Abnormal biochemistry in myocardial failure

Cardiomyocyte Proliferation from Fetal- to Adult- and from Normal- to Hypertrophy and Failing Hearts

Simple Summary

Death from injury to the heart from a variety of causes remains a major cause of mortality worldwide. The cardiomyocyte, the major contracting cell of the heart, is responsible for pumping blood to the rest of the body. During fetal development, these immature cardiomyocytes are small and rapidly divide to complete development of the heart by birth when they develop structural and functional characteristics of mature cells which prevent further division. All further growth of the heart after birth is due to an increase in the size of cardiomyocytes, hypertrophy. Following the loss of functional cardiomyocytes due to coronary artery occlusion or other causes, the heart is unable to replace the lost cells. One of the significant research goals has been to induce adult cardiomyocytes to reactivate the cell cycle and repair cardiac injury. This review explores the developmental, structural, and functional changes of the growing cardiomyocyte, and particularly the sarcomere, responsible for force generation, from the early fetal period of reproductive cell growth through the neonatal period and on to adulthood, as well as during pathological response to different forms of myocardial diseases or injury. Multiple issues relative to cardiomyocyte cell-cycle regulation in normal or diseased conditions are discussed.

Abstract

The cardiomyocyte undergoes dramatic changes in structure, metabolism, and function from the early fetal stage of hyperplastic cell growth, through birth and the conversion to hypertrophic cell growth, continuing to the adult stage and responding to various forms of stress on the myocardium, often leading to myocardial failure. The fetal cell with incompletely formed sarcomeres and other cellular and extracellular components is actively undergoing mitosis, organelle dispersion, and formation of daughter cells. In the first few days of neonatal life, the heart is able to repair fully from injury, but not after conversion to hypertrophic growth. Structural and metabolic changes occur following conversion to hypertrophic growth which forms a barrier to further cardiomyocyte division, though interstitial components continue dividing to keep pace with cardiac growth. Both intra- and extracellular structural changes occur in the stressed myocardium which together with hemodynamic alterations lead to metabolic and functional alterations of myocardial failure. This review probes some of the questions regarding conditions that regulate normal and pathologic growth of the heart.

Freshly isolated mitochondria from failing human hearts exhibit preserved respiratory function

In heart failure mitochondrial dysfunction is thought to be responsible for energy depletion and contractile dysfunction. The difficulties in procuring fresh left ventricular (LV) myocardium from humans for assessment of mitochondrial function have resulted in the reliance on surrogate markers of mitochondrial function and limited our understanding of cardiac energetics. We isolated mitochondria from fresh LV wall tissue of patients with heart failure and reduced systolic function undergoing heart transplant or left ventricular assist device placement, and compared their function to mitochondria isolated from the non-failing LV (NFLV) wall tissue with normal systolic function from patients with pulmonary hypertension undergoing heart-lung transplant. We performed detailed mitochondrial functional analyses using 4 substrates: glutamate-malate (GM), pyruvate-malate (PM) palmitoyl carnitine-malate (PC) and succinate. NFLV mitochondria showed preserved respiratory control ratios and electron chain integrity with only few differences for the 4 substrates. In contrast, HF mitochondria had greater respiration with GM, PM and PC substrates and higher electron chain capacity for PM than for PC. Surprisingly, HF mitochondria had greater respiratory control ratios and lower ADP-independent state 4 rates than NFLV mitochondria for GM, PM and PC substrates demonstrating that HF mitochondria are capable of coupled respiration ex vivo. Gene expression studies revealed decreased expression of key genes in pathways for oxidation of both fatty acids and glucose. Our results suggest that mitochondria from the failing LV myocardium are capable of tightly coupled respiration when isolated and supplied with ample substrates. Thus energy starvation in the failing heart may be the result of dysregulation of metabolic pathways, impaired substrate supply or reduced mitochondrial number but not the result of reduced mitochondrial electron transport capacity.

Mechanisms of disease: is mitochondrial function altered in heart failure?

The human heart sustains an exceptional energy transfer rate, consuming more energy per gram weight than any other organ system. The healthy heart can rapidly adapt to changes in demand, while the failing heart cannot. Cardiac energy flux systems falter in the failing heart. The purpose of this review is to characterize the fundamental role of mitochondria in this energy transfer system and describe our local research on mitochondrial respiratory capacity in failing human hearts.

Dilated cardiomyopathy with increased SR Ca2+ loading preceded by a hypercontractile state and diastolic failure in the alpha(1C)TG mouse

Mice over-expressing the alpha(1)_subunit (pore) of the L-type Ca2+ channel (alpha(1C)TG) by 4 months (mo) of age exhibit an enlarged heart, hypertrophied myocytes, increased Ca2+ current and Ca2+ transient amplitude, but a normal SR Ca2+ load. With advancing age (8-11 mo), some mice demonstrate advanced hypertrophy but are not in congestive heart failure (NFTG),while others evolve to frank dilated congestive heart failure (FTG). We demonstrate that older NFTG myocytes exhibit a hypercontractile state over a wide range of stimulation frequencies, but maintain a normal SR Ca2+ load compared to age matched non-transgenic (NTG) myocytes. However, at high stimulation rates (2-4 Hz) signs of diastolic contractile failure appear in NFTG cells. The evolution of frank congestive failure in FTG is accompanied by a further increase in heart mass and myocyte size, and phospholamban and ryanodine receptor protein levels and phosphorylation become reduced. In FTG, the SR Ca2+ load increases and Ca2+ release following excitation, increases further. An enhanced NCX function in FTG, as reflected by an accelerated relaxation of the caffeine-induced Ca2+ transient, is insufficient to maintain a normal diastolic Ca2+ during high rates of stimulation. Although a high SR Ca2+ release following excitation is maintained, the hypercontractile state is not maintained at high rates of stimulation, and signs of both systolic and diastolic contractile failure appear. Thus, the dilated cardiomyopathy that evolves in this mouse model exhibits signs of both systolic and diastolic failure, but not a deficient SR Ca2+ loading or release, as occurs in some other cardiomyopathic models.

