Positive Inotropic Effect Research Articles

NPY1 Receptors Participate in the Regulation of Myocardial Contractility in Rats.

Selective agonist (Leu(31)Pro(34)NPY) and blocker (BIBP-3226) of NPY1 receptors were used to determine the type of NPY receptors involved in myocardial contraction. Experiments with isometric contraction of myocardial strips from mature rats showed that the agonist produced the most potent effect in a concentration of 10-7 M. In this concentration, Leu(31)Pro(34)NPY showed the greatest positive inotropic effect on the contraction of the atria and ventricles. In contrast, selective blocker BIBP-3226 reduced the force of myocardial contractions. Pretreatment of myocardial strips with this blocker abolished the positive inotropic effect of Leu(31)Pro(34)NPY, which attested to important role of NPY1 receptors in myocardial contraction.

Cellular basis of angiotensin-(1-7)-induced augmentation of left ventricular functional performance in heart failure

BackgroundAngiotensin-(1-7) [Ang-(1-7)] exhibits cardiovascular effects opposite those of angiotensin II (Ang II), thus providing protection against heart disease. However, how Ang-(1-7) imparts cardioprotection is unclear, and its direct cardiac effects are controversial. Whether heart failure (HF) alters cardiac contractile responses to Ang-(1-7) remains undetermined. We tested the hypothesis that in HF, Ang-(1-7) may produce positive modulation on [Ca2+]i regulation, enhancing left ventricular (LV) and myocyte contraction and relaxation via Ang-(1-7) Mas receptor coupled with nitric oxide (NO)/bradykinin (BK)-mediated mechanism. Methods and resultsWe measured LV contractility changes after Ang-(1-7) (650ng/kg, iv) and compared myocyte functional and [Ca2+]i transient ([Ca2+]iT) responses to Ang-(1-7) superfusion in 24 normal rats and 34 rats with isoproterenol-induced HF (3months after 170mg/kg, s.q. for 2days). To assess the mechanisms of altered HF responses to Ang-(1-7), subsets of HF myocytes were pretreated to inhibit NO synthase (L-NAME), BK (HOE-140), and Mas receptor (A-779) followed with Ang-(1-7). In normal rats, Ang-(1-7) produced no significant changes in LV and myocyte function. In HF rats, Ang-(1-7) significantly augmented LV contractility and relaxation with increased EES (51%), but decreased τ compared to baseline. Ang-(1-7) also significantly increased myocyte contraction (dL/dtmax, 30%), relaxation (dR/dtmax, 41%), and [Ca2+]iT. L-NAME increased, HOE-140 decreased, and A-779 prevented HF myocyte contractile responses to Ang-(1-7). ConclusionsIn a rat model of HF, Ang-(1-7) increases [Ca2+]iT, and produces positive inotropic and lusitropic effects in the LV and myocytes. These effects are mediated by the Mas receptor and involve activation of NO/BK pathways.

The role of diadenosine pentaphosphate and nicotinamide adenine dinucleotide (NAD+) as potential nucleotide comediators in the adrenergic regulation of cardiac function

The functioning of the heart is under the tight control of the sympathetic division of the autonomous nervous system. The terminals of the postganglionary fibers release both noradrenaline (NA), which is the major sympathetic neurotransmitter, and comediators that can contribute to the fine “tuning” of the adrenergic control of cardiac function. Purine compounds, such as diadenosine pentaphosphate (Ар5А), as well as nicotinamide adenine dinucleotide (NAD+), can act as comediators. The distinctive features of the effects of these compounds on the heart have been incompletely characterized. It is not clear whether these compounds can act as comediators, i.e., to modulate the sympathetic (adrenergic) activity in the heart. Exogenous extracellular Ар5А was shown to reduce the contractility of the ventricular myocardium and to suppress conduction in the atrioventricular (AV) junction in a Langendorff-perfused isolated rat heart. Extracellular NAD+ had a weak effect on inotropy but induced a negative dromotropic effect in the AV junction, similarly to Ар5А. We found that Ар5А and NAD+ suppress both the positive inotropic effect of noradrenaline in the ventricular myocardium and the positive dromotropic effect of NA in the AV junction. The “inhibitory” effects of both purine compounds were more pronounced in the case of combined application with NA. In addition, the influence of Ар5А and NAD+ on the effects of noradrenaline was shown to depend on the timing of the application of these compounds. Our results suggest that the role of the sympathetic comediators NAD+ and Ар5А may consist of the limitation of noradrenaline effects and/or the effects of sympathetic stimulation in the heart.

