Abstract. The animal models of myocardial injury induced by systemic β-adrenergic receptor agonist administration represent an experimental approach of persisting interest. These models were found useful especially for studies of structural and functional adaptation of myocardium during the progression of cardiac adaptive response towards maladaptive hypertrophy and insufficiency. The pathological alterations induced by isoproterenol (ISO) do not develop evenly. The ISO models may contribute effectively to understanding of pathologies in signal transduction, energetics, excitability and contractility that may contribute concomitantly to cardiac dysfunction and heart failure. In this minireview we focused on the alterations in general characteristics and heart function as well as on the morphological changes of cardiomyocytes developed during ISO administration. The morphological alterations within the cellular macro-and microdomains correspond to the electrical remodeling and contractile dysfunction of ventricular myocardium that could be used to identify pathological changes ranging from hypertrophy to failing heart.

Cardiac excitation-contraction coupling relies on dyads, the intracellular calcium synapses of cardiac myocytes, where the plasma membrane contacts sarcoplasmic reticulum and where electrical excitation triggers calcium release. The morphology of dyads and dynamics of local calcium release vary substantially. To better understand the correspondence between the structure and the functionality of dyads, we estimated incidences of structurally different dyads and of kinetically different calcium release sites and tested their responsiveness to experimental myocardial injury in left ventricular myocytes of rats. According to the structure of dyads estimated in random electron microscopic images of myocardial tissue, the dyads were sorted into 'compact' or 'loose' types. The calcium release fluxes, triggered at local calcium release sites in patch-clamped ventricular myocytes and recorded by laser scanning confocal fluorescence microscopy, were decomposed into 'early' and 'late' components. ANOVA tests revealed very high correlation between the relative amplitudes of early and late calcium release flux components and the relative occurrences of compact and loose dyads in the control and in the injured myocardium. This finding ascertained the relationship between the structure of dyads and the functionality of calcium release sites and the responsiveness of calcium release sites to physical load in cardiac myocytes.

In the present work, the effect of isoproterenol on the electrical properties of the rat heart and on the cytoarchitecture of the surviving cardiomyocytes was studied. Myocardial remodelling was induced by the daily administration of 5 mg/kg isoproterenol (Iso) for 7 days. Administration resulted in a significant increase (52%) in the ratio of left ventricular weight to body weight. ECG voltage criteria confirmed the presence of left ventricular hypertrophy. QT interval prolongation by 23% and 58% was found in Iso rats and in the corresponding isolated hearts, respectively. Spontaneously beating Iso hearts had a higher incidence of dysrhythmias. The surviving cardiomyocytes showed an irregular shape with cytoplasmic processes rich in ribosomes and rough endoplasmic reticulum. In these regions, myofibril disorganization and mitochondrial fission were observed. A greatly increased incidence of caveolae was seen in the plasma membrane and in the mouth of t-tubules. The membranes of t-tubules showed vesiculation, especially near the dyads. Repeated administration of isoproterenol led to hypertrophy, characterized by the existence of myocytes with simultaneous signs of both mature and postnatally developing cardiomyocytes. Structural microheterogeneities at the level of individual cells may represent one of the factors leading to electrical imbalance in the myocardial tissue remodelled by isoproterenol.

In view of previously reported increased capacity for nitric oxide production, we suggested that L-arginine (ARG), the nitric oxide synthase (NOS) substrate, supplementation would improve cardiac function in isoproterenol (ISO)-induced heart failure. Male Wistar rats were treated with ISO for 8 days (5 mg/kg/day, i.p.) or vehicle. ARG was given to control (ARG) and ISO-treated (ISO+ARG) rats in water (0.4 g/kg/day). ISO administration was associated with 40% mortality, ventricular hypertrophy, decreased heart rate, left ventricular dysfunction, fibrosis and ECG signs of ischaemia. RT-PCR showed increased mRNA levels of cardiac hypertrophy marker atrial natriuretic peptide, but not BNP, decreased expression of myosin heavy chain isoform MYH6 and unaltered expression of pathological MYH7. ISO increased the protein levels of endothelial nitric oxide synthase, but at the same time it markedly up-regulated mRNA and protein levels of gp91phox, a catalytical subunit of superoxide-producing NADPH oxidase. Fibrosis was markedly increased by ISO. ARG treatment moderately ameliorated left ventricular dysfunction, but was without effect on cardiac hypertrophy and fibrosis. Combination of ISO and ARG led to a decrease in cav-1 expression, a further increase in MYH7 expression and a down-regulation of MYH6 that inversely correlated with gp91phox mRNA levels. Although ARG, at least partially, improved ISO-impaired basal left ventricular systolic function, it failed to reduce cardiac hypertrophy, fibrosis, oxidative stress and mortality. The protection of contractile performance might be related to increased capacity for nitric oxide production and the up-regulation of MYH7 which may compensate for the marked down-regulation of the major MYH6 isoform.L-arginine is the precursor of nitric oxide, a key regulatory molecule in the cardiovascular system. Decreased nitric oxide synthesis or bioavailability may result in endothelial dysfunction that is present in many cardiovascular diseases such as hypertension, atherosclerosis, erectile dysfunction, myocardial infarction (MI) and congestive heart failure [1]. Nitric oxide is synthesized by three isoforms of nitric oxide synthases, endothelial (eNOS), neuronal (nNOS) and inducible (iNOS), that can all be expressed in the heart [2]. Nitric oxide in the heart can regulate a number of functions such as heart rate, coronary flow, myocardial oxygen consumption, and contractility under both physiological and pathological conditions [2,3]. Nitric oxide has antihypertrophic properties for cardiac myocytes [4], can inhibit the development of cardiac fibrosis [5] and can induce angiogenesis [6], while nitric oxide deficiency can contribute to pathological cardiac remodelling [7]. However, under the conditions of oxidative stress, increased nitric oxide production may lead to cellular injury via toxic peroxynitrite formation [8].L-arginine supplementation in human heart failure leads to an improvement of endothelium-dependent vasodilation and improved exercise capacity and quality of ...

