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

The aim of the present study was to further subdivide the type II fibers of the human thyroarytenoid and posterior cricoarytenoid muscles by means of a modified myosin ATPase reaction. In order to understand the functioning of these highly strained muscles better, it is important to know the respective percentage of fatigue-resistant type IIA fibers and fatigable type IIB fibers. The material comprised the larynges of seven laryngectomized males aged between 45 and 70 years and four laryngectomized females aged between 39 and 72 years. After having been frozen in nitrogen, 10-microns-thick sections were cut from the laryngeal muscles in a cryostat. The pH-lability of the enzyme that can be utilized in a classical myosin ATPase reaction permits a differentiation between fiber types I, IIA and IIB. Evidently, this is not possible with every human muscle. The fiber types IIA and IIB of the thyroarytenoid and the posterior cricoarytenoid muscles could be clearly distinguished by means of the inhibition reactivation myofibrillar ATPase technique. Using this method, the myosin ATPase enzyme was initially inhibited by hydroxymercuribenzoate and subsequently reactivated by cysteine. Regarding the incidence of type I and IIA fibers, there was a statistically significant difference between the thyroarytenoid and the posterior cricoarytenoid muscles. The type IIA fiber content was statistically significantly higher in the arytenoid muscle than in the posterior cricoarytenoid muscle. The percentage of type IIB fibers was low, not only in the thyroarytenoid muscle and the posterior cricoarytenoid muscle but also in the other laryngeal muscles.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Fiber differentiation of the human laryngeal muscles using the inhibition reactivation myofibrillar ATPase technique. 141 83

To evaluate electrically stimulated muscle grafts for augmenting ventricular function in cardiac insufficiency, dynamic cardiomyoplasty was performed in nine sheep, using latissimus dorsi (LD) muscle wrapped as a pedicle around the left ventricle. Beginning 2 weeks postoperatively, LD was stimulated synchronously with the heart. After 6 and 12 weeks of stimulation, hemodynamic evaluation was done and biopsies were taken for histochemical and biochemical analysis. With intact heart function, stimulation of the muscle was not hemodynamically beneficial. During induced heart failure, cardiomyoplasty increased cardiac output by 25% in two sheep. Eight LD muscles contracted vigorously in synchrony with the heart, one was fibrosed and all were fixed to the thoracotomy incision by scar tissue. ATPase stain showed gradual transformation of muscle fibers into fatigue-resistant Type I. At 12 weeks only Type I were seen. Quantitative enzymatic analyses revealed increase in oxidative and decrease in glycolytic enzymes. Chronic electrical stimulation is concluded to change the muscle characteristics towards those of mainly oxidative and fatigue-resistant muscle, thereby improving opportunities for assisting the depressed heart. Dynamic cardiomyoplasty involves risks of adhesions to adjacent tissues and muscle trauma from chronic stimulation.
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PMID:Experimental dynamic cardiomyoplasty in sheep. 152 92

In adult male hamsters the influence of emphysema (EMP) on the in vitro contractile and fatigue properties and the histochemical, morphometric, and metabolic properties of muscle fibers in the costal diaphragm was determined 6 mo after the administration of either elastase or saline (controls, CTL). Isometric contractile properties were determined in vitro using supramaximal direct muscle stimulation. Optimal fiber length for force generation was significantly shorter in the EMP than in the CTL diaphragm. Maximum specific force (i.e., force per unit area) was 25% lower than CTL. Fatigue resistance was significantly improved in the EMP diaphragm compared with CTL. Diaphragm muscle fibers were classified as type I or II on the basis of histochemical staining for myofibrillar adenosinetriphosphatase after alkaline preincubation. The proportions of type I and II fibers were similar between the two groups. Cross-sectional areas of type II fibers were 30% larger in EMP than in CTL diaphragms. Succinate dehydrogenase activities of both type I and II fibers were higher in EMP than in CTL diaphragms. The number of capillaries surrounding both type I and II fibers increased with EMP, but in proportion to the hypertrophy of these fibers. Thus, capillary density (number of capillaries per fiber cross-sectional area) remained unchanged. We postulate that these contractile, morphometric, and metabolic adaptations reflect an increased activation of the diaphragm in response to the loads imposed by EMP.
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PMID:Adaptations of the diaphragm in emphysema. 156 89

1. Isolated and glycogen-depleted motor units (MUs) have been studied in normal and reinnervated tibialis anterior (TA) muscles of the rat to examine 1) the correspondence between physiological and histochemical classifications, 2) the extent to which unit properties cluster according to type, 3) the relation between unit force and fatigability, and 4) the extent to which reinnervated MUs recover their former properties. 2. MUs were isolated by ventral root dissection and stimulation in reinnervated and normal TA muscles, 3.5-8 mo after common peroneal (CP) nerve section and resuture and in age-matched control rats, respectively. The units were characterized physiologically for classification into four types: slow twitch (S), fast twitch, fatigue resistant (FR), fast twitch fatigue intermediate (FI), and fast twitch fatigue sensitive (FF). Four muscle fiber types were identified histochemically with the use of a modification of the techniques of Brooke and Kaiser, and Guth and Samaha to delineate fiber subtypes on the basis of the pH sensitivity of myofibrillar adenosine triphosphatase (ATPase). 3. Neither the time-to-peak twitch force development nor the profile of unfused tetanus ("sag test") was unambiguous in separating fast from slow MUs. However, all units with a time to peak greater than 22 ms were fatigue resistant, and this time was chosen to delineate fast from slow. The fast unit population was further subdivided on the basis of their fatigability. There is normally a small proportion of S units (6% S) that increased to 20% after reinnervation. Although the fast population was subdivided, there was a continuous distribution of fatigue indexes in normal and reinnervated muscles with the highest number of fast units falling into the FI category. The proportions of fast units were 28% FR, 45% FI, and 21% FF in normal muscles and 29% FR, 38% FI, and 13% FF in reinnervated muscles. 4. In normal muscles, delineation of fast and slow fibers and subdivision of fast fiber types on the basis of acid and alkali stability of myofibrillar ATPase provided a histochemical classification that showed 78% correspondence with physiological classification of the same identified units. In reinnervated muscles the correspondence between physiological and histochemical classifications was reduced to 72%. 5. The normal correlation between MU fatigability and isometric force in TA muscles was not seen in reinnervated muscles that contained more FR MUs. Mean fatigue index from normal units was significantly less at 0.55 +/- 0.03 (mean +/- SE) compared with 0.68 +/- 0.03 from reinnervated units.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Motor-unit categorization based on contractile and histochemical properties: a glycogen depletion analysis of normal and reinnervated rat tibialis anterior muscle. 159 22

The relationship between variations in diaphragmatic contractility and corresponding changes in total tissue levels of 45Ca and adenosine 3',5'-cyclic monophosphate (cAMP) was examined. The contractile performance of perfused contracting rat diaphragms was manipulated with theophylline (10(-4) M), induced fatigue, or both. The increased contractility associated with theophylline was related to significant increases in 45Ca levels without changes in cAMP levels. Fatigue-diminished contractility was associated with increases in both 45Ca and cAMP levels. The increased 45Ca and cAMP levels associated with fatigue persisted, even in the presence of theophylline. Calcium channel blockade with 10(-4) M verapamil blocked the positive inotropic influence of theophylline as well as the theophylline-associated increase in 45Ca levels. Verapamil had no effect on either the fatigue-associated decreases in contractility or the fatigue-enhanced 45Ca uptake. The results of this study strongly suggest that the enhanced contractility associated with theophylline is related to its influence on cellular calcium metabolism. The elevated level of isotopic calcium measured in fatigued muscle probably represents calcium sequestered in the sarcoplasmic reticulum, the result of cAMP-enhanced Ca-adenosine triphosphatase activity.
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PMID:Theophylline, fatigue, and diaphragm contractility: cellular levels of 45Ca and cAMP. 165 Jul 69

1. Physiological, enzyme-histochemical, biochemical and morphometrical properties of fast-twitch single motor units were compared between young (3-6 months) and old rats (20-24 months) using the glycogen depletion technique. Monoclonal antibodies (mAbs) were used to identify the myosin heavy chain (MHC) composition in the muscle fibres of the motor unit (motor unit fibres) in order to facilitate correlative physiological, histochemical, biochemical and morphometrical studies. 2. Earlier observations on effects of age on contractile properties of fast-twitch motor units were confirmed and extended. That is, the duration of the isometric twitch, and the twitch and tetanus forces, were increased. Further, motor unit fibres were rearranged, occupying a larger territory and displaying an increased innervation ratio in old age, indicating a denervation-reinnervation process. 3. Motor units with muscle fibres expressing the novel IIX myosin heavy chain (MHC) were observed in both young and old animals, and they constituted the predominant motor unity type identified in the old animals. In contrast to the type IIX MHC motor units in the young animals, the type IIX MHC units in old age often contained muscle fibres which expressed either the type IIA or type IIB MHC, although type IIX MHC fibres were in the majority (so called 'IIX' MHC motor units), but motor units containing all these three fibre types were never observed. There were also single fibres co-expressing IIX and IIB MHCs in old age. 4. In the young animals the IIX MHC motor units had a higher (P less than 0.001) resistance to fatigue (fatigue ratio 0.45 +/- 0.11) than the type IIB MHC units (0.03 +/- 0.05), a succinate dehydrogenase (SDH) activity (0.62 +/- .007) intermediate (P less than 0.001) between those of type IIA muscle fibres classified according to myofibrillar ATPase activity after acid pre-incubation, i.e. type IIA ATPase, (0.84 +/- 0.13) and type IIB MHC motor unit fibres (0.20 +/- 0.04), and cross-sectional fibre areas (1650 +/- 320 microns 2) which were similar to those of type IIA ATPase muscle fibres (1460 +/- 150 microns 2) but smaller (P less than 0.001) than type IIB MHC motor unit fibres (4650 +/- 1180 microns 2).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Effects of age on physiological, immunohistochemical and biochemical properties of fast-twitch single motor units in the rat. 166 38

beta-Adrenoceptor blockers are widely used clinically and can be classified as nonselective (beta 1 and beta 2) or selective (beta 1). Impairment of exercise performance is a well-known side effect of this group of drugs. This paper reviews mechanisms that could potentially be responsible for this impairment. In addition to cardiovascular and metabolic effects, beta-blockade inhibits Na(+)-K+ ATPase pumps controlling ion movement between muscle and plasma and thus may contribute to muscle fatigue through this mechanism. To investigate the relationship between the change in plasma [K+] and exercise performance, we studied healthy male subjects taking propranolol. Eight subjects performed maximal incremental cycle ergometer exercise tests during control (no drug), low dose (LD) (40 mg daily), and high dose (HD) (265 +/- 4.3 (SE) mg daily) of propranolol. The control plasma [K+] (5.8 +/- 0.12 mequiv./L) during exercise was significantly lower than either the LD (6.4 +/- 0.05 mequiv./L) or HD (6.1 +/- 0.16 mequiv./L) values. There was no significant difference between plasma [K+] for the LD and HD of propranolol. However, maximum oxygen uptake was reduced only while taking the HD of propranolol. Six of the subjects also performed three 30-s bouts of high intensity exercise on an isokinetic cycle ergometer while taking the LD and HD of propranolol. There was no significant difference between doses for the increase in plasma [K+] (LD, 7.8 +/- 0.35 mequiv./L vs. HD, 7.6 +/- 0.36 mequiv./L) during exercise. However, exercise performance was significantly reduced during HD compared with LD. These results suggest that the increases in plasma [K+] with propranolol did not play a direct significant role in the reduced performance observed during the HD.
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PMID:Factors contributing to increased muscle fatigue with beta-blockers. 167 29

