Effects of aerobic and strength training on aerobic capacity, muscle strength, and gene expression of lymphomonocytes in patients with stable CAD

This study examined the effectiveness, suitability, and safety of a mixed interval-type aerobic and strength training program (MIAST) on physical fitness in patients with stable coronary artery disease (CAD) without history of myocardial infarction (MI). Twenty-three patients with stable CAD were randomly assigned to a MIAST (n = 12; mean age 58.6 years) or control (n = 11; 63.3 years) group. The MIAST group participated in the progressive training program twice a week for 21 weeks. Peak oxygen uptake (VO_2peak), workload, and exercise time were measured as were maximal muscle strength, serum lipids, glucose concentration, and the cross-sectional area (CSA) of knee extensors. The safety and suitability of the program were assessed by wireless electrocardiogram (ECG) monitoring and exercise diaries. VO_2peak (6.9%; P < 0.05) and exercise time (11.2%; P < 0.05) improved significantly after 12 weeks of training in the MIAST group compared to the control group. Muscle strength (19.9%; P < 0.05) and CSA (2.2%; P < 0.05) increased, and serum lipids and blood glucose tended to decrease after the training. The successful training program (increase in maximal oxygen uptake) increased the gene expression of oxygen metabolism and decreased the gene expression of inflammation pathways in lymphomonocytes. The MIAST program, including interval-type aerobic and strength training, was safe, did not cause any adverse effects, and led to significant improvements in physical fitness in patients with stable CAD.

Females have a blunted cardiovascular response to one year of intensive supervised endurance training

Cross-sectional studies in athletes suggest that endurance training augments cardiovascular structure and function with apparently different phenotypes in athletic males and females. It is unclear whether the longitudinal response to endurance training leads to similar cardiovascular adaptations between sexes. We sought to determine whether males and females demonstrate similar cardiovascular adaptations to 1 yr of endurance training, matched for training volume and intensity. Twelve previously sedentary males (26 ± 7, n = 7) and females (31 ± 6, n = 5) completed 1 yr of progressive endurance training. All participants underwent a battery of tests every 3 mo to determine maximal oxygen uptake (V̇o2max) and left ventricle (LV) function and morphology (cardiac magnetic resonance imaging). Pulmonary artery catheterization was performed before and after 1 yr of training, and pressure-volume and Starling curves were constructed during decreases (lower-body negative pressure) and increases (saline infusion) in cardiac volume. Males progressively increased V̇o2max, LV mass, and mean wall thickness, before reaching a plateau from month 9 to 12 of training. In contrast, despite exactly the same training, the response in females was markedly blunted, with V̇o2max, LV mass, and mean wall thickness plateauing after only 3 mo of training. The response of LV end-diastolic volume was not influenced by sex (males +20% and females +18%). After training Starling curves were shifted upward and left, but the effect was greatest in males (interaction P = 0.06). We demonstrate for the first time clear sex differences in response to 1 yr of matched endurance training, such that the development of ventricular hypertrophy and increase in V̇o2max in females is markedly blunted compared with males.

Cardiac remodeling in response to 1 year of intensive endurance training

BACKGROUND

It is unclear whether, and to what extent, the striking cardiac morphological manifestations of endurance athletes are a result of exercise training or a genetically determined characteristic of talented athletes. We hypothesized that prolonged and intensive endurance training in previously sedentary healthy young individuals could induce cardiac remodeling similar to that observed cross-sectionally in elite endurance athletes.

METHODS AND RESULTS

Twelve previously sedentary subjects (aged 29±6 years; 7 men and 5 women) trained progressively and intensively for 12 months such that they could compete in a marathon. Magnetic resonance images for assessment of right and left ventricular mass and volumes were obtained at baseline and after 3, 6, 9, and 12 months of training. Maximum oxygen uptake ( max) and cardiac output at rest and during exercise (C2H2 rebreathing) were measured at the same time periods. Pulmonary artery catheterization was performed before and after 1 year of training, and pressure-volume and Starling curves were constructed during decreases (lower body negative pressure) and increases (saline infusion) in cardiac volume. Mean max rose from 40.3±1.6 to 48.7±2.5 mL/kg per minute after 1 year (P<0.00001), associated with an increase in both maximal cardiac output and stroke volume. Left and right ventricular mass increased progressively with training duration and intensity and reached levels similar to those observed in elite endurance athletes. In contrast, left ventricular volume did not change significantly until 6 months of training, although right ventricular volume increased progressively from the outset; Starling and pressure-volume curves approached but did not match those of elite athletes.

CONCLUSIONS

One year of prolonged and intensive endurance training leads to cardiac morphological adaptations in previously sedentary young subjects similar to those observed in elite endurance athletes; however, it is not sufficient to achieve similar levels of cardiac compliance and performance. Contrary to conventional thinking, the left ventricle responds to exercise with initial concentric but not eccentric remodeling during the first 6 to 9 months after commencement of endurance training depending on the duration and intensity of exercise. Thereafter, the left ventricle dilates and restores the baseline mass-to-volume ratio. In contrast, the right ventricle responds to endurance training with eccentric remodeling at all levels of training.

[Prevention of arterial diseases in the 2010s: the European treatment guideline]

Reduction of risk factors at the population level forms the basis of the European recommendation of 2012 for the prevention of arterial diseases. Actions at the individual level arise from risk assessment. The risk of arterial disease is graded into four categories, the uppermost ones comprising patients who have already developed the disease, diabetics, those suffering from renal insufficiency and those carrying a serious gene defect. In Finland the risk among healthy people is assessed by using the FINRISKI tool. Non-smoking, healthy diet and regular exercise are suitable for all. Statins are an effective and safe means of prevention for those at high risk regardless of lipid values.

The effect of integrated cardiac rehabilitation versus treatment as usual for atrial fibrillation patients treated with ablation: the randomised CopenHeartRFA trial protocol

INTRODUCTION

Atrial fibrillation affects almost 2% of the population in the Western world. To preserve sinus rhythm, ablation is undertaken in symptomatic patients. Observational studies show that patients with atrial fibrillation often report a low quality of life and are less prone to be physically active due to fear of triggering fibrillation. Small trials indicate that exercise training has a positive effect on exercise capacity and mental health, and both patients with recurrent atrial fibrillation and in sinus rhythm may benefit from rehabilitation in managing life after ablation. No randomised trials have been published on cardiac rehabilitation for atrial fibrillation patients treated with ablation that includes exercise and psychoeducational components.

AIM

To test the effects of an integrated cardiac rehabilitation programme versus treatment as usual for patients with atrial fibrillation treated with ablation. METHODS AND ANALYSIS DESIGN: The trial is a multicentre parallel arm design with 1:1 randomisation to the intervention and control group with blinded outcome assessment. 210 patients treated for atrial fibrillation with radiofrequency ablation will be included. The intervention consists of a rehabilitation programme including four psychoeducative consultations with a specially trained nurse and 12 weeks of individualised exercise training, plus the standard medical follow-up. Patients in the control group will receive the standard medical follow-up. The primary outcome measure is exercise capacity measured by the VO(2) peak. The secondary outcome measure is self-rated mental health measured by the Short Form 36 questionnaire. Postintervention, qualitative interviews will be conducted in 10% of the intervention group.

ETHICS AND DISSEMINATION

The protocol is approved by the regional research ethics committee (number H-1-2011-135), the Danish Data Protection Agency (reg. nr. 2007-58-0015) and follows the latest version of the Declaration of Helsinki. The results will be published in peer-reviewed journals and may possibly impact on rehabilitation guidelines.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT01523145.

Effects of 32-Year Leisure Time Physical Activity Discordance in Twin Pairs on Health (TWINACTIVE Study): Aims, Design and Results for Physical Fitness

The physically active lifestyle is associated with low future morbidity and mortality, but the causality between physical activity and health is not always clear. As some inherited biological characteristics and childhood experiences may cause selection bias in observational studies, we sought to take them into account by identifying 16 twin pairs (7 MZ, 9 DZ, mean age 60 years) discordant for leisure time physical activity habits for thirty years. We conducted detailed health-related examinations among these twin pairs. Our main aims were to study the effects of physical activity and genes on fitness and body composition, with special reference to body fat compartments, metabolic syndrome components and related diseases and risk factor levels, status of arteries, structure and function of the heart, bone properties, and muscle and fat tissue-related mechanisms linked to physical activity and chronic disease development. Our physical activity assessments showed that inactive co-twins were on average 8.8 MET hours/day less active than their active co-twins through out their midlife (2.2 ± 2.3 vs. 11.0 ± 4.1 MET h/day, p < .001). Follow-up fitness tests showed that physically inactive co-twins were less fit than their active co-twins (estimated VO2peak 26.4 ± 4.9 vs. 32.5 ± 5.5 ml/kg/min, p < .001). Similar differences were found in both MZ and DZ pairs. On the basis of earlier epidemiological observations on nonrelated individuals, these physical activity and fitness differences are large enough to cause differences in many mechanisms and risk factors related to the development of chronic diseases and to permit future analyses.

