Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rabbits were immunized versus either an acetylcholinesterase- or a cholinergic receptor-rich fraction isolated from the electric organ of Torpedo marmorata. In both groups of animals we obtained a production of specific antibodies detected by immunodiffusion without cross reaction for the two antigens. Only rabbits immunized with the receptor-rich fraction developed a progressive flaccid paralysis, which affected first the leg muscles, progressively the neck muscles and eventually the respiratory muscles. The paralysis lasted in several animals up to 20 days. Eserine reversed the paralysis only in the first days but was ineffective in the "chronic" stage of the disease. In these animals high frequency stimulation of sciatic nerve induced a rapid failure of the responses of the anterior tibialis muscle while the muscle responded normally to a direct stimulation. A period of rest allowed a complete recovery of the muscle from fatigue. Tetani did not evoke the post-tetanic potentiation. Abnormalities, such as lymphocytic infiltration, fibers atrophy and necrosis, smearing and widening of Z line were sometimes present in muscles of Cho-R-immunized rabbits. In ACh-E immunized animals the neuromuscular transmission and the muscle morphology were similar to that of normal animals. Glycogen, ATP, cytochrome C oxidase, phosphorylases and acetylcholinesterase did not change significantly in the muscles of the immunized animals, while a large increase of cholineacetyltransferase activity was present. Red blood cell acetylcholinesterase showed a particularly high activity in ACh-E-immunized animals. The autoimmune paralysis induced in Cho-R-immunized rabbits may be a useful experimental model for further studies on human myasthenia gravis.
 ...
PMID:Immunization of rabbits with secific components of postsynaptic membrane. Acetylcholinesterase and cholinergic receptor. 18 67

1. The properties of fifty-seven motor units in human medial gastrocnemius have been studied using controlled intramuscular microstimulation, glycogen depletion and muscle biopsy. 2. Motor units could be divided into three classes on the basis of their mechanical properties. Type S units were slow, small and fatigue resistant. Type FR units were fast, intermediate in size, and fatigue resistant. Type FF units were fast, large and fatigable. 3. Glycogen depletion of a number of type S and FF units revealed them to be composed of type 1 and type 2b muscle fibres respectively. 4. The results suggest that during slowly increasing voluntary contractions where units are recruited in order of size, type 1 and 2a muscle fibres would be employed at low force levels followed by type 2b muscle fibres in stronger contractions.
 ...
PMID:Motor unit organization of human medial gastrocnemius. 43 Apr 14

During studies of the regulation of phosphorylase activity and glycogenolysis in contracting muscle, it was found that conversion of phosphorlyase beta to alpha is transient. Reversal of phosphorylase activation during both continuous and intermittent stimulation in the plantaris might, in part, have been due to development of fatigue. However, a complete reversal of phosphorylase activation was also evident within 5 min in the absence of fatigue in soleus muscles stimulated tetanically with 100-ms-long trains at a rate of 60/min. These muscles showed no significant decline in contractile force. Glycogen breakdown stopped in the soleus when phosphorylase reverted to the beta form, providing evidence that phosphorylase beta was not active. This lack of activity is probably explained by the finding that ATP and AMP concentrations changed little, while glucose 6-phosphate increased. Reversal of phosphorlyase activation soon after the onset of steady-state work may be a mechanism for conserving glycogen when the supply of other substrates is adequate to meet the muscles' energy needs.
 ...
PMID:Reversal of phosphorylase activation in muscle despite continued contractile activity. 49 77

The purpose of this study was to determine the influence of diurnal variations of muscle and liver glycogen stores on exercise endurance in male albino rats. Animals were swum to exhaustion at either 0700 or 1900 h, after which samples of soleus, white vastus lateralis, and red vastus lateralis muscles as well as liver were excised and subsequently analyzed for glycogen content. Glycogen content of all tissues from nonexercising control animals was higher in the morning than in the evening. Consequently, animals at 0700 h swam 60% longer than those at 1900 h (209 +/- 20 min vs. 130 +/- 23 min, respectively). However, because the skeletal tissues of the exhausted animals were not totally depleted of glycogen, it was concluded that fatigue under the swim protocol was the result of hypoglycemia secondary to hepatic glycogen depletion. The results of this study demonstrate the physiological consequences of diurnal glycogen fluctuation and establish experimental support for the importance of controlling this variable in rodent exercise investigations.
 ...
PMID:Muscle and liver glycogen content: diurnal variation and endurance. 57 22

With the use of myosin adenosinetriphosphatase (ATPase) and immunofluorescence staining methods, the adaptive responses of intrafusal and extrafusal fibers to endurance swimming were studied in frozen sections of rat soleus (SOL) and extensor digitorum longus (EDL) muscles. Glycogen depletion confirmed muscle fatigue at the end of a standardized bout of exercise. No significant age-dependent changes in myosin isoforms were detected in any fibers. The 12-wk training increased type I fibers by 10.9% in the SOL and type IIa fibers in the EDL by 16.6%. In trained muscle sections, both staining methods identified a permuted chain fiber, expressed the same as the myosin isoform in the bag2 fiber. However, no exercise-induced change of myosin isoform profile was found in the bag1 and bag2 fibers. Myosin ATPase (and immunofluorescence) staining showed the percentage of permuted chain fibers increased from 0 to 6.7% (5.6%) after 6 wk of training and to 19.2% (14.1%) after 12 wk of training and that it was still at 6.1% (4.2%) 10 wks after training. A novel myosin isoform may thus be expressed in nuclear chain fibers by repetitive recruitment of muscle spindles.
 ...
PMID:Novel myosin isoform in nuclear chain fibers of rat muscle spindles produced in response to endurance swimming. 128 26

1. The effects of prolonged exercise on energy metabolism in type I and type II muscle fibres in the vastus lateralis muscle were investigated in six male subjects (20.0 +/- 0.5 years, mean +/- S.E.M.) who performed one-legged cycling at 61% of maximum O2 consumption (VO2,max; determined with one leg) until fatigue or for a maximum of 2 h. 2. Analysis of pools of freeze-dried fibres obtained by needle biopsy and separated into specific types by the myofibrillar ATPase histochemical procedure indicated higher (P less than 0.05) lactate concentrations in type II fibres compared to type I fibres at 15 min (43.9 +/- 9.7 and 51.2 +/- 9.8 mmol (kg dry wt)-1) and at 60 min (18.2 +/- 4.7 and 25.9 +/- 6.5 mmol (kg dry wt)-1). No differences existed in lactate concentration between fibre types for pre-exercise (10.0 +/- 1.6 and 13.3 +/- 2.8 mmol (kg dry wt)-1) or post-exercise. 3. Glycogen degradation was most pronounced in type I fibres. By the end of exercise, glycogen concentration was 82.4 +/- 45 mmol glucosyl units (kg dry wt)-1 in type I fibres and 175 +/- 62 mmol glucosyl units (kg dry wt)-1 in type II fibres. 4. No significant changes in ATP and creatine phosphate (CrP) were found in either fibre type with exercise. 5. It is concluded that, at least for lactate and glycogen, fibre-specific differences are evident in prolonged submaximal exercise. The cause of the difference probably relates both to the unique energy metabolic characteristics of each fibre type and to the manner in which they are utilized during the exercise. 6. The failure to find a reduction in ATP concentration in either fibre type during prolonged exercise in the face of a progressive increase in the number of fibres showing little or no glycogen concentration suggests that protective mechanisms exist that prevent an energy crisis. The nature of these protective mechanisms remains to be elucidated.
 ...
PMID:Energy metabolism in human slow and fast twitch fibres during prolonged cycle exercise. 189 Jun 34

Experimental myotonia was induced in rats by 2,4-dichloro-phenoxyacetic acid (2,4-D). After 4 to 24 h of treatment, the anterior tibialis muscles exhibited increased fatigue at low frequency (30 Hz) nerve stimulation, but they developed normal tension at high-frequency (100 Hz) stimulation. Glycogen content and the activities of glycogen phosphorylase, lactate dehydrogenase and malate dehydrogenase remained normal. The absence of correlation between fatigability and energetic metabolism in this experimental model of myotonia suggests a dysfunction in excitation-contraction coupling.
 ...
PMID:Energetic metabolism and fatigability in experimental myotonia. 215 93

A rat model was used to study the effects of endotoxemic shock in vivo on diaphragmatic tension generation and diaphragmatic metabolism in vitro. Animals were injected with E. coli lipopolysaccharide (30 mg/kg) and killed at fixed times after injection. The hemidiaphragms were isolated in an organ bath, and tension generation was measured during electrical stimulation of the phrenic nerve or diaphragmatic muscle. Diaphragmatic oxygen consumption was measured in vitro during rest and during in vivo stimulation. Adenosine triphosphate and glycogen concentrations were measured in vivo before the animals were killed and in vitro. Tension generation was reduced in a time-dependent fashion after endotoxin at all stimulation frequencies. Both contractile fatigue and transmission fatigue were present. Glycogen stores were reduced but not depleted. ATP concentration was reduced in vivo but recovered in vitro. Diaphragmatic oxygen consumption was reduced in vitro at rest and during stimulation. The results suggest that endotoxemic shock results in diaphragmatic fatigue in a time-dependent fashion, that impaired neural or neuromuscular transmission is present in vitro, and that impaired oxygen consumption in the shocked diaphragm is associated with reduced high-energy-phosphate stores.
 ...
PMID:Diaphragmatic fatigue after endotoxemic shock in rats: in vitro function and metabolism. 221 69

Skeletal muscle adapts to the stress of endurance and sprint exercise and training. There are 2 main types of skeletal muscle fibre--slow twitch (ST) and fast twitch (FTa, FTb, FTc). Exercise may produce transitions between FT and ST fibres. Sprint training has decreased the proportion of ST fibres and significantly increased the proportion of FTa fibres, while endurance training may convert FTb to FTa fibres, and increase the proportion of ST fibres (i.e. FTb----FTa----FTc----ST). However, the high proportion of ST fibres documented for elite endurance athletes may be simply the result of natural selection. ST fibres function predominantly during submaximal exercise, whereas FT fibres are recruited as exercise intensity approaches VO2max and/or glycogen stores are depleted. Long distance runners have greater ST and FT fibre areas than untrained controls. However, doubt remains as to whether the ST or FT fibre area is greatest in endurance athletes. Increases in FT fibre area seem to occur during the first 2 months of training whereas ST fibre areas appear to increase after 2 to 6 months of training. Sprint training leads to the preferential use of FT fibres and male, but not female sprinters have larger FT fibres than untrained controls. Mitochondrial proteins and oxidative enzymes, as opposed to VO2max, are important determinants of the duration of endurance exercise. Endurance training increases intramuscular glycogen stores in both FT and ST fibres and produces a 'glycogen-sparing' effect which is characterised by an increased free fatty acid (FFA) metabolism. The activity of glycogen synthase is also increased by endurance training. Sprint training increases glycogen concentrations similarly in all fibre types, reduces the rate of glycogen utilisation at submaximal workloads and allows supramaximal workloads to be maintained for longer periods of time. During endurance exercise the pattern of glycogen depletion varies between muscle fibre types and between muscle groups. Glycogen stores in ST fibres are utilised initially, followed by stores in FTa then FTb fibres. Sprint activities are associated with a much greater rate of glycogen depletion. However, it is unlikely that glycogen depletion causes fatigue during sprinting. Sprint work is associated with a preferential depletion of glycogen from FTb then FTa and ST fibres. Endurance training appears to increase triglyceride stores adjacent to mitochondria and ST fibres have greater triglyceride stores than FT fibres. Endurance exercise is associated with a preferential use of triglycerides from ST fibres and endogenous triglycerides may account for over 50% of the total lipid oxidised during exercise.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Acute and chronic responses of skeletal muscle to endurance and sprint exercise. A review. 229 Oct 32

The effect of high-intensity trained (6 X 4.5 min at 40 m/min, 15% grade, 2.5-min rest between bouts, 5 days/wk, for 6 wk) on contractile, biochemical, and fatigue properties of the rat diaphragm were examined. The exercise program produced significant elevations in the mitochondrial marker enzyme citrate synthase (mumol X g-1 X min-1) in the soleus (SOL) (27.2 +/- 1.5 vs. 46.7 +/- 2.4; mean +/- SE), deep vastus lateralis (DVL) (40.8 +/- 2.6 vs. 58.3 +/- 2.8), and superficial vastus lateralis (SVL) (8.5 +/- 0.6 vs. 11.4 +/- 0.7). No significant differences were observed in the crural (CRU) (45.9 +/- 2.0 vs. 44.0 +/- 2.3) or ventral costal (VEN) (41.5 +/- 2.0 vs. 45.8 +/- 2.6) diaphragmatic regions. Phosphofructokinase, the rate-limiting enzyme of glycolysis, significantly increased in the SOL (19.0 +/- 0.8 vs. 23.3 +/- 1.3 mumol X g-1 X min-1) and DVL (69.3 +/- 6.0 vs. 86.6 +/- 5.0), but no alterations were seen in the SVL (98.6 +/- 5.7 vs. 106.1 +/- 9.0), CRU (54.4 +/- 2.8 vs. 53.8 +/- 1.5), or VEN (44.7 +/- 2.4 vs. 46.4 +/- 1.4) posttraining. Diaphragm contractile properties, with the exception of an increased rate of fall in twitch tension, remained unchanged after training. Glycogen values were significantly higher in trained diaphragms at rest (6.54 +/- 0.39 vs. 4.86 +/- 0.41 mg/g) and during 1, 5, and 10 min of fatiguing stimulation. During fatigue no differences were observed in force, rate of rise in force, rate of fall in force, muscle lactate, ATP, or creatine phosphate in trained vs. control.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Contractile and biochemical properties of diaphragm: effects of exercise training and fatigue. 294 Feb 18


1 2 3 4 5 Next >>