Rat model of exercise-induced cardiac hypertrophy: hemodynamic characterization using left ventricular pressure-volume analysis

Evaluation of Left Ventricular Systolic Function Using Layer-Specific Strain in Rats Performing Endurance Exercise: A Pilot Study

OBJECTIVE

The functional characteristics of exercise-induced myocardial hypertrophy were studied in a rat model in conjunction with ultrasound layered strain technique to investigate the hidden changes in the heart brought about by exercise.

METHODS

Forty specific pathogen free (SPF) adult Sprague-Dawley rats were selected and randomly divided into two groups of 20 exercise and 20 control rats. The longitudinal and circumferential strain parameters were measured using the ultrasonic stratified strain technique. The differences between the two groups and the predictive effect of stratified strain parameters on left ventricular systolic function were analyzed.

RESULTS

The exercise group had significantly higher global endocardial myocardial longitudinal strain (GLSendo), global mid-myocardial global longitudinal strain (GLSmid) and global endocardial myocardial global longitudinal strain (GCSendo) values than the control group (p < 0.05). Even though global mid-myocardial circumferential strain (GCSmid) and global epicardial myocardial circumferential strain (GCSepi) were higher in the exercise group than in the control group, statistical significance was not reached (p > 0.05). Conventional echocardiography parameters were well correlated with GLSendo, GLSmid, and GCSendo (p < 0.05). GLSendo was the best predictor of left ventricular myocardial contractile performance in athletes determined using the receiver operating characteristic curve, with an area under the curve of 0.97, sensitivity of 95% and specificity of 90%.

CONCLUSION

Rats performing endurance exercise exhibited subclinical changes in the heart after prolonged high-intensity exercise. A stratified strain parameter, GLSendo, played an important role in the evaluation of LV systolic performance in exercising rats.

Impact of Sex and Exercise on Femoral Artery Function: More Favorable Adaptation in Male Rats

Blood flow increases in arteries of the skeletal muscles involved in active work. Our aim was to investigate the gender differences as a result of adaptation to sport in the femoral arteries. Vascular reactivity and histology of animals were compared following a 12-week swimming training. Animals were divided into sedentary male (MS), trained male (MTr), sedentary female (FS), and trained female (FTr) groups. Isolated femoral artery rings were examined by wire myography. Contraction induced by phenylephrine (Phe) did not differ between the four groups. The contractile ability in the presence of indomethacin (INDO) was decreased in both sedentary groups. However, we found a specific cyclooxygenase-2 (COX-2) role only in FS rats. After exercise training, we observed increased vasoconstriction in both sexes, when nitro-L-arginine methyl ester (L-NAME) was present. The COX-dependent vasoconstriction effect disappeared in MTr animals, and the COX-2-dependent vasoconstriction effect disappeared in FTr ones. Relaxation was reduced significantly, when L-NAME was present in MTr animals compared to in FTr rats. The training was associated with greater endothelial nitric oxide synthase (eNOS) protein expression in males, but not in females. The present study proves that there are gender differences regarding adaptation mechanisms of musculocutaneous arteries to sports training. In males, relaxation reserve capacity was markedly elevated compared to in females.

Function of left ventricle mitochondria in highland deer mice and lowland mice

To gain insight into the mitochondrial mechanisms of hypoxia tolerance in high-altitude natives, we examined left ventricle mitochondrial function of highland deer mice compared with lowland native deer mice and white-footed mice. Highland and lowland native deer mice (Peromyscus maniculatus) and lowland white-footed mice (P. leucopus) were first-generation born and raised in common lab conditions. Adult mice were acclimated to either normoxia or hypoxia (60 kPa) equivalent to ~ 4300 m for at least 6 weeks. Left ventricle mitochondrial physiology was assessed by determining respiration in permeabilized muscle fibers with carbohydrates, lipids, and lactate as substrates. We also measured the activities of several left ventricle metabolic enzymes. Permeabilized left ventricle muscle fibers of highland deer mice showed greater rates of respiration with lactate than either lowland deer mice or white-footed mice. This was associated with higher activities of lactate dehydrogenase in tissue and isolated mitochondria in highlanders. Normoxia-acclimated highlanders also showed higher respiratory rates with palmitoyl-carnitine than lowland mice. Maximal respiratory capacity through complexes I and II was also greater in highland deer mice but only compared with lowland deer mice. Acclimation to hypoxia had little effect on respiration rates with these substrates. In contrast, left ventricle activities of hexokinase increased in both lowland and highland deer mice after hypoxia acclimation. These data suggest that highland deer mice support an elevated cardiac function in hypoxia, in part, with high ventricle cardiomyocyte respiratory capacities supported by carbohydrates, fatty acids, and lactate.

Time domain adaptation of left ventricular diastolic intraventricular pressure in elite female ice hockey athletes

Background

Ice hockey is a high-intensity dynamic sport for which competitive athletes train for longer than 20 hours each week for several years. The cumulative time of myocardial exposure to hemodynamic stress affects cardiac remodeling. However, the intracardiac pressure distribution of the elite ice hockey athletes' heart during adaptation to long-term training remains to be explored. This study aimed to compare the diastolic intraventricular pressure difference (IVPD) of the left ventricle (LV) between healthy volunteers and ice hockey athletes with different training times.

Methods

Fifty-three female ice hockey athletes (27 elite and 26 casual) and 24 healthy controls were included. The diastolic IVPD of the LV during diastole was measured by vector flow mapping. The peak amplitude of the IVPD during isovolumic relaxation (P0), diastolic rapid filling (P1), and atrial systole (P4); the difference in the peak amplitude between adjacent phases (DiffP01, DiffP14); the time interval between the peak amplitude of adjacent phases (P0P1, P1P4); and the maximum decrease rate in diastolic IVPD were calculated. Differences between groups, as well as correlations between hemodynamic parameters and training time, were analyzed.

Results

Structural parameters of the LV were significantly higher in elite athletes than in casual players and controls. No significant difference in the peak amplitude of the IVPD during the diastolic phase was found among the three groups. The analysis of covariance with heart rate as a covariate showed that P1P4 in the elite athlete and casual player groups was significantly longer than that in the healthy control group (p < 0.001 for all). An increased P1P4 was significantly associated with an increased training year (β = 4.90, p < 0.001).

Conclusions

The diastolic cardiac hemodynamics of the LV in elite female ice hockey athletes could be characterized by a prolonged diastolic IVPD, and P1P4 prolonged with an increase in the training years, reflecting a time-domain adaptation in diastolic hemodynamics after long-term training.

Endurance-trained subjects and sedentary controls increase ventricular contractility and efficiency during exercise: Feasibility of hemodynamics assessed by non-invasive pressure-volume loops

INTRODUCTION

Pressure-volume (PV) loops can be used to assess both load-dependent and load-independent measures of cardiac hemodynamics. However, analysis of PV loops during exercise is challenging as it requires invasive measures. Using a novel method, it has been shown that left ventricular (LV) PV loops at rest can be obtained non-invasively from cardiac magnetic resonance imaging (CMR) and brachial pressures. Therefore, the aim of this study was to assess if LV PV loops can be obtained non-invasively from CMR during exercise to assess cardiac hemodynamics.

METHODS

Thirteen endurance trained (ET; median 48 years [IQR 34-60]) and ten age and sex matched sedentary controls (SC; 43 years [27-57]) were included. CMR images were acquired at rest and during moderate intensity supine exercise defined as 60% of expected maximal heart rate. Brachial pressures were obtained in conjunction with image acquisition.

RESULTS

Contractility measured as maximal ventricular elastance (Emax) increased in both groups during exercise (ET: 1.0 mmHg/ml [0.9-1.1] to 1.1 mmHg/ml [0.9-1.2], p<0.01; SC: 1.1 mmHg/ml [0.9-1.2] to 1.2 mmHg/ml [1.0-1.3], p<0.01). Ventricular efficiency (VE) increased in ET from 70% [66-73] at rest to 78% [75-80] (p<0.01) during exercise and in SC from 68% [63-72] to 75% [73-78] (p<0.01). Arterial elastance (EA) decreased in both groups (ET: 0.8 mmHg/ml [0.7-0.9] to 0.7 mmHg/ml [0.7-0.9], p<0.05; SC: 1.0 mmHg/ml [0.9-1.2] to 0.9 mmHg/ml [0.8-1.0], p<0.05). Ventricular-arterial coupling (EA/Emax) also decreased in both groups (ET: 0.9 [0.8-1.0] to 0.7 [0.6-0.8], p<0.01; SC: 1.0 [0.9-1.1] to 0.7 [0.7-0.8], p<0.01).

CONCLUSIONS

This study demonstrates for the first time that LV PV loops can be generated non-invasively during exercise using CMR. ET and SC increase ventricular efficiency and contractility and decrease afterload and ventricular-arterial coupling during moderate supine exercise. These results confirm known physiology. Therefore, this novel method is applicable to be used during exercise in different cardiac disease states, which has not been possible non-invasively before.