The Integration of Spontaneous Intracellular Ca2+ Cycling and Surface Membrane Ion Channel Activation Entrains Normal Automaticity in Cells of the Heart's Pacemaker

Although the ensemble of voltage- and time-dependent rhythms of surface membrane ion channels, the membrane "Clock", is the immediate cause of a sinoatrial nodal cell (SANC) action potential (AP), it does not necessarily follow that this ion channel ensemble is the formal cause of spontaneous, rhythmic APs. SANC also generates intracellular oscillatory spontaneous Ca(2+) releases that ignite excitation (SCaRIE) of the surface membrane via Na(+)/Ca(2+) exchanger activation. The idea that a rhythmic intracellular Ca(2+) Clock might keep time for normal automaticity of SANC, however, has not been assimilated into mainstream pacemaker dogma. Recent experimental evidence, derived from simultaneous, confocal imaging of submembrane Ca(2+) and membrane potential of SANC, and supported by numerical modeling, indicates that normal automaticity of SANC is entrained and stabilized by the tight integration of the SR Ca(2+) Clock that generates rhythmic SCaRIE, and the surface membrane Clock that responds to SCaRIE to immediately produce APs of an adequate shape. Thus, tightly controlled, rhythmic SCaRIE does not merely fine tune SANC AP firing, but is the formal cause of the basal and reserve rhythms, insuring pacemaker stability by rhythmically integrating multiple Ca(2+)-dependent functions, and effects normal automaticity by rhythmic ignition of the surface membrane Clock.

Transgenic overexpression of the Ca2+-binding protein S100A1 in the heart leads to increased in vivo myocardial contractile performance

S100A1, a Ca2+-sensing protein of the EF-hand family, is most highly expressed in myocardial tissue, and cardiac S100A1 overexpression in vitro has been shown to enhance myocyte contractile properties. To study the physiological consequences of S100A1 in vivo, transgenic mice were developed with cardiac-restricted overexpression of S100A1. Characterization of two independent transgenic mouse lines with approximately 4-fold overexpression of S100A1 in the myocardium revealed a marked augmentation of in vivo basal cardiac function that remained elevated after beta-adrenergic receptor stimulation. Contractile function and Ca2+ handling properties were increased in ventricular cardiomyocytes isolated from S100A1 transgenic mice. Enhanced cellular Ca2+ cycling by S100A1 was associated both with increased sarcoplasmic reticulum Ca2+ content and enhanced sarcoplasmic reticulum Ca2+-induced Ca2+ release, and S100A1 was shown to associate with the cardiac ryanodine receptor. No alterations in beta-adrenergic signal transduction or major cardiac Ca2+-cycling proteins occurred, and there were no signs of hypertrophy with chronic cardiac S100A1 overexpression. Our findings suggest that S100A1 plays an important in vivo role in the regulation of cardiac function perhaps through interacting with the ryanodine receptor. Because S100A1 protein expression is down-regulated in heart failure, increasing S100A1 expression in the heart may represent a novel means to augment contractility.

Ca(2+) signaling in cardiac myocytes overexpressing the alpha(1) subunit of L-type Ca(2+) channel

Voltage-gated L-type Ca(2+) channels (LCCs) provide Ca(2+) ingress into cardiac myocytes and play a key role in intracellular Ca(2+) homeostasis and excitation-contraction coupling. We investigated the effects of a constitutive increase of LCC density on Ca(2+) signaling in ventricular myocytes from 4-month-old transgenic (Tg) mice overexpressing the alpha(1) subunit of LCC in the heart. At this age, cells were somewhat hypertrophic as reflected by a 20% increase in cell capacitance relative to those from nontransgenic (Ntg) littermates. Whole cell I(Ca) density in Tg myocytes was elevated by 48% at 0 mV compared with the Ntg group. Single-channel analysis detected an increase in LCC density with similar conductance and gating properties. Although the overexpressed LCCs triggered an augmented SR Ca(2+) release, the "gain" function of EC coupling was uncompromised, and SR Ca(2+) content, diastolic cytosolic Ca(2+), and unitary properties of Ca(2+) sparks were unchanged. Importantly, the enhanced I(Ca) entry and SR Ca(2+) release were associated with an upregulation of the Na(+)-Ca(2+) exchange activity (indexed by the half decay time of caffeine-elicited Ca(2+) transient) by 27% and SR Ca(2+) recycling by approximately 35%. Western analysis detected a 53% increase in the Na(+)-Ca(2+) exchanger expression but no change in the abundance of ryanodine receptor (RyR), SERCA2, and phospholamban. Analysis of I(Ca) kinetics suggested that SR Ca(2+) release-dependent inactivation of LCCs remains intact in Tg cells. Thus, in spite of the modest cardiac hypertrophy, the overexpressed LCCs form functional coupling with RyRs, preserving both orthograde and retrograde Ca(2+) signaling between LCCs and RyRs. These results also suggest that a modest but sustained increase in Ca(2+) influx triggers a coordinated remodeling of Ca(2+) handling to maintain Ca(2+) homeostasis.

S100A1: a regulator of myocardial contractility

S100A1, a Ca(2+) binding protein of the EF-hand type, is preferentially expressed in myocardial tissue and has been found to colocalize with the sarcoplasmic reticulum (SR) and the contractile filaments in cardiac tissue. Because S100A1 is known to modulate SR Ca(2+) handling in skeletal muscle, we sought to investigate the specific role of S100A1 in the regulation of myocardial contractility. To address this issue, we investigated contractile properties of adult cardiomyocytes as well as of engineered heart tissue after S100A1 adenoviral gene transfer. S100A1 gene transfer resulted in a significant increase of unloaded shortening and isometric contraction in isolated cardiomyocytes and engineered heart tissues, respectively. Analysis of intracellular Ca(2+) cycling in S100A1-overexpressing cardiomyocytes revealed a significant increase in cytosolic Ca(2+) transients, whereas in functional studies on saponin-permeabilized adult cardiomyocytes, the addition of S100A1 protein significantly enhanced SR Ca(2+) uptake. Moreover, in Triton-skinned ventricular trabeculae, S100A1 protein significantly decreased myofibrillar Ca(2+) sensitivity ([EC(50%)]) and Ca(2+) cooperativity, whereas maximal isometric force remained unchanged. Our data suggest that S100A1 effects are cAMP independent because cellular cAMP levels and protein kinase A-dependent phosphorylation of phospholamban were not altered, and carbachol failed to suppress S100A1 actions. These results show that S100A1 overexpression enhances cardiac contractile performance and establish the concept of S100A1 as a regulator of myocardial contractility. S100A1 thus improves cardiac contractile performance both by regulating SR Ca(2+) handling and myofibrillar Ca(2+) responsiveness.

