The benefits of endurance training in cardiomyocyte function in hypertensive rats are reversed within four weeks of detraining

Euterpe Oleracea Martius (Açaí) Extract and Resistance Exercise Modulate Cardiac Parameters of Hypertensive Rats

BACKGROUND

The study evaluated the effects of resistance exercise training and açaí supplementation on cardiac parameters in hypertensive animals.

METHODS

For this study, rats from the Wistar and SHR lines (spontaneously hypertensive rats) were used. The animals were divided into 5 groups: Wistar Control (C); Control Hypertensive (H); Trained Hypertensive (HT); Hypertensive and Supplemented with Açaí (HA); and Hypertensive Trained and Supplemented with Açaí (HAT). Resistance exercise training was carried out through climbing. The supplemented groups received 3 g of açaí/kg of body mass. The animals' systolic blood pressure (SBP), body mass, and physical test were measured at the beginning and end of the intervention. At the end, an echocardiographic analysis was performed. Histological analysis and oxidative stress of the LV were performed.

RESULTS

It was found that hypertensive animals showed an increase in SBP, and the treatments reduced this parameter. The trained groups achieved higher values of maximum carrying load. Hypertension increased the dimension of the left ventricular free wall in diastole and reduced ejection and shortening fractions. The trained groups showed improvement in ejection and shortening fractions. The H group increased the proportion of extracellular matrix and reduced the proportion of cells, with the HAT group attenuating this change. Cell diameter was greater in group H, and all treatments reduced this parameter. Hypertension increased the concentration of malondialdehyde and decreased catalase activity in LV. The treatments managed to mitigate this damage.

CONCLUSIONS

It is concluded that the treatments managed to generate positive cardiovascular adaptations, and their combination enhanced these effects.

Resistance exercise training benefits pulmonary, cardiac, and muscular structure and function in rats with stable pulmonary artery hypertension

AIM

We tested the effects of low- to moderate-intensity resistance exercise training (RT) on the structure and function of pulmonary, right ventricle (RV), and skeletal muscle tissues in rats with stable pulmonary artery hypertension (PAH).

MAIN METHODS

After the first monocrotaline (MCT; 20 mg/kg) injection, male rats were submitted to a RT program (Ladder climbing; 55-65 % intensity), 5 times/week. Seven days later rats received the second MCT dose. Physical effort tolerance test and echocardiographic examination were performed. After euthanasia, lung, heart, and biceps brachii were processed for histological, single myocyte, and biochemical analysis.

KEY FINDINGS

RT improved survival and physical effort tolerance (i.e., maximum carrying load), mitigated the pulmonary artery resistance increase (i.e., TA/TE), and preserved cardiac function (i.e., fractional shortening, ejection fraction, stroke volume and TAPSE). RT counteracted oxidative stress (i.e., CAT, SOD, GST, MDA and NO) and adverse remodeling in lung (i.e., collapsed alveoli) and in biceps brachii (i.e., atrophy and total collagen) tissues. RT delayed RV adverse remodeling (i.e., hypertrophy, extracellular matrix, collagen types I and III, and fibrosis) and impairments in single RV myocyte contractility (i.e., amplitude and velocity to peak and relaxation). RT improved the expression of gene (i.e., miRNA 214) and intracellular Ca2+ cycling regulatory proteins (i.e., PLBser16); and of pathological (i.e., α/β-MHC and Foxo3) and physiological (i.e., Akt, p-Akt, mTOR, p-mTOR, and Bcl-xL) hypertrophy pathways markers in RV tissue.

SIGNIFICANCE

Low- to moderate-intensity RT benefits the structure and function of pulmonary, RV, and skeletal muscle tissues in rats with stable pulmonary artery hypertension.

Metabolic mitochondrial alterations prevail in the female rat heart 8 weeks after exercise cessation

BACKGROUND

The consumption of high-caloric diets strongly contributes to the development of non-communicable diseases (NCDs), including cardiovascular disease, the leading cause of mortality worldwide. Exercise (along with diet intervention) is one of the primary non-pharmacological approaches to promote a healthier lifestyle and counteract the rampant prevalence of NCDs. The present study evaluated the effects of exercise cessation after a short period training on the cardiac metabolic and mitochondrial function of female rats.

METHODS

Seven-week-old female Sprague-Dawley rats were fed a control or a high-fat, high-sugar (HFHS) diet and, after 7 weeks, the animals were kept on a sedentary lifestyle or submitted to endurance exercise for 3 weeks (6 days per week, 20-60 min/day). The cardiac samples were analysed 8 weeks after exercise cessation.

RESULTS

The consumption of the HFHS diet triggered impaired glucose tolerance, whereas the HFHS diet and physical exercise resulted in different responses in plasma adiponectin and leptin levels. Cardiac mitochondrial respiration efficiency was decreased by the HFHS diet consumption, which led to reduced ATP and increased NAD(P)H mitochondrial levels, which remained prevented by exercise 8 weeks after cessation. Exercise training-induced cardiac adaptations in redox balance, namely increased relative expression of Nrf2 and downstream antioxidant enzymes persist after an eight-week exercise cessation period.

CONCLUSIONS

Endurance exercise modulated cardiac redox balance and mitochondrial efficiency in female rats fed a HFHS diet. These findings suggest that exercise may elicit cardiac adaptations crucial for its role as a non-pharmacological intervention for individuals at risk of developing NCDs.

Cardiac changes in spontaneously hypertensive rats: Modulation by aerobic exercise

Systemic arterial hypertension is a multifactorial clinical condition characterized by high and sustained levels of blood pressure. For a better understanding of the pathophysiology of hypertension, studies are conducted with spontaneously hypertensive animals, which allow the investigation of physiological changes that in most cases cannot be studied in humans. In these animals, myocardial remodeling, increased pro-inflammatory markers, redox imbalance and contractile dysfunctions that lead to changes in cardiac function can be observed. However, it can be inferring that aerobic training improves cardiac function and cardiomyocyte contractility, in addition to controlling inflammation and reducing oxidative stress in cardiac muscle, despite this, the precise mechanisms by which physical exercise improves cardiovascular control are not fully understood. In this review, we provide an overview of the pathophysiological changes that affect the heart of spontaneously hypertensive animals and their modulation by aerobic exercise.

Effects of moderate-continuous and high-intensity interval aerobic training on cardiac function of spontaneously hypertensive rats

The aim of this study was to verify the effects of moderate-intensity continuous (MICT) and high-intensity interval (HIIT) aerobic training on cardiac morphology and function and the mechanical properties of single cardiomyocytes in spontaneously hypertensive rats (SHR) in the compensated phase of hypertension. Sixteen-week-old male SHR and normotensive Wistar (WIS) rats were allocated to six groups of six animals each: SHR CONT or WIS CONT (control); SHR MICT or WIS MICT (underwent MICT, 30 min/day, five days per week for eight weeks); and SHR HIIT or WIS HIIT (underwent HIIT, 30 min/day, five days per week for eight weeks). Total exercise time until fatigue and maximum running speed were determined using a maximal running test before and after the experimental period. Systolic (SAP), diastolic (DAP), and mean (MAP) blood pressures were measured using tail plethysmography before and after the experimental period. Echocardiographic evaluations were performed at the end of the experimental period. The rats were euthanized after in vivo assessments, and left ventricular myocytes were isolated to evaluate global intracellular Ca²⁺ transient ([Ca²⁺]_i) and contractile function. Cellular measurements were performed at basal temperature (~37°C) at 3, 5, and 7 Hz. The results showed that both training programs increased total exercise time until fatigue and, consequently, maximum running speed. In hypertensive rats, MICT decreased SAP, DAP, MAP, interventricular septal thickness during systole and diastole, and the contraction amplitude at 5 Hz. HIIT increased heart weight and left ventricular wall thickness during systole and diastole and reduced SAP, MAP, and the time to peak [Ca²⁺]_i at all pacing frequencies. In conclusion, both aerobic training protocols promoted beneficial adaptations to cardiac morphology, function, and mechanical properties of single cardiomyocytes in SHR.

Integrative physiological study of adaptations induced by aerobic physical training in hypertensive hearts

Aerobic physical training reduces arterial pressure in patients with hypertension owing to integrative systemic adaptations. One of the key factors is the decrease in cardiac sympathetic influence. Thus, we hypothesized that among other causes, cardiac sympathetic influence reduction might be associated with intrinsic cardiac adaptations that provide greater efficiency. Therefore, 14 spontaneously hypertensive rats (SHR group) and 14 normotensive Wistar Kyoto rats (WKY group) were used in this study. Half of the rats in each group were trained to swim for 12 weeks. All animals underwent the following experimental protocols: double blockade of cardiac autonomic receptors with atropine and propranolol; echocardiography; and analysis of coronary bed reactivity and left ventricle contractility using the Langendorff technique. The untrained SHR group had a higher sympathetic tone, cardiac hypertrophy, and reduced ejection fraction compared with the untrained WKY group. In addition, reduced coronary bed reactivity due to increased flow, and less ventricular contractile response to dobutamine and salbutamol administration were observed. The trained SHR group showed fewer differences in echocardiographic parameters as the untrained SHR group. However, the trained SHR group showed a reduction in the cardiac sympathetic influence, greater coronary bed reactivity, and increased left intraventricular pressure. In conclusion, aerobic physical training seems to reduce cardiac sympathetic influence and increase contractile strength in SHR rats, besides the minimal effects on cardiac morphology. This reduction suggests intrinsic cardiac adaptations resulting in beneficial adjustments of coronary bed reactivity associated with greater left ventricular contraction.

Effects of physical exercise combined with captopril or losartan on left ventricular hypertrophy of hypertensive rats

Background: Left ventricular hypertrophy (LVH) is an endpoint of hypertensive cardiac alterations. Renin-angiotensin-aldosterone system (RAAS) blockers are among the most effective on LVH regression. Physical exercise combined to antihypertensive drug contributes to arterial pressure (AP) control and LVH prevention. We evaluated the effects of physical exercise combined to captopril or losartan during eight weeks for spontaneously hypertensive rats (SHR) on some cardiac parameters.Methods: SHR (n=5-6 per group) were sedentary or trained 5 days a week in treadmill during 8 weeks; and they were treated with daily oral captopril (12.5, 25, or 50mg/kg), losartan (2.5, 5, or 10mg/kg), or vehicle. At the end, it was obtained systolic AP (SAP), electrocardiogram (ECG), and hearts metalloproteinase 2 (MMP-2) activity and histology.Results: Captopril 25 and 50 mg/kg, and losartan 10 mg/kg lowered SAP of sedentary and trained SHR. Losartan 5 mg/kg combined with physical exercise also lowered SAP. Combined with exercise, captopril 50 mg/kg lowered 13.6% of QT interval, 14.2% of QTc interval, and 22.8% of Tpeak-Tend compared to sedentary SHR. Losartan 5 and 10mg/kg lowered QT interval of sedentary and trained SHR. Losartan 2.5, 5 and 10mg/kg combined with physical exercise lowered respectively 25.4%, 24.8%, and 31.8% of MMP-2 activity. Losartan (10mg/kg) combined with exercise reduced cardiomyocyte diameter.Conclusion: These data support the hypothesis of physical exercise combined with RAAS blockers could improve the benefits on hypertensive LVH treatment.

Effects of aerobic exercise training and açai supplementation on cardiac structure and function in rats submitted to a high-fat diet

This study evaluated the effect of aerobic exercise training (AET) and supplementation with açai on cardiac structure and function in rats submitted to a high-fat diet. Two-month old Fischer male rats were divided into 5 groups: Control (C), High-fat Diet (H), High-fat Diet + Açai (HA), High-fat Diet + AET (HT), High-fat Diet + Açai + AET (HAT). The high-fat diet had 21.8% lard and 1% cholesterol (H and HT), or supplemented with 1% lyophilized açai pulp (HA and HAT). The HT and HAT groups performed AET on a treadmill (5 days/week, 1 h/day, 60% of the maximum running speed) for 8 weeks. Exercise tolerance test were performed, and adiposity index calculated. After euthanasia, the left ventricle (LV) was dissected and processed for histological, single myocyte intracellular calcium ([Ca²⁺]_i) transient and contractility, oxidative stress and gene expression analysis. AET improved running capacity and reduced the adiposity index. Both AET and açai supplementation inhibited the increase in the LV collagen content, the deleterious effects on the [Ca²⁺]_i transient and contractility in cardiomyocytes and the increment in oxidative stress, caused by the consumption of a high-fat diet. Aerobic exercise training and açai supplementation can mitigate damage caused by high-fat diet in cardiac structure and function, though the combination of treatments had no additional effects.

Continuous Aerobic Exercise Prevents Detrimental Remodeling and Right Heart Myocyte Contraction and Calcium Cycling Dysfunction in Pulmonary Artery Hypertension

ABSTRACT

Pulmonary artery hypertension (PAH) imposes right heart and lung detrimental remodeling which impairs cardiac contractility, physical effort tolerance, and survival. The effects of an early moderate-intensity continuous aerobic exercise training on the right ventricle and lung structure, and on contractility and the calcium (Ca2+) transient in isolated myocytes from rats with severe PAH induced by monocrotaline were analyzed. Rats were divided into control sedentary (CS), control exercise (CE), monocrotaline sedentary (MS), and monocrotaline exercise (ME) groups. Animals from control exercise and ME groups underwent a moderate-intensity aerobic exercise on a treadmill (60 min/d; 60% intensity) for 32 days, after a monocrotaline (60 mg/kg body weight i.p.) or saline injection. The pulmonary artery resistance was higher in MS than in control sedentary (1.36-fold) and was reduced by 39.39% in ME compared with MS. Compared with MS, the ME group presented reduced alveolus (17%) and blood vessel (46%) wall, fibrosis (25.37%) and type I collagen content (55.78%), and increased alveolus (52.96%) and blood vessel (146.97%) lumen. In the right ventricle, the ME group exhibited diminished hypertrophy index (25.53%) and type I collagen content (40.42%) and improved myocyte contraction [ie, reduced times to peak (29.27%) and to 50% relax (13.79%)] and intracellular Ca2+ transient [ie, decreased times to peak (16.06%) and to 50% decay (7.41%)] compared with MS. Thus, early moderate-intensity continuous aerobic exercise prevents detrimental remodeling in the right heart and lung increases in the pulmonary artery resistance and dysfunction in single myocyte contraction and Ca2+ cycling in this model.

Chronic Iron Overload Restrains the Benefits of Aerobic Exercise to the Vasculature

Physical exercise is a well-recognized effective non-pharmacological therapy for cardiovascular diseases. However, because iron is essential element in many physiological processes including hemoglobin and myoglobin synthesis, thereby playing a role on oxygen transport, many athletes use iron supplement to improve physical performance. Regarding this, iron overload is associated with oxidative stress and damage to various systems, including cardiovascular. Thus, we aimed to identify the vascular effects of aerobic exercise in a rat model of iron overload. Male Wistar rats were treated with 100 mg/kg/day iron-dextran, i.p., 5 days a week for 4 weeks, and then underwent aerobic exercise protocol on a treadmill at moderate intensity, 60 min/day, 5 days a week for 8 weeks. Exercise reduced vasoconstrictor response of isolated aortic rings by increasing participation of nitric oxide (NO) and reducing oxidative stress, but these benefits to the vasculature were not observed in rats previously subjected to iron overload. The reduced vasoconstriction in the exercised group was reversed by incubation with superoxide dismutase (SOD) inhibitor, suggesting that increased SOD activity by exercise was lost in iron overload rats. Iron overload groups increased serum levels of iron, transferrin saturation, and iron deposition in the liver, gastrocnemius muscle, and aorta, and the catalase was overexpressed in the aorta probably as a compensatory mechanism to the increased oxidative stress. In conclusion, despite the known beneficial effects of aerobic exercise on vasculature, our results indicate that previous iron overload impeded the anticontractile effect mediated by increased NO bioavailability and endogenous antioxidant response due to exercise protocol.

Impaired thermoregulation in spontaneously hypertensive rats during physical exercise is related to reduced hypothalamic neuronal activation

This study aimed to evaluate the physical exercise-induced neuronal activation in brain nuclei controlling thermoregulatory responses in hypertensive and normotensive rats. Sixteen-week-old male normotensive Wistar rats (NWRs) and spontaneously hypertensive rats (SHRs) were implanted with an abdominal temperature sensor. After recovery, the animals were subjected to a constant-speed treadmill running (at 60% of the maximum aerobic speed) for 30 min at 25 °C. Core (T_core) and tail-skin (T_skin) temperatures were measured every minute during exercise. Ninety minutes after the exercise, the rats were euthanized, and their brains were collected to determine the c-Fos protein expression in the following areas that modulate thermoregulatory responses: medial preoptic area (mPOA), paraventricular hypothalamic nucleus (PVN), and supraoptic nucleus (SON). During treadmill running, the SHR group exhibited a greater increase in T_core and an augmented threshold for cutaneous heat loss relative to the NWR group. In addition, the SHRs showed reduced neuronal activation in the mPOA (< 49.7%) and PVN (< 44.2%), but not in the SON. The lower exercise-induced activation in the mPOA and PVN in hypertensive rats was strongly related to the delayed onset of cutaneous heat loss. We conclude that the enhanced exercise-induced hyperthermia in hypertensive rats can be partially explained by a delayed cutaneous heat loss, which is, in turn, associated with reduced activation of brain areas modulating thermoregulatory responses.

A comprehensive study of phospholipid fatty acid rearrangements in metabolic syndrome: correlations with organ dysfunction

The balance within phospholipids (PLs) between saturated fatty acids and monounsaturated or polyunsaturated fatty acids is known to regulate the biophysical properties of cellular membranes. As a consequence, in many cell types, perturbing this balance alters crucial cellular processes, such as vesicular budding and the trafficking/function of membrane-anchored proteins. The worldwide spread of the Western diet, which is highly enriched in saturated fats, has been clearly correlated with the emergence of a complex syndrome known as metabolic syndrome (MetS). MetS is defined as a cluster of risk factors for cardiovascular diseases, type 2 diabetes and hepatic steatosis; however, no clear correlations have been established between diet-induced fatty acid redistribution within cellular PLs and the severity/chronology of the symptoms associated with MetS or the function of the targeted organs. To address this issue, in this study we analyzed PL remodeling in rats exposed to a high-fat/high-fructose diet (HFHF) over a 15-week period. PL remodeling was analyzed in several organs, including known MetS targets. We show that fatty acids from the diet can redistribute within PLs in a very selective manner, with phosphatidylcholine being the preferred sink for this redistribution. Moreover, in the HFHF rat model, most organs are protected from this redistribution, at least during the early onset of MetS, at the expense of the liver and skeletal muscles. Interestingly, such a redistribution correlates with clear-cut alterations in the function of these organs.This article has an associated First Person interview with the first author of the paper.

Chronic aerobic exercise associated to low-dose L-NAME improves contractility without changing calcium handling in rat cardiomyocytes

Nitric oxide (NO) inhibition by high-dose NG-nitro-L-arginine methyl ester (L-NAME) is associated with several detrimental effects on the cardiovascular system. However, low-dose L-NAME increases NO synthesis, which in turn induces physiological cardiovascular benefits, probably by activating a protective negative feedback mechanism. Aerobic exercise, likewise, improves several cardiovascular functions in healthy hearts, but its effects are not known when chronically associated with low-dose L-NAME. Thus, we tested whether the association between low-dose L-NAME administration and chronic aerobic exercise promotes beneficial effects to the cardiovascular system, evaluating the cardiac remodeling process. Male Wistar rats were randomly assigned to control (C), L-NAME (L), chronic aerobic exercise (Ex), and chronic aerobic exercise associated to L-NAME (ExL). Aerobic training was performed with progressive intensity for 12 weeks; L-NAME (1.5 mg·kg^-1·day^-1) was administered by orogastric gavage. Low-dose L-NAME alone did not change systolic blood pressure (SBP), but ExL significantly increased SBP at week 8 with normalization after 12 weeks. Furthermore, ExL promoted the elevation of left ventricle (LV) end-diastolic pressure without the presence of cardiac hypertrophy and fibrosis. Time to 50% shortening and relaxation were reduced in ExL, suggesting a cardiomyocyte contractile improvement. In addition, the time to 50% Ca²⁺ peak was increased without alterations in Ca²⁺ amplitude and time to 50% Ca²⁺ decay. In conclusion, the association of chronic aerobic exercise and low-dose L-NAME prevented cardiac pathological remodeling and induced cardiomyocyte contractile function improvement; however, it did not alter myocyte affinity and sensitivity to intracellular Ca²⁺ handling.

Exercise capacity in different stages of hypertension in spontaneously hypertensive rats

BACKGROUND

The aim of the present study was to investigate the exercise capacity of hypertensive rats at different stages of development of hypertension and to determine the most suitable index to evaluate the exercise capacity in different strains.

METHODS

Male spontaneously hypertensive rat (SHR) and normotensive Wistar rats (NWR) of 5, 8, 12 and 16 weeks were submitted to the exercise capacity test. The exercise running time was measured and the workload was calculated.

RESULTS

Normotensive and hypertensive rats when assess the exercise capacity by exercise running time exhibited a reduction in exercise performance over time. Moreover, hypertensive rats showed lower exercise capacity compared to normotensive control when analyzed by workload.

CONCLUSIONS

The present results indicate that hypertensive rats exhibit reduced exercise capacity compared to normotensive rats regardless of age assessed. Beside that, in experiments with strains with different body mass the most reliable index to assess exercise capacity is workload.

D2-Like Receptors Mediate Dopamine-Inhibited Insulin Secretion via Ion Channels in Rat Pancreatic β-Cells

Dopamine (DA) has a vital role in the central nervous system and also modulates lipid and glucose metabolism. The present study aimed to investigate the effect of dopamine on insulin secretion and the underlying mechanisms in rat pancreatic β-cells. Data from the radioimmunoassay indicated that dopamine inhibited insulin secretion in a glucose- and dose-dependent manner. This inhibitory effect of dopamine was mediated mainly by D2-like receptors, but not D1-like receptors. Whole-cell patch-clamp recordings showed that dopamine decreased voltage-dependent Ca²⁺ channel currents, which could be reversed by inhibition of the D2-like receptor. Dopamine increased voltage-dependent potassium (K_V) channel currents and shortened action potential duration, which was antagonized by inhibition of D2-like receptors. Further experiments showed that D2-like receptor activation by quinpirole increased K_V channel currents. In addition, using calcium imaging techniques, we found that dopamine reduced intracellular Ca²⁺ concentration, which was also reversed by D2-like receptor antagonists. Similarly, quinpirole was found to decrease intracellular Ca²⁺ levels. Taken together, these findings demonstrate that dopamine inhibits insulin secretion mainly by acting on D2-like receptors, inhibiting Ca²⁺ channels, and activating Kv channels. This process results in shortened action potential duration and decreased intracellular Ca²⁺ levels in β-cells. This work offers new insights into a glucose-dependent mechanism whereby dopamine regulates insulin secretion.

Effects of exercise training and stem cell therapy on the left ventricle of infarcted rats

INTRODUCTION AND OBJECTIVES

Stem cell therapy and aerobic exercise are non-pharmacological therapies following myocardial infarction. The aim of this study was to test whether aerobic exercise training enhances the benefits of mesenchymal stem cell (MSC) therapy on remodeling of the extracellular matrix and fetal gene expression in the left ventricle of infarcted rats.

METHODS

Myocardial infarction was surgically induced in six-week old male Wistar rats. Animals were divided into four groups: sedentary control (SC) and sedentary and stem cell treated (SCMSC); exercised (EX) and exercised and stem cell treated (EXMSC). Bone marrow-derived MSCs were immediately transplanted via the tail vein (concentration: 1×10⁶ cells). Exercise training (five days/week, 60 min/day; 60% of maximal running speed) started 24 hours after myocardial infarction and lasted for 12 weeks.

RESULTS

Exercise capacity was higher in exercised than in sedentary groups. Animals in the SCMSC, EX and EXMSC groups exhibited better cardiac function than those in SC. Collagen content was lower in the SCMSC, EX and EXMSC groups than in SC and skeletal α-actin expression was lower in EX and EXMSC than in SC. The α/β-MHC ratio was higher in EX and EXMSC than in SC. The combination of therapies further reduced collagen content in the remote region of the infarct (∼24%) and skeletal α-actin expression (∼30%).

CONCLUSION

Aerobic exercise training appears to enhance the beneficial effects of stem cell therapy on remodeling of the extracellular matrix and fetal gene expression in the left ventricle of rats with moderate infarction.

LOW-INTENSITY ENDURANCE TRAINING AND RIGHT VENTRICULAR MYOCYTES OF HYPERTENSIVE RATS

ABSTRACT Introduction The structural and mechanical adaptations of the right ventricular (RV) myocytes in response to hypertension associated with low-intensity endurance training (LIET) have not been studied in experimental models. Objective To determine the effects of LIET on the structural and mechanical properties of RV myocytes in spontaneously hypertensive rats (SHRs). Methods Male SHRs and normotensive Wistar rats (age: 16 weeks) were allocated to groups (n=7): WIS (Wistar Controls); SHR-C (SHR Controls) and SHR-T (SHR Trained; 60 min/day, 50-60% of maximal exercise capacity, 5 days/week for 8 weeks). Systolic arterial pressure (SAP), isolated RV myocyte dimensions, contractility, intracellular Ca2+ transient ([Ca2+]i), and ventricular Ca2+ regulatory proteins were measured. The statistical analysis was performed by one-way ANOVA followed by the Tukey post hoc test (α=5%). Results LIET reduced the SAP in SHR animals (SHR-C, 164 ± 2 mmHg vs. SHR-T, 152 ± 4 mmHg; P<0.05). Hypertension increased cell length (WIS, 156.8 ± 2.7 µm; SHR-C, 166.6 ± 3.1 µm; P<0.05) but did not affect cell width or volume (P>0.05). LIET did not change the cell dimensions in the SHR-T. Neither hypertension nor LIET affected myocyte contractility or the expression of Ca2+ regulatory proteins in the RV of the SHR-C and SHR-T groups. Hypertension did not affect the amplitude of the [Ca2+]i transient or the time to half resting level (P>0.05), but increased the time to peak (WIS, 58 ± 1 ms vs. SHR-C, 79 ± 2 ms; P<0.05). LIET increased the amplitude of the [Ca2+]i transient (WIS, 2.28 ± 0.07 F/F0 and SHR-C, 2.48 ± 0.08 F/F0 vs. SHR-T, 2.87 ± 0.08 F/F0 P<0.05), but did not alter the times to peak or to half resting level. Conclusion LIET had no effect on the structural and mechanical properties of RV myocytes in the SHRs, although it increased the amplitude of the [Ca2+]i transient and reduced the SAP. Level of evidence I, Therapeutic Studies - Investigating the Results of Treatment.

Thermoregulation in Hypertensive Rats during Exercise: Effects of Physical Training

Background

Spontaneously hypertensive rats (SHR) show deficit in thermal balance during physical exercise.

Objective

To assess the effects of low-intensity physical exercise training on thermal balance of hypertensive rats undergoing an acute exercise protocol.

Methods

Sixteen-week-old male Wistar rats and SHR were allocated into four groups: control Wistar rats (C-WIS), trained Wistar (T-WIS), control SHR (C-SHR) and trained SHR (T-SHR). Treadmill exercise training was performed for 12 weeks. Blood pressure, resting heart rate and total exercise time was measured before and after the physical exercise program. After the exercise program, a temperature sensor was implanted in the abdominal cavity, and the animals subjected to an acute exercise protocol, during which internal body temperature, tail skin temperature and oxygen consumption until fatigue were continuously recorded. Mechanical efficiency (ME), work, heat dissipation threshold and sensitivity were calculated. Statistical significance was set at 5%.

Results

Physical training and hypertension had no effect on thermal balance during physical exercise. Compared with C-WIS, the T-WIS group showed higher heat production, which was counterbalanced by higher heat dissipation. Hypertensive rats showed lower ME than normotensive rats, which was not reversed by the physical training.

Conclusion

Low-intensity physical training did not affect thermal balance in SHR subjected to acute exercise.

Moderate Physical Training Ameliorates Cardiovascular Dysfunction Induced by High Fat Diet After Cessation of Training in Adult Rats

We aimed to test whether moderate physical training can induce long-lasting protection against cardiovascular risk factors induced by high fat diet (HFD) intake, even after cessation of training. 90-days-old Wistar rats were submitted to a sedentary lifestyle or moderate physical training, three times a week, for 30 days. Following this, at 120 days-of age, sedentary and trained rats received a hypercaloric diet (HFD) or a commercial diet normal fat diet (NFD) for 30 days. Body weight (BW) and food intake were evaluated weekly. At 150 days-of age, hemodynamic measures (systolic, diastolic, mean blood pressure, pulse pressure, pulse interval and heart rate) were made via an indwelling femoral artery catheter. Beat-to-beat data were analyzed to calculate power spectra of systolic blood pressure (SBP) and pulse interval. After euthanasia, mesenteric fat pads were removed and weighted and total blood was stored for later analysis of lipid profile. Consumption of a HFD increased blood pressure (BP), pulse pressure, low frequency BP variability, BW gain, fat pad stores and induced dyslipidemia. Interestingly, prior physical training was able to partially protect against this rise in BP and body fat stores. Prior physical training did not totally protect against the effects of HFD consumption but previously trained animals did demonstrate resistance to the development of cardiometabolic alterations, which illustrate that the benefits of physical training may be partially maintained even after 30 days of detraining period.