Comparison of QT peak and QT end interval responses to autonomic adaptation in asymptomatic LQT1 mutation carriers

Background

LQT1 subtype of long QT syndrome is characterized by defective I_Ks, which is intrinsically stronger in the epicardium than in the midmyocardial region. Electrocardiographic QT peak and QT end intervals may reflect complete repolarization of epicardium and midmyocardial region of the ventricular wall, respectively. Repolarization abnormalities in LQT1 carriers may therefore be more easily detected in the QT peak intervals.

Methods

Asymptomatic KCNQ1 mutation carriers (LQT1, n = 9) and unaffected healthy controls (n = 8) were studied during Valsalva manoeuvre, mental stress, handgrip and supine exercise. Global QT peak and QT end intervals derived from 25 simultaneous electrocardiographic leads were measured beat to beat with an automated method.

Results

In unaffected subjects, the percentage shortening of QT peak was greater than that of QT end during mental stress and during the recovery phases of Valsalva and supine exercise. In LQT1 carriers, the percentage shortening of the intervals was similar. At the beginning of Valsalva strain under abrupt endogenous sympathetic activation, QT peak shortened in LQT1 but not in control patients yielding increased electrocardiographic transmural dispersion of repolarization in LQT1.

Conclusions

In asymptomatic KCNQ1 mutation carriers, repolarization abnormalities are more evident in the QT peak than in the QT end interval during adrenergic adaptation, possibly related to transmural differences in the degree of I_Ks block.

Supine cycling plus volume loading prevent cardiovascular deconditioning during bed rest

There are two possible mechanisms contributing to the excessive fall of stroke volume (and its contribution to orthostatic intolerance) in the upright position after bed rest or spaceflight: reduced cardiac filling due to hypovolemia and/or a less distensible heart due to cardiac atrophy. We hypothesized that preservation of cardiac mechanical function by exercise training, plus normalization of cardiac filling with volume infusion, would prevent orthostatic intolerance after bed rest. Eighteen men and three women were assigned to 1) exercise countermeasure (n=14) and 2) no exercise countermeasure (n=7) groups during bed rest. Bed rest occurred in the 6 degrees head-down tilt position for 18 days. The exercise regimen was prescribed to compensate for the estimated cardiac work reduction between bed rest and ambulatory periods. At the end of bed rest, the subjects were further divided into two additional groups for post-bed rest testing: 1) volume loading with intravenous dextran to normalize cardiac filling pressure and 2) no volume loading. Dextran infusion was given to half of the exercise group and all of the sedentary group after bed rest, leading ultimately to three groups: 1) exercise plus volume infusion; 2) exercise alone; and 3) volume infusion alone. Exercise training alone preserved left ventricular mass and distensibility as well as upright exercise capacity, but lower body negative pressure (LBNP) tolerance was still depressed. LBNP tolerance was maintained only when exercise training was accompanied by dextran infusion. Dextran infusion alone following bed rest without exercise maintained neither orthostatic tolerance nor upright exercise capacity. We conclude that daily supine cycle exercise sufficient to prevent cardiac atrophy can prevent orthostatic intolerance after bed rest only when combined with plasma volume restoration. This maintenance of orthostatic tolerance was achieved by neither exercise nor dextran infusion alone. Cardiac atrophy and hypovolemia are likely to contribute independently to orthostatic intolerance after bed rest.

Effects of long-term physical activity on cardiac structure and function: a twin study

Previous studies have shown that athletic training or other physical activity causes structural and functional adaptations in the heart, but less is known how long-term physical activity affects heart when genetic liability and childhood environment are taken into account. The aim of this study was to investigate the effects of long-term physical activity vs. inactivity on cardiac structure and function in twin pairs discordant for physical activity for 32 years. Twelve same-sex twin pairs (five monozygotic and seven dizygotic, 50-67 years) were studied as a part of the TWINACTIVE study. Discordance in physical activity was initially determined in 1975 and it remained significant throughout the follow-up. At the end of the follow-up in 2007, resting echocardiographic and electrocardiographic measurements were performed. During the follow-up period, the active co-twins were on average 8.2 (SD 4.0) MET hours/day more active than their inactive co-twins (p < 0.001). At the end of the follow-up, resting heart rate was lower in the active than inactive co-twins [59 (SD 5) vs. 68 (SD 10) bpm, p=0.03]. The heart rate-corrected QT interval was similar between the co-twins. Also, there was a tendency for left ventricular mass per body weight to be greater and T wave amplitude in lead II to be higher in the active co-twins (18% and 15%, respectively, p=0.08 for both). Similar trends were found for both monozygotic and dizygotic twin pairs. In conclusion, the main adaptation to long- term physical activity is lowered resting heart rate, even after partially or fully controlling for genetic liability and childhood environment. Key pointsThe main adaptation to long-term physical activity is lowering of resting heart rate, even after controlling for genetic liability.VO2peak is increased in the active co-twins compared with their inactive co-twins and accordingly, also submaximal heart rates during the clinical exercise test are lower in physically active co-twins.There is a tendency for increased LVM per body weight and heightened T wave amplitude in the active co-twins.

Effects of strength training on work capacity and parasympathetic heart rate modulation during exercise in physically inactive men

This study was designed to assess the effects of strength training on work capacity and parasympathetic heart rate modulation during exercise in physically inactive men. Seventy-four men aged 20-45 were randomly assigned to training (n=52) and control (n=22) groups. Training groups underwent 10-weeks of progressive strength training. Body composition, one-repetition maximum half-squat and maximal oxygen uptake were measured before and after the intervention. Respiratory gases, heart rate and blood lactate were recorded during a VO2max test on a cycle ergometer. Parasympathetic heart rate modulation was analyzed based on the standard deviation of instantaneous beat-to-beat R-R interval variability (SD1) and its normalized unit (SD1n). Muscle strength and lean body mass increased in the training group. Compared to the control group, time to exhaustion increased significantly in the training group (p<0.05). SD1 and SD1n were elevated in the training group at submaximal exercise intensities (100 W, p<0.05). Blood lactate decreased at submaximal intensities when compared to the control group. Strength training increased exercise capacity, and improved vagal modulation of heart rate at submaximal exercise intensities. These changes may have favourable cardiovascular health implications for sedentary men during normal daily activities.

System for ECG and heart rate monitoring during group training

We present a system for measuring ECG signals simultaneously from multiple persons during a group training session. The system transmits the signals to a coordinating computer where heart rate and other parameters are calculated from the signals. The heart rate values can then be shown for example through a video projector on a large display along with individual information about the training intensity.

Electrocardiographic interventricular dispersion of repolarization during autonomic adaptation in LQT1 subtype of long QT syndrome

OBJECTIVES

In LQT1 subtype of inherited long QT syndrome, repolarization abnormalities originating from defective I(Ks) render patients vulnerable to ventricular arrhythmia during sudden sympathetic activation. Experimental studies show lower I(Ks) density and longer action potential duration in left (LV) than in right (RV) ventricle. We studied interventricular dispersion of repolarization in patients with I(Ks) defect during autonomic tests.

DESIGN

We measured interventricular (difference of QT intervals between LV and RV type leads) and transmural electrocardiographic dispersion of repolarization from 25-lead electrocardiograms in nine asymptomatic KCNQ1 mutation carriers (LQT1) and eight controls during rest, Valsalva maneuver, mental stress, sustained handgrip and supine exercise.

RESULTS

LQT1 carriers showed increased interventricular dispersion of repolarization (13+/-9 ms vs. 4+/-4 ms, p=0.03) during all tests. Valsalva strain increased the difference between the study groups. In LQT1 carriers, interventricular dispersion of repolarization correlated weakly with electrocardiographic transmural dispersion of repolarization.

CONCLUSIONS

Asymptomatic KCNQ1 mutation carriers exhibit increased and by abrupt sympathetic activation augmented interventricular difference in electrocardiographic repolarization times. Interventricular and transmural repolarization dispersion behave similarly in patients with I(Ks) defect.

