Moderate intensity of regular exercise improves cardiac SR Ca2+ uptake activity in ovariectomized rats

Small peptides: could they have a big role in metabolism and the response to exercise?

Exercise is a powerful non-pharmacological intervention for the treatment and prevention of numerous chronic diseases. Contracting skeletal muscles provoke widespread perturbations in numerous cells, tissues and organs, which stimulate multiple integrated adaptations that ultimately contribute to the many health benefits associated with regular exercise. Despite much research, the molecular mechanisms driving such changes are not completely resolved. Technological advancements beginning in the early 1960s have opened new avenues to explore the mechanisms responsible for the many beneficial adaptations to exercise. This has led to increased research into the role of small peptides (<100 amino acids) and mitochondrially derived peptides in metabolism and disease, including those coded within small open reading frames (sORFs; coding sequences that encode small peptides). Recently, it has been hypothesized that sORF-encoded mitochondrially derived peptides and other small peptides play significant roles as exercise-sensitive peptides in exercise-induced physiological adaptation. In this review, we highlight the discovery of mitochondrially derived peptides and newly discovered small peptides involved in metabolism, with a specific emphasis on their functions in exercise-induced adaptations and the prevention of metabolic diseases. In light of the few studies available, we also present data on how both single exercise sessions and exercise training affect expression of sORF-encoded mitochondrially derived peptides. Finally, we outline numerous research questions that await investigation regarding the roles of mitochondrially derived peptides in metabolism and prevention of various diseases, in addition to their roles in exercise-induced physiological adaptations, for future studies.

Structure-Function Relationships and Modifications of Cardiac Sarcoplasmic Reticulum Ca2+-Transport

Sarcoplasmic reticulum (SR) is a specialized tubular network, which not only maintains the intracellular concentration of Ca2+ at a low level but is also known to release and accumulate Ca2+ for the occurrence of cardiac contraction and relaxation, respectively. This subcellular organelle is composed of several phospholipids and different Ca2+-cycling, Ca2+-binding and regulatory proteins, which work in a coordinated manner to determine its function in cardiomyocytes. Some of the major proteins in the cardiac SR membrane include Ca2+-pump ATPase (SERCA2), Ca2+-release protein (ryanodine receptor), calsequestrin (Ca2+-binding protein) and phospholamban (regulatory protein). The phosphorylation of SR Ca2+-cycling proteins by protein kinase A or Ca2+-calmodulin kinase (directly or indirectly) has been demonstrated to augment SR Ca2+-release and Ca2+-uptake activities and promote cardiac contraction and relaxation functions. The activation of phospholipases and proteases as well as changes in different gene expressions under different pathological conditions have been shown to alter the SR composition and produce Ca2+-handling abnormalities in cardiomyocytes for the development of cardiac dysfunction. The post-translational modifications of SR Ca2+ cycling proteins by processes such as oxidation, nitrosylation, glycosylation, lipidation, acetylation, sumoylation, and O GlcNacylation have also been reported to affect the SR Ca2+ release and uptake activities as well as cardiac contractile activity. The SR function in the heart is also influenced in association with changes in cardiac performance by several hormones including thyroid hormones and adiponectin as well as by exercise-training. On the basis of such observations, it is suggested that both Ca2+-cycling and regulatory proteins in the SR membranes are intimately involved in determining the status of cardiac function and are thus excellent targets for drug development for the treatment of heart disease.

Myocardial-restricted ablation of the GTPase RAD results in a pro-adaptive heart response in mice