High-intensity intermittent training is as effective as moderate continuous training, and not deleterious, in cardiomyocyte remodeling of hypertensive rats

Exercise training offers possible nonpharmacological therapy for cardiovascular diseases including hypertension. High-intensity intermittent exercise (HIIE) training has been shown to have as much or even more beneficial cardiovascular effect in patients with cardiovascular diseases than moderate-intensity continuous exercise (CMIE) training. The aim of this study was to investigate the effects of the two types of training on cardiac remodeling of spontaneously hypertensive rats (SHR) induced by hypertension. Eight-week-old male SHR and normotensive Wistar-Kyoto rats (WKY) were divided into four groups: normotensive and hypertensive control (WKY and SHR-C) and hypertensive trained with CMIE (SHR-T CMIE) or HIIE (SHR-T HIIE). After 8 wk of training or inactivity, maximal running speed (MRS), arterial pressure, and heart weight were all assessed. CMIE or HIIE protocols not only increased final MRS and left ventricular weight/body weight ratio but also reduced mean arterial pressure compared with sedentary group. Then, left ventricular tissue was enzymatically dissociated, and isolated cardiomyocytes were used to highlight the changes induced by physical activity at morphological, mechanical, and molecular levels. Both types of training induced restoration of transverse tubule regularity, decrease in spark site density, and reduction in half-relaxation time of calcium transients. HIIE training, in particular, decreased spark amplitude and width, and increased cardiomyocyte contractility and the expression of sarco(endo)plasmic reticulum Ca²⁺-ATPase and phospholamban phosphorylated on serine 16. NEW & NOTEWORTHY High-intensity intermittent exercise training induces beneficial remodeling of the left ventricular cardiomyocytes of spontaneously hypertensive rats at the morphological, mechanical, and molecular levels. Results also confirm, at the cellular level, that this type of training, as it appears not to be deleterious, could be applied in rehabilitation of hypertensive patients.

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.

The impact of aerobic and anaerobic training regimes on blood pressure in normotensive and hypertensive rats: focus on redox changes

This study was aimed to assess the impact of aerobic and anaerobic type of exercise on blood pressure and redox status in normotensive and hypertensive rats. After 1 week of preconditioning feeding and 1 week of preconditioning running regimen, Wistar albino rats (n = 72; bw: 270 ± 50 g) were randomly assigned to three groups according to running protocol (high-intensity interval training (HIIT) or moderate-intensity training (MIT)): sedentary control, MIT, HIIT; spontaneous hypertensive sedentary control (SHR), SHR + MIT and SHR + HIIT. Blood pressure (BP) measurement was performed by a tail-cuff noninvasive method BP system. After 48 h of rest following the final training, the rats were fasted for 24 h and sacrificed under ketamine/xylazine anesthesia and blood samples were collected. The level of the next prooxidants were measured: superoxide anion radical (O₂^-); hydrogen peroxide (H₂O₂); nitrite level (NO₂^-) and index of lipid peroxidation (thiobarbituric acid reactive substances), and the activity of antioxidative enzymes: reduced glutathione (GSH) superoxide dismutase (SOD) and catalase (CAT) activity. After the last week of running, HIIT strongly affected SP, DP, and HR in SHR rats compared to other hypertensive rats, as well as after MIT in normotensive conditions. We have found that HIIT training protocol induced a higher increase of O₂^- and H₂O₂ as compared to MIT. Findings of the present study pointed out that contrary to normotensive conditions, in hypertensive conditions both training regimes reduced the BP levels, which was more prominent in case of HIIT. In addition, MIT seems to be connected with milder disturbance of pro-oxidant production and better antioxidant response.

Understanding Key Mechanisms of Exercise-Induced Cardiac Protection to Mitigate Disease: Current Knowledge and Emerging Concepts

The benefits of exercise on the heart are well recognized, and clinical studies have demonstrated that exercise is an intervention that can improve cardiac function in heart failure patients. This has led to significant research into understanding the key mechanisms responsible for exercise-induced cardiac protection. Here, we summarize molecular mechanisms that regulate exercise-induced cardiac myocyte growth and proliferation. We discuss in detail the effects of exercise on other cardiac cells, organelles, and systems that have received less or little attention and require further investigation. This includes cardiac excitation and contraction, mitochondrial adaptations, cellular stress responses to promote survival (heat shock response, ubiquitin-proteasome system, autophagy-lysosomal system, endoplasmic reticulum unfolded protein response, DNA damage response), extracellular matrix, inflammatory response, and organ-to-organ crosstalk. We summarize therapeutic strategies targeting known regulators of exercise-induced protection and the challenges translating findings from bench to bedside. We conclude that technological advancements that allow for in-depth profiling of the genome, transcriptome, proteome and metabolome, combined with animal and human studies, provide new opportunities for comprehensively defining the signaling and regulatory aspects of cell/organelle functions that underpin the protective properties of exercise. This is likely to lead to the identification of novel biomarkers and therapeutic targets for heart disease.

Physical Exercise and Regulation of Intracellular Calcium in Cardiomyocytes of Hypertensive Rats

BACKGROUND

Regulation of intracellular calcium (Ca2+) in cardiomyocytes is altered by hypertension; and aerobic exercise brings benefits to hypertensive individuals.

OBJECTIVE

To verify the effects of aerobic exercise training on contractility and intracellular calcium (Ca2+) transients of cardiomyocytes and on the expression of microRNA 214 (miR-214) in the left ventricle of spontaneously hypertensive rats (SHR).

METHODS

SHR and normotensive Wistar rats of 16 weeks were divided into 4 groups -sedentary hypertensive (SH); trained hypertensive (TH); sedentary normotensive (SN); and trained normotensive (TN). Animals of the TH and TN groups were subjected to treadmill running program, 5 days/week, 1 hour/day at 60-70% of maximum running velocity for 8 weeks. We adopted a p ≤ 0.05 as significance level for all comparisons.

RESULTS

Exercise training reduced systolic arterial pressure in hypertensive rats. In normotensive rats, exercise training reduced the time to 50% cell relaxation and the time to peak contraction and increased the time to 50% decay of the intracellular Ca2+ transients. In SHR, exercise increased the amplitude and reduced the time to 50% decay of Ca2+ transients. Exercise training increased the expression of miR-214 in hypertensive rats only.

CONCLUSION

The aerobic training applied in this study increased the availability of intracellular Ca2+ and accelerated the sequestration of these ions in left ventricular myocytes of hypertensive rats, despite increased expression of miR-214 and maintenance of cell contractility.

