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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transformation of the latissimus dorsi (LD) muscle from a fast-twitch, fatigue-prone to a fatigue-resistant ("heart-like") muscle, necessary to allow its application in cardiac assist devices, can be induced by chronic electrical stimulation. In adult dogs we studied the nature and time course of myofibrillar and metabolic adaptations in the LD muscle when exposed in situ to 24 weeks of continuous electrical stimulation. In addition, the metabolic properties of the stimulated muscle were compared with those of canine cardiac muscle. The proportion of immunohistochemically identified type I fibres increased on stimulation from 28% to 80%, while that of type II fibres decreased from 69% to 16%. Fibres of intermediate type (IIC and IC) appeared transiently; the highest levels were found between 4 and 8 weeks of stimulation. The activities of fructose-6-phosphate kinase and lactate dehydrogenase (LDH), which before stimulation were similar to those in heart, decreased to 18% and 34% of their initial values respectively. However, the LDH isozyme pattern changed towards that typical for cardiac muscle. These changes indicate a markedly decreased flux capacity through the glycolytic pathway which, however, is directed more towards the oxidative conversion of substrates. The mitochondrial capacity (maximal palmitate oxidation and pyruvate dehydrogenase complex activities) of the muscle did not change and remained at a level less than half of that of cardiac ventricular muscle. Contents of adenine nucleotides and endogenous substrates were maintained during stimulation. No further changes in the observed adaptations occurred after week 12 of stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Adaptation of energy metabolism of canine latissimus dorsi muscle in response to chronic electrical stimulation. 155 54

Skeletal muscle possesses inherent plasticity of gene expression. Low frequency pulse-train stimulation can remodel the biochemical machinery that confers physiological expression and fatigue resistance approaching that of the myocardium. This fatigue-resistant muscle can generate sufficient force to meet the power requirements for useful cardiac work. This ultimate goal is currently being pursued in models of cardiomyoplasty and muscle-powered cardiac assist devices. In this article, we review the three major subcellular systems subserving canine skeletal muscle transformation and compare them to those of cardiac muscle. The magnitude of the problem of clinical heart failure and the feasibility of fatigue-resistant skeletal muscle joining the therapeutic armamentarium are addressed. The adaptation and transformation of fast-twitch skeletal muscle in response to chronic electrical stimulation augers therapeutic potential as an endogenous, readily available power source for myocardial assistance. The basis mechanisms of skeletal muscle fatigue require elucidation to gain a complete and thorough understanding of how to manipulate this property to provide continuous hemodynamic work.
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PMID:The remodelling of skeletal muscle for indefatigable hemodynamic work. 205 39

A 61-year-old woman with low grade obesity index complained of general fatigue. Cardiomegaly had been present since the age of 45. According to a roentgenogram on admission, her cardia-thoracic ratio was 61%. Pericardial effusion was strongly suspected because of extra echo spaces on both posterior and anterior walls, and unsynchronized echocardiograph waves of epicardium and pericardium. However, values of dynamic CT measured at areas equivalent to the extra echo spaces were -120. On admission, T1-emphasized MRI image showed a high signal density in those areas. After significant weight reduction, the abnormal values and signs of the clinical examinations, as well as the patient's complaints were attenuated or disappeared. Together with these results, cardiomegaly of the patient was diagnosed to be due to excessive fat deposit between the epicardium and cardiac muscle. Dissociation between mildness of obesity index and excessive deposition of fat in the pericardium was discussed from the point of view of body mass index and time course of fat deposition.
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PMID:[A case of mild obesity accompanied by epicardial fat deposition]. 214 82

Skeletal muscles, such as the latissimus dorsi muscle, can be transformed to gain considerable fatigue resistance to be suitable either for cardiomyoplasty, or to power a cardiac assist device. Such transformation of the skeletal muscle can be achieved by low frequency electrical stimulation for several weeks. In this article, we reviewed the stimulation protocol, and subsequent histochemical, biochemical, and functional changes in the skeletal muscle, and compared them to those of the cardiac muscle. The parameters that should be useful for stimulating such a muscle to assist the heart are defined. The issues currently under study, including the optimal transformation parameters, the feasibility of working transformation, and the importance of device design to minimize vascular compromise of the muscle, are also discussed. It is concluded that there is a great potential to use the plasticity of skeletal muscle for clinical purposes, specifically by transforming the skeletal muscle to resemble the myocardium in order to use it either to replace or repair the myocardium, or as the endogenous power source for a cardiac assist device.
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PMID:Biochemical and functional correlates of myocardium-like transformed skeletal muscle as a power source for cardiac assist devices. 251 95