Mitochondrial respiratory chain activity in idiopathic dilated cardiomyopathy

BACKGROUND

Cardiomyopathy is well recognized in mitochondrial diseases in which it has been associated with defects of mitochondrial function, including cytochrome-c oxidase (COX) deficiencies. This study explores the respiratory chain activity, particularly of COX, in patients with cardiomyopathy to determine whether a relationship exists between respiratory enzyme activity and cardiac function.

METHODS AND RESULTS

Myocardial specimens from the left ventricular wall of explanted hearts were obtained from subjects with ischemic (n = 6) or nonischemic dilated (n = 8) cardiomyopathy. Assays for citrate synthase (CS) and complexes II/III and IV activity were performed on cardiac mitochondria and homogenate. Enzyme activities were normalized to CS activity and compared with control activities (n = 10). A significant reduction in COX and/or CS activity was identified in mitochondrial preparations from the transplant group and correlated significantly with ejection fraction (P < .05), although this does not prove a causal relationship. Significantly reduced CS activity in homogenate was identified, suggesting decreased mitochondrial volume in addition to decreased COX activity. Measurements in cardiac homogenates failed to show a significant reduction in COX activity (P > .05) in the transplant group, suggesting that the use of prefrozen tissue homogenates may underestimate existing mitochondrial respiratory defects in cardiac tissue.

CONCLUSIONS

Mitochondrial function is altered at a number of levels in end-stage cardiomyopathy. Defective COX activity resulting in deficient adenosine triphosphate generation may contribute to impaired ventricular function in heart failure. Agents capable of improving mitochondrial function may find an adjuvant role in the treatment of cardiac failure.

Effect of aging on diastolic left ventricular myocardial velocities measured by pulsed tissue Doppler imaging in healthy subjects

We evaluated the effect of aging on diastolic left ventricular (LV) wall motion velocity in 80 healthy persons with the use of pulsed tissue Doppler imaging. The wall motion velocity patterns were recorded at the middle regions of the LV posterior wall and ventricular septum in the parasternal (along the short axis) and apical (along the long axis) LV long-axis views. In the posterior wall, the peak early diastolic wall motion velocities (Ews) along both axes correlated inversely with age (long axis: r = -0.61, P <. 0001; short axis: r = -0.55, P <.0001), and the peak atrial systolic wall motion velocities(Aws) along both axes correlated directly with age (long axis: r = 0.59, P <.0001; short axis: r = 0.65, P <.0001). In the ventricular septum, the Ew along the long axis correlated inversely with age (r = -0.51, P <.0001), and the Aws along both axes correlated directly with age (long axis: r = 0.57, P <.0001; short axis: r = 0.53, P <.0001). The Ews along both axes at the posterior wall correlated directly with the peak early diastolic transmitral flow velocity. The Aws along both axes at the ventricular septum and posterior wall correlated directly with the peak atrial systolic transmitral flow velocity. The times from the second heart sound to the peak of the early diastolic waves of the ventricular septum and posterior wall along both axes significantly increased with age. The times from the aortic component of the second heart sound to the peak of the early diastolic motion velocities along both axes were significantly longer at the ventricular septum than at the posterior wall. Pulsed tissue Doppler imaging may be useful for evaluating the effect of aging on diastolic LV function in healthy persons.

Inotropy, calcium, and heart failure: a personal perspective

The medical treatment of heart failure has improved significantly in the last decade, yet despite the reduction of morbidity and mortality, heart attacks and stroke cause 15 million deaths each year. Cardiovascular disease (CVD) constitutes 50% of all deaths worldwide. Indeed, heart disease represents a continuing global burden, despite all the advances. When considering the major objective of medical treatment of heart failure, the paradigm has shifted from increasing cardiac output of the failing heart by augmenting contractility to a decrease in afterload and inhibition of neurohumors affecting heart muscle. Nevertheless, a direct increase in contractility is still appropriate in some conditions of heart failure for a short-term beneficial effect. This article reviews certain aspects of cellular and molecular mechanisms to provide a framework for problem solving in this vital field.

Is the failing heart energy depleted?

This article takes three different approaches to the question of whether the failing heart is in an energy-starved state. A brief historical overview introduces the issue and points out problems in both models and methods. Second, current information regarding the energetic state of the failing heart is examined. Finally, the mechanistic and therapeutic implications of a defect in energy production are described.

Altered calcium handling in compensated hypertrophied rat cardiomyocytes induced by pressure overload

To investigate Ca2+ handling in compensated hypertrophied cardiomyocytes, we measured Ca2+ transients and contraction of hypertrophied rat left ventricular myocytes induced by aortic constriction (AC). The fluorescence ratio (I405/I480) after indo-1/AM loading and circumferential length were simultaneously measured in isolated myocytes. The amplitude of Ca2+ transients (Ca-Amp) was higher in rats with AC than in sham-operated rats (Sham) (0.25 +/- 0.08 vs 0.17 +/- 0.05). There was a positive correlation between Ca-Amp and fractional shortening (FS) in both AC and Sham rats, whereas the ratio of FS/Ca-Amp was smaller in AC rats. These observations suggest that compensated hypertrophied cardiomyocytes exhibit an adaptive increase in Ca-Amp, associated with reduced myofilament responsiveness to an increase in Ca2+. Isoproterenol and forskolin increased Ca-Amp and FS, and decreased time to 50% decline of Ca2+ transients. Although myocytes from AC rats exhibited reduced responsiveness to isoproterenol, responses to forskolin did not differ between the 2 groups. The reduced beta-adrenergic response in Ca2+ handling was probably due to altered beta-adrenoceptor numbers, G-protein function and/or their coupling process.

