Exercise training in normobaric hypoxia in endurance runners. II. Improvement of mitochondrial properties in skeletal muscle

This study investigates whether adaptations of mitochondrial function accompany the improvement of endurance performance capacity observed in well-trained athletes after an intermittent hypoxic training program. Fifteen endurance-trained athletes performed two weekly training sessions on treadmill at the velocity associated with the second ventilatory threshold (VT2) with inspired O2 fraction = 14.5% [hypoxic group (Hyp), n = 8] or with inspired O2 fraction = 21% [normoxic group (Nor), n = 7], integrated into their usual training, for 6 wk. Before and after training, oxygen uptake (VO2) and speed at VT2, maximal VO2 (VO2 max), and time to exhaustion at velocity of VO2 max (minimal speed associated with VO2 max) were measured, and muscle biopsies of vastus lateralis were harvested. Muscle oxidative capacities and sensitivity of mitochondrial respiration to ADP (Km) were evaluated on permeabilized muscle fibers. Time to exhaustion, VO2 at VT2, and VO2 max were significantly improved in Hyp (+42, +8, and +5%, respectively) but not in Nor. No increase in muscle oxidative capacity was obtained with either training protocol. However, mitochondrial regulation shifted to a more oxidative profile in Hyp only as shown by the increased Km for ADP (Nor: before 476 +/- 63, after 524 +/- 62 microM, not significant; Hyp: before 441 +/- 59, after 694 +/- 51 microM, P < 0.05). Thus including hypoxia sessions into the usual training of athletes qualitatively ameliorates mitochondrial function by increasing the respiratory control by creatine, providing a tighter integration between ATP demand and supply.

Endothelin A-receptor blockade in experimental diabetes improves glucose balance and gastrointestinal function

Secondary complications of diabetes mellitus often involve gastrointestinal dysfunction. In the experimental Goto Kakizaki rat, a model of Type II diabetes, hyperglycaemia and reduced glucose clearance is associated with elevated plasma endothelin (ET)-1 levels and selective decreases in nitric oxide synthase in circular muscle, longitudinal muscle and neuronal elements of the gastrointestinal tract. Functionally, this is accompanied by decreased nitrergic relaxatory responses of jejunal longitudinal muscle to tetrodotoxin-sensitive electrical field stimulation. Long-term treatment with a selective ET A-type receptor antagonist, markedly reduced hyperglycaemia and restored plasma glucose clearance rates towards normal. This was associated with a restoration of N(G)-nitro-L-arginine methyl ester-sensitive relaxatory responses of jejunal longitudinal muscle to electrical field stimulation. The results indicate that beneficial effects of ETA receptor blockade on gastrointestinal function may result from an improvement in insulin sensitivity with concomitant reduction of the severity of hyperglycaemia. ETA receptor blockade may represent a new therapeutic principle for improving glucose tolerance in Type II diabetes and could be beneficial in alleviating or preventing hyperglycaemia-related secondary complications in this condition.

ECG-triggered skeletal muscle stimulation improves hemodynamics and physical performance of heart failure patients

BACKGROUND: Muscular counterpulsation (MCP) was developed for circulatory assistance by stimulation of peripheral skeletal muscles. We report on a clinical MCP study in patients with and without chronic heart failure (CHF). METHODS AND RESULTS: MCP treatment was applied (30 patients treated, 25 controls, all under optimal therapy) for 30 minutes during eight days by an ECG-triggered, battery-powered, portable pulse generator with skin electrodes inducing light contractions of calf and thigh muscles, sequentially stimulated at early diastole. Hemodynamic parameters (ECG, blood pressure and echocardiography) were measured one day before and one day after the treatment period in two groups: Group 1 (9 MCP, 11 no MCP) with ejection fraction (EF) above 40% and Group 2 (21 MCP, 14 no MCP) below 40%. In Group 2 (all patients suffering from CHF) mean EF increased by 21% (p<0.001) and stroke volume by 13% (p<0.001), while end systolic volume decreased by 23% (p<0.001). In Group 1, the increase in EF (6%) and stroke volume (8%) was also significant (p<0.05) but less pronounced than in Group 2. Physical exercise duration and walking distance increased in Group 2 by 56% and 72%, respectively. CONCLUSIONS: Noninvasive MCP treatment for eight days substantially improves cardiac function and physical performance in patients with CHF.