Influence of Long-Term Salt Diets on Cardiac Ca2+ Handling and Contractility Proteins in Hypertensive Rats

BACKGROUND

High sodium intake contributes to the pathogenesis of hypertension and adversely affects cardiac function. Conversely, sodium reduction is associated with a blood pressure decrease and improved cardiovascular function. However, the mechanisms that underlie the cardiac effects induced by salt intake in hypertension have not been fully elucidated. Ca2+ handling is critical for efficient myocardial function; thus, we aimed to investigate the long-term effects of diets with different salt contents on cardiac function and Ca2+ handling proteins in spontaneously hypertensive rats (SHRs).

METHODS

Cardiac function was evaluated by catheterization. Ca2+ handling and contractile proteins were evaluated by immunoblotting in hearts from SHRs fed for 6 months with diets containing high (HS, 3%), low (LS, 0.03%), or normal salt content (NS, 0.3%). Diets were introduced immediately after weaning. Tail cuff pletismography was assessed at the 3rd and 7th months of follow-up.

RESULTS

Compared to the NS group, the HS group exhibited worsened hypertension, increased cardiac expression of β-myosin heavy chain (MHC), a decreased α/β-MHC ratio and reduced expression of both phospholamban (PLB) and Na+/Ca2+ exchanger (NCX). LS intake attenuated the blood pressure increase and left ventricle hypertrophy, slightly decreased the cardiac contractility and relaxation index, and increased the α/β-MHC ratio. These effects were accompanied by increased cardiac PLB expression and decreased Ca2+ L-type channel and NCX expression.

CONCLUSIONS

These findings indicate that the modulation of Ca2+ handling may be one of the molecular mechanisms underlying the effect of salt intake on myocardial function in hypertension.

Moderate Continuous Aerobic Exercise Training Improves Cardiomyocyte Contractility in Β1 Adrenergic Receptor Knockout Mice

Background

The lack of cardiac β₁-adrenergic receptors (β₁-AR) negatively affects the regulation of both cardiac inotropy and lusitropy, leading, in the long term, to heart failure (HF). Moderate-intensity aerobic exercise (MCAE) is recommended as an adjunctive therapy for patients with HF.

Objective

We tested the effects of MCAE on the contractile properties of left ventricular (LV) myocytes from β₁ adrenergic receptor knockout (β₁ARKO) mice.

Methods

Four- to five-month-old male wild type (WT) and β₁ARKO mice were divided into groups: WT control (WTc) and trained (WTt); and β₁ARKO control (β₁ARKOc) and trained (β₁ARKOt). Animals from trained groups were submitted to a MCAE regimen (60 min/day; 60% of maximal speed, 5 days/week) on a treadmill, for 8 weeks. P ≤ 0.05 was considered significant in all comparisons.

Results

The β₁ARKO and exercised mice exhibited a higher (p < 0.05) running capacity than WT and sedentary ones, respectively. The β₁ARKO mice showed higher body (BW), heart (HW) and left ventricle (LVW) weights, as well as the HW/BW and LVW/BW than WT mice. However, the MCAE did not affect these parameters. Left ventricular myocytes from β₁ARKO mice showed increased (p < 0.05) amplitude and velocities of contraction and relaxation than those from WT. In addition, MCAE increased (p < 0.05) amplitude and velocities of contraction and relaxation in β₁ARKO mice.

Conclusion

MCAE improves myocyte contractility in the left ventricle of β₁ARKO mice. This is evidence to support the therapeutic value of this type of exercise training in the treatment of heart diseases involving β₁-AR desensitization or reduction.

Swim training attenuates the adverse remodeling of LV structural and mechanical properties in the early compensated phase of hypertension

AIM

Investigate to what extent low-intensity swim training for six weeks counterbalances the adverse remodeling due to the advance of pathological hypertrophy in the left ventricle (LV) structural and mechanical properties in the early compensated phase of hypertension in male SHR.

MAIN METHODS

Four-month-old male SHR and Wistar rats were randomly divided into Sed (sedentary) and Ex (exercised) groups. The exercised rats were submitted to a swimming protocol (1h/day, 5times/week, no additional load) for six weeks. LV tissue and isolated myocytes were used to assess structural and mechanical properties. Myocytes were stimulted at frequencies (F) of 1 and 3Hz at 37°C.

KEY FINDINGS

Exercised SHR showed improvement in cardiovascular parameters compared to sedentary SHR (mean arterial pressure: 13.22%; resting HR: 14.28.%). About structural and mechanical properties, swim training induced a decrease in LV myocyte thickness (10.85%), number of inflammatory cells (21.24%); collagen type III (74.23%) and type I (85.6%) fiber areas; amplitude of single myocyte shortening (47% to F1 and 28.46% to F3), timecourses of shortening (16.5% to F1 and 7.55% to F3) and relaxation (15.31% to F3) compared to sedentary SHR.

SIGNIFICANCE

Six weeks of swim training attenuates the adverse remodeling of LV structural and mechanical properties in the early compensated phase of hypertension in male SHR.

Cardiotrophin 1 stimulates beneficial myogenic and vascular remodeling of the heart

The post-natal heart adapts to stress and overload through hypertrophic growth, a process that may be pathologic or beneficial (physiologic hypertrophy). Physiologic hypertrophy improves cardiac performance in both healthy and diseased individuals, yet the mechanisms that propagate this favorable adaptation remain poorly defined. We identify the cytokine cardiotrophin 1 (CT1) as a factor capable of recapitulating the key features of physiologic growth of the heart including transient and reversible hypertrophy of the myocardium, and stimulation of cardiomyocyte-derived angiogenic signals leading to increased vascularity. The capacity of CT1 to induce physiologic hypertrophy originates from a CK2-mediated restraining of caspase activation, preventing the transition to unrestrained pathologic growth. Exogenous CT1 protein delivery attenuated pathology and restored contractile function in a severe model of right heart failure, suggesting a novel treatment option for this intractable cardiac disease.

Structural, Contractile and Electrophysiological Adaptations of Cardiomyocytes to Chronic Exercise

Cardiac beneficial effects of chronic exercise is well admitted. These effects mainly studied at the organ and organism integrated levels find their origin in cardiomyocyte adaptation. This chapter try to highlight the main trends of the data related to the different parameters subject to such adaptations. This is addressed through cardiomyocytes size and structure, calcium and contractile properties, and finally electrophysiological alterations induced by training as they transpire from the literature. Despite the clarifications needed to decipher healthy cardiomyocyte remodeling, this overview clearly show that cardiac cell plasticity ensure the cardiac adaptation to exercise training and offers an interesting mean of action to counteract physiological disturbances induced by cardiac pathologies.

Brain Temperature in Spontaneously Hypertensive Rats during Physical Exercise in Temperate and Warm Environments

This study aimed to evaluate brain temperature (Tbrain) changes in spontaneously hypertensive rats (SHRs) subjected to two different physical exercise protocols in temperate or warm environments. We also investigated whether hypertension affects the kinetics of exercise-induced increases in Tbrain relative to the kinetics of abdominal temperature (Tabd) increases. Male 16-week-old normotensive Wistar rats (NWRs) and SHRs were implanted with an abdominal temperature sensor and a guide cannula in the frontal cortex to enable the insertion of a thermistor to measure Tbrain. Next, the animals were subjected to incremental-speed (initial speed of 10 m/min; speed was increased by 1 m/min every 3 min) or constant-speed (60% of the maximum speed) treadmill running until they were fatigued in a temperate (25°C) or warm (32°C) environment. Tbrain, Tabd and tail skin temperature were measured every min throughout the exercise trials. During incremental and constant exercise at 25°C and 32°C, the SHR group exhibited greater increases in Tbrain and Tabd relative to the NWR group. Irrespective of the environment, the heat loss threshold was attained at higher temperatures (either Tbrain or Tabd) in the SHRs. Moreover, the brain-abdominal temperature differential was lower at 32°C in the SHRs than in the NWRs during treadmill running. Overall, we conclude that SHRs exhibit enhanced brain hyperthermia during exercise and that hypertension influences the kinetics of the Tbrain relative to the Tabd increases, particularly during exercise in a warm environment.

