Reversible effects of isoproterenol-induced hypertrophy on in situ left ventricular function in rat hearts

Pomegranate Peel Extract Attenuates Isoprenaline-Induced Takotsubo-like Myocardial Injury in Rats

Takotsubo syndrome (TTS) is an acute heart failure syndrome characterised by catecholamine-induced oxidative tissue damage. Punica granatum, a fruit-bearing tree, is known to have high polyphenolic content and has been proven to be a potent antioxidant. This study aimed to investigate the effects of pomegranate peel extract (PoPEx) pre-treatment on isoprenaline-induced takotsubo-like myocardial injury in rats. Male Wistar rats were randomised into four groups. Animals in the PoPEx(P) and PoPEx + isoprenaline group (P + I) were pre-treated for 7 days with 100 mg/kg/day of PoPEx. On the sixth and the seventh day, TTS-like syndrome was induced in rats from the isoprenaline(I) and P + I groups by administering 85 mg/kg/day of isoprenaline. PoPEx pre-treatment led to the elevation of superoxide dismutase and catalase (p < 0.05), reduced glutathione (p < 0.001) levels, decreased the thiobarbituric acid reactive substances (p < 0.001), H₂O₂, O₂^- (p < 0.05), and NO₂^- (p < 0.001), in the P + I group, when compared to the I group. In addition, a significant reduction in the levels of cardiac damage markers, as well as a reduction in the extent of cardiac damage, was found. In conclusion, PoPEx pre-treatment significantly attenuated the isoprenaline-induced myocardial damage, primarily via the preservation of endogenous antioxidant capacity in the rat model of takotsubo-like cardiomyopathy.

Regression from pathological hypertrophy in mice is sexually dimorphic and stimulus-specific

Pathological cardiac hypertrophy is associated with increased morbidity and mortality. Understanding the mechanisms whereby pathological cardiac growth can be reversed could have therapeutic value. Here, we show that pathways leading to regression of pathological cardiac hypertrophy are strongly dependent on the hypertrophic trigger and are significantly modified by sex. Two pathological stimuli causing hypertrophy via distinct pathways were administered to male and female mice: Angiotensin II [Ang II] or Isoproterenol [Iso]. Stimuli were removed after 7 days of treatment, and left ventricles (LV) were studied at 1, 4, and 7 days. Ang II-treated Females did not show regression after stimulus removal. Iso-treated males showed rapid LV hypertrophy regression. Somewhat surprisingly, RNAseq analysis at day 1 after removal of triggers revealed only 45 differentially regulated genes in common among all groups, demonstrating distinct responses. Ingenuity Pathway Analysis predicted strong downregulation of the TGFβ1 pathway in all groups except for Ang II-treated females. Consistently, we found significant downregulation of Smad signaling after stimulus removal including in Ang II-treated females. Additionally, the ERK1/2 pathway was significantly reduced in the groups showing regression. Finally, protein degradation pathways were significantly activated only in Iso-treated males 1 day after stimulus removal. Our data indicate that TGFβ1 downregulation may play a role in the regression of pathological cardiac hypertrophy via downregulation of the ERK1/2 pathway and activation of autophagy and proteasome activity in Iso-treated males. This work highlights that the reversal of pathological hypertrophy does not utilize universal signaling pathways and that sex potently modifies this process.

Adaptive versus maladaptive cardiac remodelling in response to sustained β-adrenergic stimulation in a new 'ISO on/off model'

