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  • 1
    ISSN: 1432-1106
    Keywords: Key words Gabaculine ; NMR spectroscopy ; Microdialysis ; Amino acids ; Compartmentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The aim of this work was to study the neurochemical effects in the brain of GABA-transaminase inhibition by systemic administration of gabaculine (100 mg/kg, i.a.) in the rat. In order to investigate neurotransmitter and related amino-acid compartmentation and metabolism, we have developed an original tool: the coupling, in vivo, on the same animal, of 2D COSY 1H-NMR spectroscopy with intracerebral microdialysis. The main result is a continuous increase in GABA levels, both in the intracellular compartment (up to 3000±450%; P〈0.001) and extracellular compartment (up to 808±82%; P〈0.01) at the sixth hour. The intracellular increase in GABA level became significant at the first hour following gabaculine administration, whereas the extracellular level increased as of the second hour, probably indicating that accumulation of GABA in nerve endings precedes its release in synaptic clefts. Moreover, the levels of the excitatory amino acids, glutamate and aspartate, were decreased both in the intra- and extracellular compartments, thus enhancing sedative effects of the drug. We also observed a decrease in the global energetic creatine-phosphocreatine pool, which also could be related to the sedative properties of gabaculine, measurable by the diminution of cortical electrical activity and mean arterial blood pressure. Finally, the coupling between 2D 1H-NMR spectroscopy and intracerebral microdialysis appears to be an original tool for investigating the cerebral metabolic effects induced by pharmacological agents, in situ, in living animals.
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  • 2
    ISSN: 1439-6327
    Keywords: Opioid receptor antagonist ; Naltrexone ; Endogenous opioids ; αh Atrial natriuretic factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To evaluate to what extent opioid secretion in exercise induces the release of atrial natriuretic factor (ANF), six healthy male volunteers who were trained subjects, were submitted to two maximal exercise tests with and without (control) opioid receptor blockade by Naltrexone. Blood samples were drawn before (rest) and after exercise (post-exercise) in order to measure human ANF (αh ANF),β-endorphin, plasma aldosterone concentration (PAC) plasma renin activity (PRA) and adreno-cortico trophic hormone (ATCH) by radio-immunological methods. Expired gas was collected during exercise to measure oxygen consumption. On average, the same maximal oxygen consumption ( $$\dot V_{O_{2\max } } $$ ) during exercise was reached by all subjects with and without treatment. Plasma ANF level at rest slightly decreased after administration of Naltrexone; the response to physical exercise was significantly reduced by Naltrexone. There was no statistical difference between plasma levels ofβ-endorphin, PRA and ACTH at rest nor in the post-exercise situation under the influence of Naltrexone. The PAC increased significantly at rest after Naltrexone administration but there was no statistical difference between both values after exercise. These data demonstrate that: (1) ANF secretion during exercise is influenced by the level ofβ-endorphin in the plasma; (2) the possible inhibitory role of ANF on aldosterone secretion during exercise is probably over-ruled by the increase in plasma ACTH and PRA.
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  • 3
    ISSN: 1439-6327
    Keywords: Anaerobic threshold ; EMG signal ; Lactate metabolism ; Mean power frequency ; Incremental exercise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The surface electromyogram (EMG) from the vastus lateralis muscle and the metabolic and respiratory parameters were studied simultaneously during an incremental exercise in order to identify EMG signal modifications during the aerobic-anaerobic transition. Subjects performed an incremental test on the bicycle ergometer from an initial work load of 175 W to exhaustion by steps of 25 W. Ventilatory flow ( $$\dot V$$ E), oxygen uptake ( $$\dot V_{O_2 } $$ ) and carbon dioxide flow ( $$\dot V_{{\text{CO}}_{\text{2}} }$$ ) were recorded continuously. For lactate concentration determination, venous blood samples were collected during the final 30 s of each step. EMG signals were stored on magnetic tape. They were then converted into successive spectra to allow the study of EMG total power (PEMG) and mean power frequency (MPF) evolutions. A non linear increase in blood lactate reflected by a breaking point at 250 W was observed. A change in $$\dot V_E /\dot V_{O_2 } $$ ratio occured at 275 W. PEMG value showed a non linear increase reflected by a breaking point at 275 W. MPF value increased from the first to the seventh step with a tendency to decrease at the last step. A great interindividual variance of EMG data was observed indicating the difficulty of correlating mean values of EMG parameters with mean values of blood lactate in order to explain sudden lactate increase by fast twitch fibre recruitment. However, comparison of individual EMG data suggests a progressive recruitment of fast twitch fibres as work load increases.