Inotropic Effects of Prostacyclins on the Right Ventricle Are Abolished in Isolated Rat Hearts With Right-Ventricular Hypertrophy and Failure.

Prostacyclin mimetics are vasodilatory agents used in the treatment of pulmonary arterial hypertension. The direct effects of prostanoids on right-ventricular (RV) function are unknown. We aimed to investigate the direct effects of prostacyclin mimetics on RV function in hearts with and without RV hypertrophy and failure. Wistar rats were subjected to pulmonary trunk banding to induce compensated RV hypertrophy (n = 32) or manifest RV failure (n = 32). Rats without banding served as healthy controls (n = 30). The hearts were excised and perfused in a Langendorff system and subjected to iloprost, treprostinil, epoprostenol, or MRE-269 in increasing concentrations. The effect on RV function was evaluated using a balloon-tipped catheter inserted into the right ventricle. In control hearts, iloprost, treprostinil, and MRE-269 improved RV function. The effect was, however, absent in hearts with RV hypertrophy and failure. Treprostinil and MRE-269 even impaired RV function in hearts with manifest RV failure. Iloprost, treprostinil, and MRE-269 improved RV function in the healthy rat heart. RV hypertrophy abolished the positive inotropic effect, and in the failing right ventricle, MRE-269 and treprostinil impaired RV function. This may be related to changes in prostanoid receptor expression and reduced coronary flow reserve in the hypertrophic and failing right ventricle.

Phytochemical Screening, Spectroscpic Characterisation and Cardiotonic Activity of Aqueous Extract from Arieal Parts of Carmona Retusa (Vahl) Masam on Isolated Frogs Heart

The present study was undertaken to evaluate cardiotonic activity of aqueous extract of whole plant of carmona retusa (vahl) masam. Phytochemical screening of whole plant material revealed that the major constituent of Carmon retusa (Vahl.) Masam plant is an intractable mixture of alkaloids,triterpenes, flavanoids and cardiac gylcosides. Cardiotonic effect of aqueous extract of whole plant of carmona retusa was studied by using isolated frog heart perfusion technique (IFHP). Calcium free Ringer solution was used as vehicle for administration of aqueous extract of carmona retusa as a test extract and digoxin as a standard. A significant increase in height of force of contraction (positive inotropic effect) and decrease in heart rate (negative chronotropic effect) at a very low concentration (10g/ml) was observed with test extract as compared to the same dose of a standard digoxin. The present results indicated that a significant increase in height of force of contraction with decrease in heart rate was observed as the dose of test extract increased. The test extract does not produced cardiac arrest at 80g/ml, a higher concentration, as compared to standard, digoxin, a drug with narrow therapeutic window, carmona retusa showed wide therapeutic window.

Gene Therapy With Angiotensin-(1-9) Preserves Left Ventricular Systolic Function After Myocardial Infarction

BackgroundAngiotensin-(1-9) [Ang-(1-9)] is a novel peptide of the counter-regulatory axis of the renin-angiotensin-aldosterone system previously demonstrated to have therapeutic potential in hypertensive cardiomyopathy when administered via osmotic mini-pump. Here, we investigate whether gene transfer of Ang-(1-9) is cardioprotective in a murine model of myocardial infarction (MI). ObjectivesThe authors evaluated effects of Ang-(1-9) gene therapy on myocardial structural and functional remodeling post-infarction. MethodsC57BL/6 mice underwent permanent left anterior descending coronary artery ligation and cardiac function was assessed using echocardiography for 8 weeks followed by a terminal measurement of left ventricular pressure volume loops. Ang-(1-9) was delivered by adeno-associated viral vector via single tail vein injection immediately following induction of MI. Direct effects of Ang-(1-9) on cardiomyocyte excitation/contraction coupling and cardiac contraction were evaluated in isolated mouse and human cardiomyocytes and in an ex vivo Langendorff-perfused whole-heart model. ResultsGene delivery of Ang-(1-9) reduced sudden cardiac death post-MI. Pressure volume measurements revealed complete restoration of end-systolic pressure, ejection fraction, end-systolic volume, and the end-diastolic pressure volume relationship by Ang-(1-9) treatment. Stroke volume and cardiac output were significantly increased versus sham. Histological analysis revealed only mild effects on cardiac hypertrophy and fibrosis, but a significant increase in scar thickness. Direct assessment of Ang-(1-9) on isolated cardiomyocytes demonstrated a positive inotropic effect via increasing calcium transient amplitude and contractility. Ang-(1-9) increased contraction in the Langendorff model through a protein kinase A–dependent mechanism. ConclusionsOur novel findings showed that Ang-(1-9) gene therapy preserved left ventricular systolic function post-MI, restoring cardiac function. Furthermore, Ang-(1-9) directly affected cardiomyocyte calcium handling through a protein kinase A–dependent mechanism. These data emphasized Ang-(1-9) gene therapy as a potential new strategy in the context of MI.