1. Maximal calcium-activated force (Fmax) and calcium sensitivity were markedly decreased in detergent-skinned fibres from skeletal and cardiac muscle by solutions that mimicked the total milieu changes associated with fatigue and hypoxia. Further experiments determined the relative contribution of each of the individual changes in milieu. 2. Both Ca2+ sensitivity and Fmax of skeletal and cardiac fibres were decreased with increased [H+] or inorganic phosphate (Pi). These effects were greater in cardiac muscle. 3. Decreasing MgATP over the range observed with fatigue and hypoxia (6.8-4.7 mM) had no effect on Fmax or Ca2+ sensitivity of either muscle type. 4. Decreasing phosphocreatine (PCr: 15-1 mM) increased Fmax but had little effect on Ca2+ sensitivity in both muscle types. In cardiac fibres, the effect on Fmax could be mimicked by inhibition of endogenous creatine kinase. 5. ADP (0.7 mM) increased Fmax and Ca2+ sensitivity, while AMP (0.06 mM) slightly increased Fmax but had no effect on Ca2+ sensitivity of either skeletal or cardiac fibres. 6. Creatine (25 mM) had no significant effect on either Ca2+ sensitivity or Fmax of skeletal and cardiac muscle fibres. At higher levels (50 mM), however, creatine depressed Fmax and slightly altered Ca2+ sensitivity. 7. Thiophosphorylation of myosin P light chains (phosphorylatable light chains of myosin) in rabbit psoas fibres had no effect on Ca2+ sensitivity, yet slightly but significantly increased Fmax under fatigue conditions. 8. Reducing the affinity for ATP hydrolysis (by adding ADP, AMP and creatine) over the range calculated for fatigue/hypoxia (60-45 kJ/mol) produced the enhancement in Fmax expected from added ADP and AMP in cardiac but not skeletal muscle, indicating that changes in affinity influence Fmax of skeletal muscle. Reducing affinity produced little change in Ca2+ sensitivity of skeletal muscle. In contrast, the change produced in cardiac muscle was greater than that expected from addition of ADP and AMP; i.e. decreasing affinity increases calcium sensitivity of the heart. 9. Simple summation of all significant changes expected from each constituent altered by fatigue/hypoxia adequately predicted the observed changes in Fmax and Ca2+ sensitivity in both cardiac and skeletal muscle fibres with but one exception (the change in Ca2+ sensitivity of skeletal muscle at pH 7 was slightly overestimated).
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PMID:Changes of intracellular milieu with fatigue or hypoxia depress contraction of skinned rabbit skeletal and cardiac muscle. 260 Aug 30

The effect of Na-octanoate (NaC8) on the development of twitch and tetanic tension of a striated muscle (m. longitudinalis linguae) of Lampetra fluviatilis was tested at different temperatures. The muscle exhibited posttetanic potentiation as well as cold potentiation similar to other poikilotherme animals. The sensitivity to NaC8 was higher than that of striated frog or rat muscles but similar to that of mammalian smooth or cardiac muscle preparations. A decrease of temperature remarkably reduced the effect of NaC8 on the tension development. Also the fatigue of muscles during tetanic stimulation was smaller if the temperature was lower. It seems that both the process of fatigue and the action of NaC8 are delayed by the cold.
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PMID:Twitch and tetanic contraction of lamprey muscle exposed to fatty acid at different temperatures. 275 28