Relative impact of respiratory muscle activity on tidal flow and end expiratory volume in healthy neonates

INTRODUCTION: It has been suggested that infants dynamically regulate their tidal flow and end-expiratory volume level. The interaction between muscle activity, flow and lung volume in spontaneously sleeping neonates is poorly studied, since it requires the assessment of transcutaneous electromyography of respiratory muscles (rEMG) in matched comparison to lung function measurements. METHODS: After determining feasibility and repeatability of rEMG in 20 spontaneously sleeping healthy neonates, we measured the relative impact of intercostal and diaphragmatic EMG activity in direct comparison to the resulting tidal flow and FRC. RESULTS: We found good feasibility, repeatability and correlation of timing indices between rEMG activity and flow. The rEMG amplitude was significantly dependent on the resistive load of the face mask. Diaphragm and intercostal muscle activity commenced prior to the onset of flow and remained active during the expiratory cycle. The relative contribution of intercostal and diaphragmatic activity to flow was variable and changed dynamically. CONCLUSION: Using matched rEMG, air flow and lung volume measurements, we have found good feasibility and repeatability of intercostal and diaphragm rEMG measurements and provide the first quantitative measures of the temporal relationship between muscle activity and flow in spontaneously sleeping healthy neonates. Lung mechanical function is dynamically regulated and adapts on a breath to breath basis. So, non-invasive rEMG measurements alone or in combination with lung function might provide a more comprehensive picture of pulmonary mechanics in future studies. The data describing the timing of EMG and flow may be important for future studies of EMG triggered mechanical ventilation.

Upregulation of alpha-skeletal muscle actin and myosin heavy polypeptide gene products in degenerating rotator cuff muscles

Impaired function of shoulder muscles, resulting from rotator cuff tears, is associated with abnormal deposition of fat in muscle tissue, but corresponding cellular and molecular mechanisms, likely reflected by altered gene expression profiles, are largely unknown. Here, an analysis of muscle gene expression was carried out by semiquantitative RT-PCR in total RNA extracts of supraspinatus biopsies collected from 60 patients prior to shoulder surgery. A significant increase of alpha-skeletal muscle actin (p = 0.0115) and of myosin heavy polypeptide 1 (p = 0.0147) gene transcripts was observed in parallel with progressive fat deposition in the muscle, assessed on parasagittal T1-weighted turbo-spin-echo magnetic resonance images according to Goutallier. Upregulation of alpha-skeletal muscle actin and of myosin heavy polypeptide-1 has been reported to be associated with increased muscle tissue metabolism and oxidative stress. The findings of the present study, therefore, challenge the hypothesis that increased fat deposition in rotator cuff muscle after injury reflects muscle degeneration.

Velocity recovery cycles of human muscle action potentials and their sensitivity to ischemia

This study was undertaken to test whether recovery cycle measurements can provide useful information about the membrane potential of human muscle fibers. Multifiber responses to direct muscle stimulation through needle electrodes were recorded from the brachioradialis of healthy volunteers, and the latency changes measured as conditioning stimuli were applied at interstimulus intervals of 2-1000 ms. In all subjects, the relative refractory period (RRP), which lasted 3.27 +/- 0.45 ms (mean +/- SD, n = 12), was followed by a phase of supernormality, in which the velocity increased by 9.3 +/- 3.4% at 6.1 +/- 1.3 ms, and recovered over 1 s. A broad hump of additional supernormality was seen at around 100 ms. Extra conditioning stimuli had little effect on the early supernormality but increased the later component. The two phases of supernormality resembled early and late afterpotentials, attributable respectively to the passive decay of membrane charge and potassium accumulation in the t-tubules. Five minutes of ischemia progressively prolonged the RRP and reduced supernormality, confirming that these parameters are sensitive to membrane depolarization. Velocity recovery cycles may provide useful information about altered muscle membrane potential and t-tubule function in muscle disease. Muscle Nerve, 2008.

Effect of fluid resuscitation on mortality and organ function in experimental sepsis models

Introduction Several recent studies have shown that a positive fluid balance in critical illness is associated with worse outcome. We tested the effects of moderate vs. high-volume resuscitation strategies on mortality, systemic and regional blood flows, mitochondrial respiration, and organ function in two experimental sepsis models. Methods 48 pigs were randomized to continuous endotoxin infusion, fecal peritonitis, and a control group (n = 16 each), and each group further to two different basal rates of volume supply for 24 hours [moderate-volume (10 ml/kg/h, Ringer's lactate, n = 8); high-volume (15 + 5 ml/kg/h, Ringer's lactate and hydroxyethyl starch (HES), n = 8)], both supplemented by additional volume boli, as guided by urinary output, filling pressures, and responses in stroke volume. Systemic and regional hemodynamics were measured and tissue specimens taken for mitochondrial function assessment and histological analysis. Results Mortality in high-volume groups was 87% (peritonitis), 75% (endotoxemia), and 13% (controls). In moderate-volume groups mortality was 50% (peritonitis), 13% (endotoxemia) and 0% (controls). Both septic groups became hyperdynamic. While neither sepsis nor volume resuscitation strategy was associated with altered hepatic or muscle mitochondrial complex I- and II-dependent respiration, non-survivors had lower hepatic complex II-dependent respiratory control ratios (2.6 +/- 0.7, vs. 3.3 +/- 0.9 in survivors; P = 0.01). Histology revealed moderate damage in all organs, colloid plaques in lung tissue of high-volume groups, and severe kidney damage in endotoxin high-volume animals. Conclusions High-volume resuscitation including HES in experimental peritonitis and endotoxemia increased mortality despite better initial hemodynamic stability. This suggests that the strategy of early fluid management influences outcome in sepsis. The high mortality was not associated with reduced mitochondrial complex I- or II-dependent muscle and hepatic respiration.

Effects of high selenium intake on selenium status, liver function and claw health of fattening bulls

The effects of three dietary selenium (Se) levels (0.15, 0.35 and 0.5 mg/kg dry matter (dm) and of two Se-compounds (sodium selenite and Se-yeast) on the Se-status, liver function and claw health were studied using 36 fattening bulls in a two-factorial feeding trial that lasted 16 weeks. The claw health was assessed macroscopically and microscopically. Compared to the two control diets containing 0.15 mg Se/kg dm, the intake of the diets containing 0.35 and 0.50 mg Se/kg dm significantly (P < 0.05) increased the Se-concentration in serum, hair, liver and skeletal muscle. Compared to sodium selenite the intake of Se-yeast resulted in significantly (P < 0.05) higher Se-concentration in serum, liver and hair. Concerning the claw horn quality, there was no significant difference between the different groups; the animals receiving organic Se tended to have a better histological score (P = 0.06) at the coronary band than the groups fed with sodium selenite. The serum vitamin E level decreased significantly (P < 0.05) with increasing Se-intake, which had no influence (P > 0.1) on growth and liver function parameters. With the exception of the decrease of the serum vitamin E level indicating an oxidative stress caused by a high Se-intake, no negative effects of dietary selenium exceeding recommended levels for 4 months were observed.

Differential effects of captopril and nitrates on muscle sympathetic nerve activity in volunteers

BACKGROUND The sympathetic nervous system (SNS) is an important regulator of cardiovascular function. Activation of SNS plays an important role in the pathophysiology and the prognosis of cardiovascular diseases such as heart failure, acute coronary syndromes, arrhythmia, and possibly hypertension. Vasodilators such as adenosine and sodium nitroprusside are known to activate SNS via baroreflex mechanisms. Because vasodilators are widely used in the treatment of patients with cardiovascular diseases, the aim of the present study was to assess the influence of clinically used dosages of isosorbide dinitrate and captopril on sympathetic nerve activity at rest and during stimulatory maneuvers. METHODS AND RESULTS Twenty-eight healthy volunteers were included in this double-blind placebo-controlled study, and muscle sympathetic nerve activity (MSA; with microelectrodes in the peroneal nerve), blood pressure, heart rate, and neurohumoral parameters were measured before and 90 minutes after the oral administration of 40 mg isosorbide dinitrate or 6.25 mg captopril. Furthermore, a 3-minute mental stress test and a cold pressor test were performed before and 90 minutes after drug administration. Resting MSA did not change after captopril and decreased compared with placebo (P < .05 versus placebo), whereas isosorbide dinitrate led to a marked increase in MSA (P < .05). Systolic blood pressure was reduced by isosorbide dinitrate (P < .05), whereas captopril decreased diastolic blood pressure (P < .05). The increases in MSA, blood pressure, and heart rate during mental stress were comparable before and after drug administration regardless of the medication. During cold pressor test, MSA and systolic and diastolic blood pressures increased to the same degree independent of treatment, but after isosorbide dinitrate, the increase in MSA seemed to be less pronounced. Heart rate did not change during cold stimulation. Plasma renin activity increased after captopril and isosorbide dinitrate (P < .05), whereas placebo had no effect. Endothelin-1 increased after placebo and isosorbide dinitrate (P < .05) but not after captopril. CONCLUSIONS Thus, captopril suppressed MSA despite lowering of diastolic blood pressure but allowed normal adaptation of the SNS during mental or physical stress. In contrast, the nitrate strongly activated the SNS under baseline conditions. These findings demonstrate that vasodilators differentially interact with the SNS, which could be of importance in therapeutic strategies for the treatment of patients with cardiovascular diseases.

Skeletal muscle mitochondria in the elderly: effects of physical fitness and exercise training.

Context: Sarcopenia is thought to be associated with mitochondrial (M) loss. It is unclear whether the decrease in M content is consequent to aging per se or to decreased physical activity. Objectives: To examine the influence of fitness on M content and function, and to assess whether exercise could improve M function in older adults. Design and subjects: Three distinct studies were conducted: 1) a cross-sectional observation comparing M content and fitness in a large heterogeneous cohort of older adults; 2) a case-control study comparing chronically endurance-trained older adults (A) and sedentary (S) subjects matched for age and gender; 3) a 4-month exercise intervention in S. Setting: University-based clinical research center Outcomes: M volume density (Mv) was assessed by electron microscopy from vastus lateralis biopsies, electron transport chain proteins (ETC) by western blotting, mRNAs for transcription factors involved in M biogenesis by qRT-PCR and in-vivo oxidative capacity (ATPmax) by (31)P-MR spectroscopy. Peak oxygen uptake (VO2peak) was measured by GXT. Results: VO2peak was strongly correlated with Mv in eighty 60-80 yo adults. Comparison of A vs. S revealed differences in Mv, ATPmax and some ETC complexes. Finally, exercise intervention confirmed that S are able to recover Mv, ATPmax and specific transcription factors. Conclusions: These data suggest that 1) aging per se is not the primary culprit leading to M dysfunction, 2) an aerobic exercise program, even at an older age, can ameliorate the loss in skeletal muscle M content and may prevent aging muscle comorbidities and 3) the improvement of M function is all about content.

Effects of inspiratory muscle training in patients with heart failure with preserved ejection fraction

BACKGROUND Heart failure with preserved ejection fraction (HFpEF) is remarkably common in elderly people with highly prevalent comorbid conditions. Despite its increasing in prevalence, there is no evidence-based effective therapy for HFpEF. We sought to evaluate whether inspiratory muscle training (IMT) improves exercise capacity, as well as left ventricular diastolic function, biomarker profile and quality of life (QoL) in patients with advanced HFpEF and nonreduced maximal inspiratory pressure (MIP). DESIGN AND METHODS A total of 26 patients with HFpEF (median (interquartile range) age, peak exercise oxygen uptake (peak VO2) and left ventricular ejection fraction of 73 years (66-76), 10 ml/min/kg (7.6-10.5) and 72% (65-77), respectively) were randomized to receive a 12-week programme of IMT plus standard care vs. standard care alone. The primary endpoint of the study was evaluated by positive changes in cardiopulmonary exercise parameters and distance walked in 6 minutes (6MWT). Secondary endpoints were changes in QoL, echocardiogram parameters of diastolic function, and prognostic biomarkers. RESULTS The IMT group improved significantly their MIP (p < 0.001), peak VO2 (p < 0.001), exercise oxygen uptake at anaerobic threshold (p = 0.001), ventilatory efficiency (p = 0.007), metabolic equivalents (p < 0,001), 6MWT (p < 0.001), and QoL (p = 0.037) as compared to the control group. No changes on diastolic function parameters or biomarkers levels were observed between both groups. CONCLUSIONS In HFpEF patients with low aerobic capacity and non-reduced MIP, IMT was associated with marked improvement in exercise capacity and QoL.

The impact of antioxidant supplements and endurance exercise on genes of the carbohydrate and lipid metabolism in skeletal muscle of mice

To ascertain whether reactive oxygen species (ROS) contribute to training-induced adaptation of skeletal muscle, we administered ROS-scavenging antioxidants (AOX; 140 mg/l of ascorbic acid, 12 mg/l of coenzyme Q10 and 1% N-acetyl-cysteine) via drinking water to 16 C57BL/6 mice. Sixteen other mice received unadulterated tap water (CON). One cohort of both groups (CON(EXE) and AOX(EXE) ) was subjected to treadmill exercise for 4 weeks (16-26 m/min, incline of 5°-10°). The other two cohorts (CON(SED) and AOX(SED) ) remained sedentary. In skeletal muscles of the AOX(EXE) mice, GSSG and the expression levels of SOD-1 and PRDX-6 were significantly lower than those in the CON(EXE) mice after training, suggesting disturbance of ROS levels. The peak power related to the body weight and citrate synthase activity was not significantly influenced in mice receiving AOX. Supplementation with AOX significantly altered the mRNA levels of the exercise-sensitive genes HK-II, GLUT-4 and SREBF-1c and the regulator gene PGC-1alpha but not G6PDH, glycogenin, FABP-3, MCAD and CD36 in skeletal muscle. Although the administration of AOX during endurance exercise alters the expression of particular genes of the ROS metabolism, it does not influence peak power or generally shift the metabolism, but it modulates the expression of specific genes of the carbohydrate and lipid metabolism and PGC-1alpha within murine skeletal muscle.

MR Spectroscopy and Spectroscopic Imaging for Evaluation of Skeletal Muscle Metabolism: Basics and Applications in Metabolic Diseases

Magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) provide metabolic information on the musculoskeletal system, thus helping to understand the biochemical and pathophysiological nature of numerous diseases. In particular, MRS has been used to study the energy metabolism of muscular tissue since the very beginning of magnetic resonance examinations in humans when small-bore magnets for studies of the limbs became available. Even more than in other organs, the observation of non-proton-nuclei was important in muscle tissue. Spatial localization was less demanding in these studies, however, high temporal resolution was necessary to follow metabolism during exercise and recovery. The observation of high-energy phosphates during and after the application of workload gives insight into oxidative phosphorylation, a process that takes place in the mitochondria and characterizes impaired mitochondrial function. New applications in insulin-resistant patients followed the development of volume-selective 1H-MRS in whole-body magnets. Nowadays, multinuclear MRS and MRSI of the musculoskeletal system provide several windows to vital biochemical pathways noninvasively. It is shown how MRS and MRSI have been used in numerous diseases to characterize an involvement of the muscular metabolism.

Increasing mean arterial blood pressure in sepsis: effects on fluid balance, vasopressor load and renal function.

INTRODUCTION: The objective of this study was to evaluate the effects of two different mean arterial blood pressure (MAP) targets on needs for resuscitation, organ dysfunction, mitochondrial respiration and inflammatory response in a long-term model of fecal peritonitis. METHODS: Twenty-four anesthetized and mechanically ventilated pigs were randomly assigned (n = 8/group) to a septic control group (septic-CG) without resuscitation until death or one of two groups with resuscitation performed after 12 hours of untreated sepsis for 48 hours, targeting MAP 50-60 mmHg (low-MAP) or 75-85 mmHg (high-MAP). RESULTS: MAP at the end of resuscitation was 56 ± 13 mmHg (mean ± SD) and 76 ± 17 mmHg respectively, for low-MAP and high-MAP groups. One animal each in high- and low-MAP groups, and all animals in septic-CG died (median survival time: 21.8 hours, inter-quartile range: 16.3-27.5 hours). Norepinephrine was administered to all animals of the high-MAP group (0.38 (0.21-0.56) mcg/kg/min), and to three animals of the low-MAP group (0.00 (0.00-0.25) mcg/kg/min; P = 0.009). The high-MAP group had a more positive fluid balance (3.3 ± 1.0 mL/kg/h vs. 2.3 ± 0.7 mL/kg/h; P = 0.001). Inflammatory markers, skeletal muscle ATP content and hemodynamics other than MAP did not differ between low- and high-MAP groups. The incidence of acute kidney injury (AKI) after 12 hours of untreated sepsis was, respectively for low- and high-MAP groups, 50% (4/8) and 38% (3/8), and in the end of the study 57% (4/7) and 0% (P = 0.026). In septic-CG, maximal isolated skeletal muscle mitochondrial Complex I, State 3 respiration increased from 1357 ± 149 pmol/s/mg to 1822 ± 385 pmol/s/mg, (P = 0.020). In high- and low-MAP groups, permeabilized skeletal muscle fibers Complex IV-state 3 respiration increased during resuscitation (P = 0.003). CONCLUSIONS: The MAP targets during resuscitation did not alter the inflammatory response, nor affected skeletal muscle ATP content and mitochondrial respiration. While targeting a lower MAP was associated with increased incidence of AKI, targeting a higher MAP resulted in increased net positive fluid balance and vasopressor load during resuscitation. The long-term effects of different MAP targets need to be evaluated in further studies.

Combined aerobic/inspiratory muscle training vs. aerobic training in patients with chronic heart failure: The Vent-HeFT trial: a European prospective multicentre randomized trial

AIMS Vent-HeFT is a multicentre randomized trial designed to investigate the potential additive benefits of inspiratory muscle training (IMT) on aerobic training (AT) in patients with chronic heart failure (CHF). METHODS AND RESULTS Forty-three CHF patients with a mean age of 58 ± 12 years, peak oxygen consumption (peak VO2 ) 17.9 ± 5 mL/kg/min, and LVEF 29.5 ± 5% were randomized to an AT/IMT group (n = 21) or to an AT/SHAM group (n = 22) in a 12-week exercise programme. AT involved 45 min of ergometer training at 70-80% of maximum heart rate, three times a week for both groups. In the AT/IMT group, IMT was performed at 60% of sustained maximal inspiratory pressure (SPImax ) while in the AT/SHAM group it was performed at 10% of SPImax , using a computer biofeedback trainer for 30 min, three times a week. At baseline and at 3 months, patients were evaluated for exercise capacity, lung function, inspiratory muscle strength (PImax ) and work capacity (SPImax ), quality of life (QoL), LVEF and LV diameter, dyspnoea, C-reactive protein (CRP), and NT-proBNP. IMT resulted in a significantly higher benefit in SPImax (P = 0.02), QoL (P = 0.002), dyspnoea (P = 0.004), CRP (P = 0.03), and NT-proBNP (P = 0.004). In both AT/IMT and AT/SHAM groups PImax (P < 0.001, P = 0.02), peak VO2 (P = 0.008, P = 0.04), and LVEF (P = 0.005, P = 0.002) improved significantly; however, without an additional benefit for either of the groups. CONCLUSION This randomized multicentre study demonstrates that IMT combined with aerobic training provides additional benefits in functional and serum biomarkers in patients with moderate CHF. These findings advocate for application of IMT in cardiac rehabilitation programmes.