Selective Blockade of α2-Adrenoceptor Subtypes Modulates Contractility of Rat Myocardium.

The study examined the dose-dependent effects of selective antagonists of α2A/D-, α2B-, and α2C- adrenoceptors applied in concentrations of 10-9-10-5 M on atrial and ventricular contractility of rat myocardium in vitro. Selective blockade of each α2-adrenoceptor subtype affected the contractile force of the atrial and ventricular strips. Various concentrations of α2A/D- and α2C-adrenoceptor antagonists produced positive inotropic effect on ventricular strips and negative effect on atrial strips. α2B-Adrenoceptor blocker in the majority of the tested concentrations produced a positive inotropic effect in both atria and ventricles.

The Effect of a Novel Highly Selective Inhibitor of the Sodium/Calcium Exchanger (NCX) on Cardiac Arrhythmias in In Vitro and In Vivo Experiments.

BackgroundIn this study the effects of a new, highly selective sodium-calcium exchanger (NCX) inhibitor, ORM-10962 were investigated on cardiac NCX current, Ca2+ transients, cell shortening and in experimental arrhythmias. The level of selectivity of the novel inhibitor on several major transmembrane ion currents (L-type Ca2+ current, major repolarizing K+ currents, late Na+ current, Na+/K+ pump current) was also determined.MethodsIon currents in single dog ventricular cells (cardiac myocytes; CM), and action potentials in dog cardiac multicellular preparations were recorded utilizing the whole-cell patch clamp and standard microelectrode techniques, respectively. Ca2+ transients and cell shortening were measured in fluorescent dye loaded isolated dog myocytes. Antiarrhythmic effects of ORM-10962 were studied in anesthetized ouabain (10 μg/kg/min i.v.) pretreated guinea pigs and in ischemia-reperfusion models (I/R) of anesthetized coronary artery occluded rats and Langendorff perfused guinea pigs hearts.ResultsORM-10962 significantly reduced the inward/outward NCX currents with estimated EC50 values of 55/67 nM, respectively. The compound, even at a high concentration of 1 μM, did not modify significantly the magnitude of ICaL in CMs, neither had any apparent influence on the inward rectifier, transient outward, the rapid and slow components of the delayed rectifier potassium currents, the late and peak sodium and Na+/K+ pump currents. NCX inhibition exerted moderate positive inotropic effect under normal condition, negative inotropy when reverse, and further positive inotropic effect when forward mode was facilitated. In dog Purkinje fibres 1 μM ORM-10962 decreased the amplitude of digoxin induced delayed afterdepolarizations (DADs). Pre-treatment with 0.3 mg/kg ORM-10962 (i.v.) 10 min before starting ouabain infusion significantly delayed the development and recurrence of ventricular extrasystoles (by about 50%) or ventricular tachycardia (by about 30%) in anesthetized guinea pigs. On the contrary, ORM-10962 pre-treatment had no apparent influence on the time of onset or the severity of I/R induced arrhythmias in anesthetized rats and in Langendorff perfused guinea-pig hearts.ConclusionsThe present study provides strong evidence for a high efficacy and selectivity of the NCX-inhibitory effect of ORM-10962. Selective NCX inhibition can exert positive as well as negative inotropic effect depending on the actual operation mode of NCX. Selective NCX blockade may contribute to the prevention of DAD based arrhythmogenesis, in vivo, however, its effect on I/R induced arrhythmias is still uncertain.

