Mitochondrial electron transport chain function is enhanced in inspiratory muscles of patients with chronic obstructive pulmonary disease

In chronic obstructive pulmonary disease, inspiratory muscles face increased resistive and elastic workloads and therefore increased energy requirements. The adaptive response of these muscles to this higher energy demand includes increased oxidative enzymes and changes in contractile protein expression but the consequences on mitochondrial function and energy metabolism have not been assessed so far. We investigated the in situ properties of the mitochondria of costal diaphragm and external intercostal muscles using the skinned fiber technique in 9 emphysematous and 11 age-matched control patients. Biopsies obtained during thoracic surgery were placed in an oxygraphic chamber to measure maximal oxygen uptake. We observed that the maximal oxidative capacity of diaphragm and external intercostal muscles increased significantly in the emphysematous group compared with the control group (+135 and +37%, respectively). Significant correlations were found between the maximal oxidative capacity and patients' pulmonary indexes of obstruction (diaphragm: r = -0.637, intercostal: r = -0.667, p < 0.005) and hyperinflation (diaphragm: r = 0.639, p < 0.003, intercostal: r = 0.634, p < 0.01). Slow myosin heavy chain isoform increased in the diaphragm of the emphysematous group, with significant relationships between indexes of obstruction and hyperinflation and activities of biochemical mitochondrial markers. Thus, severe emphysema was associated with increased mitochondrial capacity and efficiency in the inspiratory muscles, supporting an endurance training-like effect.

Endothelial nitric oxide synthase (NOS) deficiency affects energy metabolism pattern in murine oxidative skeletal muscle

Oxidative capacity of muscles correlates with capillary density and with microcirculation, which in turn depend on various regulatory factors, including NO generated by endothelial nitric oxide synthase (eNOS). To determine the role of eNOS in patterns of regulation of energy metabolism in various muscles, we studied mitochondrial respiration in situ in saponin-permeabilized fibres as well as the energy metabolism enzyme profile in the cardiac, soleus (oxidative) and gastrocnemius (glycolytic) muscles isolated from mice lacking eNOS (eNOS(-/-)). In soleus muscle, the absence of eNOS induced a marked decrease in both basal mitochondrial respiration without ADP (-32%; P <0.05) and maximal respiration in the presence of ADP (-29%; P <0.05). Furthermore, the eNOS(-/-) soleus muscle showed a decrease in total creatine kinase (-29%; P <0.05), citrate synthase (-31%; P <0.01), adenylate kinase (-27%; P <0.05), glyceraldehyde-3-phosphate dehydrogenase (-43%; P <0.01) and pyruvate kinase (-26%; P <0.05) activities. The percentage of myosin heavy chains I (slow isoform) was significantly increased from 24.3+/-1.5% in control to 30.1+/-1.1% in eNOS(-/-) soleus muscle ( P <0.05) at the expense of a slight non-significant decrease in the three other (fast) isoforms. Besides, eNOS(-/-) soleus showed a 28% loss of weight. Interestingly, we did not find differences in any parameters in cardiac and gastrocnemius muscles compared with respective controls. These results show that eNOS knockout has an important effect on muscle oxidative capacity as well on the activities of energy metabolism enzymes in oxidative (soleus) muscle. The absence of such effects in cardiac and glycolytic (gastrocnemius) muscle suggests a specific role for eNOS-produced NO in oxidative skeletal muscle.

Physical activity changes the regulation of mitochondrial respiration in human skeletal muscle

This study explores the importance of creatine kinase (CK) in the regulation of muscle mitochondrial respiration in human subjects depending on their level of physical activity. Volunteers were classified as sedentary, active or athletic according to the total activity index as determined by the Baecke questionnaire in combination with maximal oxygen uptake values (peak V(O2), expressed in ml min(-1) kg(-1)). All volunteers underwent a cyclo-ergometric incremental exercise test to estimate their peak V(O2) and V(O2) at the ventilatory threshold (VT). Muscle biopsy samples were taken from the vastus lateralis and mitochondrial respiration was evaluated in an oxygraph cell on saponin permeabilised muscle fibres in the absence (V(0)) or in the presence (V(max)) of saturating [ADP]. While V(0) was similar, V(max) differed among groups (sedentary, 3.7 +/- 0.3, active, 5.9 +/- 0.9 and athletic, 7.9 +/- 0.5 micromol O2 min(-1) (g dry weight)(-1)). V(max) was correlated with peak V(O2) (P < 0.01, r = 0.63) and with V(T) (P < 0.01, r = 0.57). There was a significantly greater degree of coupling between oxidation and phosphorylation (V(max)/V(0)) in the athletic individuals. The mitochondrial K(m) for ADP was significantly higher in athletic subjects (P < 0.01). Mitochondrial CK (mi-CK) activation by addition of creatine induced a marked decrease in K(m) in athletic individuals only, indicative of an efficient coupling of mi-CK to ADP rephosphorylation in the athletic subjects only. It is suggested that increasing aerobic performance requires an enhancement of both muscle oxidative capacity and mechanisms of respiratory control, attesting to the importance of temporal co-ordination of energy fluxes by CK for higher efficacy.