Assessment of the effect of endurance training on left ventricular relaxation with magnetic resonance imaging

The purpose of the study was to assess the effect of endurance training on the early diastolic global and regional left ventricular (LV) relaxation with three magnetic resonance imaging (MRI) techniques. Fourteen subjects were examined with MRI before and after 3-month endurance training. Global early diastolic LV myocardial relaxation was assessed with mitral flow velocity mapping and regional LV early myocardial relaxation with myocardial tagging. LV end-diastolic and end-systolic volumes and mass were assessed with cine Magnetic resonance imaging (MRI). Mitral flow velocity mapping analysis revealed that the time to peak early filling shortened after training (before 112+/-32 ms, after 97+/-21, P<0.05), indicating more rapid global early myocardial relaxation. LV mass increased (97+/-19 g, 105+/-18, P<0.01) and end-systolic volume decreased (47+/-11 mL, 42+/-13, P<0.05). According to myocardial tagging analysis early myocardial relaxation in the septum and in the LV lateral wall increased (P<0.05). Regional tagging analysis showed enhanced myocardial relaxation in the basal septum (P<0.05). Global and regional LV early diastolic relaxation improved and physiological LV hypertrophy was found after the exercise training period for 3 months in healthy sedentary subjects.

Ventricular Repolarization and Heart Rate Responses During Cardiovascular Autonomic Function Testing in LQT1 Subtype of Long QT Syndrome

BACKGROUND

In the most prevalent LQT1 form of inherited long QT syndrome symptoms often occur during abrupt physical or emotional stress. Sympathetic stimulation aggravates repolarization abnormalities in experimental LQT1 models. We hypothesized that autonomic function tests might reveal the abnormal repolarization in asymptomatic LQT1 patients.

METHODS

We measured heart rates (HRs) and QT intervals in nine asymptomatic carriers of a C-terminal KCNQ1 mutation and 8 unaffected healthy subjects using an approach of global QT values derived from 28 simultaneous electrocardiographic leads on beat-to-beat base during Valsalva maneuver, mental stress, sustained handgrip, and light supine exercise.

RESULTS

LQT1 patients exhibited impaired shortening of both QTpeak and QTend intervals during autonomic interventions but exaggerated lengthening of the intervals--a QT overshoot--during the recovery phases. The number of tests with a QT overshoot was 2.4 +/- 1.7 in LQT1 patients and 0.8 +/- 0.7 in unaffected subjects (P = 0.02). Valsalva strain prolonged T wave peak to T wave end interval (TPE) in LQT1 but not in unaffected patients. LQT1 patients showed diminished HR acceleration in response to adrenergic challenge whereas HR responses to vagal stimuli were similar in both groups.

CONCLUSIONS

Standard cardiovascular autonomic provocations induce a QT interval overshoot during recovery in asymptomatic KCNQ1 mutation carriers. Valsalva maneuver causes an exaggerated fluctuation of QT and TPE intervals partly explaining the occurrence of cardiac events during abrupt bursts of autonomic activity in LQT1 patients.

Translation is regulated via the 3' untranslated region of alpha-myosin heavy chain mRNA by calcium but not by its localization

Posttranscriptional regulation plays an important role in alpha-myosin heavy chain (alpha-MyHC) protein synthesis in cardiac muscle cells. In the present study, we test the effects of calcium and mRNA mislocalization on alpha-MyHC translation in order to determine the mechanism(s) contributing to translational block via the 3' untranslated region (3'UTR). Neonatal rat cardiac myocytes were treated for 6 h with L-isoproterenol (10 microM) to enhance beating, with 10 microM verapamil to block beating and mislocalize mRNA, or with 3 microM colchicine to enhance beating but mislocalize mRNA by depolymerization of the microtubules. In order to determine whether translation is regulated by the 3'UTR, either a control (SV40 3'UTR) or the experimental (alpha-MyHC 3'UTR) was placed after a luciferase reporter gene and transfected into the myocytes. The amount of luciferase protein only decreased significantly in verapamil arrested cells transfected with the alpha-MyHC 3'UTR construct (P < 0.01). To control for the possibility that pharmacological treatments might affect transcription or message stability, we analyzed neomycin and luciferase mRNA levels transcribed from the same transfected plasmid. No significant changes were found with an RNase protection assay. These results suggest that calcium but not mRNA localization regulates protein synthesis and further, this is mediated by the 3' untranslated region of alpha-MyHC.