355 - Approaches for Overcoming Diabetes-Induced Cardiovascular Nitric Oxide Resistance

In patients with cardiovascular disease, impaired nitric oxide (NO●) signalling is an independent predictor of poor outcomes, including mortality. This loss of NO●-responsiveness (termed ‘NO●-resistance’) is particularly debilitating in diabetes, where cardiovascular emergencies (acute myocardial infarction [MI], transient ischaemia, cardiogenic shock) occur more frequently, but NO●-based pharmacotherapies are unable to effectively counteract platelet aggregation and vasoconstriction. Further, the extent of NO●-resistance appears critically dependent on concomitant circulating levels of blood glucose. We have now examined whether the myocardium, like platelets and vessels, is also susceptible to NO●-resistance such that NO● can no longer enhance left ventricular (LV) relaxation. Hearts isolated from anaesthetised adult male streptozotocin (STZ) diabetic rats with severe (~30mM) or moderate hyperglycaemia(titrated to ~22mM with insulin), or non-diabetic shams were Langendorff-perfused. Following U46619 preconstriction of the coronary vasculature to 50%, dose-response curves to acute bolus doses of the NO● donor diethylamine NONOate (DEA-NO 10pmol-10μmol) were performed. Results were compared to those obtained in response to a donor of the NO● redox sibling nitroxyl, isopropylamine NONOate (IPA-NO). Using the selective inhibitor of soluble guanylyl cyclase, ODQ (10µM), the relative contribution of cGMP to these haemodynamic responses under normoglycaemia, moderate and severe hyperglycaemia were also elucidated. Our results demonstrated that diabetes impairs NO●-mediated coronary vasodilatation, LV relaxation and LV contractile function. The impaired NO vasodilatation persisted in hearts from moderately hyperglycaemic rats. In contrast, nitroxyl-mediated vasodilatation was preserved, and the positive inotropic and lusitropic effects were further enhanced, in diabetic myocardium. In conclusion, we have demonstrated for the first time that the haemodynamic responses to nitroxyl are preserved or enhanced in diabetes, whereas those of NO● are attenuated. We have hence identified in nitroxyl an exciting potential strategy for circumventing impaired NO● signalling.

EFFECT OF OBESTATIN ON CARDIOVASCULAR SYSTEM IN TYPE II DIABETIC RAT MODEL

Background: Obestatin (OB) is a novel anorexiogenic peptide produced in the stomach. It has been shown to regulate glucose and lipid metabolism. However, its potential role in cardiovascular control is still not clear and controversial. Aim of the work: To evaluate the in vivo and in vitro effects of Obestatin on cardiovascular system in both normal and diabetic rats. Also, to identify the possible mechanism of its action. Material and methods: 40 healthy male albino rats weighing 180-200 gm. were used and divided into two main groups: In vivo experiments subdivided into normal (n= 10 ) and Type II Diabetes induced groups (n=10) In which heart rate and blood pressure were recorded before and after OB (100 Mg/kg body weight) injection , In vitro experiments subdivided into normal (n= 10) and Type II Diabetes induced group ( n= 10) in which the effect of OB (1 nmol/l) alone and its effect in presence of β –blocker propranolol (30Mmol/l) and α blocker prazosin (3Mmol/l) on amplitude and frequency of cardiac contractility were studied ,also effects of OB alone (100 pmol/l) and in presence of LNAME(0.3Mmol/l) on contraction induced by phenylephrine (10 Mmol/L) of isolated thoracic aorta. Type II Diabetes induced by feeding rats for two weeks a high-fat diet (58% fat, 25% protein, 17% carbohydrates as percentage of total calories). On day 13, rats were given a single intraperitoneal injection of streptozotocin (25 mg/kg body). Results: Obestatin injection showed no significant difference on blood pressure and heart rate in both normal and diabetic rats, However in vitro studies showed that OB has both positive inotropic and chronotropic effects on isolated heart of both normal and diabetic rats which were blocked by propranolol but not by prazocin. Moreover, OB produced significant vascular relaxation of isolated rat thoracic aorta of the normal group which was attenuated by L-NAME in normal rats. However, the relaxation effect of OB was much weaker in diabetic rats and was blocked by L-NAME. Conclusion: Obestatin improves cardiac function and exerts vasodilator effects via nitric oxide (NO) release, so it may be decrease systemic vascular resistance in type II diabetes. Key words: Obestatin, type II diabetic rats, propranolol, prazocin, isolated thoracic aorta.

Cardiac inotropy, lusitropy, and Ca2+ handling with major metabolic substrates in rat heart.

Fatty acid (FA)-dependent oxidation is the predominant process for energy supply in normal heart. Impaired FA metabolism and metabolic insufficiency underlie the failing of the myocardium. So far, FA metabolism in normal cardiac physiology and heart failure remains undetermined. Here, we evaluate the mechanisms of FA and major metabolic substrates (termed NF) on the contraction, relaxation, and Ca2+ handling in rat left ventricular (LV) myocytes. Our results showed that NF significantly increased myocyte contraction and facilitated relaxation. Moreover, NF increased the amplitudes of diastolic and systolic Ca2+ transients ([Ca2+]i), abbreviated time constant of [Ca2+]i decay (tau), and prolonged the peak duration of [Ca2+]i. Whole-cell patch-clamp experiments revealed that NF increased Ca2+ influx via L-type Ca2+ channels (LTCC, ICa-integral) and prolonged the action potential duration (APD). Further analysis revealed that NF shifted the relaxation phase of sarcomere lengthening vs. [Ca2+]i trajectory to the right and increased [Ca2+]i for 50 % of sarcomere relengthening (EC50), suggesting myofilament Ca2+ desensitization. Butanedione monoxime (BDM), a myosin ATPase inhibitor that reduces myofilament Ca2+ sensitivity, abolished the NF-induced enhancement of [Ca2+]i amplitude and the tau of [Ca2+]i decay, indicating the association of myofilament Ca2+ desensitization with the changes in [Ca2+]i profile in NF. NF reduced intracellular pH ([pHi]). Increasing [pH]i buffer capacity with HCO3/CO2 attenuated Δ [pH]i and reversed myofilament Ca2+ desensitization and Ca2+ handling in NF. Collectively, greater Ca2+ influx through LTCCs and myofilament Ca2+ desensitization, via reducing [pH]i, are likely responsible for the positive inotropic and lusitropic effects of NF. Computer simulation recapitulated the effects of NF.Electronic supplementary materialThe online version of this article (doi:10.1007/s00424-016-1892-8) contains supplementary material, which is available to authorized users.

Interplay Between Hydrogen Sulfide and Adrenergic and Muscarinic Receptors in the Mouse Atrium

Hydrogen sulfide (H2S) is synthesized endogenously, and it has a negative inotropic effect on myocardium of different animal species. Interaction between H2S and adrenergic and muscarinic receptors in regulation of mouse atrium contractile function was investigated in this study. Sodium hydrosulfide (NaHS, 300 μM), the H2S donor, decreased the contraction force of atrium. NaHS did not affect the positive inotropic effect of β-adrenoceptors (β-AR) activation by isoproterenol (ISO, 1 μM). The effect of the H2S donor under β-AR stimulation showed no differences comparison to control values. The agonist of muscarinic receptors carbachol (1 μM) induced a negative inotropic effect and partially prevented the reduction of cardiac muscle contractility by NaHS. Moreover, the effect of carbachol was more pronounced after preliminary application of NaHS. At the same time, after inhibition of β-AR (propranolol, 1 μM) or muscarinic receptors (atropine, 1 μM), negative inotropic effect of NaHS was the same as in control conditions. These results suggest that the H2S effects are mediated by intracellular signaling pathways activated by muscarinic receptors.

Polymorphism in Endothelin-1 Gene: An Overview.

Endothelin-1, (ET-1, EDN1) is an endogenous polypeptide which demonstrates dominant vasoconstriction activity and mitogenic effect. It has positive inotropic and chronotropic effects on the heart, stimulates the sympathetic and the renin-angiotensin-aldosterone systems and modifies homeostasis. The human ET-1 gene which consists of 6836 nucleotides located on chromosome 6p23-p24 produces Pre-pro-ET-1, which is consequently cleaved to big-ET-1. The mature 21-amino acid ET-1 is generated by subsequent enzymatic cleavage of the big-ET-1. A comprehensive review of the literature on the consequences of different ET-1 gene variants on ET-1 linked diseases has not been accomplished. Many variants of ET-1 gene, including transversion, transition, insertion, and repeated nucleotide polymorphisms, which influence the hereditary risk of cardiovascular and other related diseases have already been located, genotyped, and examined. Among them ten polymorphisms including transversion; -1370 (T-1370G) (rs1800541), +5665 (Lys198Asn) (rs5370), G2288T polymorphisms (rs2070699), and -974 C<A (rs3087459) polymorphism, transition; +3660 (Glu106Glu) (rs5369), G(8002)A (rs2071942), rs1476046 polymorphism , rs2071943 polymorphism, and rs9296345 polymorphism, and insertion/delete; +138 (+138/ex1ins/delA) (rs1800997) were studied and phenotyped extensively. Some significant associations with many different diseases (phenotypes) especially those related to cardiovascular system diseases such as hypertension, ischemic diseases, angina, and acute coronary syndrome have been described in the literature. Some are associated with other diseases such as asthma, pulmonary edema, hearing impairment, obesity and sleep apnea. Moreover, some are modifying the course and adverse effects of several drugs. Many of these polymorphisms were studied, thus some inner complex association manner was also described.

Cardiac support and replacement therapies

Circulatory support represents an integral part within the treatment of the critically ill patient. Sophisticated pharmacologic regimens help to maintain systemic perfusion pressure by increasing vascular tone as well as mediating positive inotropic effects. Besides the administration of catecholamines and phosphodiesterase-III-inhibitors, in particular the administration of levosimendan represents a promising alternative during low-cardiac-output. Nevertheless, sufficient evidence demonstrating a survival benefit for any pharmacologic regimen is nonexistent. In case pharmacological measures do not suffice mechanical cardiopulmonary support (MCS) may be used. MCS may be used during cardiopulmonary resuscitation or a "low-cardiac-output-syndrome" as bridging towards decision, recovery or long-term support. Venoarterial extracorporeal membrane oxygenation (vaECMO) may take over cardiopulmonary function and may improve survival as well as neurological outcome after cardiogenic shock or cardiopulmonary resuscitation.

Apelin-13 in blood pressure regulation and cardiovascular disease.

Despite extensive pharmacological treatment, hypertension and heart failure still pose as high health and economic burden. Thus, novel therapeutic approaches are needed to promote more effective treatment of hypertension and cardiovascular disease. In this review we summarized recent evidence supporting the therapeutic potential of apelin-13, a recently discovered endogenous ligand for the G-protein coupled receptor APJ. Systemic administration of apelin-13 or its posttranslationally modified form, pyroglutamate apelin-13, exert vasodilatory and antihypertensive effects. Yet, central application of apelin increases blood pressure and its systemic effects may be compromised in the presence of endothelial dysfunction. In addition, positive inotropic effects by exogenous apelin in the normal and failing heart, as well as cardioprotective effects after myocardial infarction, strongly suggest its therapeutic potential in preventing and treating heart failure and consequences of myocardial ischemia. However, therapeutic use of apelin is limited primarily by its short half-life and parenteral administration, and significant effort has been directed to the development of novel agonists, delivery methods, and improving the efficacy of agonists at APJ. The apelin/APJ axis may represent a new target for the development of novel therapeutic approaches for the treatment of hypertension and cardiovascular disease.

Cardiac α1-Adrenoceptors and Inotropy: Myofilament Ca2+ Sensitivity, Intracellular Ca2+ Mobilization, Signaling Pathway, and Pathophysiological Relevance.

Cardiac α1-adrenoceptor stimulation elicits a positive inotropic effect because of myofilament Ca2+ sensitization with a small increase in Ca2+ transients predominantly mediated by α1B-adrenoceptors via the intracellular alkalinization and potential myosin light chain 2 phosphorylation. However, the α1-adrenoceptor–mediated inotropy exhibits a wide range of species-dependent variation. In addition, it displays remarkable regional and subtype-dependent variations among species. The signaling pathway for α1-adrenoceptor–mediated regulation is vulnerable being markedly influenced by experimental and pathophysiological conditions. Cardiac α1-adrenoceptors may have clinical relevance in that sympathomimetic amines including norepinephrine possess higher affinity to α1-adrenoceptors than β-adrenoceptors, and α1-adrenoceptors play a compensatory role in patients with heart failure. Modulation of cardiac α1-adrenoceptor–mediated signaling pathway could provide potential targets for the development of novel therapeutic strategy. The role of cardiac α1-adrenoceptors in regulation of myocardial contractility, including mechanism of action, signaling pathway, and pathophysiological and clinical significance, has been less clarified compared with the well-established β-adrenoceptor–mediated regulation. In this viewpoint, I will focus on the state-of-the-art of cardiac α1-adrenoceptor–mediated basic mechanism and its pathophysiological relevance in relation to clinical implications. The regulation of myocardial contractility by Ca2+ is achieved by either alteration of peak Ca2+ transients (CaT) that reflect the intracellular Ca2+ ([Ca2+]i) mobilization during twitch contraction (upstream mechanism), myofilament Ca2+ sensitivity (central or downstream mechanism) or combination of both, in which the binding of Ca2+ to troponin C plays a central role (central mechanism) in cardiac EC coupling. Cardiac α1-adrenoceptor stimulation elicits a moderate increase in peak CaT (20% of the maximum of β-adrenoceptor–mediated increase), whereas it induces the maximum positive inotropic effect (PIE) in an amount of 60% of the β-adrenoceptor–mediated maximum …

Stretch-Activated Paracrine/Autocrine Signalling in the Heart: A Role for Prostaglandins?

It is well known that stretch increases the hearts contractility, although the cellular mechanisms that produce the stretch response are not fully understood. Recently, using a unique bioassay system, we showed unequivocally that stretching the left ventricle of isolated perfused rat hearts released paracrine/autocrine factors [[1]Ward M.-L. Shen X. Greenwood D.R. Use of liquid chromatography-mass spectrometry (LC-MS) to detect substances of nanomolar concentration in the coronary effluent of isolated perfused hearts.Prog Biophys Mol Biol. 2014 Jul 24; Google Scholar]. Preliminary analysis of our data using a metabolomics approach suggested these factors were prostanoids, constituting a set of signalling pathways not previously associated with regulation of the heart. Quantitative and statistical analyses using differential LCMS/MS of the coronary effluent collected from un-stretched and stretched hearts identified prostaglandins F2α and E2 as significantly different between stretched and un-stretched samples (P < 0.01). Exogenous PGF2α and PGE2 applied to isolated trabeculae from rat hearts elicited a positively inotropic response from PGF2α, but not PGE2. PGF2ɑ, over a concentration range of 1 nM - 1 μM, increased both the Ca2+ transients and isometric stress in trabeculae, reaching steady-state after 10 - 15 min, without altering the time course of Ca2+ transient decay. The positive inotropic effect of PGF2α was mediated through a protein kinase C (PKC) signalling pathway that involved activation of the sarcolemmal Na+/H+ exchanger. These data suggest PGF2α is important in maintaining homeostasis during volume loading in healthy hearts. However, under pathophysiological conditions, sustained release of PGF2α might be important in that activation of detrimental hypertrophic pathways.

Effect of the long-acting insulin analogues glargine and degludec on cardiomyocyte cell signalling and function.

BackgroundThe effects of insulin on cardiomyocytes, such as positive inotropic action and glucose uptake are well described. However, in vitro studies comparing long-acting insulin analogues with regard to cardiomyocyte signalling and function have not been systematically conducted.MethodsInsulin receptor (IR) binding was assessed using membrane embedded and solubilised IR preparations. Insulin signalling was analysed in adult rat ventricular myocytes (ARVM) and HL-1 cardiac cells. Inotropic effects were examined in ARVM and the contribution of Akt to this effect was assessed by specific inhibition with triciribine. Furthermore, beating-rate in Cor.4U® human cardiomyocytes, glucose uptake in HL-1 cells, and prevention from H2O2 induced caspase 3/7 activation in cardiac cells overexpressing the human insulin receptor (H9c2-E2) were analysed. One-way ANOVA was performed to determine significance between conditions.ResultsInsulin degludec showed significant lower IR affinity in membrane embedded IR preparations. In HL-1 cardiomyocytes, stimulation with insulin degludec resulted in a lower Akt(Ser473) and Akt(Thr308) phosphorylation compared to insulin, insulin glargine and its active metabolite M1 after 5- and 10-min incubation. After 60-min treatment, phosphorylation of Akt was comparable for all insulin analogues. Stimulation of glucose uptake in HL-1 cells was increased by 40–60 %, with a similar result for all analogues. Incubation of electrically paced ARVM resulted for all insulins in a significantly increased sarcomere shortening, contractility- and relaxation–velocity. This positive inotropic effect of all insulins was Akt dependent. Additionally, in Cor.4U® cardiomyocytes a 10–20 % increased beating-rate was detected for all insulins, with slower onset of action in cells treated with insulin degludec. H9c2-E2 cells challenged with H2O2 showed a fivefold increase in caspase 3/7 activation, which could be abrogated by all insulins used.ConclusionsIn conclusion, we compared for the first time the signalling and functional impact of the long-acting insulin analogues insulin glargine and insulin degludec in cardiomyocyte cell models. We demonstrated similar efficacy under steady-state conditions relative to regular insulin in functional endpoint experiments. However, it remains to be shown how these results translate to the in vivo situation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12933-016-0410-9) contains supplementary material, which is available to authorized users.

Effects of Acetaminophen on Left Atrial Contractility.

It has been observed that acetaminophen shows cardioprotective efficacy in mammals. In this study, we investigated the electromechanical effects of acetaminophen on the left atrium (LA). Conventional microelectrodes were used to record the action potentials (AP) in rabbit LA preparations. The action potential duration (APD) at repolarization levels of 90%, 50% and 20% of the AP amplitude (APD90, APD50, and APD20, respectively), resting membrane potential, and contractile force were measured during 2 Hz electrical stimulation before and after sequential acetaminophen administration to the LA. Acetaminophen (0.1, 0.3, 1, and 3 mM) reduced APD20 from 9.4 ± 1.2 to 8.0 ± 1.1 (p < 0.05), 7.1 ± 0.8 (p < 0.05), 7.8 ± 1.1, and 6.8 ± 1.2 ms (p < 0.05), respectively, and APD50 from 20.2 ± 1.9 to 17.4 ± 2.0, 15.6 ± 1.8 (p < 0.05), 15.8 ± 2.2 (p < 0.05), and 14.1 ± 2.4 ms (p < 0.05), respectively, in a concentration-dependent manner. APD90 was reduced from 72.0 ± 3.6 to 64.7 ± 4.2, 61.9 ± 4.3, 60.5 ± 3.7, and 53.4 ± 4.4 ms (p < 0.05), respectively. Acetaminophen increased LA contractility from 45 ± 9 to 52 ± 10 (p < 0.05), 55 ± 9 (p < 0.01), 58 ± 9 (p < 0.01), and 60 ± 9 mg (p < 0.01), respectively, in a concentration-dependent manner. In the presence of the NOS inhibitor L-NAME or PKG-I inhibitor DT-2, additional acetaminophen treatment did not significantly increase LA contractility. Acetaminophen modulated the electromechanical characteristics of LA by inhibiting the NOS and PKG I pathway, and then contributed to the positive inotropic effect.

Positive Inotropic Effect of Prostaglandin F2α in Rat Ventricular Trabeculae.

Prostaglandins are ubiquitous signaling molecules in the body that produce autocrine/paracrine effects on target cells in response to mechanical or chemical signals. In the heart, long-term exposure to prostaglandin (PG) F2α has been linked to the development of hypertrophy; however, there is no consensus on the acute effect of PGF2α. Our aim was to determine the response to exogenous PGF2α in isolated trabeculae from rat hearts. PGF2α (1 μM) increased both the Ca transients and the isometric stress in trabeculae, reaching steady state after 10-15 minutes, without altering the time course of Ca transient decay. The precursor of PGF2α, arachidonic acid, also stimulated a similar response. The positive inotropic effect of PGF2α was mediated through a protein kinase C signaling pathway that involved activation of the sarcolemmal Na/H exchanger. We also found that the slow force response to stretch was attenuated in the presence of PGF2α and by addition of indomethacin, a blocker of prostaglandin synthesis. In conclusion, PGF2α was positively inotropic when acutely applied to trabeculae and contributed to the increased Ca transients during the slow force response to stretch. Together, these data suggest that PGF2α is important in maintaining homeostasis during volume loading in healthy hearts.