term experimental diseased heart models do not mimic long-term diseased hearts that one often clinically encountered. The left ventricle (LV) function in rat cardiac hypertrophy models treated with isoproterenol (ISO) up to 16 weeks was followed up with a non-invasive echocardiography. Infusion of either ISO (1.2mgkg(-1)day(-1) for 3 days-16 weeks) or vehicle (saline 24μlday(-1) for 3 days-16 weeks; SA group) was performed by subcutaneously implanting osmotic minipump. LV and right ventricle (RV) weight ratios to body weight (mgg(-1)) in SA, ISO3d, ISO7d and ISO4w were: 1.94±0.10 and 0.54±0.04 (n=7), 2.56±0.10 and 0.66±0.05 (n=7), 2.50±0.25 and 0.64±0.07 (n=10) and 2.40±0.08 and 0.59±0.08 (n=9), respectively. From echocardiography, the LV function of the hypertrophy models at 3 days, 1 and 2 weeks was unchanged but the model at the longer-term than 4 weeks resulted in prolonged systolic failure. These results indicated that only 3-day ISO infusion induced the hypertrophy model similar in shape and function to that induced by 2-week ISO infusion; the 3-day model sufficiently represents the effects of 2-week ISO infusion. In this review, left ventricular (LV) function was compared between rat cardiac hypertrophy models treated with ISO for 3 days (ISO3d) and 7 days (ISO7d) by analyzing LV mechanical work and energetics. The LV mechanical work and energetics was unchanged in SA, ISO3d and ISO7d groups. The LV relaxation rate at 240bpm in ISO3d and ISO7d groups was significantly slower than that in SA group with unchanged contraction rate. The amounts of expression of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a), phospholamban (PLB), phosphorylated-Ser(16) PLB (p-PLB), phospholemman (PLM) and Na(+)-K(+)-ATPase (NKA) are significantly decreased in ISO3d and ISO7d groups. Furthermore, the marked collagen production (types I and III) was observed in ISO3d and ISO7d groups. These results suggested the possibility that physiological LV function is compensated, although molecular changes have been generated even in the short-term hypertrophy model. Although a novel histone deacetylase (HDAC) inhibitor, has some beneficial effects on hemodynamics, it has no effects of anti-hypertrophic modalities in ISO3d model. However, a selective sodium proton exchanger-1 (NHE-1) inhibitor normalized ISO-induced down-regulation of SERCA2a without changes in pPLB/PLB expression in the ISO7d model and ameliorates cardiac Ca(2+) handling impairment and prevents the development of cardiac dysfunction. This result indicated that SERCA2a is a key molecule in the ISO7d model. Slow LV relaxation rate in ISO7d model may be due to down-regulation of SERCA2a. In conclusion, lowering the heart rate make it possible to rescue the impairment of LV mechanical work and energetics in the ISO-induced compensatory hypertrophied rat hearts, providing basic evidence for clinical therapy for patients with some types of cardiac failure.

NHE-1 participates in isoproterenol-induced downregulation of SERCA2a and development of cardiac remodeling in rat hearts

Impaired Ca2+ handling is one of the main characteristics in heart failure patients. Recently, we reported abnormal expressions of Ca2+-handling proteins in isoproterenol (ISO)-induced hypertrophied rat hearts. On the other hand, Na+/H+ exchanger (NHE)-1 inhibitor has been demonstrated to exert beneficial effects in ischemic-reperfusion injury and in the development of cardiac remodeling. The aims of the present study are to investigate the role of NHE-1 on Ca2+ handling and development of cardiac hypertrophy in ISO-infused rats. Male Wistar rats were randomly divided into vehicle [control (CTL)] and ISO groups without or with pretreatment with a selective NHE-1 inhibitor, BIIB-723. ISO infusion for 1 wk significantly increased the ratios of heart to body weight and left ventricle (LV) to body weight and collagen accumulation. All of these increases were antagonized by coadministration with BIIB-723. The ISO-induced significant increase in LV wall thickness was suppressed significantly ( P < 0.05) by BIIB-723. ISO-induced decreases in cardiac stroke volume and a total mechanical energy per beat index, systolic pressure-volume area at midrange LV volume, were normalized by BIIB-723. The markedly higher expression of NHE-1 protein in the ISO group than that in CTL group was suppressed ( P < 0.05) by BIIB-723. Surprisingly, ISO induced downregulation of the important Ca2+-handling protein sarcoplasmic reticulum Ca2+-ATPase 2a, the expression of which was also normalized by BIIB-723 without changes in phosphorylated phospholamban (PLB)/PLB expression. We conclude that NHE-1 contributes to ISO-induced abnormal Ca2+ handling associated with cardiac hypertrophy. Inhibition of NHE-1 ameliorates cardiac Ca2+-handling impairment and prevents the development of cardiac dysfunction in ISO-infused rats.