Mechanical activity in heart regulates translation of alpha-myosin heavy chain mRNA but not its localization

Mechanical inactivity depresses protein expression in cardiac muscle tissue and results in atrophy. We explore the mechanical transduction mechanism in spontaneously beating neonatal rat cardiomyocytes expressing the alpha-myosin heavy chain (alpha-MyHC) isoform by interfering with cross-bridge function [2,3-butanedione monoxime (BDM), 7.5 mM] without affecting cell calcium. The polysome content and alpha-MyHC mRNA levels in fractions from a sucrose gradient were analyzed. BDM treatment blocked translation at initiation (162 +/- 12% in the nonpolysomal RNA fraction and 43 +/- 6% in the polysomal fraction, relative to control as 100%; P < 0.05). There was an increase in alpha-MyHC mRNA from the nonpolysomal fraction (120.5 +/- 7.7%; P < 0.05 compared with control) with no significant change in the heavy polysomes. In situ hybridization of alpha-MyHC mRNA was used to estimate message abundance as a function of the distance from the nucleus. The mRNA was dispersed through the cytoplasm in spontaneously beating cells as well as in BDM-treated cells (no significant difference). We conclude that direct inhibition of contractile machinery, but not calcium, regulates initiation of alpha-MyHC mRNA translation. However, calcium, not pure mechanical signals, appears to be important for message localization.

Microtubules are needed for dispersal of alpha-myosin heavy chain mRNA in rat neonatal cardiac myocytes

In some cell types, microtubules are used for transport of mRNA through the cytoplasm to the translation site. The number of microtubules increases during growth of cardiac myocytes, suggesting a functional role exists. Here, we test the need for microtubules to transport alpha-myosin heavy chain (alpha-MyHC) mRNA through the cytoplasm of neonatal cardiac myocytes. The alpha-MyHC mRNA concentration was assessed by non-radioactive in situ hybridization. The relative mRNA distributions were expressed as slopes (m=OD/micrometer), since optical density declined linearly from the nucleus to the cell periphery. Spontaneously-contracting myocytes displayed a gradual decrease in alpha-MyHC mRNA away from the nucleus (m=-1.27+/-0.12 OD/micrometer). To test whether microtubules were necessary for alpha-MyHC mRNA dispersal, contraction was first arrested with the Ca2+-channel blocker verapamil (10 micrometer) for 18 h, which aggregated the mRNA perinuclearly. Contractile activity was then resumed by washing out verapamil and using isoproterenol (10 micrometer) in the presence or absence of a microtubule depolymerizing drug, colchicine (3 micrometer). Within 6 h, the alpha-MyHC mRNA distribution in myocytes with microtubules returned to normal values (m=-1.11+/-0.14 OD/micrometer), while cells lacking microtubules maintained a perinuclear mRNA distribution (m-1.50+/-0.16 OD/micrometer; P<0.05 from control). Despite this perinuclear pattern of mRNA distribution, the myocytes still produced new myofibrils. These data indicate that microtubules are necessary for dispersal of alpha-MyHC mRNA outward from the nucleus. Furthermore, myofibrillogenesis may occur independently of mRNA localization and microtubule organization.

Right ventricular collagen type III and IV gene expression increases during early phases of endurance training in hypobaric hypoxic condition

The objective of this study was to examine the effects of prolonged exposure to hypobaric hypoxic condition, physical training and their combination on collagen type I, III and IV gene expression in the ventricles and atria of rat heart. Male rats were assigned to four groups: normobaric sedentary (NS) and trained (NT), and hypobaric sedentary (HS) and trained (HT). Exposure to and treadmill running training in hypobaric condition were carried out in a hypobaric chamber (770-740 mbar, 2250-2550 m). Experimental periods were 10, 21 and 56 days; the groups of 91 days served as recovery groups from experimental settings of 56 days. Exposure to hypobaric condition as such and in combination with endurance training for 10 days increased right ventricular weight-to-body weight ratio (RV/BW) by 26% (p < 0.001) and 23% (p < 0.01), respectively, when compared to 10NS. RV/BW was significantly increased also in 21HT and 56HT. Left ventricular weight-to-body weight ratio was 13% (p < 0.01) and 14% (p < 0.01) higher in 21HT and 56HT, respectively, than in the respective NS. Right ventricular collagen type III mRNA level was 33% (p = 0.065) and 38% (p < 0.01) higher in 10HT than in 10NS and 10NT, respectively. Right ventricular collagen type IV mRNA level was 29% (p < 0.001) higher in 10HT than in 10NS. Relatively slight left ventricular hypertrophy was not associated with significant changes in collagen mRNA levels. Decreased left ventricular subepicardial prolyl 4-hydroxylase activity in 10HS and 10HT suggests transient corresponding decrease in the rate of collagen synthesis. This study shows that combination of endurance training and moderate hypobaric hypoxic condition leads to increased right ventricular collagen type III and IV gene expression associated with right ventricular hypertrophy.