Endurance training-induced cardiac remodeling in a guinea pig athlete's heart model

Besides the health benefits of regular exercise, high-level training-above an optimal level-may have adverse effects. In this study, we investigated the effects of long-term vigorous training and its potentially detrimental structural-functional changes in a small animal athlete's heart model. Thirty-eight 4-month-old male guinea pigs were randomized into sedentary and exercised groups. The latter underwent a 15-week-long endurance-training program. To investigate the effects of the intense long-term exercise, in vivo (echocardiography, electrocardiography), ex vivo, and in vitro (histopathology, patch-clamp) measurements were performed. Following the training protocol, the exercised animals exhibited structural left ventricular enlargement and a significantly higher degree of myocardial fibrosis. Furthermore, resting bradycardia accompanied by elevated heart rate variability occurred, representing increased parasympathetic activity in the exercised hearts. The observed prolonged QTc intervals and increased repolarization variability parameters may raise the risk of electrical instability in exercised animals. Complex arrhythmias did not occur in either group, and there were no differences between the groups in ex vivo or cellular electrophysiological experiments. Accordingly, the high parasympathetic activity may promote impaired repolarization in conscious exercised animals. The detected structural-functional changes share similarities with the human athlete's heart; therefore, this model might be useful for investigations on cardiac remodeling.

A high-whey-protein diet does not enhance mechanical and structural remodeling of cardiac muscle in response to aerobic exercise in rats

PURPOSE

Aerobic exercise training results in distinct structural and mechanical myocardial adaptations. In skeletal muscle, whey protein supplementation is effective in enhancing muscle adaptation following resistance exercise. However, it is unclear whether cardiac adaptation to aerobic exercise can be enhanced by systematic protein supplementation.

METHODS

Twelve-week-old rats were assigned to 12 weeks of either sedentary or aerobic exercise with either a standard (Sed+Standard, Ex+Standard) or high-protein (Sed+Pro, Ex+Pro) diet. Echocardiography was used to measure cardiac structural remodeling and performance. Skinned cardiac fiber bundles were used to determine the active and passive stress properties, maximum shortening velocity, and calcium sensitivity.

RESULTS

Aerobic training was characterized structurally by increases in ventricle volume (Ex+Standard, 19%; Ex+Pro, 29%) and myocardial thickness (Ex+Standard, 26%; Ex+- Pro, 12%) compared to that of baseline. Skinned trabecula r fiber bundles also had a greater unloaded shortening velocity (Sed+Standard, 1.04±0.05; Sed+Pro, 1.07±0.03; Ex- +Standard, 1.16±0.04; Ex+Pro, 1.18±0.05 FL/s) and calcium sensitivity (pCa50: Sed+Standard, 6.04±0.17; Sed+Pro, 6.08±0.19; Ex+Standard, 6.30±0.09; Ex+Pro, 6.36±0.12) in trained hearts compared to that of hearts from sedentary animals. However, the addition of a high-protein diet did not provide additional benefits to either the structural or mechanical adaptations of the myocardium.

CONCLUSION

Therefore, it seems that a high-whey-protein diet does not significantly enhance adaptations of the heart to aerobic exercise in comparison to that of a standard diet.

Long-Term Endurance Exercise Training Alters Repolarization in a New Rabbit Athlete’s Heart Model

In the present study, the effect of long-term exercise training was investigated on myocardial morphological and functional remodeling and on proarrhythmic sensitivity in a rabbit athlete’s heart model. New-Zealand white rabbits were trained during a 12-week long treadmill running protocol and compared with their sedentary controls. At the end of the training protocol, echocardiography, in vivo and in vitro ECG recordings, proarrhythmic sensitivity with dofetilide (nM) were performed in isolated hearts, and action potential duration (APD) measurements at different potassium concentrations (4.5 and 2 mM) were made in the isolated papillary muscles. Expression levels of the slow component of delayed rectifier potassium current and fibrosis synthesis and degradation biomarkers were quantified. Echocardiography showed a significantly dilated left ventricle in the running rabbits. ECG PQ and RR intervals were significantly longer in the exercised group (79 ± 2 vs. 69 ± 2 ms and 325 ± 11 vs. 265 ± 6 ms, p &lt; 0.05, respectively). The in vivo heart rate variability (HRV) (SD of root mean square: 5.2 ± 1.4 ms vs. 1.4 ± 0.2 ms, p &lt; 0.05) and Tpeak-Tend variability were higher in the running rabbits. Bradycardia disappeared in the exercised group in vitro. Dofetilide tended to increase the QTc interval in a greater extent, and significantly increased the number of arrhythmic beats in the trained animals in vitro. APD was longer in the exercised group at a low potassium level. Real-time quantitative PCR (RT-qPCR) showed significantly greater messenger RNA expression of fibrotic biomarkers in the exercised group. Increased repolarization variability and higher arrhythmia incidences, lengthened APD at a low potassium level, increased fibrotic biomarker gene expressions may indicate higher sensitivity of the rabbit “athlete’s heart” to life-threatening arrhythmias.

Sex differences in rat renal arterial responses following exercise training

During aerobic exercise, hemodynamic alterations occure; while blood flow in skeletal muscle arteries increases, it decreases in visceral vessels due to mesenterial vasoconstriction. However, maintaining renal blood flow during intensive sport is also a priority. Our aim was to investigate the changes of vascular reactivity and histology of isolated renal artery of male and female rats in response to swim-training. Wistar rats were distributed into four groups: male sedentary (MSed), male trained (MTr), female sedentary (FSed), and female trained (FTr). Trained animals underwent a 12-week-long intensive swimming program. Vascular function of isolated renal artery segments was examined by wire myography. Phenylephrine-induced contraction was lower in FSed compared to MSed animals, and it was decreased by training in male but not in female animals. Inhibition of cyclooxygenases by indomethacin reduced contraction in both sedentary groups, and in MTr but not in FTr animals. Inhibition of nitric oxide production increased contraction in both trained groups. Acetylcholine induced relaxation was similar in all experimental groups showing predominant NO-dependency. Elastin and smooth muscle cell actin density was reduced in female rats after aerobic training. This study shows that, as a result of 12-weeks-long training, there are sex differences in renal arterial responses following exercise training. Swimming moderates renal artery vasoconstriction in male animals, while it depresses elastic fiber and smooth muscle actin density in females.

Morphological and functional characterization of diabetic cardiomyopathy in db/db mice following exercise, metformin alone, or combination treatments

The aim of the study was to explore different effects of exercise, metformin alone, or exercise combined with metformin on cardiovascular morphological and functional changes in early stage of type 2 diabetes mellitus. Eight-week-old diabetic db/db mice and BKS mice were recruited and exposed to three different treatments (exercise, metformin alone, or their combination) for 8 weeks. Metformin was administered intragastrically, and aerobic exercise was performed using treadmill with 7-12 m/min, 30-40 min/day, 5 days/week. In the combination group, aerobic exercise was carried out for 30 min after intragastric administration of metformin. The results showed that all three treatments improved cardiac fibrosis and aortic lipid deposition. Exercise intervention failed to alleviate myocardial hypertrophy, but it improved the declined heart rate and diastolic blood pressure in diabetic db/db mice. In contrast, metformin caused opposite effects in these mice. The combination of exercise and metformin had additive effects on glucose intolerance and insulin sensitivity rather than on the improvement of myocardial and aortic structure. In conclusion, metformin improved changes in the morphology and structure of the heart and aorta, while exercise alone or in combination with metformin demonstrated more advantages in cardiac functional reserve through the physiological hypertrophy of myocardium in diabetic db/db mice.

Evaluation of muscle-specific and metabolism regulating microRNAs in a chronic swimming rat model

Making benefit from the epigenetic effects of environmental factors such as physical activity may result in a considerable improvement in the prevention of chronic civilization diseases. In our chronic swimming rat model, the expression levels of such microRNAs were characterized, that are involved in skeletal muscle differentiation, hypertrophy and fine-tuning of metabolism, which processes are influenced by chronic endurance training, contributing to the metabolic adaptation of skeletal muscle during physical activity. After chronic swimming, the level of miR-128a increased significantly in EDL muscles, which may influence metabolic adaptation and stress response as well. In SOL, the expression level of miR-15b and miR-451 decreased significantly after chronic swimming, which changes are opposite to their previously described increment in insulin resistant skeletal muscle. MiR-451 also targets PGC-1α mRNA, whiches expression level significantly increased in SOL muscles, resulting in enhanced biogenesis and oxidative capacity of mitochondria. In summary, the microRNA expression changes that were observed during our experiments suggest that chronic swim training contributes to a beneficial metabolic profile of skeletal muscle.

AMPK activator O304 improves metabolic and cardiac function, and exercise capacity in aged mice

Age is associated with progressively impaired, metabolic, cardiac and vascular function, as well as reduced work/exercise capacity, mobility, and hence quality of life. Exercise exhibit positive effects on age-related dysfunctions and diseases. However, for a variety of reasons many aged individuals are unable to engage in regular physical activity, making the development of pharmacological treatments that mimics the beneficial effects of exercise highly desirable. Here we show that the pan-AMPK activator O304, which is well tolerated in humans, prevented and reverted age-associated hyperinsulinemia and insulin resistance, and improved cardiac function and exercise capacity in aged mice. These results provide preclinical evidence that O304 mimics the beneficial effects of exercise. Thus, as an exercise mimetic in clinical development, AMPK activator O304 holds great potential to mitigate metabolic dysfunction, and to improve cardiac function and exercise capacity, and hence quality of life in aged individuals.