Involvement of the sarcoplasmic reticulum calcium pump in myocardial contractile dysfunction: comparison between chronic pressure-overload and stunning

Acute as well as chronic forms of heart failure involve mechanical dysfunction during systole and/or diastole. The rapid Ca2+ release from and Ca2+ reuptake into the tubuli of the sarcoplasmic reticulum are processes that critically determine normal systolic and diastolic myocardial function, which explains why in the last fifteen years so much attention has been paid to understand the performance of the sarcoplasmic reticulum Ca2+ pump during myocardial contractile dysfunction. In this communication we have reviewed the literature data on sarcoplasmic reticulum Ca2+ pump function in the chronically pressure-overloaded hypertrophied and stunned (post-ischemic reversibly injured) myocardium in the light of some new data from our laboratory. Results on the pressure-overloaded hypertrophied myocardium provide evidence that impaired relaxation is most likely due to a low capacity of the sarcoplasmic reticulum to pump Ca2+, a consequence of a lower density of Ca(2+)-pumping sites within the sarcotubular membranes. Contractile dysfunction in stunned myocardium is accompanied by an upregulation of the sarcoplasmic reticulum Ca2+ ATPase gene resulting in a slight increase of the Ca2+ pumping activity. The latter increase is likely an adaptive response of the reversibly injured myocardium which may contribute to the slow recovery of contractile function.

Metabolic regulation of in vivo myocardial contractile function: multiparameter analysis

To gain insight into the mechanisms of myocardial regulation as it relates to the interaction of mechanical and metabolic function and perfusion, intact animal models were instrumented for routine physiological measurements of mechanical function and for measurements of metabolism (31P NMR, NADH fluorescence (redox state)) and perfusion (2H NMR and Laser doppler techniques). These techniques were applied to canine and cat models of volume and/or pressure loading, hypoxia, ischemia and cardiomyopathic states. Data generated using these techniques indicate that myocardial bioenergetic function is quite stable under most loading conditions as long as the heart is not ischemic. In addition, these data indicate that there is no universal regulator and that different biochemical regulators appear to mediate stable function under different physiological and pathophysiological conditions: for example; during hypoxia, NADH redox state appears to play a regulatory role; and in pressure loading, ADP, phosphorylation potential and free energy of ATP hydrolysis as well as NADH redox state appear to be regulatory.

In vivo phosphorus-31 spectroscopic imaging in patients with global myocardial disease

The goals of this study were to determine whether abnormalities in phosphorus metabolism could be noninvasively detected using phosphorus-31 nuclear magnetic resonance spectroscopy in patients with dilated cardiomyopathy and left ventricular hypertrophy, and whether these patient groups could be distinguished from each other based on parameters obtained using this technique. Seventeen patients and 14 control subjects were studied using nuclear magnetic resonance spectroscopy. Spectra were obtained from the human heart at rest using 3-dimensional spectroscopic imaging as a localization technique. Data were acquired over an average volume of 48 cc in 26.3 minutes using a 2 tesla imaging and spectroscopy unit. The ratio of phosphocreatine to adenosine triphosphate was 0.89 +/- 0.88 (mean +/- standard error) in normal subjects and did not differ significantly in patients with dilated cardiomyopathy or left ventricular hypertrophy. A prominent peak in the phosphodiester region was seen much more frequently in patients with dilated cardiomyopathy, resulting in significantly higher ratios of phosphodiester to phosphocreatine (1.28 +/- 0.35) and phosphodiester to adenosine triphosphate (0.79 +/- 0.18) in this group compared to normal subjects (0.33 +/- 0.08 and 0.29 +/- 0.08, respectively). However, the various patient groups could not be reliably distinguished from each other based on spectral patterns. These studies demonstrate the feasibility of performing phosphorus-31 nuclear magnetic resonance spectroscopic imaging in patients with myocardial disease. The initial results indicate that, under resting conditions, the ratio of phosphocreatine to adenosine triphosphate is not consistently altered in patients with severe global cardiomyopathies or hypertrophy. Phosphodiesters are elevated in some patients with dilated cardiomyopathy, a finding that may signify abnormal phospholipid metabolism in this condition.

Myocardial biochemical changes in furazolidone-induced cardiomyopathy of turkeys

This study tested the hypothesis that membrane transport is the major biochemical system of the myocardium altered in furazolidone-induced cardiomyopathy (round heart disease), before the development of myocardial failure, and that metabolic enzymes and contractile proteins are less affected. Compared with controls, maximal percentage depression of activities of myocardium from furazolidone-treated birds were 40 for creatine kinase, 30 for glycolysis, 30 for glycogen, 20 for myofibrils, 20 for Krebs's cycle enzymes, 15 for fatty acid oxidation and 10 for total soluble protein. Sodium and potassium transport, antioxidant system activity, myosin, myosin isoenzyme patterns and amino acid aminotransferases were unaffected. In marked contrast, the calcium-transport ATPase activity of the sarcoplasmic reticulum had undergone a 60 per cent compensatory increase in activity. The pattern of biochemical changes observed is consistent with a role of ischaemia in the pathogenesis of round heart disease and indicates that calcium transport by the sarcoplasmic reticulum is the major biochemical system affected.