Existing therapies to improve heart function target β-adrenergic receptor (β-AR) signaling and Ca²⁺ handling and often lead to adverse outcomes. This underscores an unmet need for positive inotropes that improve heart function without any adverse effects. The GTPase Ras associated with diabetes (RAD) regulates L-type Ca²⁺ channel (LTCC) current (I_Ca,L). Global RAD-knockout mice (gRAD^-/-) have elevated Ca²⁺ handling and increased cardiac hypertrophy, but RAD is expressed also in noncardiac tissues, suggesting the possibility that pathological remodeling is due also to noncardiac effects. Here, we engineered a myocardial-restricted inducible RAD-knockout mouse (RAD^Δ/Δ). Using an array of methods and techniques, including single-cell electrophysiological and calcium transient recordings, echocardiography, and radiotelemetry monitoring, we found that RAD deficiency results in a sustained increase of inotropy without structural or functional remodeling of the heart. I_Ca,L was significantly increased, with RAD loss conferring a β-AR-modulated phenotype on basal I_Ca,L Cardiomyocytes from RAD^Δ/Δ hearts exhibited enhanced cytosolic Ca²⁺ handling, increased contractile function, elevated sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2a) expression, and faster lusitropy. These results argue that myocardial RAD ablation promotes a beneficial elevation in Ca²⁺ dynamics, which would obviate a need for increased β-AR signaling to improve cardiac function.

In-situ optical assessment of rat epicardial kinematic parameters reveals frequency-dependent mechanic heterogeneity related to gender

BACKGROUND

Gender-related cardiac mechanics following the electrical activity has been investigated from basic to clinical research, but results are still controversial. The aim of this work is to study the gender related cardiac mechanics and to focus on its heart rate dependency.

METHODS

We employed 12 Sprague Dawley rats (5 males and 7 females) of the same age and, through a novel high resolution artificial vision contactless approach, we evaluated in-situ cardiac kinematic. The hearts were paced on the right atria appendage via cathodal stimuli at rising frequency.

RESULTS

Kinematic data obtained at rising pacing rates are different between male and female rat hearts: male tended to maintain the same level of cardiac force, energy and contractility, while female responded with an increment of such parameters at increasing heart rate. Female hearts preserved their pattern of contraction and epicardial torsion (vorticity) at rising pacing rates compared to male. Furthermore, we observed a difference in the mechanical restitution: systolic time vs. diastolic time, as an index of cardiac performance, reached higher value in male compared to female hearts.

CONCLUSION

Our innovative technology was capable to evaluate in-situ rat epicardial kinematic at high stimulation frequency, revealing that male preserved kinematic parameters but varying the pattern of contraction/relaxation. On the contrary, female preserved the pattern of contraction/relaxation increasing kinematic parameters.

Endurance training restores spatially distinct cardiac mitochondrial function and myocardial contractility in ovariectomized rats

We previously demonstrated that the loss of female hormones induces cardiac and mitochondrial dysfunction in the female heart. Here, we show the impact of endurance training for twelve weeks, a nonpharmacological therapy against cardiovascular disease caused by ovariectomy and its contribution to cardiac contractility, mitochondrial quality control, bioenergetics and oxidative damage. We found that ovariectomy induced cardiac hypertrophy and dysfunction by decreasing SERCA2 and increasing phospholamban protein expression. Endurance training restored myocardial contractility, SERCA2 levels, increased calcium transient in ovariectomized rats but did not change phospholamban protein expression or cardiac hypertrophy. Additionally, ovariectomy decreased the amount of intermyofibrillar mitochondria and induced mitochondrial fragmentation that were accompanied by decreased levels of mitofusin 1, PGC-1α, NRF-1, total AMPK-α and mitochondrial Tfam. Endurance training prevented all these features except for mitofusin 1. Ovariectomy reduced O₂ consumption, elevated O₂^.- release and increased Ca²⁺-induced mitochondrial permeability transition pore opening in both mitochondrial subpopulations. Ovariectomy also increased NOX-4 protein expression in the heart, reduced mitochondrial Mn-SOD, catalase protein expression and increased protein carbonylation in both mitochondrial subpopulations, which were prevented by endurance training. Taken together, our findings show that endurance training prevented cardiac contractile dysfunction and mitochondrial quality control in ovariectomized rats.