Induction of cardiac natriuretic peptide gene expression in rats trained in hypobaric hypoxic conditions

Adaptation of cardiac muscle to prolonged hypobaric hypoxia (770-740 mbar, 2,250-2,550 m), endurance training, and their combination was studied in rats by investigating the gene expression of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in atria and ventricles. Rats were assigned into the following groups according to the barometric conditions and physical activity; normobaric sedentary (NS), normobaric training, hypobaric sedentary (HS), and hypobaric training (HT). Experimental periods were 10, 21, and 56 days; the groups at 91 days served as recovery groups from exposure to and training in normobaric and hypobaric conditions for 56 days. The right ventricular hypertrophy in HT rats at 10 days and 56 days was associated with elevated BNP mRNA levels (2.1- and 1.7-fold, P < 0.05, respectively), whereas hypobaric exposure without training was not sufficient to significantly increase ventricular BNP gene expression, although it lead to hypertrophy of the right ventricle. Right and left atrial BNP mRNA levels were also increased (up to 3.9-fold, P < 0.01) in 10-day HS and 10-day HT groups. ANP mRNA levels in right ventricle and left ventricular epicardium were over twofold higher (P < 0.05-0.01) in 10-day HS and 10-day HT groups in comparison to 10-day NS group. Plasma immunoreactive ANP concentration was increased (P < 0.05) in both hypobaric groups up to 21 days. The results show that exposure to hypobaric hypoxia itself and endurance training in hypobaric, hypoxic conditions lead to a marked early increase in ventricular and atrial ANP and BNP mRNA levels. The adaptational response to hypoxia was more pronounced when the oxygen availability was lowered additionally by endurance training carried out in hypobaric hypoxic conditions.

Skeletal muscle collagen type I and III mRNA, [corrected] prolyl 4-hydroxylase, and collagen in hypobaric trained rats

Skeletal muscle collagen expression was studied in normobaric sedentary (NS) and training (NT) and hypobaric sedentary (HS) and training (HT) rats after experimental periods of 10, 21, and 56 days. The weights of fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles were increased between the experimental period of 21 and 56 days so that EDL weight was 57 (P < 0.01) and 36% (P < 0.05) higher in 56 days HS (56HS) and 56 days HT (56HT), respectively, than in 56 days NS (56NS). Soleus muscle weight was higher in 56HS (61%; P < 0.01) and in 56HT (27%; P < 0.05) than in 56NT. In EDL muscle, collagen type I mRNA level was lower in 56HT than in 56NS (36%; P < 0.05) and 56NT (44%; P < 0.01). In 56HT, collagen type III mRNA level was 39 (P < 0.01) and 42% (P < 0.05) lower than in 56NS and 56HS, respectively. In soleus muscle, prolyl 4-hydroxylase activity was greater (P < 0.05) in 56NT, 56HS, and 56HT than in 56NS. Total hydroxyproline content in EDL muscle was increased in 56HS and 56HT and in soleus muscle of 56HS. In conclusion, although collagen types I and III mRNA levels in EDL muscle decreased in 56HT, the prolyl 4-hydroxylase data suggest unchanged synthesis of total collagen. Exposure to hypobaric conditions as such, its combination to endurance training, as well as training in normobaric conditions increased prolyl 4-hydroxylation capacity in soleus muscle, which may indicate respective change in collagen synthesis rate.