Increased Expression of N2BA Titin Corresponds to More Compliant Myofibrils in Athlete's Heart

Long-term exercise induces physiological cardiac adaptation, a condition referred to as athlete’s heart. Exercise tolerance is known to be associated with decreased cardiac passive stiffness. Passive stiffness of the heart muscle is determined by the giant elastic protein titin. The adult cardiac muscle contains two titin isoforms: the more compliant N2BA and the stiffer N2B. Titin-based passive stiffness may be controlled by altering the expression of the different isoforms or via post-translational modifications such as phosphorylation. Currently, there is very limited knowledge about titin’s role in cardiac adaptation during long-term exercise. Our aim was to determine the N2BA/N2B ratio and post-translational phosphorylation of titin in the left ventricle and to correlate the changes with the structure and transverse stiffness of cardiac sarcomeres in a rat model of an athlete’s heart. The athlete’s heart was induced by a 12-week-long swim-based training. In the exercised myocardium the N2BA/N2B ratio was significantly increased, Ser11878 of the PEVK domain was hypophosphorlyated, and the sarcomeric transverse elastic modulus was reduced. Thus, the reduced passive stiffness in the athlete’s heart is likely caused by a shift towards the expression of the longer cardiac titin isoform and a phosphorylation-induced softening of the PEVK domain which is manifested in a mechanical rearrangement locally, within the cardiac sarcomere.

The mitochondrial signaling peptide MOTS-c improves myocardial performance during exercise training in rats

Cardiac remodeling is a physiological adaptation to aerobic exercise and which is characterized by increases in ventricular volume and the number of cardiomyocytes. The mitochondrial derived peptide MOTS-c functions as an important regulator in physical capacity and performance. Exercise elevates levels of endogenous MOTS-c in circulation and in myocardium, while MOTS-c can significantly enhance exercise capacity. However, the effects of aerobic exercise combined with MOTS-c on cardiac structure and function are unclear. We used pressure–volume conductance catheter technique to examine cardiac function in exercised rats with and without treatment with MOTS-c. Surprisingly, MOTS-c improved myocardial mechanical efficiency, enhanced cardiac systolic function, and had a tendency to improve the diastolic function. The findings suggest that using exercise supplements could be used to modulate the cardiovascular benefits of athletic training.

Novel insights into the athlete's heart: is myocardial work the new champion of systolic function?

Aims

We sought to investigate the correlation between speckle-tracking echocardiography (STE)-derived myocardial work (MW) and invasively measured contractility in a rat model of athlete's heart. We also assessed MW in elite athletes and explored its association with cardiopulmonary exercise test (CPET)-derived aerobic capacity.

Methods and results

Sixteen rats underwent a 12-week swim training program and were compared to controls (n = 16). STE was performed to assess global longitudinal strain (GLS), which was followed by invasive pressure-volume analysis to measure contractility [slope of end-systolic pressure–volume relationship (ESPVR)]. Global MW index (GMWI) was calculated from GLS curves and left ventricular (LV) pressure recordings. In the human investigations, 20 elite swimmers and 20 healthy sedentary controls were enrolled. GMWI was calculated through the simultaneous evaluation of GLS and non-invasively approximated LV pressure curves at rest. All subjects underwent CPET to determine peak oxygen uptake (VO₂/kg). Exercised rats exhibited higher values of GLS, GMWI, and ESPVR than controls (−20.9 ± 1.7 vs. −17.6 ± 1.9%, 2745 ± 280 vs. 2119 ± 272 mmHg·%, 3.72 ± 0.72 vs. 2.61 ± 0.40 mmHg/μL, all P_Exercise < 0.001). GMWI correlated robustly with ESPVR (r = 0.764, P < 0.001). In humans, regular exercise training was associated with decreased GLS (−17.6 ± 1.5 vs. −18.8 ± 0.9%, P_Exercise = 0.002) but increased values of GMWI at rest (1899 ± 136 vs. 1755 ± 234 mmHg·%, P_Exercise = 0.025). GMWI exhibited a positive correlation with VO₂/kg (r = 0.527, P < 0.001).

Conclusions

GMWI precisely reflected LV contractility in a rat model of exercise-induced LV hypertrophy and captured the supernormal systolic performance in human athletes even at rest. Our findings endorse the utilization of MW analysis in the evaluation of the athlete’s heart.

Sex Differences in Exercise-Training-Related Functional and Morphological Adaptation of Rat Gracilis Muscle Arterioles

Background

The cardiovascular effects of training have been widely investigated; however, few studies have addressed sex differences in arteriolar adaptation. In the current study, we examined the adaptation of the gracilis arterioles of male and female rats in response to intensive training.

Methods

Wistar rats were divided into four groups: male exercise (ME) and female exercise (FE) animals that underwent a 12-week intensive swim-training program (5 days/week, 200 min/day); and male control (MC) and female control (FC) animals that were placed in water for 5 min daily. Exercise-induced cardiac hypertrophy was confirmed by echocardiography. Following the training, the gracilis muscle arterioles were prepared, and their biomechanical properties and functional reactivity were tested, using pressure arteriography. Collagen and smooth muscle remodeling were observed in the histological sections.

Results

Left ventricular mass was elevated in both sexes in response to chronic training. In the gracilis arterioles, the inner radius and wall tension increased in female animals, and the wall thickness and elastic modulus were reduced in males. Myogenic tone was reduced in the ME group, whereas norepinephrine-induced vasoconstriction was elevated in the FE group. More pronounced collagen staining was observed in the ME group than in the MC group. Relative hypertrophy and tangential stress of the gracilis arterioles were higher in females than in males. The direct vasoconstriction induced by testosterone was lower in females and was reduced as an effect of exercise in males.

Conclusion

The gracilis muscle arteriole was remodeled as a result of swim training, and this adaptation was sex dependent.

Network analysis of the left anterior descending coronary arteries in swim-trained rats by an in situ video microscopic technique

BACKGROUND

We aimed to identify sex differences in the network properties and to recognize the geometric alteration effects of long-term swim training in a rat model of exercise-induced left ventricular (LV) hypertrophy.

METHODS

Thirty-eight Wistar rats were divided into four groups: male sedentary, female sedentary, male exercised and female exercised. After training sessions, LV morphology and function were checked by echocardiography. The geometry of the left coronary artery system was analysed on pressure-perfused, microsurgically prepared resistance artery networks using in situ video microscopy. All segments over > 80 μm in diameter were studied using divided 50-μm-long cylindrical ring units of the networks. Oxidative-nitrative (O-N) stress markers, adenosine A2A and estrogen receptor (ER) were investigated by immunohistochemistry.

RESULTS

The LV mass index, ejection fraction and fractional shortening significantly increased in exercised animals. We found substantial sex differences in the coronary network in the control groups and in the swim-trained animals. Ring frequency spectra were significantly different between male and female animals in both the sedentary and trained groups. The thickness of the wall was higher in males as a result of training. There were elevations in the populations of 200- and 400-μm vessel units in males; the thinner ones developed farther and the thicker ones closer to the orifice. In females, a new population of 200- to 250-μm vessels appeared unusually close to the orifice.

CONCLUSIONS

Physical activity and LV hypertrophy were accompanied by a remodelling of coronary resistance artery network geometry that was different in both sexes.

Omecamtiv mecarbil evokes diastolic dysfunction and leads to periodic electromechanical alternans

Omecamtiv mecarbil (OM) is a promising novel drug for improving cardiac contractility. We tested the therapeutic range of OM and identified previously unrecognized side effects. The Ca2+ sensitivity of isometric force production (pCa50) and force at low Ca2+ levels increased with OM concentration in human permeabilized cardiomyocytes. OM (1 µM) slowed the kinetics of contractions and relaxations and evoked an oscillation between normal and reduced intracellular Ca2+ transients, action potential lengths and contractions in isolated canine cardiomyocytes. Echocardiographic studies and left ventricular pressure-volume analyses demonstrated concentration-dependent improvements in cardiac systolic function at OM concentrations of 600-1200 µg/kg in rats. Administration of OM at a concentration of 1200 µg/kg was associated with hypotension, while doses of 600-1200 µg/kg were associated with the following aspects of diastolic dysfunction: decreases in E/A ratio and the maximal rate of diastolic pressure decrement (dP/dtmin) and increases in isovolumic relaxation time, left atrial diameter, the isovolumic relaxation constant Tau, left ventricular end-diastolic pressure and the slope of the end-diastolic pressure-volume relationship. Moreover, OM 1200 µg/kg frequently evoked transient electromechanical alternans in the rat in vivo in which normal systoles were followed by smaller contractions (and T-wave amplitudes) without major differences on the QRS complexes. Besides improving systolic function, OM evoked diastolic dysfunction and pulsus alternans. The narrow therapeutic window for OM may necessitate the monitoring of additional clinical safety parameters in clinical application.

Exercise alters cardiovascular and renal pregnancy adaptations in female rats born small on a high-fat diet

Intrauterine growth restriction programs adult cardiorenal disease, which may be exacerbated by pregnancy and obesity. Importantly, exercise has positive cardiovascular effects. This study determined if high-fat feeding exacerbates the known adverse cardiorenal adaptations to pregnancy in rats born small and whether endurance exercise can prevent these complications. Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham (Control) surgery on embryonic day 18 (E18) in Wistar-Kyoto rats. Female offspring consumed a Chow or high-fat diet (HFD) from weaning and were randomly allocated to either a sedentary (Sedentary) or an exercise protocol at 16 wk; exercised before and during pregnancy (Exercise), or exercised during pregnancy only (PregEx). Systolic blood pressure was measured prepregnancy and rats were mated at 20 wk. During pregnancy, systolic blood pressure (E18) and renal function (E19) were assessed. Sedentary HFD Control females had increased estimated glomerular filtration rate (eGFR) compared with Chow. Compared with Control, Sedentary-Restricted females had increased eGFR, which was not influenced by HFD. Renal function was not affected by exercise and prepregnancy blood pressure was not altered. Restricted Chow-fed dams and dams fed a high-fat diet had a greater reduction in systolic blood pressure during late gestation, which was only prevented by Exercise. In summary, high-fat fed females born small are at a greater risk of altered cardiorenal adaptations to pregnancy. Although cardiovascular dysfunction was prevented by Exercise, renal dysfunction was not affected by exercise interventions. This study highlights that modifiable risk factors can have beneficial effects in the mother during pregnancy, which may impact fetal growth and development.