Effect of ovariectomy on intracellular Ca2+ regulation in guinea pig cardiomyocytes

This study addressed the hypothesis that long-term deficiency of ovarian hormones after ovariectomy (OVx) alters cellular Ca²⁺-handling mechanisms in the heart, resulting in the formation of a proarrhythmic substrate. It also tested whether estrogen supplementation to OVx animals reverses any alterations to cardiac Ca²⁺ handling and rescues proarrhythmic behavior. OVx or sham operations were performed on female guinea pigs using appropriate anesthetic and analgesic regimes. Pellets containing 17β-estradiol (1 mg, 60-day release) were placed subcutaneously in selected OVx animals (OVx + E). Cardiac myocytes were enzymatically isolated, and electrophysiological measurements were conducted with a switch-clamp system. In fluo-4-loaded cells, Ca²⁺ transients were 20% larger, and fractional sarcoplasmic reticulum (SR) Ca²⁺ release was 7% greater in the OVx group compared with the sham group. Peak L-type Ca²⁺ current was 16% larger in OVx myocytes with channel inactivation shifting to more positive membrane potentials, creating a larger "window" current. SR Ca²⁺ stores were 22% greater in the OVx group, and these cells showed a higher frequency of Ca²⁺ sparks and waves and shorter wave-free intervals. OVx myocytes showed higher frequencies of early afterdepolarizations, and a greater percentage of these cells showed delayed afterdepolarizations after exposure to isoprenaline compared with sham myocytes. The altered Ca²⁺ regulation occurring in the OVx group was not observed in the OVx + E group. These findings suggest that long-term deprivation of ovarian hormones in guinea pigs lead to changes in myocyte Ca²⁺-handling mechanisms that are considered proarrhythmogenic. 17β-Estradiol replacement prevented these adverse effects.NEW & NOTEWORTHY Ovariectomized guinea pig cardiomyocytes have higher frequencies of Ca²⁺ waves, and isoprenaline-challenged cells display more early afterdepolarizations, delayed afterdepolarizations, and extra beats compared with sham myocytes. These alterations to Ca²⁺ regulation were not observed in myocytes from ovariectomized guinea pigs supplemented with 17β-estradiol, suggesting that ovarian hormone deficiency modifies cardiac Ca²⁺ regulation, potentially creating proarrhythmic substrates.

Regular exercise modulates cardiac mast cell activation in ovariectomized rats

It is well accepted that regular exercise is a significant factor in the prevention of cardiac dysfunction; however, the cardioprotective mechanism is as yet not well defined. We have examined whether regular exercise can modulate the activity of cardiac mast cells (CMC) after deprivation of female sex hormones, as well as the density and percentage degranulation of mast cells, in ventricular tissue of ovariectomized (OVX) rats after an 11-week running program. A significant increase in CMC density with a greater percentage degranulation was induced after ovarian sex hormone deprivation. Increased CMC density was prevented by estrogen supplements, but not by regular training. To the contrary, increased CMC degranulation in the OVX rat heart was attenuated by exercise training, but not by estrogen supplement. These findings indicate a significant correlation between the degree of CMC degranulation and myocyte cross-section area. However, no change in the expression of inflammatory mediators, including chymase, interleukin-6, and interleukin-10, was detected. Taken together, these results clearly indicate one of the cardioprotective mechanisms of regular aerobic exercise is the modulation of CMC activation.

EFFECTS OF EXERCISE ON MIR-29 AND IGF-1 EXPRESSION AND LIPID PROFILE IN THE HEART OF OVARIECTOMIZED RAT

Introduction

Menopause increases the risk of cardiovascular disease in women. The aims of the present study were to evaluate the effects of swimming training on cardiac histology and expression of miR-29 and IGF-1 in the ovariectomized rats.

Materials and methods

Thirty female Wistar rats were divided into sham and ovariectomized groups: sedentary control (OVX) and trained with 8 weeks exercise (OVX.E). On 57^th day, blood was collected and used for lipid profile measurement. In addition, heart tissue was analyzed by reverse transcription-polymerase chain reaction for IGF-1 mRNA and miR-29, and studied for histopathological changes.

Results

Ovariectomy significantly decreased miR-29 and IGF-1 expression in the heart compared to sham animals group (p<0.05). Exercise training increased miR-29 and IGF-1 expression in the trained rats and improved histology and lipid profile compared with OVX group (p<0.05).