Effect of endurance training on seizure susceptibility, behavioral changes and neuronal damage after kainate-induced status epilepticus in spontaneously hypertensive rats

The therapeutic efficacy of regular physical exercises in an animal model of epilepsy and depression comorbidity has been confirmed previously. In the present study, we examined the effects of endurance training on susceptibility to kainate (KA)-induced status epilepticus (SE), behavioral changes and neuronal damage in spontaneously hypertensive rats (SHRs). Male SHRs were randomly divided into two groups. One group was exercised on a treadmill with submaximal loading for four weeks and the other group was sedentary. Immediately after the training period, SE was evoked in half of the sedentary and trained rats by KA, while the other half of the two groups received saline. Basal systolic (SP), diastolic (DP) and mean arterial pressure (MAP) of all rats were measured at the beginning and at the end of the training period. Anxiety, memory and depression-like behaviour were evaluated a month after SE. The release of 5-HT in the hippocampus was measured using a liquid scintillation method and neuronal damage was analyzed by hematoxylin and eosin staining. SP and MAP of exercised SHRs decreased in comparison with the initial values. The increased resistance of SHRs to KA-induced SE was accompanied by an elongated latent seizure-free period, improved object recognition memory and antidepressant effect after the training program. While the anticonvulsant and positive behavioral effects of endurance training were accompanied by an increase of 5-HT release in the hippocampus, it did not exert neuroprotective activity. Our results indicate that prior exercise is an effective means to attenuate KA-induced seizures and comorbid behavioral changes in a model of hypertension and epilepsy suggesting a potential influence of hippocampal 5-HT on a comorbid depression. However, this beneficial impact does not prevent the development of epilepsy and concomitant brain damage.

A single resistance exercise session improves myocardial contractility in spontaneously hypertensive rats

Resistance training evokes myocardial adaptation; however, the effects of a single resistance exercise session on cardiac performance are poorly understood or investigated. This study aimed to investigate the effects of a single resistance exercise session on the myocardial contractility of spontaneously hypertensive rats (SHRs). Male 3-month-old SHRs were divided into two groups: control (Ct) and exercise (Ex). Control animals were submitted to sham exercise. Blood pressure was measured in conscious rats before the exercise session to confirm the presence of arterial hypertension. Ten minutes after the exercise session, the animals were anesthetized and killed, and the hearts were removed. Cardiac contractility was evaluated in the whole heart by the Langendorff technique and by isometric contractions of isolated left ventricular papillary muscles. SERCA2a, phospholamban (PLB), and phosphorylated PLB expression were investigated by Western blot. Exercise increased force development of isolated papillary muscles (Ex=1.0±0.1 g/mg vs Ct=0.63±0.2 g/mg, P<0.05). Post-rest contraction was greater in the exercised animals (Ex=4.1±0.4% vs Ct=1.7±0.2%, P<0.05). Papillary muscles of exercised animals developed greater force under increasing isoproterenol concentrations (P<0.05). In the isolated heart, exercise increased left ventricular isovolumetric systolic pressure (LVISP; Δ +39 mmHg; P<0.05) from baseline conditions. Hearts from the exercised rats presented a greater response to increasing diastolic pressure. Positive inotropic intervention to calcium and isoproterenol resulted in greater LVISP in exercised animals (P<0.05). The results demonstrated that a single resistance exercise session improved myocardial contractility in SHRs.

Exercise improves cardiac function and attenuates insulin resistance in Dahl salt-sensitive rats

BACKGROUND

The development of heart failure (HF) secondary to hypertension is a complex process related to a series of physiological and molecular factors including glucose dysregulation. The overall objective of this study was to investigate whether exercise training could improve cardiac function and insulin resistance in a rat model of hypertensive HF.

METHODS

Seven week old Dahl salt-sensitive rats received either 8% NaCl (n = 30) or 0.3% NaCl (n = 18) diet. After a 5-week diet, animals were randomly assigned to exercise training (treadmill running at 18 m/min, 5% inclination for 60 min, 5 days/week) or kept sedentary for 6 additional weeks. 2D echocardiography was used to calculate left ventricular (LV) dimensions, volumes and global functional parameters. LV global deformation parameters were measured with speckle tracking echocardiography. Insulin resistance was assessed using 1h oral glucose tolerance testing.

RESULTS

High salt diet led to cardiac hypertrophy and HF, characterized by increased wall thicknesses and LV volumes as well as reduced deformation parameters. In addition, high salt diet was associated with the development of insulin resistance. Exercise training improved cardiac function, reduced the extent of interstitial fibrosis and reduced insulin levels 60 min post-glucose administration.

CONCLUSIONS

Even if not fully reversed, exercise training in HF animals improved cardiac function and insulin resistance. Adjusted modalities of exercise training might offer new insights not only as a preventive strategy, but also as a treatment for HF patients.

Cardiac adaptations from 4 weeks of intensity-controlled vigorous exercise are lost after a similar period of detraining

Intensity-controlled (relative to VO_2max) treadmill exercise training in adult rats results in the activation and ensuing differentiation of endogenous c-kit^pos cardiac stem/progenitor cells (eCSCs) into newly formed cardiomyocytes and capillaries. Whether these training-induced adaptations persist following detraining is undetermined. Twelve male Wistar rats (∼230 g) were exercised at 80–85% of their VO_2max for 30 min day⁻¹, 4 days week⁻¹ for 4 weeks (TR;n = 6), followed by 4 weeks of detraining (DTR; n = 6). Twelve untrained rats acted as controls (CTRL). Exercise training significantly enhanced VO_2max (11.34 mL kg⁻¹ min⁻¹) and wet heart weight (29%) above CTRL (P < 0.05). Echocardiography revealed that exercise training increased LV mass (∼32%), posterior and septal wall thickness (∼15%), ejection fraction and fractional shortening (∼10%) compared to CTRL (P < 0.05). Cardiomyocyte diameter (17.9 ± 0.1 μm vs. 14.9 ± 0.6 μm), newly formed (BrdU^pos/Ki67^pos) cardiomyocytes (7.2 ± 1.3%/1.9 ± 0.7% vs. 0.2 ± 0.1%/0.1 ± 0.1%), total cardiomyocyte number (45.6 ± 0.6 × 10⁶ vs. 42.5 ± 0.4 × 10⁶), c-kit^pos eCSC number (884 ± 112 per 10⁶ cardiomyocytes vs. 482 ± 132 per 10⁶ cardiomyocytes), and capillary density (4123 ± 227 per mm² vs. 2117 ± 118 per mm²) were significantly greater in the LV of trained animals (P < 0.05) than CTRL. Detraining removed the stimulus for c-kit^pos eCSC activation (640 ± 98 per 10⁶ cardiomyocytes) and resultant cardiomyocyte hyperplasia (0.4 ± 0.3% BrdU^pos/0.2 ± 0.2% Ki67^pos cardiomyocytes). Capillary density (3673 ± 374 per mm²) and total myocyte number (44.7 ± 0.5 × 10⁶) remained elevated following detraining, but cardiomyocyte hypertrophy (15.0 ± 0.4 μm) was lost, resulting in a reduction of anatomical (wall thickness ∼4%; LV mass ∼10% and cardiac mass ∼8%, above CTRL) and functional (EF & FS ∼2% above CTRL) parameters gained through exercise training. These findings demonstrate that cardiac adaptations, produced by 4 weeks of intensity-controlled exercise training are lost after a similar period of detraining.