Balanced Intense Exercise Training Induces Atrial Oxidative Stress Counterbalanced by the Antioxidant System and Atrial Hypertrophy That Is Not Associated with Pathological Remodeling or Arrhythmogenicity

Although regular exercise training is associated with cardiovascular benefits, the increased risk of atrial arrhythmias has been observed after vigorous exercise and has been related to oxidative stress. We aimed at investigating exercise-induced atrial remodeling in a rat model of an athlete’s heart and determining sex-specific differences. Age-matched young adult rats were divided into female exercised, female control, male exercised, and male control groups. After exercised animals completed a 12-week-long swim training protocol, echocardiography and in vivo cardiac electrophysiologic investigation were performed. Additionally, atrial histological and gene expression analyses were carried out. Post-mortem atrial weight data and histological examination confirmed marked atrial hypertrophy. We found increased atrial gene expression of antioxidant enzymes along with increased nitro-oxidative stress. No gene expression alteration was found regarding markers of pathological remodeling, apoptotic, proinflammatoric, and profibrotic processes. Exercise training was associated with a prolonged right atrial effective refractory period. We could not induce arrhythmias by programmed stimulation in any groups. We found decreased expression of potassium channels. Female gender was associated with lower profibrotic expression and collagen density. Long-term, balanced exercise training-induced atrial hypertrophy is not associated with harmful electrical remodeling, and no inflammatory or profibrotic response was observed in the atrium of exercised rats.

Cardiac Effects of Treadmill Running at Different Intensities in a Rat Model

Purpose: In this study, we investigated the effect of treadmill exercise training on cardiac hypertrophy, collagen deposition, echo parameters and serum levels of cardiac troponin I (cTnI) in rats, and how they differ with various exercise intensities, hence exploring potential signal transduction. Methods: Male Sprague-Dawley rats were randomly divided into sedentary (SED), low-intensity running (LIR), medium-intensity running (MIR), and high-intensity running (HIR) groups. Each exercise group had 3 subgroups that were sacrificed for cardiac tissue analyses at 1, 4, and 8 weeks, respectively, and all rats participated in a daily 1 h treadmill routine 5 days per week. Echocardiographic measurements were performed 24 h after the last exercise session. Additionally, myocardium samples and blood were collected for histological and biochemical examinations. Changes in the extracellular signal-regulated kinases 1/2 (ERK1/2) signal pathway were detected by Western blotting. Results: After a week of running, ventricular myocyte size and the phosphorylation of ERK1/2 increased in the HIR group, while left ventricular (LV) diastolic diameter values and LV relative wall thickness increased in the LIR and MIR groups. In addition, we observed heart enlargement, cTnI decrease, and ERK1/2 signal activation in each of the exercise groups after 4 weeks of running. However, the HIR group displayed substantial rupture and increased fibrosis in myocardial tissue. In addition, compared with the LIR and MIR groups, 8 weeks of HIR resulted in structural damage, fiber deposition, and increased cTnI. However, there was no difference in the activation of ERK1/2 signaling between the exercise and SED groups. Conclusion: The effect of running on cardiac hypertrophy was intensity dependent. In contrast to LIR and MIR, the cardiac hypertrophy induced by 8 weeks of HIR was characterized by potential cardiomyocyte injury, which increased the risk of pathological development. Furthermore, the ERK signaling pathway was mainly involved in the compensatory hypertrophy process of the myocardium in the early stage of exercise and was positively correlated with exercise load. However, long-term exercise may attenuate ERK signaling activation.

Increased Ca2+ content of the sarcoplasmic reticulum provides arrhythmogenic trigger source in swimming-induced rat athlete's heart model

Sudden cardiac death among top athletes is very rare, however, it is 2–4 times more frequent than in the age-matched control population. In the present study, the electrophysiological consequences of long-term exercise training were investigated on Ca²⁺ homeostasis and ventricular repolarization, together with the underlying alterations of ion channel expression, in a rat athlete's heart model. 12-week swimming exercise-trained and control Wistar rats were used. Electrophysiological data were obtained by using ECG, patch clamp and fluorescent optical measurements. Protein and mRNA levels were determined by the Western immunoblot and qRT-PCR techniques. Animals in the trained group exhibited significantly lower resting heart rate, higher incidence of extrasystoles and spontaneous Ca²⁺ release events. The Ca²⁺ content of the sarcoplasmic reticulum (SR) and the Ca²⁺ transient amplitude were significantly larger in the trained group. Intensive physical training is associated with elevated SR Ca²⁺ content, which could be an important part of physiological cardiac adaptation mechanism to training. However, it may also sensitize the heart for the development of spontaneous Ca²⁺ release and extrasystoles. Training-associated remodeling may promote elevated incidence of life threatening arrhythmias in top athletes.

Chronic swimming training resulted in more relaxed coronary arterioles in male and enhanced vasoconstrictor ability in female rats

BACKGROUND

Exercise training is associated with hypertrophy of left ventricle (LV). The aim of the present study is to evaluate sex differences in the adaptation of the coronary contractile function in physiological left ventricular hypertrophy induced by long-term swim training.

METHODS

Thirty-two Wistar rats were randomly divided into 4 groups: exercised male (ExM), exercised female (ExF), untrained control male (CoM), and untrained control female (CoF). The trained animals underwent a 12-week-long swim training program. After finishing the training program, LV morphology and function were checked by echocardiography. The spontaneous tone, thromboxane (TxA<inf>2</inf>) agonist-induced vascular contractility and non-endothelial dilatation of the isolated intramural coronary resistance artery were examined by pressure microangiometry. The thromboxane receptor (TxA<inf>2</inf>R) protein expression in the wall of coronary arteries was examined using immunohistochemistry.

RESULTS

The LV mass index was significantly higher in the ExM and ExF groups, furthermore the LV mass index was significantly higher in female than in male animals. ExM animals had lower spontaneous tone than ExF. TxA<inf>2</inf> agonist-induced tone was raised only in ExF animals. The resistance coronary artery of exercised male animals had a significantly lower level of TxA<inf>2</inf>R positivity compared to exercised females.

CONCLUSIONS

Both sexes broaden their range of contractility following chronic swimming, but the vessel tone shifted toward contraction in exercised female rats, while these values shifted toward relaxation in males. These observations underline the significance of identifying potential gender differences in the chronic exercise-induced coronary vascular remodeling in human athletes.

Long-term exercise results in morphological and biomechanical changes in coronary resistance arterioles in male and female rats

Background

Biomechanical remodeling of coronary resistance arteries in physiological left ventricular hypertrophy has not yet been analyzed, and the possible sex differences are unknown.

Methods

Wistar rats were divided into four groups: male and female sedentary controls (MSe and FSe) and male and female animals undergoing a 12-week intensive swim training program (MEx and FEx). On the last day, the in vitro contractility, endothelium-dependent dilatation, and biomechanical properties of the intramural coronary resistance arteries were investigated by pressure microarteriography. Elastica and collagen remodeling were studied in histological sections.

Results

A similar outer radius and reduced inner radius resulted in an elevated wall to lumen ratio in the MEx and FEx animals compared to that in the sedentary controls. The wall elastic moduli increased in the MEx and FEx rats. Spontaneous and TxA₂ agonist-induced tone was increased in the FEx animals, whereas endothelium-dependent relaxation became more effective in MEx rats. Arteries of FEx rats had stronger contraction, while arteries of MEx animals had improved dilation.

Conclusions

According to our results, the coronary arterioles adapted to an elevated load during long-term exercise, and this adaptation depended on sex. It is important to emphasize that in addition to differences, we also found many similarities between the sexes in the adaptive response to exercise. The observed sport adaptation in the coronary resistance arteries of rats may contribute to a better understanding of the physiological and pathological function of these arteries in active and retired athletes of different sexes.

Myogenic vasoconstriction requires G12/G13 and LARG to maintain local and systemic vascular resistance

Myogenic vasoconstriction is an autoregulatory function of small arteries. Recently, G-protein-coupled receptors have been involved in myogenic vasoconstriction, but the downstream signalling mechanisms and the in-vivo-function of this myogenic autoregulation are poorly understood. Here, we show that small arteries from mice with smooth muscle-specific loss of G₁₂/G₁₃ or the Rho guanine nucleotide exchange factor ARHGEF12 have lost myogenic vasoconstriction. This defect was accompanied by loss of RhoA activation, while vessels showed normal increases in intracellular [Ca²⁺]. In the absence of myogenic vasoconstriction, perfusion of peripheral organs was increased, systemic vascular resistance was reduced and cardiac output and left ventricular mass were increased. In addition, animals with defective myogenic vasoconstriction showed aggravated hypotension in response to endotoxin. We conclude that G₁₂/G₁₃- and Rho-mediated signaling plays a key role in myogenic vasoconstriction and that myogenic tone is required to maintain local and systemic vascular resistance under physiological and pathological condition.