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  • 4
    ISSN: 1439-6327
    Keywords: Glucose and fat feeding ; Glycogen sparing ; Ketone bodies ; Insulin ; Lipolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The purpose of this study was to test the hypothesis that oral ingestion of lipids could increase endurance by slowing the rate of glycogen depletion. Trained rats were killed after a 2 h run on a rodent treadmill, following an intragastric infusion of water, glucose, medium chain triglycerides (MCT) or long chain triglycerides (LCT). Glucose and triglycerides were administered in equicaloric concentrations (50 kJ). The results show that oral ingestion of lipids (MCT or LCT) did not reduce glycogen depletion in liver, heart or skeletal muscle after exercise whereas the fat diet increased muscle and heart glycogen stores in resting conditions. In contrast, glucose feeding induced a significant sparing effect on endogenous carbohydrate utilization and reduced physical exercise lipolysis. These data indicated, firstly, that enhanced lipid availability induced by a single lipid meal before exercise was not able to modify the glycogen depletion occuring after exercise and, secondly, that the glucose/fatty acid cycle was not effective in these conditions. The comparison between lipids indicated that the effect on glycogen use of MCT did not differ from that of LCT, and did not seem to be of any particular importance during physical exercise.
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  • 5
    ISSN: 1439-6327
    Keywords: Skeletal muscle ; Pyridine nucleotide fluorescence ; Nondestructive oxidative metabolism monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The aim of the present study was to use nicotinamide adenine dinucleotide phosphate, reduced (NADH) fluorimetry, to investigate in situ NADH changes during muscle contraction in humans on an isokinetic dynamometer. Thirteen healthy male subjects each performed one maximal voluntary contraction (MVC) with the knee extensor muscle. The NADH muscle fluorescence was monitored by a double beam laser fluorimeter which uses an optical fibre, percutaneously inserted through a needle into the vastus lateral muscle, to guide the light. The NADH fluorescence was continuously measured at a wavelength of 337 nm. To estimate the haemodynamic artefact, blood backscattering was simultaneously determined at a wavelength of 586 nm. The fluorescence signal was recorded before, during and after contractions at 50% of MVC. The fibre was kept out of contact with the muscle during contractions at 100% of MVC and was only put into contact with it at the end of the contraction. At the onset of contractions at 50% of MVC, NADH fluorescence increased rapidly for 3 s and remained stable thereafter until exhaustion. After a muscle measurement had been made, the optical fibre was put successively into solutions of increasing NADH concentration to ascertain the relationship between the muscle fluorescence signal and the muscle NADH level. This procedure yielded estimated mean values for muscle NADH of 0.172 mmol · kg−1, SEM 0.028 and of 0.184 mmol·kg−1 SEM 0.027 after contractions at 50% and 100% of MVC, respectively, from a resting value of 0.087 mmol·kg−1, SEM 0.015. These results indicated that in situ laser fluorimetry could be used to evaluate NADH changes in humans during muscle contraction. The early increase in NADH at the onset of muscle contraction suggested that metabolic factors other than local hypoxia were involved in the NADH increase during contraction. The comparison between contractions at 50% and 100% of MVC suggested that the NADH concentration was increased maximally within the first seconds of a submaximal muscle contraction.
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  • 6
    ISSN: 1439-6327
    Keywords: Fat and protein feeding ; Glucose feeding ; Glycogen resynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This study examined the effect on glycogen resynthesis during recovery from exercise of feeding glucose orally to physically trained rats which had been fed for 5 weeks on high-protein low fat (HP), high-protein/long-chain triglyceride (LCT) or high carbohydrate (CHO) diets. Muscle glycogen remained low and hepatic gluconeogenesis was stimulated by long-term fat or high-protein diets. The trained rats received, via a stomach tube, 3 ml of a 34% glucose solution immediately after exercise (2 h at 20 m · min−1), followed by 1ml portions at hourly intervals until the end of the experiments. When fed glucose soleus muscle glycogen overcompensation occurred rapidly in the rats fed all three diets following prolonged exercise. In LCT- and CHO-fed rats, glucose feeding appeared more effective for soleus muscle repletion than in HP-fed rats. The liver demonstrated no appreciable glycogen overcompensation. A complete restoration of liver glycogen occurred within a 2- to 4-h recovery period in the rats fed HP-diet, while the liver glycogen store had been restored by only 67% in CHO-fed rats and 84% in LCT-fed rats within a 6-h recovery period. This coincides with low gluconeogenesis efficiency in these animals.
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  • 7
    ISSN: 1439-6327
    Keywords: Myosin light chains ; Muscle ; Physical exercise ; Hindlimb suspension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The purpose of this study was to ascertain the time course of changes, whilst suspending the hindlimb and physical exercise training, of myosin light chain (LC) isoform expression in rat soleus and vastus lateralis muscles. Two groups of six rats were suspended by their tails for 1 or 2 weeks, two other groups of ten rats each were subjected to exercise training on a treadmill for 9 weeks, one to an endurance training programme (1-h running at 20 m · min−1 5 days · week−1), and the other to a sprint programme (30-s bouts of running at 60 m · min−1 with rest periods of 5 min). At the end of these experimental procedures, soleus and vastus lateralis superficialis muscles were removed for myosin LC isoform determination by two-dimensional gel electrophoresis. Hindlimb suspension for 2 weeks significantly increased the proportion of fast myosin LC and decreased slow myosin LC expression in the soleus muscle. The pattern of myosin LC was unchanged in the vastus lateralis muscle. Sprint training or endurance training for 9 weeks increased the percentage of slow myosin LC in vastus lateralis muscle, whereas soleus muscle myosin LC was not modified. These data indicate that hindlimb suspension influences myosin LC expression in postural muscle, whereas physical training acts essentially on phasic muscle. There were no differences in myosin LC observed under the influence of sprint- or endurance-training programme.
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  • 8
    ISSN: 1439-6327
    Keywords: Growth hormone ; Hindlimb suspension ; Muscle atrophy ; Pituitary-intact rats ; Soleus muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 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 (CGH, 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 CGH (+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). The activity of 3-hydroxyacyl coenzyme A dehydrogenase was enhanced by the rhGH treatment (P〈0.05) with similar magnitude in both C (+25%) and HS rats (+24%). Therefore, GH prevented only slightly the atrophy of SOL, occurring after 21 days of HS. The effects of rhGH treatment appeared most effective in C rats, suggesting that HS impaired the growth-promoting effects of this hormone on skeletal muscle.
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  • 9
    ISSN: 1439-6327
    Keywords: Triathlon ; Oxygen uptake ; ventilation ; Biochemical variables ; Plasma volume
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The purpose of the present study was to verify the increase in energy cost of running at the end of a triathlon. A group 11 trained male subjects performed a triathlon (15-km swimming, 40-km cycling, 10-km running). At least 1 week later the subjects ran 10-km as a control at the same pace as the triathlon. Oxygen uptake ( $$\dot V$$ O2), ventilation ( $$\dot V$$ E) and heart rate (HR) were measured during both 10-km runs with a portable telemetry system. Blood samples were taken prior to the start of the triathlon and control run, after swimming, cycling, triathlon run and control run. Compared to the control values the results demonstrated that triathlon running elicited a significantly higher (P 〈 0.005) mean $$\dot V$$ O2 [51.2 (SEM 0.4) vs 47.8 (SEM 0.4) ml·min−1·kg−] $$\dot V$$ E [86 (SEM 4.2) vs 74 (SEM 5.3) l·min−1], and HR [162 (SEM 2) vs 156 (SEM 1.9) beats·min−1)]. The triathlon run induced a greater loss in body mass than the control run [2 (SEM 0.2) vs 0.6 (SEM 0.2) kg], and a greater decrease in plasma volume [14.4% (SEM 1.5) vs 6.7% (SEM 0.9)]. The lactate concentrations observed at the end of both 10-km runs did not differ [2.9 (SEM 0.2) vs 2.5 (SEM 0.2) m·mol·l−1]. Plasma free fatty acids concentrations were higher (P 〈 0.01) after the triathlon than after the control run [1.53 (SEM 0.2) to 0.51 (SEM 0.07) mmol·l−1]. Plasma creatine kinase concentrations rose under both conditions from 58 (SEM 12) to 112 (SEM 14) UI·l−1 after the triathlon, and from 61 (SEM 7) to 80 (SEM 6) UI·l−1 after the control run. This outdoor study of running economy at the end of an Olympic distance triathlon demonstrated a decrease in running efficiency.
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  • 10
    ISSN: 1439-6327
    Keywords: Key words Unloading  ;  Degeneration  ;  Muscle regeneration  ;  Muscle fibre necrosis  ;  Myosin heavy chain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 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° 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 MHC 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.
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