On the one hand, sustained β-adrenergic stress is a hallmark of heart failure (HF) and exerts maladaptive cardiac remodelling. On the other hand, acute β-adrenergic stimulation maintains cardiac function under physiological stress. However, it is still incompletely understood to what extent the adaptive component of β-adrenergic signaling contributes to the maintenance of cardiac function during chronic β-adrenergic stress. We developed an experimental catecholamine-based protocol to distinguish adaptive from maladaptive effects. Mice were for 28 days infused with 30 mg/kg body weight/day isoproterenol (ISO) by subcutaneously implanted osmotic minipumps ('ISO on'). In a second and third group, ISO infusion was stopped after 26 days and the mice were observed for additional two or seven days without further ISO infusion ('ISO off short', 'ISO off long'). In this setup, 'ISO on' led to cardiac hypertrophy and slightly improved cardiac contractility. In stark contrast, 'ISO off' mice displayed progressive worsening of left ventricular ejection fraction that dropped down below 40%. While fetal and pathological gene expression (increase in Nppa, decrease in Myh6/Myh7 ratios, increase in Xirp2) was not induced in 'ISO on', it was activated in 'ISO off' mice. After ISO withdrawal, phosphorylation of phospholamban (PLN) at the protein kinase A (PKA) phosphorylation site Ser-16 dropped down to 20% as compared to only 50% at the Ca2+/Calmodulin-dependent kinase II (CaMKII) phosphorylation site Thr-17 in 'ISO off' mice. PKA-dependent cardioprotective production of the N-terminal proteolytic product of histone deacetylase 4 (HDAC4-NT) was reduced in 'ISO off' as compared to 'ISO on'. Taken together, these data indicate that chronic ISO infusion induces besides maladaptive remodelling also adaptive PKA signalling to maintain cardiac function. The use of the 'ISO on/off' model will further enable the separation of the underlying adaptive from maladaptive components of β-adrenergic signalling and may help to better define and test therapeutic targets downstream of β-adrenergic receptors.

Cardioprotective and Anti-arrhythmic Effects of Magnesium Pretreatment Against Ischaemia/Reperfusion Injury in Isoprenaline-Induced Hypertrophic Rat Heart

The effects of magnesium (Mg²⁺) on ischaemic complications of pathological cardiac hypertrophy are unclear. In this study, we investigated effects of Mg²⁺ pretreatment on ischaemia/reperfusion (I/R) injury in isoprenaline (ISO)-induced hypertrophic hearts. Wistar rats were treated for 7 days with different combinations of ISO (1.25 mg/kg) subcutaneously, MgSO₄ (270 mg/kg) intraperitoneally, or vehicle (saline). On the eighth day, hearts were either subjected to regional I/R during Langendorff perfusion or histologically stained with haematoxylin and eosin and Masson's trichrome. Haemodynamic and electrocardiographic parameters were recorded using the PowerLab data-acquisition system. Infarcts were identified by triphenyltetrazolium chloride staining. Plasma Mg²⁺ was measured using photometric assays. Mg²⁺ pretreatment significantly decreased I/R-induced infarct size (p = 0.001) and the overall arrhythmia score (p < 0.001) of I/R-induced ventricular ectopics, ventricular tachycardia, and ventricular fibrillation in hypertrophic hearts, but not non-hypertrophied hearts. Mg²⁺ also improved post-I/R left ventricular developed pressure in hypertrophic hearts. However, Mg²⁺ did not reverse the ISO-induced myocyte thickening and interstitial fibrosis or increases in heart weight. Plasma Mg²⁺ was not different among treatment groups. These results suggest that Mg²⁺ pretreatment may protect against I/R-induced injury and malignant arrhythmias in hypertrophic hearts, possibly via mechanisms unrelated to long-lasting changes in plasma Mg²⁺ or prevention of structural changes such as fibrosis.

Cardioprotective effect of nesfatin-1 against isoproterenol-induced myocardial infarction in rats: Role of the Akt/GSK-3β pathway

The present study was designed to evaluate the cardioprotective effects of nesfatin-1, a novel peptide with anorexigenic properties, in rats with isoproterenol (ISO)-induced myocardial infarction (MI), and to further investigate the role of Akt/GSK-3β signaling pathway in the protective effect of nesfatin-1. To induce MI, ISO was subcutaneously injected into the rats for two consecutive days at a dosage of 85mg/kg/day. ISO-induced myocardial damage was indicated by elevated levels of cardiac specific troponin-T, enhanced myocardial expression of proinflammatory cytokines (interleukin-1β, interleukin-6 and tumor necrosis factor-α), and increased number of cells with apoptotic and necrotic appearance in the myocardial tissue. Levels of p-Akt/Akt and p-GSK-3β/GSK-3β significantly decreased in heart tissue after ISO-induced MI. However, intraperitoneal administration of nesfatin-1 (10μg/kg/day) elicited a significant cardioprotective activity by lowering the levels of cardiac troponin-T and proinflammatory cytokines, indicating the protective effect of nesfatin-1 against ISO-induced MI. The biochemical findings were further confirmed by histopathological examination, which was demonstrated by reduced number of apoptotic and necrotic cells. Moreover, expressions of p-Akt/Akt and p-GSK-3β/GSK-3β in the myocardium of MI group rats were significantly increased by nesfatin-1 administration, suggesting that nesfatin-1, which appears to possess anti-apoptotic and anti-inflammatory properties, may confer protection against ISO-induced MI via an Akt/GSK-3β-dependent mechanism.