Conclusion

Estrogen deficiency could lead to cardiac fibrosis through deregulation miR-29 and IGF-1 expression. The findings of the current study suggests a protective effect of exercise on heart against fibrotic changes in ovariectomized rats and support a potential preventive value of exercise in improving cardiac function after menopause.

Exercise training restores the cardiac microRNA-1 and -214 levels regulating Ca2+ handling after myocardial infarction

BACKGROUND

Impaired cardiomyocyte contractility and calcium handling are hallmarks of left ventricular contractile dysfunction. Exercise training has been used as a remarkable strategy in the treatment of heart disease. The microRNA-1, which targets sodium/calcium exchanger 1 (NCX), and microRNA-214, which targets sarcoplasmic reticulum calcium ATPase-2a (Serca2a), are involved in cardiac function regulation. Thus, the aim of this study was to evaluate the effect of exercise training on cardiac microRNA-1 and -214 expression after myocardial infarction.

METHODS

Wistar rats were randomized into four groups: sedentary sham (S-SHAM), sedentary infarction (S-INF), trained sham (T-SHAM), and trained infarction (T-INF). Exercise training consisted of 60 min/days, 5 days/week for 10 weeks with 3 % of body weight as overload beginning four weeks after myocardial infarction.

RESULTS

MicroRNA-1 and -214 expressions were, respectively, decreased (52 %) and increased (54 %) in the S-INF compared to the S-SHAM, while exercise training normalized the expression of these microRNAs. The microRNA targets NCX and Serca-2a protein expression were, respectively, decreased (55 %) and increased (34 %) in the T-INF group compared to the S-INF group.

CONCLUSIONS

These results suggest that exercise training restores microRNA-1 and -214 expression levels and prevents change in both NCX and Serca-2a protein and gene expressions. Altogether, our data suggest a molecular mechanism to restore ventricular function after exercise training in myocardial infarction rats.

Loss of Rad-GTPase produces a novel adaptive cardiac phenotype resistant to systolic decline with aging

Rad-GTPase is a regulator of L-type calcium current (LTCC), with increased calcium current observed in Rad knockout models. While mouse models that result in elevated LTCC have been associated with heart failure, our laboratory and others observe a hypercontractile phenotype with enhanced calcium homeostasis in Rad(-/-). It is currently unclear whether this observation represents an early time point in a decompensatory progression towards heart failure or whether Rad loss drives a novel phenotype with stable enhanced function. We test the hypothesis that Rad(-/-) drives a stable nonfailing hypercontractile phenotype in adult hearts, and we examine compensatory regulation of sarcoplasmic reticulum (SR) loading and protein changes. Heart function was measured in vivo with echocardiography. In vivo heart function was significantly improved in adult Rad(-/-) hearts compared with wild type. Heart wall dimensions were significantly increased, while heart size was decreased, and cardiac output was not changed. Cardiac function was maintained through 18 mo of age with no decompensation. SR releasable Ca(2+) was increased in isolated Rad(-/-) ventricular myocytes. Higher Ca(2+) load was accompanied by sarco/endoplasmic reticulum Ca(2+) ATPase 2a (SERCA2a) protein elevation as determined by immunoblotting and a rightward shift in the thapsigargan inhibitor-response curve. Rad(-/-) promotes morphological changes accompanied by a stable increase in contractility with aging and preserved cardiac output. The Rad(-/-) phenotype is marked by enhanced systolic and diastolic function with increased SR uptake, which is consistent with a model that does not progress into heart failure.

Regular exercise improves cardiac contractile activation by modulating MHC isoforms and SERCA activity in orchidectomized rats