Subcellular calcium content in cardiomyopathic hamster hearts in vivo: an electron probe study

In the Syrian cardiomyopathic hamster heart, abnormal cellular calcium regulation, resulting in cellular calcium overload, is believed to play a role in the pathogenesis of cardiac hypertrophy and failure. Alternatively, the primary abnormality may be coronary vasospasm, resulting in reperfusion-induced necrosis. According to the latter hypothesis, only those cells that suffer an ischemic insult would contain elevated calcium levels. To determine whether a generalized elevation in myocytic calcium exists in myopathic hamster hearts, we measured cellular and subcellular calcium concentrations by electron probe microanalysis in cryosections of 50-day and 96-day myopathic and control hearts, rapidly frozen in vivo. Total calcium content of ventricular homogenates from each group was also measured by atomic absorption spectrophotometry. No significant differences in subcellular calcium were found by electron probe microanalysis among 50-day and 96-day myopathics and their age-matched controls. In 50-day myopathic and control hearts, mitochondrial calcium was 0.7 +/- 0.2 and 0.9 +/- 0.2, respectively, and A-band calcium was 3.0 +/- 0.4 and 2.6 +/- 0.4 mmol calcium/kg dry wt(+/- SEM). Results from 96-day animals were similar. Localized regions of elevated calcium were found only at sites of necrotic foci: in Na+-loaded cells (mitochondria: 4.7 +/- 1.3 (SEM) mmol/kg dry wt), in dying cells (mitochondria: 72 +/- 22 (SEM) mmol/kg dry wt) or as extracellular deposits (7-10 mol/kg dry wt). Total calcium content of hearts from myopathic hamsters, as determined by atomic absorption spectrophotometry, was also 13 times (50-day) and 50 times (96-day) higher than controls. These results demonstrate that there is a marked heterogeneity in cellular calcium content in myopathic hamster hearts, but the data do not support the hypothesis of a generalized cellular calcium overload.

Role of adrenoceptors and dopamine receptors in modulating left ventricular diastolic function

Although both dopamine and dobutamine are potent positive inotropic agents, multiple studies indicate that dopamine may produce a rise in left ventricular (LV) filling pressure, while dobutamine often has the opposite effect. To ascertain the pharmacological and hemodynamic mechanisms responsible for the elevation in LV filling pressure observed with dopamine, we administered incremental infusions (2, 4, and 6 micrograms/kg/min) of dopamine to 18 open-chest, anesthetized dogs in the presence and absence of rauwolscine (selective alpha 2-adrenoceptor antagonist) (n = 7), terazosin (selective alpha 1-antagonist) (n = 6), and domperidone (selective dopamine2 antagonist) (n = 5), while measuring pressures in the LV and left atrium and changes in dimension in the LV short-axis (with ultrasonic piezo crystals). Dobutamine (2, 4, and 6 micrograms/kg/min) was infused in five additional dogs before and after administration of rauwolscine. The time constant of isovolumic pressure decay, peak lengthening rate (mm/sec), LV end-diastolic pressure, and diastolic pressure-dimension relation were computed. A significant elevation in LV end-diastolic pressure and a parallel increase in LV end-diastolic chamber size was observed with dopamine, while a decline in LV end-diastolic pressure occurred with dobutamine. Yet both dopamine and dobutamine caused a dose-related acceleration of pressure decay and augmentation of peak lengthening rate. Furthermore, heart rate declined during the administration of dopamine but rose with dobutamine. In the presence of either rauwolscine or terazosin, dopamine infusion resulted in a positive chronotropic effect and dose-dependent reductions in LV end-diastolic pressure and end-diastolic chamber dimension; arterial pressure fell only after terazosin administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Human myocardial adenosine triphosphatase activities in health and heart failure

This study was designed to determine: (1) the myocardial adenosine triphosphatase (ATPase) activities of normal humans and patients with dilated cardiomyopathy and (2) whether ATPase activity is related to age, cause and severity of heart failure, and digitalis therapy. Endomyocardial biopsies were performed in 32 subjects. Results from six were normal. Ventricular failure in the other 26 was idiopathic (n = 15), familial (n = 3), alcohol induced (n = 5), or related to doxorubicin therapy (n = 3). The biopsies were analyzed for total, mitochondrial, Na+-K+, Ca++, and Mg++ ATPase activities. Total and mitochondrial ATPase activities correlated with left ventricular ejection fraction (r = 0.65 and 0.67, respectively; both p = 0.0001). Residual Mg++ ATPase activity correlated weakly with ventricular function as measured by echocardiography (p = 0.05). Na+-K+ ATPase activity was depressed in patients receiving digitalis (p = 0.01). These results suggest that progressive ventricular dysfunction may be associated with a progressive loss of total ATPase, mitochondrial ATPase and, to a lesser extent, Mg++ ATPase activity. Although depressed mitochondrial ATPase activity is not likely to be the primary cause of ventricular dysfunction, it could perpetuate failure by leading to inadequate production of adenosine triphosphate. Further study of ATPase activities may provide additional insight into the pathogenesis of cardiac failure.

Major alterations in relaxation during cardiac hypertrophy induced by aortic stenosis in guinea pig

Left ventricular hypertrophy (LVH) was produced in guinea pigs after aortic stenosis (AS). The percentage of LVH in AS was determined by normalizing left ventricular (LV) weight by the mean LV weight of sham-operated controls (n = 12). After 3 weeks of cardiac overload, a mild LVH (30 +/- 3%) was induced in 17 animals and a relatively severe LVH (56 +/- 3%) was induced in 7 animals. LV papillary muscles were rapidly excised for mechanical studies. No significant differences were observed between control and mild hypertrophy groups. In contrast, a marked decrease in myocardial performance was seen in the more severe cardiac hypertrophy group and was expressed as a percentage of sham-operated levels (Vmax, 22%; active isometric force/mm2, 23%; +dF/dt max/mm2, 26%). Relaxation in this group was still more impaired than contraction (peak lengthening velocity, 14%; -dF/dt max/mm2, 19%). Moreover, the load sensitivity of relaxation was present in both sham-operated controls and mild hypertrophy but almost disappeared in more severe hypertrophy. Isometric relaxation was delayed in the latter group, as shown by the 15% increase of the half-time of the decline of isometric relaxation (t 1/2). On the other hand, acute hypoxia (95% N2-5% CO2 for 20 minutes) also induced a fall in contractility and the disappearance of the load sensitivity of relaxation but with a 67% decrease of t 1/2. Thus, the mechanical analysis of relaxation allows the effects of chronic overload in relatively severe cardiac hypertrophy to be separated from those of acute hypoxia. Moreover, in severe cardiac hypertrophy, the impairment of the load sensitivity of relaxation with increased t 1/2 strongly suggests alterations of the sarcoplasmic reticulum, especially since the moderate decrease in the myofibrillar ATPase activity, which has been observed previously in guinea pig pressure overload, cannot account completely for the marked fall in myocardial performance.