Sex Differences in Morphological and Functional Aspects of Exercise-Induced Cardiac Hypertrophy in a Rat Model

Background: Recent evidences suggest that sex hormones may be involved in the regulation of exercise-induced left ventricular (LV) hypertrophy. However, the sex-specific functional consequences of exercise-induced myocardial hypertrophy is still not investigated in detail. We aimed at understanding the sex-specific functional and morphological alterations in the LV and the underlying molecular changes in a rat model of athlete’s heart.

Methods: We divided our young, adult male and female rats into control and exercised groups. Athlete’s heart was induced by a 12-week long swim training. Following the training period, we assessed LV hypertrophy with echocardiography, while pressure-volume analysis was performed to investigate in vivo LV function. After in vivo experiments, molecular biological studies and histological investigations were performed.

Results: Echocardiography and post-mortem measured heart weight data indicated LV hypertrophy in both genders, nevertheless it was more pronounced in females. Despite the more significant relative hypertrophy in females, characteristic functional parameters did not show notable differences between the genders. LV pressure-volume analysis showed increased stroke volume, improved contractility and stroke work and unaltered LV stiffness in both male and female exercised rats, while active relaxation was ameliorated solely in male animals. The induction of Akt signaling was more significant in females compared to males. There was also a characteristic difference in the mitogen-activated protein kinase pathway as suppressed phosphorylation of p44/42 MAPK (Erk) and mTOR was observed in female exercised rats, but not in male ones. Myosin heavy chain α (MHC)/β-MHC ratio did not differ in males, but increased markedly in females.

Conclusion: Our results confirm that there is a more pronounced exercise-induced LV hypertrophy in females as compared to the males, however, there are only minor differences regarding LV function. There are characteristic molecular differences between male and female animals, that can explain different degrees of LV hypertrophy.

Acute canagliflozin treatment protects against in vivo myocardial ischemia-reperfusion injury in non-diabetic male rats and enhances endothelium-dependent vasorelaxation

Background

The sodium–glucose cotransporter-2 (SGLT2) inhibitor canagliflozin has been shown to reduce major cardiovascular events in type 2 diabetic patients, with a pronounced decrease in hospitalization for heart failure (HF) especially in those with HF at baseline. These might indicate a potent direct cardioprotective effect, which is currently incompletely understood. We sought to characterize the cardiovascular effects of acute canagliflozin treatment in healthy and infarcted rat hearts.

Methods

Non-diabetic male rats were subjected to sham operation or coronary artery occlusion for 30 min, followed by 120 min reperfusion in vivo. Vehicle or canagliflozin (3 µg/kg bodyweight) was administered as an intravenous bolus 5 min after the onset of ischemia. Rats underwent either infarct size determination with serum troponin-T measurement, or functional assessment using left ventricular (LV) pressure–volume analysis. Protein, mRNA expressions, and 4-hydroxynonenal (HNE) content of myocardial samples from sham-operated and infarcted rats were investigated. In vitro organ bath experiments with aortic rings from healthy rats were performed to characterize a possible effect of canagliflozin on vascular function.

Results

Acute treatment with canagliflozin significantly reduced myocardial infarct size compared to vehicle (42.5 ± 2.9% vs. 59.3 ± 4.2%, P = 0.006), as well as serum troponin-T levels. Canagliflozin therapy alleviated LV systolic and diastolic dysfunction following myocardial ischemia–reperfusion injury (IRI), and preserved LV mechanoenergetics. Western blot analysis revealed an increased phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and endothelial nitric-oxide synthase (eNOS), which were not disease-specific effects. Canagliflozin elevated the phosphorylation of Akt only in infarcted hearts. Furthermore, canagliflozin reduced the expression of apoptotic markers (Bax/Bcl-2 ratio) and that of genes related to myocardial nitro-oxidative stress. In addition, treated hearts showed significantly lower HNE positivity. Organ bath experiments with aortic rings revealed that preincubation with canagliflozin significantly enhanced endothelium-dependent vasodilation in vitro, which might explain the slight LV afterload reducing effect of canagliflozin in healthy rats in vivo.

Conclusions

Acute intravenous administration of canagliflozin after the onset of ischemia protects against myocardial IRI. The medication enhances endothelium dependent vasodilation independently of antidiabetic action. These findings might further contribute to our understanding of the cardiovascular protective effects of canagliflozin reported in clinical trials.

Temporal analysis of cardiovascular control and function following incomplete T3 and T10 spinal cord injury in rodents

Spinal cord injury (SCI) is a devastating condition that results in whole‐body dysfunction, notably cardiovascular (CV) disruption and disease. Injury‐induced destruction of autonomic pathways in conjunction with a progressive decline in physical fitness contribute to the poor CV status of SCI individuals. Despite the wide use of exercise training as a therapeutic option to reduce CV dysfunction, little is known about the acute hemodynamic responses to the exercise itself. We investigated CV responses to an exercise challenge (swimming) following both high and low thoracic contusion to determine if the CV system is able to respond appropriately to the challenge of swimming. Blood pressure (BP) telemetry and echocardiography were used to track the progression of dysfunction in rodents with T3 and T10 SCI (n = 8 each) for 10 weeks postcontusion. At 1 week postinjury, all animals displayed a drastic decline in heart rate (HR) during the exercise challenge, likely a consequence of neurogenic shock. Furthermore, over time, all groups developed a progressive inability to maintain BP within a narrow range during the exercise challenge despite displaying normal hemodynamic parameters at rest. Echocardiography of T10 animals revealed no persistent signs of cardiac dysfunction; T3 animals exhibited a transient decline in systolic function that returned to preinjury levels by 10 weeks postinjury. Novel evidence provided here illustrates that incomplete injuries produce hemodynamic instability that only becomes apparent during an exercise challenge. Further, this dysfunction lasts into the chronic phase of disease progression despite significant recovery of hindlimb locomotion and cardiac function.

Characterization of the dynamic changes in left ventricular morphology and function induced by exercise training and detraining

BACKGROUND

Although exercise-induced cardiac hypertrophy has been intensively investigated, its development and regression dynamics have not been comprehensively described. In the current study, we aimed to characterize the effects of regular exercise training and detraining on left ventricular (LV) morphology and function.

METHODS

Rats were divided into exercised (n = 12) and control (n = 12) groups. Exercised rats swam 200 min/day for 12 weeks. After completion of the training protocol, rats remained sedentary for 8 weeks (detraining period). Echocardiographic follow-up was performed regularly to obtain LV long- and short-axis recordings for speckle-tracking echocardiography analysis. Global longitudinal and circumferential strain and systolic strain rate were measured. LV pressure-volume analysis was performed using additional groups of rats to obtain haemodynamic data.

RESULTS

Echocardiographic examinations showed the development of LV hypertrophy in the exercised group. These differences disappeared during the detraining period. Strain and strain rate values were all increased after the training period, whereas supernormal values rapidly reversed to the control level after training cessation. Load-independent haemodynamic indices, e.g., preload recruitable stroke work, confirmed the exercise-induced systolic improvement and complete regression after detraining.

CONCLUSIONS AND TRANSLATIONAL ASPECT

Our results provide the first comprehensive data to describe the development and regression dynamics of morphological and functional aspects of physiological hypertrophy in detail. Speckle-tracking echocardiography has been proven to be feasible to follow-up changes induced by exercise training and detraining and might provide an early possibility to differentiate between physiological and pathological conditions.

Effects of exercise training and TrkB blockade on cardiac function and BDNF-TrkB signaling postmyocardial infarction in rats

Exercise training is beneficial for preserving cardiac function postmyocardial infarction (post-MI), but the underlying mechanisms are not well understood. We investigated one possible mechanism, brain-derived neurotrophic factor (BDNF)-tropomyosin-related kinase B (TrkB) signaling, with the TrkB blocker ANA-12 (0.5 mg·kg^-1·day^-1). Male Wistar rats underwent sham surgery or ligation of the left descending coronary artery. The surviving MI rats were allocated as follows: sedentary MI rats treated with vehicle, exercise-trained MI rats treated with vehicle, and exercise-trained MI rats treated with ANA-12. Exercise training was done 5 days/wk for 4 wk on a motor-driven treadmill. At the end, left ventricular (LV) function was evaluated by echocardiography and a Millar catheter. Mature BDNF and downstream effectors of BDNF-TrkB signaling, Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), Akt, and AMP-activated protein kinase (AMPK), were assessed in the noninfarct area of the LV by Western blot analysis. Exercise training increased stroke volume and cardiac index and attenuated the decrease in ejection fraction (EF) and increase in LV end-diastolic pressure post-MI. ANA-12 blocked the improvement of EF and attenuated the increases in stroke volume and cardiac index but did not affect LV end-diastolic pressure. Exercise training post-MI prevented decreases in mature BDNF, phosphorylated (p-)CaMKII, p-Akt, and p-AMPKα expression. These effects were all blocked by ANA-12 except for p-AMPKα. In conclusion, the exercise-induced improvement of EF is mediated by the BDNF-TrkB axis and the downstream effectors CaMKII and Akt. BDNF-TrkB signaling appears to contribute to the improvement in systolic function by exercise training. NEW & NOTEWORTHY Exercise training improves ejection fraction and left ventricular end-diastolic pressure (LVEDP) and increases stroke volume and cardiac index in rats postmyocardial infarction (post-MI). The improvement of EF but not LVEDP is mediated by activation of the brain-derived neurotrophic factor (BDNF)-tropomyosin-related kinase B (TrkB) axis and downstream effectors Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and Akt. This suggests that activation of BDNF-TrkB signaling and CaMKII and Akt is a promising target to attenuate progressive cardiac dysfunction post-MI.