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.

Effect of exercise training on Ca²⁺ release units of left ventricular myocytes of spontaneously hypertensive rats

In cardiomyocytes, calcium (Ca²⁺) release units comprise clusters of intracellular Ca²⁺ release channels located on the sarcoplasmic reticulum, and hypertension is well established as a cause of defects in calcium release unit function. Our objective was to determine whether endurance exercise training could attenuate the deleterious effects of hypertension on calcium release unit components and Ca²⁺ sparks in left ventricular myocytes of spontaneously hypertensive rats. Male Wistar and spontaneously hypertensive rats (4 months of age) were divided into 4 groups: normotensive (NC) and hypertensive control (HC), and normotensive (NT) and hypertensive trained (HT) animals (7 rats per group). NC and HC rats were submitted to a low-intensity treadmill running protocol (5 days/week, 1 h/day, 0% grade, and 50-60% of maximal running speed) for 8 weeks. Gene expression of the ryanodine receptor type 2 (RyR2) and FK506 binding protein (FKBP12.6) increased (270%) and decreased (88%), respectively, in HC compared to NC rats. Endurance exercise training reversed these changes by reducing RyR2 (230%) and normalizing FKBP12.6 gene expression (112%). Hypertension also increased the frequency of Ca²⁺ sparks (HC=7.61±0.26 vs NC=4.79±0.19 per 100 µm/s) and decreased its amplitude (HC=0.260±0.08 vs NC=0.324±0.10 ΔF/F₀), full width at half-maximum amplitude (HC=1.05±0.08 vs NC=1.26±0.01 µm), total duration (HC=11.51±0.12 vs NC=14.97±0.24 ms), time to peak (HC=4.84±0.06 vs NC=6.31±0.14 ms), and time constant of decay (HC=8.68±0.12 vs NC=10.21±0.22 ms). These changes were partially reversed in HT rats (frequency of Ca²⁺ sparks=6.26±0.19 µm/s, amplitude=0.282±0.10 ΔF/F₀, full width at half-maximum amplitude=1.14±0.01 µm, total duration=13.34±0.17 ms, time to peak=5.43±0.08 ms, and time constant of decay=9.43±0.15 ms). Endurance exercise training attenuated the deleterious effects of hypertension on calcium release units of left ventricular myocytes.

Pregnancy as a cardiac stress model

Cardiac hypertrophy occurs during pregnancy as a consequence of both volume overload and hormonal changes. Both pregnancy- and exercise-induced cardiac hypertrophy are generally thought to be similar and physiological. Despite the fact that there are shared transcriptional responses in both forms of cardiac adaptation, pregnancy results in a distinct signature of gene expression in the heart. In some cases, however, pregnancy can induce adverse cardiac events in previously healthy women without any known cardiovascular disease. Peripartum cardiomyopathy is the leading cause of non-obstetric mortality during pregnancy. To understand how pregnancy can cause heart disease, it is first important to understand cardiac adaptation during normal pregnancy. This review provides an overview of the cardiac consequences of pregnancy, including haemodynamic, functional, structural, and morphological adaptations, as well as molecular phenotypes. In addition, this review describes the signalling pathways responsible for pregnancy-induced cardiac hypertrophy and angiogenesis. We also compare and contrast cardiac adaptation in response to disease, exercise, and pregnancy. The comparisons of these settings of cardiac hypertrophy provide insight into pregnancy-associated cardiac adaptation.

Exercise training starting at weaning age preserves cardiac pacemaker function in adulthood of diet-induced obese rats

Peripheral sympathetic overdrive in young obese subjects contributes to further aggravation of insulin resistance, diabetes, and hypertension, thus inducing worsening clinical conditions in adulthood. Exercise training has been considered a strategy to repair obesity autonomic dysfunction, thereby reducing the cardiometabolic risk. Therefore, the aim of this study was to assess the effect of early exercise training, starting immediately after weaning, on cardiac autonomic control in diet-induced obese rats. Male Wistar rats (weaning) were divided into four groups: (i) a control group (n = 6); (ii) an exercise-trained control group (n = 6); (iii) a diet-induced obesity group (n = 6); and (iv) an exercise-trained diet-induced obesity group (n = 6). The development of obesity was induced by 9 weeks of palatable diet intake, and the training program was implemented in a motor-driven treadmill (5 times per week) during the same period. After this period, animals were submitted to vein and artery catheter implantation to assess cardiac autonomic balance by methylatropine (3 mg/kg) and propranolol (4 mg/kg) administration. Exercise training increased running performance in both groups (p < 0.05). Exercise training also prevented the increased resting heart rate in obese rats, which seemed to be related to cardiac pacemaker activity preservation (p < 0.05). Additionally, the training program preserved the pressure and bradycardia responses to autonomic blockade in obese rats (p < 0.05). An exercise program beginning at weaning age prevents cardiovascular dysfunction in obese rats, indicating that exercise training may be used as a nonpharmacological therapeutic strategy for the treatment of cardiometabolic diseases.

Regional effects of low-intensity endurance training on structural and mechanical properties of rat ventricular myocytes

We tested the effects of low-intensity endurance training (LIET) on the structural and mechanical properties of right (RV) and left ventricular (LV) myocytes. Male Wistar rats (4 mo old) were randomly divided into control (C, n = 7) and trained (T, n = 7, treadmill running at 50–60% of maximal running speed for 8 wk) groups. Isolated ventricular myocyte dimensions, contractility, Ca2+ transients {intracellular Ca2+ concentration ([Ca2+]i)}, and ventricular [Ca2+]i regulatory proteins were measured. LIET augmented cell length (C, 152.5 ± 2.0 μm vs. T, 162.2 ± 2.1 μm; P < 0.05) and volume (C, 5,162 ± 131 μm3 vs. T, 5,506 ± 132 μm3; P < 0.05) in the LV but not in the RV. LIET increased cell shortening (C, 7.5 ± 0.3% vs. T, 8.6 ± 0.3%; P < 0.05), the [Ca2+]i transient amplitude (C, 2.49 ± 0.06 F/F0 vs. T, 2.82 ± 0.06 F/F0; P < 0.05), the expression of sarcoplasmic reticulum Ca2+-ATPase 2a (C, 1.07 ± 0.13 vs. T, 1.59 ± 0.12; P < 0.05), and the levels of phosphorylated phospholamban at serine 16 (C, 0.99 ± 0.11 vs. T, 1.34 ± 0.10; P < 0.05), and reduced the total phospholamban-to-sarcoplasmic reticulum Ca2+-ATPase 2a ratio (C, 1.19 ± 0.15 vs. T, 0.40 ± 0.16; P < 0.05) in the LV without changing such parameters in the RV. In conclusion, LIET affected the structure and improved the mechanical properties of LV but not of RV myocytes in rats, helping to characterize the functional and morphological changes that accompany the endurance training-induced cardiac remodeling.