Noninvasive findings in patients with hypertrophic and dilative cardiomyopathy: a combined echocardiographic and radionuclide angiographic study

Fifteen patients with hypertrophic (HCM) and 15 with dilative cardiomyopathy (DCM) were examined with radionuclide angiography and M-mode echocardiography to evaluate the combination of two noninvasive methods for measuring left ventricular performance. The patients with HCM had delayed myocardial relaxation and rapid filling time with preserved peak rate of early ventricular filling. DCM patients, on the contrary, had low values of left ventricular systolic performance and low peak filling rate. Myocardial relaxation and rapid filling time, however, were short, indicating compensatory mechanisms in the failing ventricle improving rapid filling.

The differential effects of positive inotropic and vasodilator therapy on diastolic properties in patients with congestive cardiomyopathy

Symptoms of congestive heart failure frequently reflect abnormalities in both systolic and diastolic performance. While much work has been reported regarding the mechanisms by which positive inotropic and vasodilator therapy affect systolic performance, little is known about their effect on diastolic function. In 12 patients with diffuse congestive cardiomyopathy micromanometer left ventricular and aortic pressure measurements were recorded simultaneously with two-dimensionally targeted M mode echocardiograms and thermodilution-determined cardiac output. Each patient received dopamine (2, 4, and 6 micrograms/kg/min), and dobutamine (2, 6, and 10 micrograms/kg/min), and 10 received nitroprusside (0.125 to 2.0 micrograms/kg/min). Baseline hemodynamics were characterized by low cardiac index (2.1 +/- 0.7 liter/min/m2, mean +/- SD), high left ventricular end-diastolic pressure (24 +/- 10 mm Hg), and increased end-diastolic (6.8 +/- 1.0 cm) and end-systolic dimensions (6.0 +/- 1.0 cm). All patients had abnormal left ventricular pressure decay with a prolonged time constant (67 +/- 20 msec) and reduced peak diastolic lengthening rates. Dopamine and dobutamine decreased the time constant of relaxation and increased the peak lengthening rate. Dobutamine also reduced the minimum diastolic pressure from 14 +/- 7 to 10 +/- 9 mm Hg (p less than .01); neither drug reduced end-diastolic pressure. In fact, dopamine elevated end-diastolic pressures in seven patients, despite more rapid pressure decay. Diastolic pressure-dimension relations after dopamine and dobutamine showed a leftward shift with a reduced end-systolic chamber size, but no significant changes in passive chamber stiffness. Nitroprusside decreased left ventricular minimum diastolic pressure by 4 +/- 2 mm Hg and end-diastolic pressure by 7 +/- 4 mm Hg (p less than .01). It did not consistently accelerate left ventricular pressure decay at the doses tested. The decreased end-diastolic pressure with nitroprusside was due to a reduced end-diastolic dimension in five patients. In the other patients, all of whom had elevated right atrial pressures, diastolic pressure-dimension relations showed a parallel downward shift after nitroprusside. Thus, positive inotropic therapy with beta 1-adrenoceptor agonists enhances early diastolic distensibility by accelerating relaxation, augmenting filling, and reducing end-systolic chamber size. Vasodilator therapy is much more effective in lowering diastolic pressures.(ABSTRACT TRUNCATED AT 400 WORDS)

Compartmentation and functional mechanisms in myocardial failure and myocardial infarction

Changes in compartmentation and specific mechanism in acute myocardial failure due to global ischemia and in regional myocardial ischemia in dog hearts are described. Ischemic failure was produced by periodic arrest of flow to supported heart preparations perfused with a fluorocarbon (FC-43). Sarcolemmal vesicles (SL) prepared from ischemic failing heart preparations exhibited diminished Ca++ binding and phosphorylation. TA-064, a beta-1-agonist partially abolished the reduction in Ca++ binding and phosphorylation of SL vesicles. The addition of cyclic-AMP (cAMP) and of protein kinase (PK) increased phosphorylation of SL vesicles obtained from non failing heart preparations. Combination of cAMP and of PK had the greatest effect. In contrast to myocardial failure, myocardial infarction is known to produce a large variety of specific disturbances in intermediary cardiac metabolism. Apparently in ischemic failing heart preparations, Ca++ binding and phosphorylation by SL are deficient. The results with TA-064 and isoproterenol suggest that phosphorylation of SL may play a role in the positive inotropic effect of beta-1-agonists.

Biochemical mechanisms responsible for alcohol-associated myocardiopathy

An overview of alcohol metabolism is presented followed by a discussion of the unique pathways for the metabolism of ethanol by the heart. The evidence for cardiac metabolic injury produced as a result of ethanol metabolism is then presented. Such injury involves the mitochondria, contractile proteins, and alterations in calcium fluxes and storage.

Improvement in indexes of diastolic performance in patients with congestive heart failure treated with milrinone

To elucidate the mechanisms by which the new bipyridine inotropic agent milrinone improves cardiac function, we examined multiple indexes of left ventricular diastolic function before and after administration of milrinone to patients with advanced (NYHA class III or IV) congestive heart failure. In 13 patients left ventricular pressure measurements were made with a micromanometer to permit assessment of peak negative dP/dt and the time constant of left ventricular isovolumic relaxation, T, before and after milrinone. In nine patients radionuclide ventriculographic studies were performed during left heart catheterization, allowing calculation of left ventricular peak filling rate, volumes, and the diastolic pressure-volume relationship before and after milrinone. After intravenous administration of milrinone, peak negative dP/dt increased (+ 18%; p less than .01) and T decreased (-30%; p less than .01), while heart rate increased by only 8% (87 +/- 12 to 94 +/- 15 beats/min; p less than .01), left ventricular systolic pressure did not change, and mean aortic pressure fell by 11% (p less than .01). Left ventricular peak filling rate increased (1.2 +/- 0.6 to 1.7 +/- 0.7 end-diastolic volumes/sec; p less than or equal to .02) despite a decrease in left ventricular filling pressure (mean pulmonary wedge pressure 27 +/- 7 to 18 +/- 9 mm Hg; p less than .01). There was a fall in left ventricular end-diastolic pressure (28.6 +/- 6 to 19 +/- 7 mm Hg; p less than or equal to .01), with no significant change in left ventricular end-diastolic volume. This was associated with a downward shift in the left ventricular diastolic pressure-volume relationship in most cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Echocardiographic assessment of left ventricular diastolic function in a normal population and a group of patients with myocardial hypertrophy

In order to study left ventricular diastolic function, digitized M-mode echocardiograms of the free wall endocardium were analyzed. A population of 117 healthy individuals was compared with a group of 22 patients with myocardial hypertrophy due to aortic stenosis (AS), and a group of 21 with hypertrophic cardiomyopathy (HCMP). The time constant Te of endocardial retraction in normals (66 +/- 13 ms) differed significantly from Te in the patients (AS, 105 +/- 23 ms, p less than 0.001; HCMP, 113 +/- 31 ms, p less than 0.001). Peak velocity of endocardial retraction (peak neg. dEnd/dt, in the normals 8.6 +/- 2.7 s-1) did not differ between normals and patients (AS, 7.0 +/- 2.3 s-1; HCMP, 7.3 +/- 2.4 s-1). Fractional shortening (FS) of the internal diameter, a parameter of left ventricular systolic function, tended to be higher in the AS patients than in the normal group, but was on the average significantly increased in the group of HCMP. However, most patients in the hypertrophic groups had FS within normal limits +/- 2 SD. The discrepancy between normal or supernormal systolic function and a pathological prolonged time constant Te in myocardial hypertrophy demonstrates the importance of diastolic parameters in left ventricular characterization. Te is a useful parameter of left ventricular diastolic function which can be provided noninvasively from echocardiographic M-mode curves of the free wall endocardium.

The biochemical basis of myocardial failure

Cardiac failure can begin with metabolic disturbances within the myocardial cell--in the mitochondria, contractile proteins, or other cellular organelles. It also can result from faulty adrenergic regulation of contraction. New technology is making it possible to synthesize the contributing factors into a clinical model that will greatly enhance our understanding of these mechanisms.

The effect of chemical sympathectomy on mitochondrial function in the ischaemic and reperfused myocardium

1 Isolated rabbit hearts were perfused aerobically for 120 min, made ischaemic for 90 min, or made ischaemic for 90 min and then reperfused for 30 min. 2 Some rabbits were pretreated with 6-hydroxydopamine (6-OHDA), given as three separate intravenous doses of 30, 20 and 20 mg/kg, 20 to 48 h before they were killed; others (controls) received saline according to the same regime. 3 Mitochondria were harvested from left ventricular homogenates and their function assessed by measuring state 3O2 consumption (state 3 QO2), respiratory control index (RCI), phosphate: oxygen ratio (ADP:O), Ca2+ content, and ATP-producing activity. In other experiments peak left ventricular developed tension was recorded. 4 In hearts from saline-treated animals, mitochondrial state 3 QO2, RCI and ATP producing activities were reduced after global ischaemia, with or without reperfusion. There was a small gain in mitochondrial Ca2+ after ischaemia, and a large gain upon reperfusion. 5 6-OHDA pretreatment provided some protection against the effects of ischaemia and reperfusion on mitochondrial function and on peak developed tension. 6 It was concluded that chemical sympathectomy with 6-OHDA does not duplicate the effect of prolonged beta-adrenoceptor blockade in protecting mitochondrial function against the deleterious effects of ischaemia and reperfusion.

Decreased catecholamine sensitivity and beta-adrenergic-receptor density in failing human hearts

To identify the role of the myocardial beta-adrenergic pathway in congestive heart failure, we examined beta-adrenergic-receptor density, adenylate cyclase and creatine kinase activities, muscle contraction in vitro, and myocardial contractile protein levels in the left ventricles of failing and normally functioning hearts from cardiac-transplant recipients or prospective donors. Eleven failing left ventricles had a 50 to 56 per cent reduction in beta-receptor density, a 45 per cent reduction in maximal isoproterenol-mediated adenylate cyclase stimulation, and a 54 to 73 per cent reduction in maximal isoproterenol-stimulated muscle contraction, as compared with six normally functioning ventricles (P less than 0.05 for each comparison). In contrast, cytoplasmic creatine kinase activity, adenylate cyclase activities stimulated by fluoride ion and by histamine, histamine-stimulated muscle contraction, and levels of contractile protein were not different in the two groups (P less than 0.05). We conclude that in failing human hearts a decrease in beta-receptor density leads to subsensitivity of the beta-adrenergic pathway and decreased beta-agonist-stimulated muscle contraction. Regulation of beta-adrenergic receptors may be an important variable in cardiac failure.