Vasostatin-1 Stops Structural Remodeling and Improves Calcium Handling via the eNOS-NO-PKG Pathway in Rat Hearts Subjected to Chronic β-Adrenergic Receptor Activation

PURPOSE

Chronically elevated catecholamine levels activate cardiac β-adrenergic receptors, which play a vital role in the pathogenesis of heart failure. Evidence suggests that vasostatin-1 (VS-1) exerts anti-adrenergic effects on isolated and perfused hearts in vitro. Whether VS-1 ameliorates hypertrophy/remodeling by inducing the chronic activation of β-adrenergic receptors is unknown. The present study aims to test the efficacy of using VS-1 to treat the advanced hypertrophy/remodeling that result from chronic β-adrenergic receptor activation and to determine the cellular and molecular mechanisms that underlie this response.

METHODS AND RESULT

Rats were subjected to infusion with either isoprenaline (ISO, 5 mg/kg/d), ISO plus VS-1 (30 mg/kg/d) or placebo for 2 weeks. VS-1 suppressed chamber dilation, myocyte hypertrophy and fibrosis and improved in vivo heart function in the rats subjected to ISO infusion. VS-1 increased phosphorylated nitric oxide synthase levels and induced the activation of protein kinase G. VS-1 also deactivated multiple hypertrophy signaling pathways that were triggered by the chronic activation of β-adrenergic receptors, such as the phosphoinositide-3 kinase (PI3K)/Akt and Ca²⁺/calmodulin-dependent kinase (CaMK-II) pathways. Myocytes isolated from ISO + VS-1 hearts displayed higher Ca²⁺ transients, shorter Ca²⁺ decays, higher sarcoplasmic reticulum Ca²⁺ levels and higher L-type Ca²⁺ current densities than the ISO rat hearts. VS-1 treatment restored the protein expression of sarcoplasmic reticulum Ca²⁺ uptake ATPase, phospholamban and Cav1.2, indicating improved calcium handling.

CONCLUSIONS

Chronic VS-1 treatment inhibited the progression of hypertrophy, fibrosis, and chamber remodeling, and improved cardiac function in a rat model of ISO infusion. In addition, Ca²⁺ handling and its molecular modulation were also improved by VS-1. The beneficial effects of VS-1 on cardiac remodeling may be mediated by the enhanced activation of the eNOS-cGMP-PKG pathway.

Assessing structural and functional responses of murine hearts to acute and sustained β-adrenergic stimulation in vivo

Introduction

Given the importance of β-adrenoceptor signalling in regulating cardiac structure and function, robust protocols are required to assess potential alterations in such regulation in murine models in vivo.

Methods

Echocardiography was performed in naïve and stressed (isoprenaline; 30 μg/g/day s.c. for up to 14 days) mice, in the absence or presence of acute β-adrenergic stimulation (dobutamine 0.75 μg/g, i.p.). Controls received saline infusion and/or injection. Hearts were additionally analysed gravimetrically, histologically and biochemically.

Results

In naïve mice, acute β-adrenoceptor stimulation with dobutamine increased heart rate, left ventricular (LV) fractional shortening (LVFS), ejection fraction (LVEF) and wall thickness and decreased LV diameter (p < 0.05). In stressed mice, dobutamine failed to induce further inotropic and chronotropic responses. Furthermore, following dobutamine injection, these mice exhibited lower LVEF and LVFS at identical heart rates, relative to corresponding controls. Sustained isoprenaline infusion induced LV hypertrophy (increased heart weight, heart weight/body weight ratio, heart weight/tibia length ratio and LV wall thickness (p < 0.05)) by 3 days, with little further change at 14 days. In contrast, increases in LVEF and LVFS were seen only at 14 days (p < 0.05).