The neutral alkaloid, ryanodine, has several actions on cardiac muscle. To delineate better its mode of action, we studied ryanodine's effect upon contracting cat papillary muscles under changing loading conditions and stimulation frequencies. We also studied ryanodine's physiologic and metabolic effects upon isolated rat hearts. The results of our study suggest the following: (1) ryanodine causes both decreased release and decreased uptake of calcium by the sarcoplasmic reticulum; (2) elevation of high-energy phosphates secondary to decreased energy requirements is due to decreased calcium availability to the myofilaments during systole; (3) the slowed or incomplete relaxation caused by ryanodine may be a stimulus for myosin phosphorylation; (4) ryanodine probably decreases calcium movement through the sarcolemma and so increases adenosine and inorganic phosphate and decreased cyclic adenosine monophosphate (AMP) concentration in the myocardium; and (5) the effect of ryanodine on altered loading conditions and contraction velocities can be understood in terms of decreased calcium availability to the myofilaments.
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PMID:Effects of ryanodine on cat papillary muscle and isolated rat heart. 299 60

Relaxation of rat diaphragm was shown to be sensitive to load, as previously described for adult mammalian ventricular muscle, because the time course of isotonic relaxation could be changed by changing the load: the lighter the load, the greater the shortening, the quicker the relaxation. Maximum velocity of isotonic relaxation was linearly related to the extent of shortening (r = 0.90). To quantify the degree of load sensitivity, we measured the tRi, i.e., the ratio of time at which the isometric relaxation of the twitch afterloaded at 50% of the isometric peak active tension began to time at which the isometric twitch was relaxed to 50% of the isometric peak active twitch tension. tRi was 0.76 +/- 0.03 (SE) in control conditions but significantly increased to 0.91 +/- 0.02 after ryanodine, which is an inhibitor of the sarcoplasmic reticulum (SR) function, and to 0.89 +/- 0.03 after fatigue. These results suggest that in adult rat diaphragm, as in cardiac muscle, the load sensitivity of relaxation requires a well-functioning SR and that the relaxation abnormalities observed in fatigued diaphragm are related to a dysfunction of the SR.
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PMID:Relaxation of the diaphragm muscle: influence of ryanodine and fatigue. 320 44

Chronic stimulation converts skeletal muscle of mixed fiber type to a uniform muscle made up of type I, fatigue-resistant fibers. Here, the bioenergetic correlates of fatigue resistance in conditioned canine latissimus dorsi are assessed with in vivo phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy. After chronic electrical stimulation, five dogs underwent 31P-NMR spectroscopic and isometric tension measurements on conditioned and contralateral control muscle during stimulation for 200, 300, 500, and 800 ms of an 1,100-ms duty cycle. With stimulation, phosphocreatine (PCr) fell proportional to the degree of stimulation in both conditioned and control muscle but fell significantly less in conditioned muscle at all but the least intense stimulation period (200 ms). Isometric tension, expressed as a tension time index per gram muscle, was significantly greater in the conditioned muscle at the two longest stimulation periods. The overall small change in PCr and the lack of a plateau in tension observed in the conditioned muscle are similar to that seen in cardiac muscle during increased energy demand. This study indicates that the conditioned muscle's markedly enhanced resistance to fatigue is in part the result of its increased capacity for oxidative phosphorylation.
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PMID:In vivo 31P-NMR spectroscopy of chronically stimulated canine skeletal muscle. 334 65

Our previous work showed that myosin phosphorylation decreased the ATPase activity of skeletal muscle myofibrils that were lightly fixed with glutaraldehyde. The fixation process prevented sarcomere shortening and destruction of the ordered filament array upon the addition of ATP. We have now extended these results to myofibrils prepared from hearts of rabbits, dogs and rats. Myofibrils were phosphorylated by incubation with myosin light chain kinase, calmodulin and either ATP-gamma s or ATP, for 15 minutes at 25 degrees C. The extent of myosin light chain phosphorylation was 50% to 80%. The ATPase activity of unphosphorylated myofibrils was not altered by reaction with 0.01% glutaraldehyde for 5 minutes at 0 degrees C, and the ATPase activity of unfixed myofibrils was not changed by phosphorylation. However, phosphorylation decreased the ATPase activity of fixed myofibrils by 50%. The effect on myocardial myofibrillar ATPase activity of phosphorylation was similar in the three animal species. These results suggest that in both skeletal and cardiac muscle, myosin phosphorylation decreases the rate of cross-bridge cycling resulting in decreased energy expenditure. It also appears that the effect of myosin light chain phosphorylation on ATPase activity requires an ordered myofilament structure.
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PMID:Myosin phosphorylation decreases the ATPase activity of cardiac myofibrils. 623


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