A clinical study of left ventricular relaxation

Left ventricular (LV) relaxation was studied in patients with hypertrophic cardiomyopathy (HCM, n =18), congestive cardiomyopathy (CCM, n = 11), hypertensive heart disease (HHD, n = 8), coronary artery disease (CAD) without left ventricular (LV) asynergy (n = 9) and with LV asynergy (n =17), mitral stenosis (MS, n = 16), and mitral regurgitation (MR, n = 8). The time constant T and peak negative dP/dt were used as indexes of LV relaxation, and 18 normal subjects served as controls. The time constant T was higher in elderly patients among normal contros (r = 0.652, p < 0.01), which suggests that prolongation of relaxation is a phenomenon of aging. The normal value of the time constant T was 33 +/- 8 msec (mean +/- SD), and that of peak negative dp/dt was 1864 +/- 390 mm Hg/sec. The time constant T was significantly higher in HCM (64 +/- 20 msec), CCM (56 +/- 14 msec), CAD without asynergy (53 +/- 16 msec), CAD with asynergy (57 +/- 13 msec) and MS (47 +/- 12 msec). Peak negative dP/dt was significantly lower in HCM (998 +/- 303 mm Hg/sec), CCM (1060 +/- 334 mm Hg/sec), CAD with asynergy (1370 +/- 299 mm Hg/sec), MS (1367 +/- 313 mm Hg/sec) and MR (1139 +/- 305 mm Hg/sec). Although the genesis of LV relaxation abnormality is not clear from this investigation, it seems to have multiple causes. Relaxation abnormality seems to be one of the earliest manifestations of mechanical dysfunction of the human left ventricle.

Determination of maximal ischemic tolerance of the human heart by ultrastructural recording of preischemic degree of myocardial hypertrophy and degeneration

Three biopsies were taken transmurally in different time intervals (before and after ischemia and during the reperfusion phase) from 20 patients undergoing open-heart operation for acquired valvular heart disease, and the myocardial cylinders were examined with the electron microscope. They were scrutinized to see if there is a relationship between the degree of hypertrophy and degeneration before ischemia and the extent of ischemic damage after a certain ischemia period, and between the damage before ischemia and the postoperative outcome of the patients. Our results show that the ischemic changes are not dependent on the preischemic extent of hypertrophy and degeneration. It seems that they are mainly dependent on the duration of ischemia because the degree of ischemic damage increases with prolongation of the ischemia interval. However, a good correlation was found between the preischemic changes and the postoperative outcome. Especially the combination of marked hypertrophy and the appearance of degenerative signs in the biopsy taken before ischemia seems to predestine a bad postoperative course. Therefore, it can be concluded that the total damage to the myocardial cells, which results from the sum of previous damage (hypertrophy and degeneration) and ischemic alterations, is responsible for the postoperative outcome.

Effects of calcium and pH on the mechanical performance of heart muscle in the frog, Rana temporaria, during anoxia and subsequent recovery

Heart ventricular muscle strips from Rana temporaria recover their isometric contractile tension completely within 20 min of reoxygenation following an anoxic period of 60 min in a physiological solution at pH 7.6. Corresponding recovery at pH 6.6 is only 43% of pretreatment values. High calcium concentration during the period of anoxia at pH 6.6 and subsequent recovery, returns contractile tension to almost pre-anoxic values within 1 h. If, however, the calcium concentration is increased at the moment of reoxygenation, contractile tension is restored even faster than if high calcium levels were present during anoxia. The loss of contractile tension caused by anoxia is the same at both pH 7.6 and 6.6 with the same calcium concentration. Comparison of the velocity parameters between high and low calcium experiments always shows a greater difference for the contraction velocities than for the corresponding relaxation velocities, independently of the pH. The quotient of these two velocities is used as an index of their relative rate of change. The results are interpreted in terms of calcium and hydrogen ion competition at various subcellular structures and the different influences these ions may have on contractile tension and both contraction and relaxation velocities.

Decreased myocardial contractility in papillary muscles from atherosclerotic rabbits

To determine the effect atherosclerosis has on myocardial contractility, we studied the contractile properties of right ventricular papillary muscles from 34 atherosclerotic and 17 control rabbits. We produced atherosclerosis by feeding for 2 to 8 months a diet of 5% lard, 5% peanut oil, 0.5% cholesterol, and 89.5% rabbit pellets. The controls received only rabbit pellets during the same time interval. Contracting isometrically 12 times per minute at 25 degrees C, muscles from the atherosclerotic rabbits developed tension at a lower maximum rate (max dT/dt), had a longer latency, and required longer to develop tension at the maximum rate and to develop peak tension. In isotonic contractions, they shortened with lower maximum velocities and required longer to accelerate to maximum velocity and to shorten maximally. We found no evidence that developed tension or distance shortened differed between the two groups of muscles. Raising the contraction frequency to 24 contractions per minute between the two groups of muscles. Raising the contraction frequency to 24 contractions per minute brought performance of the two groups of muscles closer in both types of contraction. Norepinephrine (1.5 x 10-5 M) nearly abolished differences between performance of the two groups. The loss of contractility correlates poorly with coronary and aortic atherosclerosis. It occurred early in the feeding of the atherogenic diet. We think it was due to a lipid-induced defect in the cardiac cell's handling of calcium.

Cardiac metabolsim: its contributions to alcoholic heart disease and myocardial failure

Changes in cardiac metabolism in myocardial failure and after alcohol ingestion are discussed. The main effect of alcohol ingestion is loss of cardiac contractility. Since heart muscle does not contain alcohol dehydrogenase, its toxicity is probably the result of a direct toxic effect of ethanol and acetaldehyde on the myocardial cell, possibly involving various membrane systems. Alcohol inhibits mitochondrial respiration and the activity of enzymes in the tricarboxylic acid cycle, and its interferes with both mitochondrial calcium uptake and binding. Ethanol profoundly affects myocardial lipid metabolism. Acetaldehyde diminishes myocardial protein synthesis and inhibits Ca++-activated myofibrillar ATPase. In myocardial failure, a series of possibilities may be responsible for the loss of contractility. Excitation-contraction coupling could be disturbed at the level of the sarcolemma, at the sarcoplasmic reticulum, at the mitochondria, and between calcium and the regulatory proteins. Deficiencies in Ca++ delivery systems of excitation-contraction coupling on the myosin ATPase activity could be responsible for the dimunition in cardiac contractility. Mitochondrial function may also be involved, since mitochondria from failing human hearts are defective with respect to respiratory control and calcium accumulation. Under certain conditions, the relationship of mitochondria to calcium sequestration is very important in influencing contractility. The involvement of contractile and regulatory proteins in myocardial failure cannot be excluded.