Dietary salt exacerbates isoproterenol-induced cardiomyopathy in rats

Spontaneously hypertensive heart failure rats (SHHFs) take longer to develop compensated heart failure (HF) and congestive decompensation than common surgical models of HF. Isoproterenol (ISO) infusion can accelerate cardiomyopathy in young SHHFs, while dietary salt loading in hypertensive rats induces cardiac fibrosis, hypertrophy, and--in a minority-congestive HF. By combining ISO with dietary salt loading in young SHHFs, the authors sought a nonsurgical model that is more time--and resource-efficient than any of these factors alone. The authors hypothesized that salt loading would enhance ISO-accelerated cardiomyopathy, promoting fibrosis, hypertrophy, and biochemical characteristics of HF. SHHFs (lean male, 90d) were infused for 4 wk with ISO (2.5 mg/kg/day) or saline. After 2 wk of infusion, a 6-wk high-salt diet (4%, 6%, or 8% NaCl) was initiated. Eight percent salt increased heart weight, HF markers (plasma B-type natriuretic peptide, IL-6), lung lymphocytes, and indicators of lung injury and edema (albumin and protein) relative to control diet, while increasing urine pro-atrial natriuretic peptide relative to ISO-only. High salt also exacerbated ISO-cardiomyopathy and fibrosis. Thus, combining ISO infusion with dietary salt loading in SHHFs holds promise for a new rat HF model that may help researchers to elucidate HF mechanisms and unearth effective treatments.

Merits of non-invasive rat models of left ventricular heart failure

Heart failure (HF) is characterized as a limitation to cardiac output that prevents the heart from supplying tissues with adequate oxygen and predisposes individuals to pulmonary edema. Impaired cardiac function is secondary to either decreased contractility reducing ejection (systolic failure), diminished ventricular compliance preventing filling (diastolic failure), or both. To study HF etiology, many different techniques have been developed to elicit this condition in experimental animals, with varying degrees of success. Among rats, surgically induced HF models are the most prevalent, but they bear several shortcomings, including high mortality rates and limited recapitulation of the pathophysiology, etiology, and progression of human HF. Alternatively, a number of non-invasive HF induction methods avoid many of these pitfalls, and their merits in technical simplicity, reliability, survivability, and comparability to the pathophysiologic and pathogenic characteristics of HF are reviewed herein. In particular, this review focuses on the primary pathogenic mechanisms common to genetic strains (spontaneously hypertensive and spontaneously hypertensive heart failure), pharmacological models of toxic cardiomyopathy (doxorubicin and isoproterenol), and dietary salt models, all of which have been shown to induce left ventricular HF in the rat. Additional non-invasive techniques that may potentially enable the development of new HF models are also discussed.

Particulate matter inhalation exacerbates cardiopulmonary injury in a rat model of isoproterenol-induced cardiomyopathy

Ambient particulate matter (PM) exposure is linked to cardiovascular events and death, especially among individuals with heart disease. A model of toxic cardiomyopathy was developed in Spontaneously Hypertensive Heart Failure (SHHF) rats to explore potential mechanisms. Rats were infused with isoproterenol (ISO; 2.5 mg/kg/day subcutaneous [sc]), a beta-adrenergic agonist, for 28 days and subsequently exposed to PM by inhalation. ISO induced tachycardia and hypotension throughout treatment followed by postinfusion decrements in heart rate, contractility, and blood pressures (systolic, diastolic, pulse), and fibrotic cardiomyopathy. Changes in heart rate and heart rate variability (HRV) 17 days after ISO cessation indicated parasympathetic dominance with concomitantly altered ventilation. Rats were subsequently exposed to filtered air or Harvard Particle 12 (HP12) (12 mg/m(3))--a metal-rich oil combustion-derived PM--at 18 and 19 days (4 h/day) after ISO infusion via nose-only inhalation to determine if cardio-impaired rats were more responsive to the effects of PM exposure. Inhalation of PM among ISO-pretreated rats significantly increased pulmonary lactate dehydrogenase, serum high-density lipoprotein (HDL) cholesterol, and heart-to-body mass ratio. PM exposure increased the number of ISO-pretreated rats that experienced bradyarrhythmic events, which occurred concomitantly with acute alterations of HRV. PM, however, did not significantly affect mean HRV in the ISO- or saline-pretreated groups. In summary, subchronic ISO treatment elicited some pathophysiologic and histopathological features of heart failure, including cardiomyopathy. The enhanced sensitivity to PM exposure in SHHF rats with ISO-accelerated cardiomyopathy suggests that this model may be useful for elucidating the mechanisms by which PM exposure exacerbates heart disease.