1. Muscle fatigue following long-duration rhythmic activity is often characterized by reduced force following a single impulse and at low-frequencies of stimulation. 2. Although this response is generally attributed to an alteration in excitation-contraction coupling, the possibility that the responsiveness of myofibrillar proteins to a given Ca2+ signal is altered has never been ruled out. 3. In this study, rat plantaris muscles were subjected to an in situ regimen of contractions (100 Hz, lasting 100 msec, once every 750 msec, for 1 hr), and allowed to recover for 15 min. 4. Twitch, 100 Hz, and 200 Hz forces were reduced by 79%, 49% and 17% respectively, at this time. 5. In myofibrils isolated from these muscles, maximum activity of Ca2+ activated myofibrillar ATPase, Ca2+ sensitivity (pCa 50), and co-operatively (Hill n), were not different from non-fatigued muscles. 6. It appears, therefore, that the Ca2+ activation properties of myofibrillar ATPase do not contribute to this pattern of fatigue.
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PMID:Ca2+ activation properties of myofibrillar ATPase from fatigued rat plantaris. 168 96

A study was made of the role of prolactin (PRL) in the regulation of thyroid function in intact animals and in those exposed to stress (swimming was used as physical exercise). A single daily dose of 125 micrograms of PRL per 100 g of body mass was injected subcutaneously in 0.5 ml of saline solution during a week to male rats (control: intact rats; injection of 0.5 ml of saline solution subcutaneously). Redox enzymes; succinate dehydrogenase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, NAD.H2 and NADP.H2, ATPase and monoamine oxidase, total protein, RNA and glycogen in glandular cells were investigated histochemically 24 h after the last injection of PRL or saline, 30 min., 1, 2, 3, 5 and 7 hours after swimming or right after complete fatigue (in the presence of experimental hyperprolactinemia). A conclusion has been made that one of the most important mechanisms of the adaptive effect of PRL is its ability to suppress thyroid function, thus decreasing the metabolism level, which results in reduction of oxygen consumption and improves body tolerance to stress.
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PMID:[Metabolism of thyroid gland cells as affected by prolactin and emotional-physical stress]. 178 Feb 95

Sheep under general anesthesia had their left and right latissimus dorsi muscles mobilized for paraneuroelectrode and pulse generator implantation. After a 10-day recovery period, the left-side muscles were stimulated with a gradually increasing duration and rate over 3 months. At 4 months after operation, the tendinous end of each latissimus dorsi muscle was freed from its humeral insertion and attached to a strain gauge force transducer. Both left and right latissimus dorsi muscles, from each animal, were stimulated to contract for 2 hours for the fatigue study before being isolated, trimmed, and weighed. Frozen tissue biopsies were used to determine creatine phosphate, adenosine triphosphate, lactate, and glycogen content and muscle myosine ATPase, and succinate dehydrogenase activities. The arterial diameter in the conditioned muscle was 30% larger than that of the control muscle and had a 40% higher blood flow at rest. A three- to fivefold increase in blood flow during the fatigue test was observed. The force decreased 47% for the conditioned muscle and 91% for the control muscle. The mass and cross-sectional area of conditioned and unconditioned muscles were similar. Electric conditioning increased fatigue resistant fiber content from 33% to 92%, as evidenced by myosine ATPase activity. During the early phase of the fatigue test, higher glucose uptake but significantly lower lactate production were found for the conditioned muscle. This study indicates that it is possible to produce fatigue resistant muscle with preserved force and mass. In addition to skeletal muscle fiber transformation, metabolic adaptations appear to be important factors for fatigue resistance of skeletal muscle.
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PMID:Fatigue resistant muscle with preserved force and mass for cardiac assist. 180 6


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