Aim: The aim of the study was to describe experience with falls, fear of falling, perceptions of the consequences of falls and how the fear of falling affects daily life in community-dwelling older adults. Design: The study used a qualitative design to describe the lived experiences of community-dwelling older adults with the fear of falling. Methods: Semi-structured interviews were conducted individually with six participants who reported the fear of falling. Results: Five main areas emerged from data analysis: development of the fear of falling, feared consequences of falling, activities curtailment, fall prevention behavior and meaning of social support in daily life. The fear of falling was described as a negative experience, directly linked to fall consequences such as physical injury, incapacitation, loss of autonomy, fear of dependence and experience of humiliating conditions. To maintain a certain level of independence in daily life, the participants chose to avoid falls by activity curtailment, organizing their lives more carefully and getting support from others. Conclusion: All participants identified that they had discovered their fear of falling after experiencing falls. The fear of falling was associated with feared consequences of a potential fall and had an impact on their daily life. The participant also mentioned other contributors to their fear of falling, including ill health and aging.

The progression of diabetes mellitus leads in time to the development of serious cardiovascular complications. Pycnogenol® (PYC) belongs to strong antioxidants that may interfere with different pathways playing an important role in diseases associated with oxidative stress. Metformin (MET), commonly used antidiabetic drug, has cardio-protective effects via activation of AMP kinase (AMPK). In our study, we examined the effects of PYC as add-on drug to metformin therapy in streptozotocin (STZ)-induced diabetic rats. Our results revealed that both used agents, PYC and MET, showed improvement of blood glucose levels, vascular reactivity, left ventricular hypertrophy, expression of AMPK, glucose transporter 4 (GLUT4) and calcium/calmodulin-dependent protein kinase II (CaMKII) in left ventricle of the hearts. However, the combination of these interventions has failed to possess higher efficacy. Copyright © 2016 John Wiley & Sons, Ltd.

Background In spite of disrupted repolarization of diabetic heart, some studies report less tendency of diabetic heart to develop ventricular arrhythmias suggesting effective compensatory mechanism. We hypothesized that myocardial alterations in HCN2 and HCN4 channels occur under hyperglycaemia. Methods Diabetes was induced in rats using a single injection of streptozotocin (STZ; 55 mg/kg body weight, i.p.). Basal ECG was measured. Expression of mRNA for HCN channels, potassium channels and microRNA 1 and 133a were measured in ventricular tissues. Protein expression of HCN2 channel isoform was assessed in five different regions of the heart by western blotting. Differentiated H9c2 cell line was used to examine HCN channels expression under hyperglycaemia in vitro. Results Six weeks after STZ administration, heart rate was reduced, QRS complex duration, QT interval and T-wave were prolonged in diabetic rats compared to controls. mRNA and protein expressions of HCN2 decreased exclusively in the ventricles of diabetic rats. HCN2 expression levels in atria of STZ rats and H9c2 cells treated with excess of glucose were not changed. MicroRNA levels were stable in STZ rat hearts. We found significantly decreased mRNA levels of several potassium channels participating in repolarization, namely Kcnd2 (Ito1), Kcnh2 (IKr), Kcnq1 (IKs) and Kcnj11 (IKATP). Conclusions This result together with downregulated HCN2 channels suggest that HCN channels might be an integral part of ventricular electric remodelling and might play a role in cardiac repolarization projected in altered arrhythmogenic profile of diabetic heart.

Tyrosine kinases inhibitors (TKIs) may alter glycaemia and may be cardiotoxic with importance in diabetic heart. We investigated the effect of multi-TKI crizotinib after short-term administration on metabolic modulators of the heart of diabetic rats. Experimental diabetes mellitus (DM) was induced by streptozotocin (STZ; 80 mg/kg, i.p.), controls received vehicle (CON). Three days after STZ, crizotinib (STZ+CRI; 25 mg/kg/day p.o.) or vehicle was administered for 7 days. Blood glucose, C-peptide and glucagon were assessed in plasma samples. Receptor tyrosine kinases (RTKs), cardiac glucose transporters and PPARs were determined in rat left ventricle by RT-qPCR method. Crizotinib moderately reduced blood glucose (by 25%, P<0.05) when compared to STZ rats. The drug did not affect levels of C-peptide, an indicator of insulin secretion, suggesting altered tissue glucose utilization. Crizotinib had no impact on cardiac RTKs. However, an mRNA downregulation of insulin-dependent glucose transporter Glut4 in hearts of STZ rats was attenuated after crizotinib treatment. Moreover, crizotinib normalized Ppard and reduced Pparg mRNA expression in diabetic hearts. Crizotinib decreased blood glucose independently of insulin and glucagon. This could be related to changes in regulators of cardiac metabolism such as GLUT4 and PPARs.