Left ventricular function of isoproterenol-induced hypertrophied rat hearts perfused with blood: mechanical work and energetics

We investigated left ventricular (LV) mechanical work and energetics in the cross-circulated (blood-perfused) isoproterenol [Iso 1.2 mg x kg(-1).day(-1) for 3 days (Iso3) or 7 days (Iso7)]-induced hypertrophied rat heart preparation under isovolumic contraction-relaxation. We evaluated pressure-time curves per beat, end-systolic pressure-volume and end-diastolic pressure-volume relations, and myocardial O(2) consumption per beat (Vo(2))-systolic pressure-volume area (PVA; a total mechanical energy per beat) linear relations at 240 beats/min, because Iso-induced hypertrophied hearts failed to completely relax at 300 beats/min. The LV relaxation rate at 240 beats/min in Iso-induced hypertrophied hearts was significantly slower than that in control hearts [saline 24 microl/day for 3 and 7 days (Sa)] with unchanged contraction rate. The Vo(2)-intercepts (composed of basal metabolism and Ca(2+) cycling energy consumption in excitation-contraction coupling) of Vo(2)-PVA linear relations were unchanged associated with their unchanged slopes in Sa, Iso3, and Iso7 groups. The oxygen costs of LV contractility were also unchanged in all three groups. The amounts of expression of sarcoplasmic reticulum Ca(2+)-ATPase, phospholamban (PLB), phosphorylated-Ser(16) PLB, phospholemman, and Na(+)-K(+)-ATPase are significantly decreased in Iso3 and Iso7 groups, although the amount of expression of NCX1 is unchanged in all three groups. Furthermore, the marked collagen production (types I and III) was observed in Iso3 and Iso7 groups. These results suggested the possibility that lowering the heart rate was beneficial to improve mechanical work and energetics in isoproterenol-induced hypertrophied rat hearts, although LV relaxation rate was slower than in normal hearts.

Effects of formaldehyde on cardiovascular system in in situ rat hearts

The aim of the present study was to examine the effects of formaldehyde solution on rat left ventricular function and compare it with those in hypertrophic hearts treated with isoproterenol by pressure-volume measurements with the catheter method. After 20-30 min. of intravenous infusion of 3.7% formaldehyde solution (FA) at 10 μl (3.7 mg)/kg/min, normal and hypertrophic hearts showed significant decreases in left ventricle end-systolic pressure (ESP), heart rate and cardiac output per minute, indicating an acute pumping failure. Hypertrophic hearts showed significantly smaller ESP, stroke volumes and cardiac output than those in normal hearts. Systolic pressure-volume area at midrange left ventricular volume (PVA(mLVV) : a mechanical work capability index) was significantly smaller than that in normal hearts and per cent of mean PVA(mLVV) versus pre-infusion mean value in hypertrophic hearts was significantly decreased compared to normal hearts 30 min. after FA infusion. The marked decrease in pH, base excess and no changes in PaO₂ and PaCO₂ suggest metabolic acidosis. The correction of metabolic acidosis with 9% NaHCO₃ did not influence on the acute pumping failure, indicating that metabolic acidosis did not cause it. Ultrastructural observations revealed marked dilation of the sarcoplasmic reticulum with intact sarcolemmal membranes and no disintegration of muscle myofibrils. Ryanodine receptors and calcium (Ca²⁺) pumps (SERCA2A) located in the sarcoplasmic reticulum have major roles in the cytosolic Ca²⁺ handling. Taken together, acute pumping failure by FA may derive from the impairment of Ca²⁺ handling in the cardiac excitation-contraction coupling.

Increased O2 consumption in excitation-contraction coupling in hypertrophied rat heart slices related to increased Na+ -Ca2+ exchange activity

The goal of our study was to evaluate the origin of the increased O(2) consumption in electrically stimulated left ventricular slices of isoproterenol-induced hypertrophied rat hearts with normal left ventricular pressure. O(2) consumption per minute (mVO(2)) of mechanically unloaded left ventricular slices was measured in the absence and presence of 1-Hz field stimulation. Basal metabolic mVO(2), i.e., mVO(2) without electrical stimulation, was significantly smaller, but mVO(2) for the total Ca(2+) handling in excitation-contraction coupling (E-C coupling mVO(2)), i.e., delta mVO(2) (=mVO(2) with stimulation - mVO(2) without stimulation), was significantly larger in the hypertrophied heart. Furthermore, the fraction of E-C coupling mVO(2) was markedly altered in the hypertrophied heart. Namely, mVO(2) consumed by sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2) was depressed by 40%; mVO(2) consumed by the Na(+)/K(+)-ATPase (NKA)-Na(+)/Ca(2+) exchange (NCX) coupling was increased by 100%. The depressed mVO(2) consumption by SERCA2 was supported by lower protein expressions of phosphorylated-Ser(16) phospholamban and SERCA2. The increase in NKA-NCX coupling mVO(2) was supported by marked augmentation of NCX current. However, the increase in NCX current was not due to the increase in NCX1 protein expression, but was attributable to attenuation of the intrinsic inactivation mechanisms. The present results demonstrated that the altered origin of the increased E-C coupling mVO(2) in hypertrophy was derived from decreased SERCA2 activity (1ATP: 2Ca(2+)) and increased NCX activity coupled to NKA activity (1ATP: Ca(2+)). Taken together, we conclude that the energetically less efficient Ca(2+) extrusion pathway evenly contributes to Ca(2+) handling in E-C coupling in the present hypertrophy model.