摘要:

Five male endurance‐trained subjects performed exhaustive exercise on a cycle ergometer at a work rate corresponding to 75% of their Vo2maxafter reduction of their muscle glycogen stores. During exercise the subjects were given in random order a 6% carbohydrate solution contining 7 g L‐1of branched‐chain amino acids (BCAA), a 6% CHO solution and flavoured water. The physical performance was lowered in four of the five subjects when they were given flavoured water during exercise as compared with the two conditions when CHO was supplied. No difference in performance was found when the subjects were given CHO+BCAA or only CHO during exercise. When CHO+BCAA was supplied the plasma and muscle (vastus lateralis) concentrations of BCAA increased during exercise by 120 and 35%, respectively. In the other conditions there was no change or a slight decrease in the plama concentrations of BCAA, but the muscle concentrations of BCAA were decreased after exercise. The plasma concentration of glutamine over the whole exercise period and 5 min after exercise was higher when CHO+BCAA were supplied during exercise compared with a supply of CHO alone or water. However, exercise caused no change in the muscle concentration of glutamine, whereas that of glutamate decreased in all three conditions. A supply of CHO+BCAA or CHO alone did not affect the exercise‐induced increase in the plasma and muscle concentration of aromatic amino acids, indicating that neither BCAA nor CHO influenced the net protein degradation during e

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09839.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The possible alteration of metabolism of the m. vastus medialis was investigated during exercise after eccentric loading. Twelve male subjects performed stepping exercise for 25–60 min. One week before and 24 h after stepping they performed concentric leg exercise at stepwise increasing intensity, while power output was measured. During this concentric exercise and recovery therefrom, phosphorous metabolites were also measured in the m. vastus medialis with magnetic resonance spectroscopy. Creatine kinase and myoglobin in blood were measured before and 72 h after stepping. T1 and T21H‐relaxation times for water were calculated from magnetic resonance images collected 72 h after stepping, and used as measures for oedema. The subjects perceived substantial soreness from 24 to 72 h after stepping. The ratio of inorganic phosphate over phosphocreatine at rest increased from 0.12± 0.02 (before) to 0.19± 0.04 (24 h after stepping) (P<0.05). Creatine kinase activity was slightly elevated 72 h after stepping (71 [49–812] U L‐1[median, range]; P<0.05) compared with baseline values (58 [26–409] U L‐1), whereas myoglobin concentration was not significantly elevated (15 [8–120] μg L‐1compared with 8 [8–41] μg L‐1). In the eccentrically exercised muscles, T1 and T2 values were not or only slightly higher than in the concentrically exercised contralateral muscles. The relation between power and the ratio of inorganic phosphate over phosphocreatine during concentric exercise, and the recovery data for inorganic phosphate, phosphocreatine and pH did not alter after stepping. These data suggest that quadriceps metabolism during concentric exercise and recovery therefrom is not affected by prior eccentric overload, but it cannot be excluded that metabolism will alter during exercise after more strenuous p

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09840.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The effects of 4 weeks of thyroid hormone (3,5,3′‐triiodothyronine, T3) treatment on the myosin heavy chain (MHC) composition were compared in the slow‐twitch soleus and the fast‐twitch extensor digitorum longus (EDL) muscles from young (3–6 months) and old (20–24 months) male albino rats. Four MHC isoforms were separated on silverstained 6% sodium dodecyl sulphate polyacrylamide gel electrophoresis. According to immunoblotting experiments with specific MHC monoclonal antibodies, the four MHCs corresponded to types I, IIB, IIX and IIA. In the soleus, the type I MHC content was higher in the old than in the young animals, and the type IIA content lower. Type IIX myosin was observed in some young control soleus, but not in old ones. After T3treatment, the content of type I MHC decreased substantially in both young and old animals and that of type IIA increased. After T3treatment, type IIX myosin was observed in both young and old animals, with a slighty higher IIX myosin content in old age, but the age‐related different in the contents of types I and IIA was diminished. In EDL, the type IIX MHC content was significantly higher in the old animals, at the significantly by T3treatment in EDL, either in young or old animals. In conclusion, an age‐related motor unit transformation is observed in both the slow‐twich soleus and the fast‐twitch EDL and the capacity for MHC isoform switching in response to T3treatment is not