Nandrolone decanoate treatment induces changes in contractile responses of rat untrained fast-twitch skeletal muscle

This investigation was designed to examine whether short-term administration of anabolic-androgenic steroids (AAS) (nandrolone decanoate) could produce changes in contractile responses of untrained rat fast- (edl) and slow- (soleus) twitch skeletal muscle. Twenty male rats were divided into two groups, one group received weekly (for 6 weeks) an intramuscular injection of AAS, nandrolone decanoate (15 mg kg(-1)) and the second group received weekly the similar doses of vehicle (sterile peanut oil). In edl intact isolated small bundles (two to four cells), it was found that nandrolone decanoate treatment increases the K+ contracture tension (146 mM) relative to maximum tension by 56%, whereas no change was observed in the time to peak tension and in the time constant of relaxation. By contrast, in treated soleus muscle, compared with control, no significant modification was found in the K+ contracture characteristics. The change in edl contractile responses was associated with a shift to more negative potential of the voltage-dependence activation and the steady-state inactivation curves which also shifted leftward in treated soleus fibres. Furthermore, in edl skinned Triton X-100 fibres, the Ca2+ sensitivity of contractile proteins (pCa50) was increased, while electrophoresis analysis indicates no significant effect of nandrolone decanoate treatment on myosin heavy chain (MHC) isoforms. The present results show that nandrolone decanoate treatment produces more pronounced changes in untrained fast muscle function rather than soleus by acting at different levels of the excitation-contraction coupling mechanism without changes in the MHC isoforms and that contractile responses became similar to those found in soleus muscle.

Response of mitochondrial function to hypothyroidism in normal and regenerated rat skeletal muscle

Although thyroid hormones induce a well known decrease in muscle oxidative capacity, nothing is known concerning their effects on mitochondrial function and regulation in situ. Similarly, the influence of regeneration process is not completely understood. We investigated the effects of hypothyroidism on mitochondrial function in fast gastrocnemius (GS) and slow soleus (SOL) muscles either intact or having undergone a cycle of degeneration/regeneration (Rg SOL) following a local injection of myotoxin. Thyroid hormone deficiency was induced by thyroidectomy and propylthiouracyl via drinking water. Respiration was measured in muscle fibres permeabilised by saponin in order to assess the oxidative capacity of the muscles and the regulation of mitochondria in situ. Oxidative capacities were 8.9 in SOL, 8.5 in Rg SOL and 5.9 micromol O2/min/g dry weight in GS and decreased by 52, 42 and 39% respectively (P < 0.001) in hypothyroid rats. Moreover, the Km of mitochondrial respiration for the phosphate acceptor ADP exhibited a two-fold decrease in Rg SOL and intact SOL by hypothyroidism (P < 0.01), while mitochondrial creatine kinase activity and sensitivity of mitochondrial respiration to creatine were not altered. The results of this study demonstrate that hypothyroidism markedly altered the sensitivity of mitochondrial respiration to ADP but not to creatine in SOL muscles, suggesting that mitochondrial regulation could be partially controlled by thyroid hormones. On the other hand, mitochondrial function completely recovered following regeneration/degeneration, suggesting that thyroid hormones are not involved in the regeneration process per se.

Diet restriction plays an important role in the alterations of heart mitochondrial function following exposure of young rats to chronic hypoxia

Male Wistar rats aged 4 weeks, were subjected to hypobaric hypoxia (barometric pressure 505 hPa, PI,O2 106 hPa) or to diet restriction (reproducing the effect of hypoxia-induced anorexia) for 4 weeks. Each group (control, hypoxic, pair-fed, n = 16), was divided into two sub-groups housed individually in either normal cages or cages with running wheels allowing evaluation of voluntary activity (n = 8 each). The skinned-fibre technique was used to evaluate the functional properties of myofibrillar mitochondria from right and left ventricles in situ. The oxidative fibres from the soleus and diaphragm muscles were also investigated for comparison. Analysis of variance did not detect any significant effect of voluntary running activity. With calorie restriction, the maximal respiratory rate (Vmax) in the presence of 1 mM adenosine 5'-diphosphate (ADP) in myocardial fibres fell significantly (by about 25%) but was unchanged in skeletal myocytes. Following hypoxia, Vmax in myocardial fibres increased by 25% compared with the calorie restricted group and in soleus and diaphragm muscle fibres by about 30% compared with control. In myocardial fibres of control rats, creatine (20 mM) increased the sub-maximal respiratory rate by 80% in the presence of 0.1 mM ADP. Under calorie restriction or hypoxia the stimulatory effect was significantly reduced to 34-56%. This alteration was due to a decrease in the apparent Michaelis-Menten constant (Km) of mitochondrial respiration for ADP evaluated in the absence of creatine, while the Km in presence of creatine 20 mM was unchanged. In conclusion, reduced food intake decreased the oxidative capacity (Vmax) and the apparent Km for ADP of mitochondria in both left and right ventricles. Chronic hypoxia per se was responsible for an increase in the oxidative capacity of all oxidative muscles but did not exert significant effects on the control of respiration by ADP and creatine in myocardium.

Influence of overload on phenotypic remodeling in regenerated skeletal muscle

We studied the effects of 10 wk of functional overload on the expression of myosin heavy chain (MHC), sarcoplasmic reticulum Ca(2+)-ATPase isoforms (SERCA), and the activity of several metabolic enzymes in sham and regenerated plantaris muscles. Overload was accomplished by bilateral surgical ablation of its synergists 4 wk after right plantaris muscles regenerated after myotoxic infiltration. The overload-induced muscle enlargement was slightly less in regenerated than in sham muscles [28% (P < 0.005) and 43% (P < 0.001), respectively]. Overload led to an increase in type I MHC expression (P < 0.01) to a similar extent in sham and regenerated plantaris, while the expected shift from type IIb to type IIa MHC was less marked in regenerated than in sham plantaris. The overload-induced decrease in the expression of the fast SERCA isoform and in the activity of the M subunit of lactate dehydrogenase occurred to a similar extent in sham and regenerated plantaris [66% (P < 0.01) and 27% (P < 0.005), respectively]. In conclusion, the lesser responses of muscle mass and fast MHC composition of regenerated plantaris to mechanical overload suggest an alteration of the transcriptional, translational, and/or posttranslational control of gene expression in regenerated muscle.

Dual influence of disease and increased load on diaphragm muscle in heart failure

We have recently shown that mitochondrial function and energy metabolism are altered in the myocardium as well as in slow and fast locomotor muscles of rats subjected to prolonged congestive heart failure (CHF) suggesting a generalized metabolic myopathy in heart failure. Here, we investigate whether the diaphragm of CHF animals, which experiences both increased work and the general systemic influence of heart failure, will also be susceptible to altered energy metabolism. Biopsies were obtained from the costal diaphragm of failing rats 8 months after aortic banding. A marked increase in type I and type IIa myosin heavy chains at the expense of types IIx and IIb, suggests an adaptation towards a slower phenotype. Glycolytic enzymes decreased in CHF diaphragm with an increase in the H:M lactate dehydrogenase isoenzyme ratio. These results suggest a reorientation of the diaphragm muscle towards a slow, fatigue-resistant phenotype. However, maximal oxidative capacity assessed in saponin-permeabilized fibers in the presence of ADP was considerably reduced in CHF diaphragm (7.7+/-0.4 v 11.8+/-0.7 micromol O2/min/g dry weight in sham P<0.001), suggesting an alteration in oxidative phosphorylation. Furthermore, ADP sensitivity of CHF mitochondria was significantly increased (apparent Km for ADP 308+/-21 v 945+/-106 microM in sham P<0.001), whereas sensitivity to ADP in the presence of creatine was comparable (Km 79+/-12 v 90+/-11 microM in sham). In heart failure, therefore, the diaphragm muscle seems to adapt towards a more slow and economical contraction as a result of increased workload, but this adaptation is limited by the disease-induced altered mitochondrial function.

Lack of coordinated changes in metabolic enzymes and myosin heavy chain isoforms in regenerated muscles of trained rats

We investigated training-induced changes in biochemical properties and myosin heavy chain (MHC) composition of regenerated (cardiotoxin-injected) plantaris muscles (PLA) in rats either maintained sedentary (S, n = 9) or endurance trained on a treadmill over a 8-week period (T, n = 7). Both endurance training and regeneration altered the pattern of fast MHC expression. An analysis of the two-way interaction between training and regeneration showed that the relative content of type IIa MHC was affected (P < 0.05). The 140% increase in type IIa MHC observed in regenerated PLA from T rats compared with nontreated muscle of S rats, exceeded the 102% increase resulting from the combination of regeneration alone (26%) and training alone (61%). A similar interaction between training and regeneration was shown for the percentage of fibres expressing either type IIa or type lIb MHC (P < 0.05). In contrast, a significant increase in the citrate synthase (CS) activity was shown in PLA as a result of endurance training, without specific effect of regeneration. Furthermore, training-induced changes in CK and LDH isoenzyme distribution occurred to a similar extent in regenerated and non-treated PLA muscles, and thus did not follow the changes in MHC isoforms. An increase in the mitochondrial CK isozyme activity (mi-CK) was shown in both non-treated and previously degenerated PLA muscles (123 and 117%, P < 0.01, respectively), without specific effect of regeneration. The ratio of mi-CK to CS activity, an estimate of the mitochondrial specific activity of mi-CK was significantly increased by training (P < 0.02) and decreased by regeneration (P < 0.05). Taken together, these data suggest that while training and regeneration have cumulative effects on the pattern of fast MHC expression, the training-induced changes in the energy metabolism shown in mature non-treated myofibres are similar to those observed in regenerated fibres.

Myosin heavy chain composition of skeletal muscles in young rats growing under hypobaric hypoxia conditions

This study investigated the effects of voluntary wheel running on the myosin heavy chain (MHC) composition of the soleus (Sol) and plantaris muscles (Pla) in rats developing under hypobaric choronic hypoxia (CH) conditions during 4 wk in comparison with those of control rats maintained under local barometric pressure conditions (C) or rats pair-fed an equivalent quantity of food to that consumed by CH animals (PF). Compared with C animals, sedentary rats subjected to CH conditions showed a significant decrease in type I MHC in Sol (-12%, P < 0.01). Although strongly decreased under hypoxia, spontaneous running activity increased the expression of type I MHC (P < 0.01) so that no difference in the MHC profile of Sol was shown between CH active and C active rats. The MHC distribution in Sol of PF rats was not significantly different from that found in C animals. CH resulted in a significant decrease in type I (P < 0.01) and type IIA (P < 0.005) MHC, concomitant with an increase in type IIB MHC in Pla (P < 0.001), compared with C and PF animals. In contrast to results in Sol muscle, this slow-to-fast shift in the MHC profile was unaffected by spontaneous running activity. These results suggest that running exercise suppresses the hypoxia-induced slow-to-fast transition in the MHC expression in Sol muscles only. The hypoxia-induced decrease in food intake has no major influence on MHC expression in developing rats.

Subcellular creatine kinase alterations. Implications in heart failure

We have tested the hypothesis that decreased functioning of creatine kinase (CK) at sites of energy production and utilization may contribute to alterations in energy fluxes and calcium homeostasis in congestive heart failure (CHF). Heart failure was induced by aortic banding in 3-week-old rats. Myofilaments, sarcoplasmic reticulum (SR), mitochondrial functions, and CK compartmentation were studied in situ using selective membrane permeabilization of left ventricular fibers with detergents (saponin for mitochondria and SR and Triton X-100 for myofibrils). Seven months after surgery, animals were in CHF. A decrease in total CK activity could be accounted for by a 4-fold decrease in activity and content (Western blots) of mitochondrial CK and a 30% decrease in M isoform of CK (MM-CK) activity. In myofibrils, maximal force, crossbridge kinetics, and alpha-myosin heavy-chain expression decreased, whereas calcium sensitivity of tension development remained unaltered. Myofibrillar CK efficacy was unchanged. Calcium uptake capacities of SR were estimated from the surface of caffeine-induced tension transient (SCa) after loading with different substrates. In CHF, SCa decreased by 23%, and phosphocreatine was 2 times less efficient in enhancing calcium uptake. Oxidative capacities of the failing myocardium measured as oxygen consumption per gram of fiber dry weight decreased by 28%. Moreover, the control of respiration by creatine, ADP, and AMP was severely impaired. Our observations provide evidence that alterations in CK compartmentation may contribute to alterations of energy fluxes and calcium homeostasis in CHF.

Changes in myosin heavy chain profile of mature regenerated muscle with endurance training in rat

The objective of the present study was to examine the response of fast-twitch muscle to endurance training long after the muscle had regenerated from toxin injury. Seventeen male Wistar rats were randomly assigned to a sedentary (S, n = 10) or a trained group (T, n = 7). Endurance training by treadmill running (5 days week(-1), 30 m min(-1), 7% grade, 2 h day(-1) for 5 weeks) was initiated 5 weeks after myofibre degeneration was induced in the right extensor digitorum longus muscle (EDL) by two injections of 0.2 mL of the unfractionated venom from Naja nigricollis snake. Gel electrophoresis analyses showed that training alone resulted in a 140% increase in type IIX myosin heavy chain (MHC) (P < 0.01) and a slight decrease in type IIB MHC (-14% P < 0.05). Regeneration alone induced an increase in both type IIA and IIX MHC expression (103%, P < 0.05, and 131%, P < 0.01, respectively), and a concomitant decrease in the percentage of type IIB MHC (P < 0.05). The shift from type IIB toward type IIA MHC composition observed in regenerated muscles of T rats resulted not only from an additive, but from a cumulative effect of training and regeneration. Immunohistochemical analysis of MHC content in individual fibres showed similar changes. These data suggest that the impact of endurance training on fast-type MHCs was more marked in mature regenerated muscles than in regenerating ones, and provide evidence of the heightened plasticity of fully regenerated muscles to repeated exercise.

Effects of prolonged exercise on brain ammonia and amino acids

The aim of this study was to investigate if enhanced peripheral ammonia production during exhaustive exercise increases ammonia detoxication in brain mediated by glutamine synthesis, and subsequently influences glutamate and gamma-aminobutyric acid (GABA) levels. This neurotransmitter production is related to the metabolism of glutamine. A group of rats was trained for 6 weeks by treadmill running (TR). They were compared to a group of untrained rats (UN). At the end of training, half of TR and UN rats were submitted to one session of treadmill running until exhaustion (288+/-12 min and 62+/-5 min in TR and UN group, respectively). At exhaustion, running and control rats were sacrificed in order to collect blood and to take samples of the following brain structures: cortex, striatum and cerebellum. Treadmill running until exhaustion induced an increase in blood ammonia by 140% without significant differences between TR and UN groups. Brain ammonia increased in both groups. However, TR group exhibited values 50% higher than those observed in UN group. Brain glutamine was increased at exhaustion in all groups of running rats by 30-75% of basal value whereas the glutamate only decreased in TR rats which were able to run for a longer time. In this group, the GABA level decreased in striatum. These data confirm that enhanced brain ammonia level during exercise stimulates glutamine synthesis as a mechanism of detoxication. After several hours of running, a reduction in brain glutamate levels was observed in all brain structures in trained rats but only in the striatum in untrained animals. The reduced availability of this GABA precursor decreases GABA levels only in the striatum of TR group by 45% of the resting value. These results suggest a relation between cerebral changes in neurotransmitters and excitatory amino acids, such as glutamate and GABA, and central fatigue.

Muscle damage induced by running training during recovery from hindlimb suspension: the effect of dantrolene sodium

We examined the extent of morphological alterations and the myosin heavy chain (MHC) distribution in the rat soleus muscle after a 4-week period of spontaneous recovery or retraining after hindlimb suspension (HS). Moreover, we tested the hypothesis that dantrolene sodium, which affects the flux of calcium over the sarcoplasmic reticulum membrane, was able to attenuate muscle damage. Three groups of rats were submitted to 3 weeks of HS, followed by either 4 weeks of unrestricted cage activity (HC, n = 7), or running training for the same period and were compared to age-matched animals (C, n = 8). Trained rats were treated with either placebo or dantrolene sodium (HTP, HTD, n = 8 each, respectively). Four weeks after HS recovery, the percentage of myofibres with internal nuclei (%in) was determined by histological staining with hematoxylin and eosin. %in was affected by the individual rat (P < 0.001), and was higher in the mid-belly region of the muscle (P < 0.05). Muscle damage, as estimated by %in, was more extensive in trained rats (i.e. HTP and HTD) than in HC animals (23% and 12%, respectively). Moreover, dantrolene sodium tended to exert a protective effect on training-induced muscle injury. A 12% increase in type I MHC was observed in both HTP and HTD rats, in comparison with group C animals (P < 0.001). The relative proportion of type-I MHC was inversely correlated with %in (r = -0.65, P < 0.001). Running recovery led to an increased citrate synthase activity in comparison with that of C or HC rats. In conclusion, the present findings demonstrate that running recovery from HS increases the incidence of muscle damage, and that dantrolene sodium administration has only limited protective effects against exercise-induced muscle injury.

Myosin heavy chain composition of regenerated soleus muscles during hindlimb suspension

The aim of this study was to determine the MHC profile of regenerated soleus muscles in control (C, n = 8) and hindlimb suspended rats (HS, n = 8). After muscle degeneration was induced by injection of snake venom containing notexin, male rats were either tail suspended for 21 days or submitted to normal weight-bearing activity. Separation and detection of MHCs by sodium dodecyl sulphate-polyarcylamide gel electrophoresis (SDS-PAGE) showed that regenerated soleus muscles from C rats contained only type I and type IIa MHCs. The relative amount of type I MHC was higher in regenerated (93.9 +/- 1.7%) than in untreated muscles (86.5 +/- 2.3%)(P < 0.01). In the HS group, the immunohistochemical analysis showed that the majority of regenerated myofibres reacted positively with the antibody against fast MHCs. SDS-PAGE analysis demonstrated that HS resulted in a shift toward faster MHCs in both intact and regenerated myofibres. Regenerated soleus muscle from HS rats contained approximately 34% type IIa MHC, approximately 37% type IIx/d MHC and approximately 18% type IIb MHC, when type I MHC contributed to only approximately 12% of total myosin. The proportions of fast MHC isoforms in regenerated muscles were higher than those recorded in untreated muscles. Collectively, these results suggest that the shift in the MHC profile associated with hindlimb unweighting in adult undamaged soleus muscles is also related to the heterogeneity of early myoblasts.

Comparison of T cell depletion strategies from bone marrow, umbilical cord and peripheral blood using five separation systems

The development of bone marrow transplantation in mismatched or matched unrelated donor situations, the recent use of peripheral blood stem cells for allogeneic transplants, the standardization and respect of good methodology practices highlight the need to evaluate new safe methods of T cell depletion (TCD). We have performed 79 in vitro TCD using five techniques: rabbit complement cytotoxicity, CD2-CD7 immunomagnetic depletion, CD5-CD8 panning system, CD34 positive purging and counterflow centrifugation elutriation (CCE). We analyzed these different approaches with regard to the degree of T and B depletion, recovery of progenitors and NK cells. In our hands, the 5 systems evaluated showed a TCD of between 1.3 and 3 log. The CCE, immunomagnetic, complement and panning methods all give similar a TCD of around 2 log. In contrast, we obtained a TCD of approximately 3 log with CD34 positive purging. The progenitor yield was around 50% regardless of the technique used. However, the degree of B and NK cell depletion was dependent on the method: specific TCD resulted in low BCD (under 0.5 log), whereas CCE or CD34 positive purging gave a BCD of greater than 1 log. Moreover, CD34 positive selection resulted in a virtually complete elimination of NK cells. CCE was the only technique allowing isolation of the small lymphocyte population which can be useful for adoptive therapy. To obtain TCD over three logarithms, double purging techniques are necessary. Because specific roles of T cells subsets in engraftment, graft versus host disease, Epstein Barr virus associated B cell lymphoproliferative disorders and disease relapse have not yet been completely elucidated, new techniques such as CD34 positive purging and double purging methods (positive and negative purging) need to be clinically evaluated, especially with respect to peripheral blood stem cells.

Quantitative assessment of degenerative changes in soleus muscle after hindlimb suspension and recovery

The aim of this study was to quantify the degenerative and regenerative changes in rat soleus muscle resulting from 3-week hindlimb suspension at 45 degrees tilt (HS group, n = 8) and 4-week normal cage recovery (HS-R group, n = 7). Degenerative changes were quantified by microscope examination of muscle cross sections, and the myosin heavy chain (MHC) composition of soleus muscles was studied by sodium dodecyl sulphate polyacrylamide gel electrophoresis. At the end of 3-week hindlimb suspension, histological signs of muscle degenerative changes were detected in soleus muscles. There was a significant variability in the percentage of fibres referred to as degenerating (%dg) in individual animals in the HS group [%dg = 8.41 (SEM 0.5)%, range 4.66%-14.08%]. Moreover, %dg varied significantly along the length of the soleus muscle. The percentage of fibres with internal nuclei was less than %dg in HS-soleus muscles [4.12 (SEM 0.3)%, range 1.24%-8.86%]. In 4-week recovery rats, the greater part of the fibres that were not referred to as normal, retained central nuclei [15.8 (SEM 2.2)%, range 6.2%-21.1%]. A significant increase in the slow isoform of MHG was recorded in the HS-R rats, compared to muscles from age-matched rats (P < 0.01). These results would suggest that a cycle of myofibre degeneration-regeneration occurred during HS and passive recovery, and that the increased accumulation of slow MHC observed in soleus muscles after recovery from HS could be related to the prevalence of newly formed fibres.

G-induced myocardium functional alterations are not related to structural changes in rat heart

BACKGROUND

Left ventricular myocardial hypertrophy with a redistribution of the isomyosins is classically observed under chronic pressure overload.

HYPOTHESIS

Structural changes will also occur in myocardial cells after repeated exposures to high sustained +Gz acceleration.

METHOD

Rats were exposed to three plateaus of 30 s at 10 +Gz, 4 times a week, for 4 weeks. The myocardial mass was evaluated by measuring the ratio between left ventricular weight and body weight, and the myocardial fiber cross-sectional area. Changes in capillary density were evaluated using the myosin ATPase method. The distribution of myosin isoforms was determined by electrophoresis.

RESULTS

Contrary to expectations, no myocardial hypertrophy developed, and no transition was observed in myosin isoforms of centrifuged rats.

CONCLUSION

The functional mechanical and energetic transformations observed in a previous investigation using an identical experimental protocol probably took place at an early stage of myocardial adaptation to +Gz acceleration. We conclude that our protocol of repeated +Gz exposures is a model of chronic overloading very different from classical models.

Role of weight-bearing function on expression of myosin isoforms during regeneration of rat soleus muscles

The expression of myosin isoforms was studied in regenerated rat soleus muscle during either normal or altered postural activity. Regeneration was induced following injury by venom from the Notechis scutatus scutatus snake. Immunohistochemical analysis showed that, in regenerating soleus muscle after 3 wk of hindlimb suspension, nearly all fibers reacted positively with the myosin heavy chain (MHC) antibody associated with fast-twitch muscle fibers (fast MHC). When 3 wk of recovery with normal weight-bearing activity followed hindlimb suspension, the regeneration soleus muscle exhibited a nearly homogeneous staining with the MHC antibody associated with the slow-twitch muscle fibers (slow MHC). These findings were in accordance with quantitative analysis of the electrophoretic separation of the native myosin isoforms. Immunohistochemical data showed that removal of weight bearing in the 21-day old regenerated soleus muscles resulted in an increase in fast MHC expression. Together, the results of the present study clearly demonstrate that the postural load is an important component in the induction of slow MHC in regenerating muscle and that the control of the expression of MHC in muscle comprising a homogeneous population of fibers deriving from satellite cells appears more homogeneous and more complete than in a nondegenerated one.

Effect of competition stress on tests used to assess testosterone administration in athletes

The drug test for exogenous administration of testosterone is based on the testosterone/epitestosterone ratio (T/E) in urine. Physiological and psychological stresses may alter plasma testosterone concentrations. The question is to know how much the psychological conditions of competition can modify the T/E ratio. In order to study this issue, 20 athletes practising modern pentathlon participated in a study designed to determine the effects of a pistol shooting trial on their hormonal response. Pistol shooting induces a high psychological stress without increasing energy expenditure. Venous blood samples were drawn before and after the trial according to the usual drug testing procedure. Athletes were separated into two groups: a group of young athletes (n = 10; mean age 19 +/- 0.3 years) and another group of aged subjects (n = 10; mean age 45 +/- 1.5 years). The rise in plasma testosterone concentrations reached 75% in older subjects versus 55% in younger ones. The plasma luteinizing hormone (LH) concentrations were not influenced by the trial. After shooting trial the elevation in cortisol concentrations was greater for older subjects than for younger ones (273 +/- 30 ng.ml-1 vs 173 +/- 7 ng.ml-1). The catecholamine response was identical in both groups. The urinary T/E ratio remained unchanged after the shooting trial and always remained lower than the International Olympic Committee limit of 6. These results indicate that the psychological stress associated with competition increases the production of steroid hormones (testosterone, cortisol), and that this phenomenon is more pronounced in older athletes. These hormonal changes do not influence the urinary excretion of steroid metabolites used as criterion for drug testing.

Altered response of protein synthesis to nutritional state and endurance training in old rats

This study was undertaken to determine whether the loss of muscle protein mass during aging could be explained by a reduced sensitivity of muscle protein synthesis to feeding and exercise. Male Wistar rats aged 12 and 24 mo were exercised by treadmill running for 4 mo. Protein synthesis was measured by the flooding dose method in tibialis anterior, soleus, and liver of conscious rested, trained rats and age-matched controls in the postprandial or in the postabsorptive state. No marked change with age could be detected in basal muscle protein synthesis. In contrast, protein synthesis was stimulated in adult but not in old rats by feeding in tibialis anterior and by exercise in soleus. In liver, protein synthesis was not modified by age but was stimulated by feeding and by exercise, which improved the response to feeding. We conclude that the impact of nutrition on muscle protein synthesis is blunted in old age, which could contribute to the age-related loss of nutrition-sensitive muscle proteins.

Effects of growth hormone on rat skeletal muscle after hindlimb suspension

To examine the effects of growth hormone (GH) on the preferential atrophy of the soleus muscle (SOL) occurring after hindlimb suspension (HS), two groups of male rats received daily injections of 2 IU.kg-1 body mass of recombinant human growth hormone (rhGH). Rats were either suspended by the tail for 21 days (HS-GH, n = 5) or nonsuspended (C-GH, n = 5). The effects of rhGH treatment on SOL and extensor digitorum longus muscles (EDL) were compared in two groups of animals receiving daily injections of saline, either suspended by the tail (HS-SA, n = 5) or nonsuspended (C-SA, n = 5). The results showed that the SOL hypertrophy in response to rhGH administration was mostly observed in C rats (+33%, P < 0.01). This increase in muscle mass was correlated with a concomitant increase in the size of type I fibres (+21%, P < 0.05). Although SOL mass decreased during HS in rhGH treated animals (-44%, P < 0.001), the mean normalized mass of this muscle did not significantly differ between C-SA and HS-GH groups. A statistically significant increase in the absolute mass of EDL occurred with rhGH treatment in C-GH (+12%, P < 0.05). The HS-induced decrease in the percentage distribution of type I fibres in SOL was unaffected by the rhGH treatment. In addition, a decrease in the citrate synthase activity in the whole SOL was observed in the two groups of tail-suspended rats (-31%, P < 0.05; -21%, P < 0.05 in SA and GH animals, respectively).2+ f1p4

Structural and biochemical properties of the rat myocardium after 21 days of head-down suspension

The effects of 21 d of head-down suspension on the biochemical and structural properties of the myocardium were determined in male rats (HDS, n = 10), and compared with control non-suspended animals (C, n = 10). HDS rats were prepared using Morey's tail-suspension model, and maintained at 45 degrees tilt. At the end of the conditioning period, hearts were excised and dissected into right (RV) and left plus intraventricular septum (LV). We observed that HDS rats had lower LV- and RV-absolute weights than C animals (-8.5%, p < 0.05, and -12%, p < 0.05, respectively). The relative ventricle weights (ventricle weight/body weight, mg.g-1) were unaffected by HDS. Native myosin isoform analysis revealed that HDS did not alter myosin expression in both LV and RV. The capillary bed, examined using histochemical methods, was found to be unaffected by HDS. A significant decrease in the lactate dehydrogenase activity was detected in LV after 21 d of HDS (-16%, p < 0.05). Collectively, these results suggest that the early neurohumoral changes occurring in response to HDS-induced hemodynamic overload are sufficient to prevent any alteration in the biochemical and structural properties of the myocardial tissue.

Effects of surface electrostimulation on the structure and metabolic properties in monkey skeletal muscle

Adaptative changes in skeletal muscle following surface electrical stimulation (SES) were investigated in rhesus monkeys. SES was performed on the triceps brachialis muscle (TB) according to an intermittent pattern. The procedure was carried out for 3 wk, using a current with a medium frequency of 60 Hz normally observed in fast motor axons. The histochemical assays performed on biopsies taken from proximal and distal parts of the TB muscle, before and after the SES program, showed that the distribution of fibers typed by ATPase was unaffected. On the other hand, SES led to an overall increase in the mean fiber cross-sectional area (FCSA); P < 0.01 (+13.7%, NS, in proximal portion, vs +31%, P < 0.01 in distal portion). This increase in size occurred in all fiber types. SES was shown to induce an overall increase in capillary to fiber ratio (C/F; +11.06%, NS, in proximal portion, vs +25.93%, P < 0.05 in distal portion). The number of capillaries surrounding fiber Type II (CAFII) was significantly increased by SES (P < 0.05): +3.21%, NS, in proximal portion, versus +21.47%, P < 0.05 in distal portion. Moreover, the number of capillaries surrounding fiber Type I (CAFI) was statistically unaffected by SES. These results suggest that a stimulation of capillary growth may occur following SES-training. Citrate synthase activity was significantly increased after SES. This enhancement in oxidative potential was shown to occur in all fiber types (NADH-diaphorase staining).(ABSTRACT TRUNCATED AT 250 WORDS)