Discussion

We describe protocols for and illustrative data from the assessment of murine cardiac responses to acute and sustained β-adrenergic stimulation in vivo, which would be of value in determining the impact of genetic or pharmacological interventions on such responses. Additionally, our data indicate that acute dobutamine stimulation unmasks early signs of LV dysfunction in the remodelled heart, even at a stage when basal function is enhanced.

Effects of Dantrolene Treatment on Ventricular Electrophysiology and Arrhythmogenesis in Rats With Chronic β-Adrenergic Receptor Activation

Dantrolene, which is primarily used to treat malignant hyperthermia, has recently been suggested for the prevention of arrhythmogenesis in various animal models. In this study, the effects of dantrolene treatment on electrophysiological properties and ventricular arrhythmias (VAs) in rats with chronic β-adrenergic receptor (β-AR) activation were investigated. Rats were randomized to treatment with saline (control group), isoproterenol (ISO; ISO group), or ISO + dantrolene (ID group) for 2 weeks. An electrophysiological study was performed to assess action potential duration restitution (APDR) and induce action potential duration (APD) alternans or VA in vitro. The protein levels of Cav1.2, sarcoplasmic reticulum Ca2+-ATPase (SERCA2a), and ryanodine receptor 2 (RyR2) were detected by Western blot. Compared with the control group, chronic administration of ISO significantly increased APD, the maximum slope (Smax) of APDR curve, and the spatial dispersions of Smax and APD (all P < .01), and all effects were attenuated by dantrolene treatment (all P < .05). Additionally, chronic ISO administration significantly reduced the protein levels of SERCA2 and RyR2, but increased the Cav1.2 protein expression (all P < .05). However, compared with the ISO group, dantrolene treatment preserved SERCA2a and RyR2 protein levels and decreased Cav1.2 protein levels in the ID group (all P < .05). The intracellular Ca2+ ([Ca2+]i) levels measured by incubating isolated cardiomyocytes with Fluo-3/alveolar macrophages were significantly increased in the ISO group compared with the control group ( P < .01). Dantrolene treatment markedly reduced the rise of [Ca2+]i levels caused by chronic administration of ISO ( P < .05). Dantrolene treatment also prevented the reductions in the APD alternans and VA thresholds induced by chronic ISO stimulation (all P < .05). These data suggest that dantrolene stabilizes ventricular electrophysiological characteristics and increases the expression of key sarcoplasmic reticulum calcium cycling proteins to reduce vulnerability to VA in rats with chronic β-AR activation.

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.

Novel rat model reveals important roles of β-adrenoreceptors in stress-induced cardiomyopathy

BACKGROUND

Stress-induced cardiomyopathy (SIC), also known as Takotsubo cardiomyopathy, is an acute cardiac syndrome with substantial morbidity and mortality. The unique hallmark of SIC is extensive ventricular akinesia involving apical segments with preserved function in basal segments. Adrenergic overstimulation plays an important role in initiating SIC but the pathophysiological pathways and receptors involved are unknown.

METHODS

Sprague Dawley rats (~300 g) were injected with a single dose of the β-adrenergic agonist isoprenaline (ISO, i.p.) and echocardiography was used to study cardiac function. The akinetic part of the left ventricle was biopsied in six SIC patients. Amount of intracellular lipid and glycogen as well as degree of permanent cardiac damage were assessed by histology.

RESULTS

In rats, ISO at doses ≥ 50 mg/kg induced severe SIC-like regional akinesia that completely resolved within seven days. Intracellular lipid content was higher in akinetic, but not in normokinetic myocardium in both SIC patients and rats. β2-receptor blockade or Gi-pathway inhibition was associated with less widespread akinesia and low lipid accumulation but significantly increased acute mortality.

CONCLUSIONS

We provide a novel rat model of SIC that supports the hypothesis of circulating catecholamines as initiators of SIC. We propose that the β-adrenoreceptor pathway is important in the setting of severe catecholamine overstimulation and that perturbations of cardiac metabolism occur in SIC.

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.

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.