Data from the trial known as Testosterone in Older Men with Mobility Limitations (TOM) has indicated an association between testosterone administration and a greater risk for adverse cardiovascular events. We therefore propose that regular exercise is a cardioprotective alternative that prevents detrimental changes in contractile activation when a deficiency in male sex hormones exists. Ten-week-old orchidectomized (ORX) rats were subjected to a 9-wk treadmill running program at moderate intensity starting 1 wk after surgery. Although exercise-induced cardiac hypertrophy was observed both in rats that underwent ORX and sham surgery, regular exercise enhanced cardiac myofilament Ca(2+) sensitivity and myosin light-chain 2 phosphorylation only in rats that underwent a sham operation. Although the rats that had sham surgery and and given exercise exhibited no change in maximum developed tension, regular running prevented the suppression of maximum active tension in the hearts of ORX rats. Regular exercise also prevented a shift in myosin heavy chain (MHC) isoforms toward β-MHC, a reduction in sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) activity, and an increase in SERCA sensitivity in the hearts of ORX rats. Neither SERCA content nor its modulating component, phospholamban (PLB), was altered by exercise in either sham-operated or ORX rats. However, decreases in the phosphorylated Thr(17) form of PLB and the phosphorylated Thr(287) form of Ca(2+)/calmodulin-dependent kinase II in the hearts of ORX rats were abolished after regular exercise. These results thus support the use of regular running as a cardioprotective alternative to testosterone replacement in hypogonadal conditions.

MiR-22/Sp-1 Links Estrogens With the Up-Regulation of Cystathionine γ-Lyase in Myocardium, Which Contributes to Estrogenic Cardioprotection Against Oxidative Stress

Hydrogen sulfide, generated in the myocardium predominantly via cystathionine-γ-lyase (CSE), is cardioprotective. Our previous study has shown that estrogens enhance CSE expression in myocardium of female rats. The present study aims to explore the mechanisms by which estrogens regulate CSE expression, in particular to clarify the role of estrogen receptor subtypes and the transcriptional factor responsible for the estrogenic effects. We found that either the CSE inhibitor or the CSE small interfering RNA attenuated the protective effect of 17β-estradiol (E2) against H2O2- and hypoxia/reoxygenation-induced injury in primary cultured neonatal cardiomyocytes. E2 stimulates CSE expression via estrogen receptor (ER)-α both in cultured cardiomyocytes in vitro and in the myocardium of female mice in vivo. A specificity protein-1 (Sp-1) consensus site was identified in the rat CSE promoter and was found to mediate the E2-induced CSE expression. E2 increases ERα and Sp-1 and inhibits microRNA (miR)-22 expression in myocardium of ovariectomized rats. In primary cardiomyocytes, E2 stimulates Sp-1 expression through the ERα-mediated down-regulation of miR-22. It was confirmed that both ERα and Sp-1 were targeted by miR-22. In the myocardium of ovariectomized rats, the level of miR-22 inversely correlated to CSE, ERα, Sp-1, and antioxidant biomarkers and positively correlated to oxidative biomarkers. In summary, this study demonstrates that estrogens stimulate Sp-1 through the ERα-mediated down-regulation of miR-22 in cardiomyocytes, leading to the up-regulation of CSE, which in turn results in an increase of antioxidative defense. Interaction of ERα, miR-22, and Sp-1 may play a critical role in the control of oxidative stress status in the myocardium of female rats.

Swimming training promotes cardiac remodeling and alters the expression of mRNA and protein levels involved in calcium handling in hypertensive rats

AIM

The aim of this study was to identify the effects of swimming training on the mRNA expression and protein levels of the calcium handling proteins in the hearts of renovascular hypertensive rats submitted to swimming protocol during 6 weeks.

MAIN METHODS

Fischer rats with renovascular hypertension 2-kidney 1-clip (2K1C) and SHAM groups were divided among sedentary and exercised groups. The exercise protocol lasted for 6 weeks (1 h/day, 5×/week), and the mean arterial pressure, cardiomyocytes hypertrophy parameters, mRNA expression and protein levels of some calcium handling proteins in the left ventricle were evaluated.

KEY FINDINGS

Swimming training was able to reduce the levels of mean arterial pressure in the hypertensive group compared to 2K1C SED, and to promote cardiac hypertrophy in SHAM EX and 2K1C EX groups in comparison to the respective control groups. The mRNA levels of B-type natriuretic peptide were reduced in the 2K1C EX when compared to 2K1C SED. The mRNA and protein levels of the sarcoplasmic reticulum Ca2 +-ATPase increased after the swimming training in SHAM and 2K1C groups. The mRNA and protein levels of phospholamban, displayed an increase in their levels in the exercised SHAM and in hypertensive rats in comparison to their respective controls; while mRNA levels of Na+/Ca2 + exchanger was reduced in the left ventricle comparing to the sedentary hypertensive rats.