Effects of prolonged exposure to and physical training in hypobaric conditions on skeletal muscle morphology and metabolic enzymes in rats

Adaptations of skeletal muscle morphology and metabolic enzymes were studied after prolonged training in and exposure to hypobaric (740 -770 mbar) as well as normobaric conditions in rats performing treadmill running training for 10, 21 and 56 days. Animals sacrificed after 91 days served as recovery groups from training and hypobaric exposure for 56 days. The rats were divided into normobaric sedentary (NS) and training (NT) groups and hypobaric sedentary (HS) and training (HT) groups. The weights of extensor digitorum longus (EDL) and soleus (SOL) muscles increased significantly in the 56HS and the 56HT groups compared with the 56NS group, the increase being greatest in the 56HS group. No differences in the mean fibre areas (MFA) of these muscles could be seen, whereas clearly reduced MFAs of type IIA and IIB were observed in the tibialis anterior (TA) muscle. However, fibre area distribution analyses in the EDL and TA muscles showed a higher proportion of larger fibers in the 56HS and 56HT groups than in the respective normobaric groups. On the contrary, in SOL muscles the proportion of smaller fibers was higher in the hypobaric than in normobaric groups at 56 days. Increased activities of citrate synthase and beta-hydroxyacyl-CoA-dehydrogenase in SOL and TA muscles in the 56HT group indicate an increase in oxidative capacity. It is concluded that exposure to, and training in moderate hypobaric conditions leads to a positive muscle protein balance which is reflected in increased muscle weights. However, the sites of increased protein synthesis and the possible hyperplasia remain to be studied further.

Stress hormones after prolonged physical training in normo- and hypobaric conditions in rats

In order to study the long-term effects of prolonged physical training in hypobaric hypoxia on plasma stress hormone concentrations, male rats (N = 84) were exposed to progressive running training on a motordriven treadmill for 10, 21 or 56 days, twice a day and 5 days a week either in hypobaric hypoxic (O2-pressure 740-770 mbar) or in normobaric conditions. The plasma samples were taken 14-16 hours after the last exercise bout. Plasma corticosterone concentration was higher in animals trained 10 days in hypobaric conditions than in those trained in normobaric conditions (1127 +/- 158 nmol/l and 710 +/- 87 nmol/l, p < 0.05, respectively) while no effect of hypobaric conditions were seen in resting animals. Rats trained for 21 and 56 days in both normo- and hypobaria had significantly higher plasma corticosterone levels than the untrained animals. The changes in plasma ACTH and beta-endorphin concentrations were not significant in any group. According to our corticosterone results, we suggest that hypobaric hypoxia increases stress of training animals at the beginning of long-term training. The absolute work load was the same in both conditions, which probably at the beginning of training causes more stress to hypobaria trained rats than those trained in normobaria. Later when the adaptation to hypobaric hypoxia occurs, physical training itself seems to be responsible for increased plasma corticosterone levels in hypobaria as well as in normobaria.

Effect of endurance training on atrial natriuretic peptide gene expression in normal and hypertrophied hearts

We studied the effects of physical endurance training on atrial natriuretic peptide (ANP) gene expression in beagle dogs, Wistar rats, and spontaneously hypertensive rats (SHR). The dogs underwent a gradually increased running training up to 40 km/day on a treadmill for 55 wk while the nontrained sibling control dogs were kept in their cages throughout the study. Endurance training caused a significant 13% (P < 0.05) increase in ventricular hypertrophy but did not change plasma immunoreactive (ir)-ANP levels at rest or ventricular ANP mRNA or irANP levels. When normotensive Wistar rats ran up to 2,200 m/day for 8 wk, no significant change was seen in ventricular hypertrophy or in plasma or ventricular irANP levels at rest compared with nontrained controls. However, endurance training caused a 2.2-fold increase in epicardial ANP mRNA levels (P < 0.05). In the SHR strain, running training up to 900 m/day for 31 wk increased ventricular hypertrophy of trained SHR by 7% (P < 0.01) and caused a concomitant 1.6- to 1.7-fold elevation in ventricular irANP and ANP mRNA levels (P < 0.01-0.001) compared with nontrained SHR. In contrast, changes in atrial ANP mRNA or irANP levels in response to training were small in all three protocols. This study shows that in the normal heart induction of ANP synthesis by endurance training is not associated with ventricular hypertrophy. Moreover, the common stimulus for ventricular ANP synthesis induced by both chronic pressure overload and physical training may be mechanical stretching of cardiac myocytes, because endurance training further stimulated ANP synthesis in hypertrophied ventricles in SHR.