Comparative proteomic analysis of mouse models of pathological and physiological cardiac hypertrophy, with selection of biomarkers of pathological hypertrophy by integrative Proteogenomics

To determine fundamental characteristics of pathological cardiac hypertrophy, protein expression profiles in two widely accepted models of cardiac hypertrophy (swimming-trained mouse for physiological hypertrophy and pressure-overload-induced mouse for pathological hypertrophy) were compared using a label-free quantitative proteomics approach. Among 3955 proteins (19,235 peptides, false-discovery rate < 0.01) identified in these models, 486 were differentially expressed with a log2 fold difference ≥ 0.58, or were detected in only one hypertrophy model (each protein from 4 technical replicates, p < .05). Analysis of gene ontology biological processes and KEGG pathways identified cellular processes enriched in one or both hypertrophy models. Processes unique to pathological hypertrophy were compared with processes previously identified in cardiac-hypertrophy models. Individual proteins with differential expression in processes unique to pathological hypertrophy were further confirmed using the results of previous targeted functional analysis studies. Using a proteogenomic approach combining transcriptomic and proteomic analyses, similar patterns of differential expression were observed for 23 proteins and corresponding genes associated with pathological hypertrophy. A total of 11 proteins were selected as early-stage pathological-hypertrophy biomarker candidates, and the results of western blotting for five of these proteins in independent samples confirmed the patterns of differential expression in mouse models of pathological and physiological cardiac hypertrophy.

Role of the β3-adrenergic receptor subtype in catecholamine-induced myocardial remodeling

β₃-Adrenoceptors (AR) stimulate cardiac Na⁺/K⁺ pump in healthy hearts. β₃-ARs are upregulated by persistent sympathetic hyperactivity; however, their effect on Na⁺/K⁺ ATPase activity and ventricular function in this condition is still unknown. Here, we investigate preventive effects of additional β₃-AR activation (BRL) on Na⁺/K⁺ ATPase activity and in vivo hemodynamics in a model of noradrenaline-induced hypertrophy. Rats received NA or NA plus simultaneously administered BRL in vivo infusion for 14 days; their cardiac function was investigated by left ventricular pressure-volume analysis. Moreover, fibrosis and apoptosis were also assessed histologically. NA induced an hypertrophic pattern, as detected by morphological, histological, and biochemical markers. Additional BRL exposure reversed the hypertrophic pattern and restored Na⁺/K⁺ ATPase activity. NA treatment increased systolic function and depressed diastolic function (slowed relaxation). Additional BRL treatment reversed most NA-induced hemodynamic changes. NA decreased Na⁺/K⁺ pump α2 subunit expression selectively, a change also reversed by additional BRL treatment. Increasing β₃-AR stimulation may prevent the consequences of chronic NA exposure on Na⁺/K⁺ pump and in vivo hemodynamics. β₃-AR agonism may thus represent a new therapeutic strategy for pharmacological modulation of hypertrophy under conditions of chronically enhanced sympathetic activity.

Comparison of speckle-tracking echocardiography with invasive hemodynamics for the detection of characteristic cardiac dysfunction in type-1 and type-2 diabetic rat models

Background

Measurement of systolic and diastolic function in animal models is challenging by conventional non-invasive methods. Therefore, we aimed at comparing speckle-tracking echocardiography (STE)-derived parameters to the indices of left ventricular (LV) pressure–volume (PV) analysis to detect cardiac dysfunction in rat models of type-1 (T1DM) and type-2 (T2DM) diabetes mellitus.

Methods

Rat models of T1DM (induced by 60 mg/kg streptozotocin, n = 8) and T2DM (32-week-old Zucker Diabetic Fatty rats, n = 7) and corresponding control animals (n = 5 and n = 8, respectively) were compared. Echocardiography and LV PV analysis were performed. LV short-axis recordings were used for STE analysis. Global circumferential strain, peak strain rate values in systole (SrS), isovolumic relaxation (SrIVR) and early diastole (SrE) were measured. LV contractility, active relaxation and stiffness were measured by PV analysis.

Results

In T1DM, contractility and active relaxation were deteriorated to a greater extent compared to T2DM. In contrast, diastolic stiffness was impaired in T2DM. Correspondingly, STE described more severe systolic dysfunction in T1DM. Among diastolic STE parameters, SrIVR was more decreased in T1DM, however, SrE was more reduced in T2DM. In T1DM, SrS correlated with contractility, SrIVR with active relaxation, while in T2DM SrE was related to cardiac stiffness, cardiomyocyte diameter and fibrosis.

Conclusions

Strain and strain rate parameters can be valuable and feasible measures to describe the dynamic changes in contractility, active relaxation and LV stiffness in animal models of T1DM and T2DM. STE corresponds to PV analysis and also correlates with markers of histological myocardial remodeling.

Electronic supplementary material

The online version of this article (10.1186/s12933-017-0645-0) contains supplementary material, which is available to authorized users.

A comparison of passive hindlimb cycling and active upper-limb exercise provides new insights into systolic dysfunction after spinal cord injury

Active upper-limb and passive lower-limb exercise are two interventions used in the spinal cord injury (SCI) population. Although the global cardiac responses have been previously studied, it is unclear how either exercise influences contractile cardiac function. Here, the cardiac contractile and volumetric responses to upper-limb (swim) and passive lower-limb exercise were investigated in rodents with a severe high-thoracic SCI. Animals were divided into control (CON), SCI no exercise (NO-EX), SCI passive hindlimb cycling (PHLC), or SCI swim (SWIM) groups. Severe contusion SCI was administered at the T2 level. PHLC and SWIM interventions began on day 8 postinjury and lasted 25 days. Echocardiography and dobutamine stress echocardiography were performed before and after injury. Cardiac contractile indexes were assessed in vivo at study termination via a left ventricular pressure-volume conductance catheter. Stroke volume was reduced after SCI (91 µl in the NO-EX group vs. 188 µl in the CON group, P < 0.05) and was reversed at study termination in the PHLC (167 µl) but not SWIM (90 µl) group. Rates of contraction were reduced in NO-EX versus CON groups (6,079 vs. 9,225 mmHg, respectively, P < 0.05) and were unchanged by PHLC and SWIM training. Similarly, end-systolic elastance was reduced in the NO-EX versus CON groups (0.67 vs. 1.37 mmHg/µl, respectively, P < 0.05) and was unchanged by PHLC or SWIM training. Dobutamine infusion normalized all pressure indexes in each SCI group (all P < 0.05). In conclusion, PHLC improves flow-derived cardiac indexes, whereas SWIM training displayed no cardiobeneficial effect. Pressure-derived deficits were corrected only with dobutamine, suggesting that reduced β-adrenergic stimulation is principally responsible for the impaired cardiac contractile function after SCI.NEW & NOTEWORTHY This is the first direct comparison between the cardiac changes elicited by active upper-limb or passive lower-limb exercise after spinal cord injury. Here, we demonstrate that lower-limb exercise positively influences flow-derived cardiac indexes, whereas upper-limb exercise does not. Furthermore, neither intervention corrects the cardiac contractile dysfunction associated with spinal cord injury.

Complete Reversion of Cardiac Functional Adaptation Induced by Exercise Training

PURPOSE

Long-term exercise training is associated with characteristic cardiac adaptation, termed athlete's heart. Our research group previously characterized in vivo left ventricular (LV) function of exercise-induced cardiac hypertrophy in detail in a rat model; however, the effect of detraining on LV function is still unclear. We aimed at evaluating the reversibility of functional alterations of athlete's heart after detraining.

METHODS

Rats (n = 16) were divided into detrained exercised (DEx) and detrained control (DCo) groups. Trained rats swam 200 min·d for 12 wk, and control rats were taken into water for 5 min·d. After the training period, both groups remained sedentary for 8 wk. We performed echocardiography at weeks 12 and 20 to investigate the development and regression of exercise-induced structural changes. LV pressure-volume analysis was performed to calculate cardiac functional parameters. LV samples were harvested for histological examination.

RESULTS

Echocardiography showed robust LV hypertrophy after completing the training protocol (LV mass index = 2.61 ± 0.08 DEx vs 2.04 ± 0.04 g·kg DCo, P < 0.05). This adaptation regressed after detraining (LV mass index = 2.01 ± 0.03 vs 1.97 ± 0.05 g·kg, n.s.), which was confirmed by postmortem measured heart weight and histological morphometry. After the 8-wk-long detraining period, a regression of the previously described exercise-induced cardiac functional alterations was observed (DEx vs DCo): stroke volume (SV; 144.8 ± 9.0 vs 143.9 ± 9.6 μL, P = 0.949), active relaxation (τ = 11.5 ± 0.3 vs 11.3 ± 0.4 ms, P = 0.760), contractility (preload recruitable stroke work = 69.5 ± 2.7 vs 70.9 ± 2.4 mm Hg, P = 0.709), and mechanoenergetic (mechanical efficiency = 68.7 ± 1.2 vs 69.4 ± 1.8, P = 0.742) enhancement reverted completely to control values. Myocardial stiffness remained unchanged; moreover, no fibrosis was observed after the detraining period.

CONCLUSION

Functional consequences of exercise-induced physiological LV hypertrophy completely regressed after 8 wk of deconditioning.

Prevention against renal damage in rats with subtotal nephrectomy by sacubitril/valsartan (LCZ696), a dual-acting angiotensin receptor-neprilysin inhibitor

Although patients with chronic kidney disease (CKD) are at increased risk for end‐stage renal disease and cardiovascular events, adequate drug therapies for preventing the deterioration of these conditions are still not established. This study was undertaken to evaluate a preventive effect of an angiotensin receptor‐neprilysin inhibitor sacubitril/valsartan (LCZ696), which is converted to sacubitril and valsartan in the body, against the progression of renal disease in rats with subtotal nephrectomy, an animal model of human CKD. Mean survival time after subtotal nephrectomy was about 100 days in Wistar rats with vehicle. LCZ696‐(30 mg/kg) and valsartan‐(15 mg/kg) prolonged the survival of these animals, and the effect of LCZ696 on survival was significantly greater than that of valsartan. Renoprotective effects of LCZ696 judged by serum creatinine and urinary protein excretions were larger than those of valsartan. Cardioprotective effects judged by cardiac left ventricular mass, fractional shortening, and fibrosis of LCZ696 and valsartan were not detected under the present condition. Thus, the renoprotective effect of LCZ696 was stronger than that of valsartan in rats with subtotal nephrectomy. This study provides the idea that, compared to valsartan, LCZ696 is more effective for the treatment of human CKD.

Ascending Aortic Constriction Promotes Cardiomyocyte Proliferation in Neonatal Rats

Adult heart suffering from increased workload will undergo myocardial hypertrophy, subsequent cardiomyocyte (CM) death, and eventually heart failure. However, the effect of increasing afterload on the neonatal heart remains unknown. We performed ascending aortic constriction (AAC) in neonatal rats 8-12 hours after birth (P0, P indicates postpartum). Seven days after surgery, in vivo heart function was evaluated using cardiac ultrasonography. Haematoxylineosin and Masson staining were used to assess CM diameter and collagen deposition. Moreover, expression of both EdU and Ki67 were evaluated to determine DNA synthesis levels, and pH3 and aurora B as markers for mitosis in CMs. CM isolation was performed by heart perfusion at P0, P3, P5, and P7, respectively. CM number on P0 was 1.01 ± 0.29 × 10⁶. We found that CM cell cycle activation was significantly increased among constricted hearts, as demonstrated by increased Ki67, EdU, pH3, and aurora B positive cells/1000 CMs. At day 7 (P7), constriction group hearts manifested increased wall thickness (0.55 ± 0.05 mm versus 0.85 ± 0.10 mm, P < 0.01, n = 6), and improved hemodynamics as well as left ventricular ejection fraction (65.5 ± 3.7% versus 77.7 ± 4.8%, P < 0.01, n = 6). Of note, the population of CMs was also markedly increased in the constriction group (2.92 ± 0.27 × 10⁶ versus 3.41 ± 0.40 × 10⁶, P < 0.05, n = 6). In summary, we found that during the first week after birth significant numbers of neonatal CMs can reenter the cell cycle. Ascending aortic constriction promotes neonatal rat CM proliferation resulting in 16.7% more CMs in the heart.

Acute and Chronic Exercise in Animal Models

Numerous animal cardiac exercise models using animal subjects have been established to uncover the cardiovascular physiological mechanism of exercise or to determine the effects of exercise on cardiovascular health and disease. In most cases, animal-based cardiovascular exercise modalities include treadmill running, swimming, and voluntary wheel running with a series of intensities, times, and durations. Those used animals include small rodents (e.g., mice and rats) and large animals (e.g., rabbits, dogs, goats, sheep, pigs, and horses). Depending on the research goal, each experimental protocol should also describe whether its respective exercise treatment can produce the anticipated acute or chronic cardiovascular adaptive response. In this chapter, we will briefly describe the most common kinds of animal models of acute and chronic cardiovascular exercises that are currently being conducted and are likely to be chosen in the near future. Strengths and weakness of animal-based cardiac exercise modalities are also discussed.

Prevention of the development of heart failure with preserved ejection fraction by the phosphodiesterase-5A inhibitor vardenafil in rats with type 2 diabetes

Aims

Heart failure with preserved ejection fraction (HFpEF) has a great epidemiological burden. The pathophysiological role of cyclic guanosine monophosphate (cGMP) signalling has been intensively investigated in HFpEF. Elevated levels of cGMP have been shown to exert cardioprotective effects in various cardiovascular diseases, including diabetic cardiomyopathy. We investigated the effect of long‐term preventive application of the phosphodiesterase‐5A (PDE5A) inhibitor vardenafil in diabetic cardiomyopathy‐associated HFpEF.

Methods and results

Zucker diabetic fatty (ZDF) rats were used as a model of HFpEF and ZDF lean rats served as controls. Animals received vehicle or 10 mg/kg body weight vardenafil per os from weeks 7 to 32 of age. Cardiac function, morphology was assessed by left ventricular (LV) pressure–volume analysis and echocardiography at week 32. Cardiomyocyte force measurements were performed. The key markers of cGMP signalling, nitro‐oxidative stress, apoptosis, myocardial hypertrophy and fibrosis were examined. The ZDF animals showed diastolic dysfunction (increased LV/cardiomyocyte stiffness, prolonged LV relaxation time), preserved systolic performance, decreased myocardial cGMP level coupled with impaired protein kinase G (PKG) activity, increased nitro‐oxidative stress, enhanced cardiomyocyte apoptosis, and hypertrophic and fibrotic remodelling of the myocardium. Vardenafil effectively prevented the development of HFpEF by maintaining diastolic function (decreased LV/cardiomyocyte stiffness and LV relaxation time), by restoring cGMP levels and PKG activation, by lowering apoptosis and by alleviating nitro‐oxidative stress, myocardial hypertrophy and fibrotic remodelling.

Conclusions

We report that vardenafil successfully prevented the development of diabetes mellitus‐associated HFpEF. Thus, PDE5A inhibition as a preventive approach might be a promising option in the management of HFpEF patients with diabetes mellitus.

Association of Exercise Training with Tobacco Smoking Prevents Fibrosis but has Adverse Impact on Myocardial Mechanics

INTRODUCTION

There was no data for cardiac repercussion of exercise training associated with tobacco smoking. This issue is interesting because some smoking people can be enrolled in an exercise-training program. Thus, we evaluated swimming training effects on the function and structural myocardial in rats exposed to tobacco smoking.

METHODS

Male Wistar rats were assigned to one of four groups: C, untrained rats without exposure to tobacco smoking; E, exercised rats without exposure to tobacco smoking; CS, untrained rats exposed to tobacco smoking; ECS, exercised rats exposed to tobacco smoking. Rats swam five times a week twice daily (60min per session) for 8 weeks. Before each bout exercise, rats breathed smoke from 20 cigarettes for 60min. Twenty-four hours after the last day of the protocol, papillary muscles were isolated for in vitro analysis of myocardial mechanics. The myocardial mass and nuclear cardiomyocyte volume were used as hypertrophy markers, and collagen content was determined by picrosirius red staining.

RESULTS

There was a well-pronounced myocardial hypertrophic effect for two interventions. The exercise blunted myocardial collagen increases induced by tobacco smoking. However, exercise and tobacco-smoking association was deleterious to myocardial performance. Thereby, in vitro experiments with papillary muscles contracting in isometric showed impairment myocardial inotropism in exercised rats exposed to tobacco smoking.

CONCLUSIONS

This work presents novel findings on the role of exercise training on cardiac remodeling induced by tobacco smoking. Although exercise has mitigated tissue fibrosis, their association with tobacco smoking exacerbated hypertrophy and in vitro myocardial dysfunction.

IMPLICATIONS

This is first study to show that the association of an aerobic exercise training with tobacco smoking intensifies the phenotype of pathological cardiac hypertrophy. Therefore, the combination of interventions resulted in exacerbated myocardial hypertrophy and contractility dysfunction. These findings have significant clinical implication because some smoking people can be enrolled in an exercise-training program.

Cinaciguat prevents the development of pathologic hypertrophy in a rat model of left ventricular pressure overload

Pathologic myocardial hypertrophy develops when the heart is chronically pressure-overloaded. Elevated intracellular cGMP-levels have been reported to prevent the development of pathologic myocardial hypertrophy, therefore we investigated the effects of chronic activation of the cGMP producing enzyme, soluble guanylate cyclase by Cinaciguat in a rat model of pressure overload-induced cardiac hypertrophy. Abdominal aortic banding (AAB) was used to evoke pressure overload-induced cardiac hypertrophy in male Wistar rats. Sham operated animals served as controls. Experimental and control groups were treated with 10 mg/kg/day Cinaciguat (Cin) or placebo (Co) p.o. for six weeks, respectively. Pathologic myocardial hypertrophy was present in the AABCo group following 6 weeks of pressure overload of the heart, evidenced by increased relative heart weight, average cardiomyocyte diameter, collagen content and apoptosis. Cinaciguat did not significantly alter blood pressure, but effectively attenuated all features of pathologic myocardial hypertrophy, and normalized functional changes, such as the increase in contractility following AAB. Our results demonstrate that chronic enhancement of cGMP signalling by pharmacological activation of sGC might be a novel therapeutic approach in the prevention of pathologic myocardial hypertrophy.