SIGNIFICANCE

Taken altogether, we provide evidence that the aerobic training may lead to cardiac remodeling, and modulate the calcium handling proteins expression in the heart of hypertensive rats.

The regulation of sarco(endo)plasmic reticulum calcium-ATPases (SERCA)

The sarco(endo)plasmic reticulum calcium ATPase (SERCA) is responsible for transporting calcium (Ca(2+)) from the cytosol into the lumen of the sarcoplasmic reticulum (SR) following muscular contraction. The Ca(2+) sequestering activity of SERCA facilitates muscular relaxation in both cardiac and skeletal muscle. There are more than 10 distinct isoforms of SERCA expressed in different tissues. SERCA2a is the primary isoform expressed in cardiac tissue, whereas SERCA1a is the predominant isoform expressed in fast-twitch skeletal muscle. The Ca(2+) sequestering activity of SERCA is regulated at the level of protein content and is further modified by the endogenous proteins phospholamban (PLN) and sarcolipin (SLN). Additionally, several novel mechanisms, including post-translational modifications and microRNAs (miRNAs) are emerging as integral regulators of Ca(2+) transport activity. These regulatory mechanisms are clinically relevant, as dysregulated SERCA function has been implicated in the pathology of several disease states, including heart failure. Currently, several clinical trials are underway that utilize novel therapeutic approaches to restore SERCA2a activity in humans. The purpose of this review is to examine the regulatory mechanisms of the SERCA pump, with a particular emphasis on the influence of exercise in preventing the pathological conditions associated with impaired SERCA function.

Oestrogen upregulates the sarcoplasmic reticulum Ca(2+) ATPase pump in coronary arteries

The presence of circulating plasma 17β-oestradiol (E2) is beneficial in women against abnormal vascular tone development, such as coronary arterial vasospasms. Several vascular diseases have demonstrated that increased expression of the sarcoplasmic reticulum Ca(2+) -ATPase pump (SERCA2b) serves to limit the excessive accumulation of intracellular Ca(2+) . Therefore, the hypothesis of the present study was that E2 would increase SERCA2b expression in the coronary vasculature. Coronary arteries were dissected from hearts obtained from mature female pigs. Artery segments were cultured for 24 h in E2 (1 pmol/L or 1 nmol/L) and homogenized for western blot analysis. At 1 nmol/L, E2 induced an approximate 50% increase in immunoreactivity for SERCA2b. In addition, E2 increased the protein expression of the known SERCA regulatory proteins, protein kinase A (PKA) and protein kinase G (PKG). The E2-induced increase in SERCA2b was attenuated when the culture medium was supplemented with the oestrogen receptor (ER) α/β antagonist ICI 182,780 and the PKG antagonist KT5823 (10 μmol/L, 24 h for both). The PKA antagonist (KT5720; 10 μmol/L, 24 h) had no effect on SERCA2b expression. Removal of the endothelium (using a wooden toothpick) from artery segments prior to culture decreased the E2-mediated increase in SERCA2b and PKG expression by 45% and 47%, respectively. Overall, the findings suggest that one of the potential cardiovascular benefits of E2 in women is upregulation of SERCA2b, via activation of the classic ERα and ERβ pathway.

Effects of biological sex on the pathophysiology of the heart

Cardiovascular diseases are the leading causes of death in men and women in industrialized countries. While the effects of biological sex on cardiovascular pathophysiology have long been known, the sex-specific mechanisms mediating these processes have been further elucidated over recent years. This review aims at analysing the sex-based differences in cardiac structure and function in adult mammals, and the sex-based differences in the main molecular mechanisms involved in the response of the heart to pathological situations. It emerged from this review that the sex-based difference is a variable that should be dealt with, not only in basic science or clinical research, but also with regards to therapeutic approaches.

Ageing-related cardiomyocyte functional decline is sex and angiotensin II dependent

Clinically, heart failure is an age-dependent pathological phenomenon and displays sex-specific characteristics. The renin-angiotensin system mediates cardiac pathology in heart failure. This study investigated the sexually dimorphic functional effects of ageing combined with angiotensin II (AngII) on cardiac muscle cell function, twitch and Ca(2+)-handling characteristics of isolated cardiomyocytes from young (~13 weeks) and aged (~87 weeks) adult wild type (WT) and AngII-transgenic (TG) mice. We hypothesised that AngII-induced contractile impairment would be exacerbated in aged female cardiomyocytes and linked to Ca(2+)-handling disturbances. AngII-induced cardiomyocyte hypertrophy was evident in young adult mice of both sexes and accentuated by age (aged adult ~21-23 % increases in cell length relative to WT). In female AngII-TG mice, ageing was associated with suppressed cardiomyocyte contractility (% shortening, maximum rate of shortening, maximum rate of relaxation). This was associated with delayed cytosolic Ca(2+) removal during twitch relaxation (Tau ~20 % increase relative to young adult female WT), and myofilament responsiveness to Ca(2+) was maintained. In contrast, aged AngII-TG male cardiomyocytes exhibited peak shortening equivalent to young TG; yet, myofilament Ca(2+) responsiveness was profoundly reduced with ageing. Increased pro-arrhythmogenic spontaneous activity was evident with age and cardiac AngII overexpression in male mice (42-55 % of myocytes) but relatively suppressed in female aged transgenic mice. Female myocytes with elevated AngII appear more susceptible to an age-related contractile deficit, whereas male AngII-TG myocytes preserve contractile function with age but exhibit desensitisation of myofilaments to Ca(2+) and a heightened vulnerability to arrhythmic activity. These findings support the contention that sex-specific therapies are required for the treatment of age-progressive heart failure.

Sex differences in mechanisms of cardiac excitation-contraction coupling

The incidence and expression of cardiovascular diseases differs between the sexes. This is not surprising, as cardiac physiology differs between men and women. Clinical and basic science investigations have shown important sex differences in cardiac structure and function. The pervasiveness of sex differences suggests that such differences must be fundamental, likely operating at a cellular level. Indeed, studies have shown that isolated ventricular myocytes from female animals have smaller and slower contractions and underlying calcium transients compared to males. Recent evidence suggests that this arises from sex differences in components of the cardiac excitation–contraction coupling pathway, the sequence of events linking myocyte depolarization to calcium release from the sarcoplasmic reticulum and subsequent contraction. The concept that sex hormones may regulate intracellular calcium at the level of the cardiomyocyte is important, as levels of these hormones decline in both men and women as the incidence of cardiovascular disease rises. This review focuses on the impact of sex on cardiac contraction, in particular at the cellular level, and highlights specific components of the excitation–contraction coupling pathway that differ between the sexes. Understanding sex hormone regulation of calcium homeostasis in the heart may reveal new avenues for therapeutic strategies to treat cardiac dysfunction and cardiovascular diseases.

Carvedilol prevents ovariectomy-induced myocardial contractile dysfunction in female rat

Carvedilol has beneficial effects on cardiac function in patients with heart failure but its effect on ovariectomy-induced myocardial contractile dysfunction remains unclear. Estrogen deficiency induces myocardial contractile dysfunction and increases cardiovascular disease risk in postmenopausal women. Our aim was to investigate whether carvedilol, a beta receptor blocker, would prevent ovariectomy-induced myocardial contractile dysfunction. Female rats (8 weeks old) that underwent bilateral ovariectomy were randomly assigned to receive daily treatment with carvedilol (OVX+CAR, 20 mg/kg), placebo (OVX) and SHAM for 58 days. Left ventricle papillary muscle was mounted for isometric tension recordings. The inotropic response to Ca²⁺ (0.62 to 3.75 mM) and isoproterenol (Iso 10⁻⁸ to 10⁻² M) were assessed. Expression of calcium handling proteins was measured by western blot analysis. Carvedilol treatment in the OVX animals: prevented weight gain and slight hypertrophy, restored the reduced positive inotropic responses to Ca²⁺ and isoproterenol, prevented the reduction in SERCA2a expression, abolished the increase in superoxide anion production, normalized the increase in p22^phox expression, and decreased serum angiotensin converting enzyme (ACE) activity. This study demonstrated that myocardial contractile dysfunction and SERCA2a down regulation were prevented by carvedilol treatment. Superoxide anion production and NADPH oxidase seem to be involved in this response.

Cardiac response to doxorubicin and dexrazoxane in intact and ovariectomized young female rats at rest and after swim training

The impact of cancer therapies on adult cardiac function is becoming a concern as more children survive their initial cancer. Cardiovascular disease is now a significant problem to adult survivors of childhood cancer. Specifically, doxorubicin (DOX) may be particularly harmful in young girls. The objective of this study was to characterize DOX damage and determine the ability of dexrazoxane (DEX) to reduce DOX-mediated cardiac damage in sedentary and swim-trained female rats. Female Sprague-Dawley rats were left intact or ovariectomized (OVX) at weaning then injected with DEX (60 mg/kg) before DOX (3 mg/kg), DOX alone, or PBS. Rats were separated into sedentary and swim cohorts. Body weight was reduced in DOX:DEX- but not PBS- or DOX-treated rats. Echocardiographic parameters were similar in sedentary rats. Swim training revealed greater concentric remodeling in DOX-treated rats and reduced fractional shortening in DOX:DEX-treated rats. Calsequestrin 2 was reduced with DOX and increased with DOX:DEX postswim. Sarco(endo)plasmic reticulum Ca2+-ATPase 2a was reduced and calsequestrin 2 reduced further by swim training only in intact rats. OVX rats were heavier and developed eccentric remodeling post-swim with DOX and eccentric hypertrophy with DOX:DEX. Changes in SERCA2a and calsequestrin 2 expression were not observed. Ovariectomized DOX- and DOX:DEX-treated rats stopped growing during swim training. DEX coinjection did not relieve DOX-mediated cardiotoxicity in intact or hormone-deficient rats. DOX-mediated reductions in growth, cardiac function, and expression of calcium homeostasis proteins were exacerbated by swim. DEX coadministration did not substantially relieve DOX-mediated cardiotoxicity in young female rats. Ovarian hormones reduce DOX-induced cardiotoxicity.

Prior exercise training does not prevent acute cardiac alterations after myocardial infarction in female rats

OBJECTIVE

This study aimed to investigate whether previous exercise training could prevent or attenuate acute cardiac alterations after myocardial infarction.

METHODS

Female rats were submitted to swim training (1 h/day; 5 days/week) or allowed to remain sedentary for 8 weeks. Afterwards, they were randomly assigned to left coronary artery occlusion or sham surgery. After this procedure, the rats remained sedentary for one week until euthanasia. Cardiac structural and functional analyses were performed using Doppler echocardiography. The rats that had a moderate or large infarct size were included in the evaluations. The data (mean ± SEM) were analyzed using a two-way ANOVA model followed by Tukey's post-hoc test.

RESULTS

After the surgery, no significant difference between the exercise and sedentary groups was observed in the left ventricular infarct sizes (34.58 ± 3.04 vs. 37.59 ± 3.07). In another group of rats evaluated with Evans blue 1 h after myocardial infarction, no siginificant difference in the area at risk was observed between the exercised and sedentary rats (49.73 ± 1.52 vs. 45.48 ± 3.49). The changes in the left ventricular fractional areas for the exercised and sedentary myocardial infarction groups (36 ± 2% and 39 ± 3%, respectively) were smaller than those for the exercise sham surgery (ES, 67 ± 1%) and sedentary sham surgery (SS, 69 ± 2%) groups. The E/A was higher in the sedentary myocardial infarction (4.4 ± 0.3) and exercised myocardial infarction (5.5 ± 0.3) rats than in the SS (2.4 ± 0.1) and ES (2.2 ± 0.1) rats.

CONCLUSION

Previous swim training of female rats does not attenuate systolic and diastolic function alterations after myocardial infarction induced by left coronary artery occlusion, suggesting that cardioprotection cannot be provided by exercise training in this experimental model.