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09841.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The purpose of this study was to evaluate the specificity of maximal oxygen uptake (Vo2max) and the dynamic response of oxygen uptake (Vo2) to sinusoidal work load in distance runners and in American‐football players. Sinusoidal work load during ergometer cycling was carried from 30 W to 60% toVo2max(60% Vo2max) for a 2 min period. Vo2was measured by the breath‐by‐breath method. The subjects were 10 distance runners (DRs), 10 American‐football players (AFPs), and 11 untrained men (UTM). Mean Vo2maxwas 64.4 mL kg‐1min‐1in the DRs, 53.1 mL kg‐1min‐1in the AFPs and 47.3 mL kg‐1min‐1in the UTM. The fundamental amplitudes ofthe Vo2response, nomalized by dividing by steady state Vo2at 60% Vo2maxwere similar in the AFPs (20.3%) and the UTM (19.5%), and both were significantly less than in the DRs (25.5%). Phase shift to work load expressed in degrees was similar in the AFPs (87.7d̀) and UTM (88.0d̀), but significantly greater than in the DRs (80.4d̀). HR dynamics in all three groups were similar to a dynamicVo2response. These findings suggest that development of the dynamicVo2response and higherVo2maxin the AFPs there is no improvement in the dynamicVo2response. The results of the present study demonstrate that athletes participating in different sports have characteristic dynamicVo2responses d

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09842.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The recent use of spectral analysis of the R‐R interval variability to assess the autonomic drive during exercise has produced inconsistent results. The purpose of this study was to assess whether the spectral components of the R‐R interval variability reflect different mechanisms at rest and during exercise.Autoregressive spectral analysis of the electrocardiographic and breathing signals was performed in 11 healthy young men at rest and during incremental cycle ergometry. The amplitude of respiratory sinus arrhythmia, i.e. the absolute power of the high frequency spectral component, fell at the onset of exercise, consistent with a reduction in cardiac vagal activity. Conversely, the normalized power of the high frequency component, (i.e. the percentage of R‐R interval variance due to the respiratory sinus arrhythmia) increased with increasing work rates. The low frequency spectral component of the R‐R interval variability, which when expressed in normalized units is believed to reflect cardiac sympathetic activity, was no longer detectable in severe exercise when the adrenergic drive is known to be elevated.In conclusion, autoregressive spectral analysis of the R‐R interval variability does not adequately reflect the autonomic changes that occur during incremental exercise. In particular, the evidence indicates that as the cardiac vagal tone falls with increasing levels of exercise, a greater percentage of the residual power of the high frequency component may be due to non‐neural

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09843.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Several parameters of excitation‐contraction coupling were compared in two types of muscle, using thin strips from the left atria and papillary muscles from the right ventricles of guinea‐pigs. (1) The duration of the action potential and twitch is much longer in ventricular than in atrial muscle. (2) Mechanical restitution can usually be described by a monoexponential function in ventricular and biexponential function in atrial muscle. (3) Post‐extrasystolic potentiation, when related to the steady state force, is greater in ventricular muscle. (4) When priming with paired‐pulse stimulation, mechanical restitution can be studied after the short interval and after the long interval. In atrial muscle, mechanical restitution is very similar after the short and long intervals but in ventricular muscle they are different in size. (5) Ryanodine (10‐6M) can decrease the steady state force to about 10% of control in atrial but only to about 35% in ventricular muscle. Ryanodine (10‐8M) causes the slow phase of restitution in atrial muscle to disappear but in ventricular muscle only increases the rate of mechanical restitution. (6) Ca‐antagonists (Cd2+0.2 mM) can decrease the steady state force to zero in atrial and ventricular muscle. Ca‐antagonists, in low concentrations (Cd2+0.01 mM), mainly affected the fast phase of mechanical restitution. (7) The recirculation fraction of calcium was about 0.64 in atrial and 0.27 in ventricular muscle.The findings are discussed in the light of known ultrastructural differences between atrial and ventric

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09844.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A possible interrelation between IP3and cAMP was studied in rat myocardium through circumvention of the receptor mediated stimulatory step of adenylyl cyclase by the administration of dibutyryl cAMP (db‐cAMP). Changes in IP3and cyclic nucleotide contents were correlated to changes in contractility after 40 min ofβ‐ andα‐adrenergic stimulation. Rat hearts (n= 23) were perfused with Krebs‐Henseleit buffer in a modified Langendorff apparatus as a working preparation. The hearts were allocated to perfusion as control (n= 6); or with phenylephrine (10‐6mol L‐1,n= 6); (—)‐isoproterenol (10‐6mol L‐1,n= 6); db‐cAMP (2 times 10‐4mol L‐1,n= 5). All hearts were freeze‐clamped after 40 min of perfusion. Phenylephrine produced a slow increase inmaxdP/dtreaching a maximal value after 10 min (P<0.05); thereafter it decreased, reaching the control level at 30 min. Isoproterenol perfusion resulted in an early (20 s) increase inmaxdP/dt(P<0.05). Over the next 10 smaxdP/dtdecreased markedly reaching an inflection point at 30 s. Thereafter only a slow increase during the rest of the perfusion was seen. Dibutyryl cAMP increasedmaxdP/dtslowly during the whole perfusion period reaching maximum after 40 min. Cyclic‐AMP was increased by 21% after 40 min of phenylephrine perfusion while the corresponding increases by isoproterenol and db‐cAMP were 131 and 105%, respectively (P<0.05). Phenlyephrine increased IP3content to the same extent as isoproterenol perfusion (P<0.05). On the other hand, a decreased IP3content was seen at 40 min of db‐cAMP perfusion. Cyclic‐AMPper sedepressed basal myocardial IP3content in myocardial tissue. Despite normalization of contractility after 40 min of phenylephrine perfusion the IP3content was 27% higher than in control hearts pointing out the unclearness of the relationship between myocardial

