Mitochondrial uncoupling reduces exercise capacity despite several skeletal muscle metabolic adaptations.

The effects of mitochondrial uncoupling on skeletal muscle mitochondrial adaptation and maximal exercise capacity are unknown. In this study, rats were divided into a control group (CTL, n = 8) and a group treated with 2,4-dinitrophenol, a mitochondrial uncoupler, for 28 days (DNP, 30 mg·kg(-1)·day(-1) in drinking water, n = 8). The DNP group had a significantly lower body mass (P < 0.05) and a higher resting oxygen uptake (Vo2, P < 0.005). The incremental treadmill test showed that maximal running speed and running economy (P < 0.01) were impaired but that maximal Vo2 (Vo2max) was higher in the DNP-treated rats (P < 0.05). In skinned gastrocnemius fibers, basal respiration (V0) was higher (P < 0.01) in the DNP-treated animals, whereas the acceptor control ratio (ACR, Vmax/V0) was significantly lower (P < 0.05), indicating a reduction in OXPHOS efficiency. In skeletal muscle, DNP activated the mitochondrial biogenesis pathway, as indicated by changes in the mRNA expression of PGC1-α and -ß, NRF-1 and -2, and TFAM, and increased the mRNA expression of cytochrome oxidase 1 (P < 0.01). The expression of two mitochondrial proteins (prohibitin and Ndufs 3) was higher after DNP treatment. Mitochondrial fission 1 protein (Fis-1) was increased in the DNP group (P < 0.01), but mitofusin-1 and -2 were unchanged. Histochemical staining for NADH dehydrogenase and succinate dehydrogenase activity in the gastrocnemius muscle revealed an increase in the proportion of oxidative fibers after DNP treatment. Our study shows that mitochondrial uncoupling induces several skeletal muscle adaptations, highlighting the role of mitochondrial coupling as a critical factor for maximal exercise capacities. These results emphasize the importance of investigating the qualitative aspects of mitochondrial function in addition to the amount of mitochondria.

Methylene blue protects liver oxidative capacity after gut ischaemia-reperfusion in the rat.

OBJECTIVES: Mesenteric ischaemia/reperfusion (IR) may lead to liver mitochondrial dysfunction and multiple organ failure. We determined whether gut IR induces early impairment of liver mitochondrial oxidative activity and whether methylene blue (MB) might afford protection. DESIGN: Controlled animal study. MATERIALS AND METHODS: Rats were randomised into three groups: controls (n = 18), gut IR group (mesenteric ischaemia (60 min)/reperfusion (60 min)) (n = 18) and gut IR + MB group (15 mg kg(-1) MB intra-peritoneally) (n = 16). Study parameters were: serum liver function markers, blood lactate, standard histology and DNA fragmentation (apoptosis) on intestinal and liver tissue, maximal oxidative capacity of liver mitochondria (state 3) and activity of complexes II, III and IV of the respiratory chain measured using a Clark oxygen electrode. RESULTS: Gut IR increased lactate deshydrogenase (+982%), aspartate and alanine aminotransferases (+43% and +74%, respectively) and lactate levels (+271%). It induced segmental loss of intestinal villi and cryptic apoptosis. It reduced liver state 3 respiration by 30% from 50.1 ± 3 to 35.2 ± 3.5 µM O(2) min(-1) g(-1) (P < 0.01) and the activity of complexes II, III and IV of the mitochondrial respiratory chain. Early impairment of liver mitochondrial respiration was related to blood lactate levels (r(2) = 0.45). MB restored liver mitochondrial function. CONCLUSIONS: MB protected against gut IR-induced liver mitochondria dysfunction.

Effect of postconditioning on mitochondrial dysfunction in experimental aortic cross-clamping.

BACKGROUND: Cross-clamping of the aorta during abdominal aortic aneurysm surgery induces muscle ischaemia with resultant morbidity. This study tested whether ischaemic postconditioning would decrease mitochondrial dysfunction in skeletal muscle by reducing oxidative stress. METHODS: Three groups (9 rats each) underwent surgery, including a control group without ischaemia and an ischaemia-reperfusion group that had 3 h ischaemia induced by aortic clamping and collateral vessel ligation, followed by 2 h of reperfusion. The third group had ischaemia for 3 h then underwent postconditioning comprising three short intervals of ischaemia-reperfusion at the onset of reperfusion. Activity of complexes I, II, III and IV of the mitochondrial respiratory chain was monitored in gastrocnemius muscle, along with oxidative stress measured by dihydroethidium (DHE) staining and antioxidant defence determined by measurement of glutathione levels. RESULTS: Ischaemia-reperfusion alone caused a significant reduction in maximal oxidative capacity (-31.8 per cent; P = 0.002), activity of complexes II, III and IV (-34.5 per cent; P = 0.007) and complex IV activity (-30.6 per cent; P = 0.039). It also increased reactive oxygen species (DHE staining increased to 223.1 per cent of control value; P = 0.027) and reduced antioxidant defence (glutathione level -28.6 per cent; P = 0.039). Postconditioning counteracted these deleterious effects by increasing mitochondrial complex I, II, III and IV activities, restoring muscle DHE staining and preserving glutathione content. CONCLUSION: Ischaemic postconditioning protects skeletal muscle mitochondria against ischaemia-reperfusion injury by reducing oxidative stress and preserving antioxidant defence in an experimental model. Mitochondrial protection to reduce reperfusion injury in clinical vascular surgery may be warranted.

Diffusing capacity of the lung for CO and pulmonary blood flow during incremental and intermittent exercise.

The aims of this study were to evaluate the feasibility of successive diffusing capacity of the lung for carbon monoxide (DLCO) measurements during two different exercise tests (upright cycling), and to compare the relationships between DLCO and pulmonary blood flow (Qc). Eight healthy subjects performed an incremental test (1-min step) and a strenuous 30-min intermittent-work exercise test (4 min at low and 2 min at high workload). Intrabreath DLCO and Qc were calculated by assessing the uptake of CO and C2H2 during exhalation. DLCO could be measured reliably up to 73-90% of peak oxygen consumption (VO2) during the incremental test, and up to 85-95% of peak VO2 during the intermittent test. The coefficients of variation of DLCO and Qc measured during two successive constant-load exercise tests were 5-6% and 7-11%, respectively. The highest values of DLCO, Qc and VO2 measured during the incremental and intermittent tests were similar (56 and 51 mL/mmHg/min for DLCO, 18.7 and 18.3 L/min, for Qc and 2.4 and 2.3 L/min for VO2, respectively). The main observed result was that the linear relationships between DLCO and Qc were similar whatever the exercise type. This allows DLCO comparisons, with regards to Qc, during different exercise protocols.

Does circulating BNP normalize after heart transplantation in patients with normal hemodynamic and right and left heart functions?

BACKGROUND: Increased brain natriuretic peptide (BNP) in cardiovascular disease is thought to be a compensatory protective mechanism allowing to delay the occurrence of terminal heart failure. Heart transplantation should normalize the neuroendocrine balance but BNP remains elevated in stable heart-transplant recipients (Htx). Such increase has been related to persistent endothelial and cardiac dysfunctions. The purpose of this study was to determine whether selected Htx, presenting with normal hemodynamic and cardiac systolic and diastolic functions on both side of the heart, show a normalization of their BNP plasma values. METHODS: Of a cohort of well-being 26 Htx, we selected 12 patients with normal hemodynamics and left and right heart systolic and diastolic functions and compared their circulating BNP, cyclic guanosine monophosphate (cGMP) (the BNP second messenger) and endothelin-1 (ET) values with that of 12 age-, body mass index- and mean arterial pressure-matched controls. Cardiac function determination by echodoppler included cardiac filling pressures assessment using tissue Doppler imaging. Blood samples for biological and hormonal determinations were drawn at rest, within 15 min before echocardiography. RESULTS: As selected, hemodynamic and left and right heart systolic and diastolic functions were located in the normal range in Htx. Plasma ET value was also similar in Htx and controls (20.7 +/- 0.9 vs. 19.6 +/- 0.9 fmol/mL). However, circulating BNP, like cGMP, was still significantly increased after heart transplantation, when compared with controls (33.8 +/- 8.5 vs. 4.0 +/- 0.9 pg/mL, p = 0.002 and 8.2 +/- 1.1 vs. 4.4 +/- 0.3 nmol/L, p = 0.003) for BNP and cGMP, respectively, in Htx and controls. Interestingly, the sole correlation observed was between BNP and cGMP (r = 0.85, p < 0.0001) after heart transplantation. CONCLUSIONS: After heart transplantation, BNP remained increased despite the normalization of hemodynamic and cardiac systolic and diastolic functions. This suggests that such endocrine heart stimulation should not be viewed only as a hemodynamic marker in Htx. Further studies will be useful to investigate the role of pro-inflammatory cytokines and whether elevated BNP still possesses antifibrotic properties, further supporting the interest of enhancing its activity after heart transplantation.

Relationship between very high physical activity energy expenditure, heart rate variability and self-estimate of health status in middle-aged individuals.

In middle-aged persons, moderate physical activity energy expenditure (PAEE) has been shown to be associated with increased vagal-related heart rate variability (HRV) indexes and better health status. The purpose of this study was to determine whether a very high PAEE has greater effect on vagal-related HRV indexes and self-estimates of well-being in middle-aged subjects having distinct long-term physical activity profiles. Forty-four subjects were divided into three groups on the basis of the sport score of the Modified Baecke Questionnaire for Older Adults: sedentary (SED, n = 15), moderately-trained (MT, n = 16), and highly-trained subjects (HT, n = 13). PAEE was estimated by triaxial accelerometry during one week. Time and frequency domain HRV indexes were determined during quiet periods in the morning on 5-min R-R interval segments under controlled breathing. Quality of life was evaluated using the SF-36 health survey questionnaire. PAEE was significantly different for each group (374.5 +/- 13.8, 616.8 +/- 22.4, and 1086.6 +/- 43.2 kcal . day (-1) for SED, MT, and HT, respectively, p < 0.001). MT presented significantly higher vagal-related HRV indexes than SED and HT (p < 0.05). None of the HRV indexes was significantly greater in HT than in SED. MT and HT had similar health status scores, which were significantly higher than for SED. These results indicate that in middle-aged subjects, habitual moderate PAEE is associated with greater vagal tone and self-estimates of well-being compared to low PAEE. In contrast, very high PAEE is associated with similar vagal-related indexes as low PAEE, despite better overall health status.

Chronic L-arginine supplementation enhances endurance exercise tolerance in heart failure patients.

The purpose of the study was to determine the potential beneficial effect of six weeks oral L-arginine supplementation (LAS) on endurance exercise, an important determinant of daily-life activity in patients with chronic stable heart failure (CHF). After an initial incremental maximal exercise test, CHF patients performed an identical thirty-minute interval endurance exercise test before and after six weeks with (L-arginine group; ARG) or without LAS (control group; CTL). Hemodynamic, respiratory, and metabolic parameters were determined at rest, during exercise, and during recovery. Mean heart rate decreased throughout exercise and recovery after LAS (- 8.2 +/- 1.4 b x min(-1); p = 0.003 and - 6.7 +/- 1.6 b x min(-1); p < 0.001, respectively), systemic blood pressure and respiratory parameters remaining unchanged. Resting L-argininaemia increased from 102 +/- 11 to 181 +/- 37 micromol x l(-1) (p < 0.004) and exercise-induced peak increase in plasma lactate was blunted after LAS (4.13 +/- 0.75 vs. 3.13 +/- 0.39 mmol x l(-1); p = 0.02). No significant change was observed in the control group. In heart failure patients, six weeks oral LAS enhances endurance exercise tolerance, reducing both heart rate and circulating lactates. This suggests that chronic LAS might be useful as a therapeutic adjuvant in order to improve the patient's physical fitness.

Acute myocardial ischaemia induces specific alterations of ventricular mitochondrial function in experimental pigs.

AIMS: As cardiac metabolic flexibility is crucial, this study examined whether acute ischaemia can induce specific qualitative alterations of the mitochondrial metabolic pathways as well as energy transfer systems. METHODS: Left descending coronary artery ligation was performed after sternotomy in eight pigs and the heart was excised after 45 min of ischaemia. Maximal O2 uptake (V(max), micromol O2 min(-1) g(-1) dry weight) of saponin-skinned myofibres were measured from ischaemic and non-ischaemic area of ventricular myocardium. RESULTS: V(max) decreased by approximately 20% in ischaemic myocardium with both glutamate-malate (18.1 +/- 1.3 vs. 22.1 +/- 1.7 in control, P < 0.05) and pyruvate substrates (19.3 +/- 1.0 vs. 23.3 +/- 2.0 in control, P < 0.05) whereas no difference was observed with palmitoyl carnitine (15.6 +/- 1.8 vs. 16.6 +/- 0.9 in control). The K(m) of mitochondrial respiration for ADP decreased in ischaemic heart by 24% (679 +/- 79 vs. 899 +/- 84 microm of ADP in control, P < 0.05). Moreover, the mitochondrial creatine kinase efficacy (K(m) without creatine/K(m) with creatine), representative of the coupling of oxidative phosphorylation process with the mitochondrial creatine kinase, was reduced in ischaemic heart (11.6 +/- 2.5 in ischaemic vs. 18.0 +/- 2.2 in control, P < 0.05). CONCLUSIONS: These findings argue for specific mitochondrial impairments at the level of pyruvate oxidation and creatine kinase channelling system after an acute period of in vivo ischaemia, whereas the lipid mitochondrial oxidation pathway seems to be preserved. Such a loss of metabolic flexibility following acute ischaemia could become an early feature of metabolic dysregulation of the heart.

Effects of increased training load on vagal-related indexes of heart rate variability: a novel sleep approach.

There is little doubt that moderate training improves cardiac vagal activity and thus has a cardioprotective effect against lethal arrhythmias. Our purpose was to learn whether a higher training load would further increase this beneficial effect. Cardiac autonomic control was inferred from heart rate variability (HRV) and analyzed in three groups of young subjects (24.5 +/- 3.0 yr) with different training states in a period free of stressful stimuli or overload. HRV was analyzed in 5-min segments during slow-wave sleep (SWS, a parasympathetic state that offers high electrocardiographic stationarity) and compared with data collected during quiet waking periods in the morning. Sleep parameters, fatigue, and stress levels checked by questionnaire were identical for all three groups with no signs of overtraining in the highly trained (HT) participants. During SWS, a significant (P <0.05) increase in absolute and normalized vagal-related HRV indexes was observed in moderately trained (MT) individuals compared with sedentary (Sed) subjects; this increase did not persist in HT athletes. During waking periods, most of the absolute HRV indexes indistinctly increased in MT individuals compared with controls (P < 0.05) but did not increase in HT athletes. Normalized spectral HRV indexes did not change significantly among the three groups. Heart rate was similar for MT and Sed subjects but was significantly (P <0.05) lower in HT athletes under both recording conditions. These results indicate that SWS discriminates the state of sympathovagal balance better than waking periods. A moderate training load is sufficient to increase vagal-related HRV indexes. However, in HT individuals, despite lower heart rate, vagal-related HRV indexes return to Sed values even in the absence of competition, fatigue, or overload.

Abnormal heart rate variability in a subject with second degree atrioventricular blocks during sleep.

OBJECTIVE: We compare the profiles of heart rate variability (HRV) during sleep stages in 9 healthy controls and one subject with second degree atrioventricular blocks (AVB), investigating the role of sympathovagal balance in such pathology. METHOD: Sleep and cardiac records were taken for one night in 9 male subjects from 21:00 to 07:00 h and for two nights in a male subject with AVB. Time and frequency domain indexes of HRV were calculated over 5 min-periods. RESULTS: In one subject without any daytime heart disease, 253 and 318 AVB of type 2 (Mobitz 2) were observed during the two experimental nights, predominantly during rapid eye movement (REM) sleep and the surrounding sleep stage 2 in the second half of the night. In the 9 control subjects, absolute HRV indexes and low frequency (LF)/(LF+high frequency, HF) (where LF and HF are low frequency and high frequency power) were low during slow wave sleep, and significantly increased during REM sleep and the preceding sleep stage 2. In the subject with AVB, these HRV indexes were abnormally low during all sleep stages, with a predominant increase in parasympathetic activity as inferred from low LF/(LF+HF). During wake, however, LF/(LF+HF) normally increased, and the tachycardia observed with the arousal that terminates SWS was preserved in the subject with AVB. CONCLUSION: These results suggest that in the subject with second degree atrioventricular blocks, sleep processes, particularly during REM sleep, create a specific neurological background that prevents an increase in sympathetic tone and triggers cardiac pauses.

Mechanisms of renal hyporesponsiveness to ANP in heart failure.

The atrial natriuretic peptide (ANP) plays an important role in chronic heart failure (CHF), delaying the progression of the disease. However, despite high ANP levels, natriuresis falls when CHF progresses from a compensated to a decompensated state, suggesting emergence of renal resistance to ANP. Several mechanisms have been proposed to explain renal hyporesponsiveness, including decreased renal ANP availability, down-regulation of natriuretic peptide receptors and altered ANP intracellular transduction signal. It has been demonstrated that the activity of neutral endopeptidase (NEP) is increased in CHF, and that its inhibition enhances renal cGMP production and renal sodium excretion. In vitro as well as in vivo studies have provided strong evidence of an increased degradation of intracellular cGMP by phosphodiesterase in CHF. In experimental models, ANP-dependent natriuresis is improved by phosphodiesterase inhibitors, which may arise as new therapeutic agents in CHF. Sodium-retaining systems likely contribute to renal hyporesponsiveness to ANP through different mechanisms. Among these systems, the renin-angiotensin-aldosterone system has received particular attention, as angiotensin II and ANP have renal actions at the same sites and inhibition of angiotensin-converting enzyme and angiotensin-receptor blockade improve ANP hyporesponsiveness. Less is known about the interactions between the sympathetic nervous system, endothelin or vasopressin and ANP, which may also blunt ANP-induced natriuresis. To summarize, renal hyporesponsiveness to ANP is probably multifactorial. New treatments designed to restore renal ANP efficiency should limit sodium retention in CHF patients and thus delay the progression to overt heart failure.

L-arginine reduces exercise-induced increase in plasma lactate and ammonia.

To investigate the effect of L-arginine supplementation (L-ARG) on physiological and metabolic changes during exercise, we determined in a double-blind study the cardiorespiratory (heart rate, oxygen consumption (VO(2)) and carbon dioxide production (VCO(2)) and the metabolic (lactate and ammonia) responses to maximal exercise after either an intravenous L-ARG hydrochloride salt or placebo load in 8 healthy subjects. Exercise-induced increases in heart rate, VO(2) and VCO(2) were not significantly different after L-ARG or placebo. By contrast, peak plasma ammonia and lactate were significantly decreased after L-ARG load (60.6 +/- 8.2 vs. 73.1 +/- 9.1 micro mol x l(-1), p < 0.01 and 7.1 +/- 0.7 vs. 8.2 +/- 1.1 mmol x l(-1), p < 0.01, for ammonia and lactate, respectively). Plasma L-citrulline increased significantly during exercise only after L-ARG load, despite a concomitant decrease in plasma L-ARG. Furthermore, a significant inverse relationship was observed between changes in lactate and L-citrulline concentrations after L-ARG load (r = -0.84, p = 0.009). These results demonstrate that intravenous L-ARG reduces significantly exercise-induced increase in plasma lactate and ammonia. Taken together, the specific L-citrulline increase and the inverse relationship observed between L-citrulline and plasma lactate after L-ARG might support that L-ARG supplementation enhances the L-arginine-nitric oxide (NO) pathway during exercise.

Time-courses in renin and blood pressure during sleep in humans.

We previously described a strong concordance between nocturnal oscillations in plasma renin activity (PRA) and the rapid eye movement (REM) and non-REM (NREM) sleep cycles, but the mechanisms inducing PRA oscillations remain to be identified. This study was designed to examine whether they are linked to sleep stage-related changes in arterial blood pressure (ABP). Analysis of sleep electroencephalographic (EEG) activity in the delta frequency band, intra-arterial pressure, and PRA measured every 10 min was performed in eight healthy subjects. Simultaneously, the ratio of low frequency power to low frequency power + high frequency power [LF/(LF + HF)] was calculated using spectral analysis of R--R intervals. The cascade of physiological events that led to increased renin release during NREM sleep could be characterized. First, the LF/(LF + HF) ratio significantly (P < 10(-4) decreased, indicating a reduction in sympathetic tone, concomitantly to a significant (P < 10(- 3) decrease in mean arterial pressure (MAP). Delta wave activity increased (P < 10(-4) 10-20 min later and was associated with a lag of 0-10 min with a significant rise in PRA (P < 10(-4) . Rapid eye movement sleep was characterized by a significant increase (P < 10(-4) in the LF/(LF + HF) ratio and a decrease (P < 10(-4) in delta wave activity and PRA, whereas MAP levels were highly variable. Overnight cross-correlation analysis revealed that MAP was inversely correlated with delta wave activity and with PRA (P < 0.01 in all subjects but one). These results suggest that pressure-dependent mechanisms elicit the nocturnal PRA oscillations rather than common central processes controlling both the generation of slow waves and the release of renin from the kidney.