Diastolic dysfunction in prediabetic male rats: Role of mitochondrial oxidative stress

Although incidence and prevalence of prediabetes are increasing, little is known about its cardiac effects. Therefore, our aim was to investigate the effect of prediabetes on cardiac function and to characterize parameters and pathways associated with deteriorated cardiac performance. Long-Evans rats were fed with either control or high-fat chow for 21 wk and treated with a single low dose (20 mg/kg) of streptozotocin at week 4 High-fat and streptozotocin treatment induced prediabetes as characterized by slightly elevated fasting blood glucose, impaired glucose and insulin tolerance, increased visceral adipose tissue and plasma leptin levels, as well as sensory neuropathy. In prediabetic animals, a mild diastolic dysfunction was observed, the number of myocardial lipid droplets increased, and left ventricular mass and wall thickness were elevated; however, no molecular sign of fibrosis or cardiac hypertrophy was shown. In prediabetes, production of reactive oxygen species was elevated in subsarcolemmal mitochondria. Expression of mitofusin-2 was increased, while the phosphorylation of phospholamban and expression of Bcl-2/adenovirus E1B 19-kDa protein-interacting protein 3 (BNIP3, a marker of mitophagy) decreased. However, expression of other markers of cardiac auto- and mitophagy, mitochondrial dynamics, inflammation, heat shock proteins, Ca²⁺/calmodulin-dependent protein kinase II, mammalian target of rapamycin, or apoptotic pathways were unchanged in prediabetes. This is the first comprehensive analysis of cardiac effects of prediabetes indicating that mild diastolic dysfunction and cardiac hypertrophy are multifactorial phenomena that are associated with early changes in mitophagy, cardiac lipid accumulation, and elevated oxidative stress and that prediabetes-induced oxidative stress originates from the subsarcolemmal mitochondria.

Cardiac fibrosis and down regulation of GLUT4 in experimental diabetic cardiomyopathy are ameliorated by chronic exposures to intermittent altitude

Introduction: Chronic intermittent hypoxia is considered as a preconditioning status in cardiovascular health to inducing resistance to the low oxygen supply. Diabetic cardiomyopathy leads to inability of the heart to effective circulation of blood preventing of consequent tissue damages so; the aim of this study was elucidation of effect of chronic exposure to hypoxia on Cardiac fibrosis and expression of GLUT4 in experimental diabetic cardiomyopathy.

Methods: A total number of 30 rats were randomly divided into three groups; 1: Normoxia control group (NN, n = 10). 2: Normoxia diabetic group (ND, n = 10) that took fat diet for 2 weeks then were injected by streptozotocin (37 mg/kg) and 3: Hypoxia diabetic group (HD, n = 10): that were exposed to chronic intermittent hypoxia (CIH) (altitude ≈3400 m, 14% oxygen for 8 weeks). After hypoxia challenge, plasma metabolic parameters including: fasting blood glucose (FBS), triglyceride (TG) and total cholesterol (TC) were measured by colorimetric assay. Cardiac expression of GLUT4 protein and cardiac collagen accumulation were determined in the excised left ventricle by western blotting, and Masson trichrome staining respectively.

Results: Based on resultant data, FBS, TG and TC were significantly (P < 0.05) decreased in HD vs. ND. Homeostasis Model Assessment (HOMA) were also significantly attenuated after exposed to CIH in HD group compared to ND group (P < 0.05). Significant increase in packed cell volume and hemoglobin concentration was observed in HD group compared to ND group (P < 0.05). Comparison of heart wet weight between three groups showed a significant difference (P < 0.05) with lower amount in HD and ND versus NN. Myocardial fibrosis was significantly more pronounced in ND when compared to NN. Eight weeks exposure to hypoxia ameliorated this increase in HD group. Intermittent hypoxia significantly increased GLUT4 protein expression in HD compared to ND group (P < 0.05).

Conclusion: Data suggested that CIH might potentiate to improve glucose homeostasis and cardiac tissue structural damages created in type 2 diabetes (T2D).

Physiological and pathological left ventricular hypertrophy of comparable degree is associated with characteristic differences of in vivo hemodynamics

Left ventricular (LV) hypertrophy is a physiological or pathological response of LV myocardium to increased cardiac load. We aimed at investigating and comparing hemodynamic alterations in well-established rat models of physiological hypertrophy (PhyH) and pathological hypertrophy (PaH) by using LV pressure-volume (P-V) analysis. PhyH and PaH were induced in rats by swim training and by abdominal aortic banding, respectively. Morphology of the heart was investigated by echocardiography. Characterization of cardiac function was completed by LV P-V analysis. In addition, histological and molecular biological measurements were performed. Echocardiography revealed myocardial hypertrophy of similar degree in both models, which was confirmed by post-mortem heart weight data. In aortic-banded rats we detected subendocardial fibrosis. Reactivation of fetal gene program could be observed only in the PaH model. PhyH was associated with increased stroke volume, whereas unaltered stroke volume was detected in PaH along with markedly elevated end-systolic pressure values. Sensitive indexes of LV contractility were increased in both models, in parallel with the degree of hypertrophy. Active relaxation was ameliorated in athlete's heart, whereas it showed marked impairment in PaH. Mechanical efficiency and ventriculo-arterial coupling were improved in PhyH, whereas they remained unchanged in PaH. Myocardial gene expression of mitochondrial regulators showed marked differences between PaH and PhyH. We provided the first comparative hemodynamic characterization of PhyH and PaH in relevant rodent models. Increased LV contractility could be observed in both types of LV hypertrophy; characteristic distinction was detected in diastolic function (active relaxation) and mechanoenergetics (mechanical efficiency), which might be explained by mitochondrial differences.

The soluble guanylate cyclase activator cinaciguat prevents cardiac dysfunction in a rat model of type-1 diabetes mellitus

BACKGROUND

Diabetes mellitus (DM) leads to the development of diabetic cardiomyopathy, which is associated with altered nitric oxide (NO)--soluble guanylate cyclase (sGC)--cyclic guanosine monophosphate (cGMP) signalling. Cardioprotective effects of elevated intracellular cGMP-levels have been described in different heart diseases. In the current study we aimed at investigating the effects of pharmacological activation of sGC in diabetic cardiomyopathy.

METHODS

Type-1 DM was induced in rats by streptozotocin. Animals were treated either with the sGC activator cinaciguat (10 mg/kg/day) or with placebo orally for 8 weeks. Left ventricular (LV) pressure-volume (P-V) analysis was used to assess cardiac performance. Additionally, gene expression (qRT-PCR) and protein expression analysis (western blot) were performed. Cardiac structure, markers of fibrotic remodelling and DNA damage were examined by histology, immunohistochemistry and TUNEL assay, respectively.

RESULTS

DM was associated with deteriorated cGMP signalling in the myocardium (elevated phosphodiesterase-5 expression, lower cGMP-level and impaired PKG activity). Cardiomyocyte hypertrophy, fibrotic remodelling and DNA fragmentation were present in DM that was associated with impaired LV contractility (preload recruitable stroke work (PRSW): 49.5 ± 3.3 vs. 83.0 ± 5.5 mmHg, P < 0.05) and diastolic function (time constant of LV pressure decay (Tau): 17.3 ± 0.8 vs. 10.3 ± 0.3 ms, P < 0.05). Cinaciguat treatment effectively prevented DM related molecular, histological alterations and significantly improved systolic (PRSW: 66.8 ± 3.6 mmHg) and diastolic (Tau: 14.9 ± 0.6 ms) function.

CONCLUSIONS

Cinaciguat prevented structural, molecular alterations and improved cardiac performance of the diabetic heart. Pharmacological activation of sGC might represent a new therapy approach for diabetic cardiomyopathy.

Knockout of p21-activated kinase-1 attenuates exercise-induced cardiac remodelling through altered calcineurin signalling

AIMS

Despite its known cardiovascular benefits, the intracellular signalling mechanisms underlying physiological cardiac growth remain poorly understood. Therefore, the purpose of this study was to investigate a novel role of p21-activated kinase-1 (Pak1) in the regulation of exercise-induced cardiac hypertrophy.

METHODS AND RESULTS

Wild-type (WT) and Pak1 KO mice were subjected to 6 weeks of treadmill endurance exercise training (ex-training). Cardiac function was assessed via echocardiography, in situ haemodynamics, and the pCa-force relations in skinned fibre preparations at baseline and at the end of the training regimen. Post-translational modifications to the sarcomeric proteins and expression levels of calcium-regulating proteins were also assessed following ex-training. Heart weight/tibia length and echocardiography data revealed that there was marked hypertrophy following ex-training in the WT mice, which was not evident in the KO mice. Additionally, following ex-training, WT mice demonstrated an increase in cardiac contractility, myofilament calcium sensitivity, and phosphorylation of cardiac myosin-binding protein C, cardiac TnT, and tropomyosin compared with KO mice. With ex-training in WT mice, there were also increased protein levels of calcineurin and increased phosphorylation of phospholamban.

CONCLUSIONS

Our data suggest that Pak1 is essential for adaptive physiological cardiac remodelling and support previous evidence that demonstrates Pak1 signalling is important for cardiac growth and survival.