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

In consideration of clinical implications, it is often complained that short-term experimental diseased heart models do not mimic long-term diseased hearts that are often clinically encountered. The aim of the present study was (i) to compare the left ventricular function between rat cardiac hypertrophy models treated with isoproterenol for 3 days (Iso 3d) and 7 days (Iso 7d) by pressure-volume measurements with a catheter method, and (ii) to follow up the left ventricular function in the same model treated with Iso up to 16 weeks with a less-invasive echocardiography. An infusion of either Iso (1.2 mg x kg(-1) x day(-1) for 3 days-16 weeks) or vehicle (saline 24 microl x day(-1) for 3 days-16 weeks; Sa group) was performed by subcutaneously implanting an osmotic minipump. There were no significant differences in the systolic pressure-volume area at midrange left ventricular volume (PVA(mLVV): a mechanical work capability index) between Iso 3d and 7d groups, though PVA(mLVV) in both groups was significantly reduced from that in the Sa group. From echocardiography, the left ventricular function of the hypertrophy models at 3 days, 1 week, and 2 weeks was unchanged, but the model at a term longer than 4 weeks resulted in prolonged systolic failure. The results indicated that (i) no marked differences in the left ventricular mechanical work capability were found between the Iso 3d and 7d groups, and that (ii) only a 3-day Iso infusion induced the hypertrophy model similar in shape and function to that induced by a 2-week Iso infusion. We concluded that the 3-day model was sufficient.

Effects of a novel histone deacetylase inhibitor, N-(2-aminophenyl) benzamide, on a reversible hypertrophy induced by isoproterenol in in situ rat hearts

The aim of the present study was performed to determine whether a novel histone deacetylase (HDAC) inhibitor, N-(2-aminophenyl)-4-{[benzyl(2-hydroxyethyl)amino]methyl} benzamide (K-183), prevents a reversible cardiac hypertrophy induced by isoproterenol and improves left ventricular (LV) dysfunction in rats. Either isoproterenol or vehicle was infused for 3 days by osmotic minipump. One hour prior to the implantation of isoproterenol, K-183 or trichostatin A (TSA) was injected twice a day for 3 days. We recorded continuous LV pressure-volume (P-V) loops of in situ hearts one hour after removal of the osmotic minipump. LV work capability (systolic P-V area at midrange LV volume: PVA(mLVV)) and hemodynamics were evaluated. K-183 per se induced neither cardiac hypertrophy nor collagen production. Although K-183 did not prevent the hypertrophy, where PVA(mLVV) remained decreased, K-183, differently from TSA, significantly attenuated the decrease of cardiac output and the increase of effective arterial elastance in the hypertrophied heart. These results indicate that the novel HDAC inhibitor K-183 has some beneficial effects on hemodynamics, although K-183 has no effects of anti-hypertrophic modalities.

Left Ventricular Mechanoenergetics in Small Animals

Studies on left ventricular mechanical work and energetics in rat and mouse hearts are reviewed. First, left ventricular linear end-systolic pressure-volume relation (ESPVR) and curved end-diastolic pressure-volume relation (EDPVR) in canine hearts and left ventricular curved ESPVR and curved EDPVR in rat hearts are reviewed. Second, as an index for total mechanical energy per beat in rat hearts as in canine hearts, a systolic pressure-volume area (PVA) is proposed. By the use of our original system for measuring continuous oxygen consumption for rat left ventricular mechanical work, the linear left ventricular myocardial oxygen consumption per beat (VO2)-PVA relation is obtained as in canine hearts. The slope of VO2-PVA relation (oxygen cost of PVA) indicates a ratio of chemomechanical energy transduction. VO2 intercept (PVA-independent VO2) indicates the summation of oxygen consumption for Ca2+ handling in excitation-contraction coupling and for basal metabolism. An equivalent maximal elastance (eEmax) is proposed as a new left ventricular contractility index based on PVA at the midrange left ventricular volume. The slope of the linear relation between PVA-independent VO2 and eEmax (oxygen cost of eEmax) indicates changes in oxygen consumption for Ca2+ handling in excitation-contraction coupling per unit changes in left ventricular contractility. The key framework of VO2-PVA-eEmax can give us a better understanding for the biology and mechanisms of physiological and various failing rat heart models in terms of mechanical work and energetics.