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09845.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The interrelated responses of concomitant adrenergic and muscarinic receptor stimulation on second messengers and mechanical activity in the isolated perfused working rat heart were studied. The hearts were perfused with Krebs‐Henseleit buffer in a modified Langendorff apparatus. The hearts were perfused with noradrenaline (10‐6mol L‐1,n= 20), with carbachol (3 times 10‐7mol L‐1n= 11) or with noradrenaline plus carbachol (n= 20) in the above‐mentioned concentrations. The hearts were frozen at 20 s, 30 s and 40 min after addition of noradrenaline and noradrenaline plus carbachol and at 20 s and 40 min after addition of carbachol. Five hearts were freeze‐clamped directly after preperfusion and another five hearts after 40 min of perfusion and used as controls. Myocardial cAMP increased at 20 s and 40 min after noradrenaline perfusion. In contrast to this cAMP was unchanged at 20 s and decreased at 40 min after perfusion with noradrenaline plus carbachol. IP3content increased after 20 s of carbachol‐ and after 40 min of noradrenaline perfusion (P<0.05). However, noradrenaline plus carbachol did not induced any significant increase in IP3content after 20 s and 30 s, but after 40 min a decrease below basal level was found (P<0.05). Noradrenaline stimulation attenuated muscarinic agonist induced IP3formation. A reciprocity existed in that noradrenaline induced IP3formation was attenuated by carbachol. No direct relationship was observed between the IP3response and contractility, also valid for cAMP. Hence, a significant increase in contractility was found in spite of a blunted cAMP response probably not accounted for by an anα1‐adren

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09846.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The question addressed in this study was whether a relation between myocardial lipid droplet accumulation and depressed myocardial function existed following intralipid infusion for 45 min in open chest, anaesthetized rabbits. One group of rabbits (n = 8) received intralipid infusion whereas a control group (n = 8) received sodium chloride. Local myocardial performance was obtained by sonomicrometry and the fractional volume of myocardial lipid droplets was measured by morphometric methods. The fractional volume of lipid droplets was 0.667 ± 0.1160% in the intralipid group compared with 0.318 ± 0.080% in the control group (P<0.03). Cardiac output and stroke volume fell 26% (P<0.0001) and 34% (P<0.000), respectively, as a result of intralipid infusion. However, myocardial blood flow obtained by radiolabelled microspheres remained unchanged. Local myocardial function was reduced for both segments after intralipid infusion; maximal systolic shortening was reduced from 15.63 ± 1.45 to 12.07 ± 1.55% (P<0.002) in the circumferential segment and from 9.46 ± 1.17 to 7.40 ± 0.53% (P<0.05) in the longitudinal segment. The end‐diastolic length of the circumferential segment was reduced by 3% (P<0.05) after intralipid infusion. The reduced end‐diastolic length of circumferential segments together with unchanged left ventricular end‐diastolic pressure might indicate reduced left ventricular end‐diastolic compliance. We conclude that acute intralipid infusion in rabbits results in myocardial lipid droplet accumulation and depressed local myocar

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09847.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Spontaneously hypertensive rats (SHR) and normotensive Wistar‐Kyoto (WKY) rats that had been on a low sodium diet for 3 days were given 1.5 mmol sodium chloride kg‐1body weight either orally or intravenously. The rats receiving an oral sodium load showed a greater natriuresis than those receiving the same saline load intravenously. No increase of renal sodium excretion was observed when the rats received a hypertonic mannitol solution orally. The cumulative sodium excretion during the 8 h following oral loading was two to three times larger in SHR than in WKY, whereas no difference between strains could be demonstrated after giving saline intravenously. Furthermore, after switching from normal to low sodium diet the rate of decrease of renal sodium excretion was greater in SHR than in WKY rats. It is proposed that there exists a gastrointestinal sensory mechanism for sodium controlling the renal sodium excretion. Furthermore, it is suggested that the function of this mechanism differs between SHR and

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09848.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY