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

1. The differential effects of beta-adrenoceptor subtypes on potassium fluxes and exercise capacity were compared in eight healthy young men using single oral doses of the selective beta 2-adrenoceptor antagonist ICI-118551, the selective beta 1-adrenoceptor antagonist atenolol or the non-selective beta-adrenoceptor antagonist propranolol. The study was randomized, double-blind and placebo controlled. 2. Potassium in the venous effluent from the exercising muscles increased progressively with increasing exercise intensity. This response was augmented by propranolol, whereas neither atenolol nor ICI-118551 modified the response. After exercise potassium concentration fell exponentially with no difference between the treatment regimens. 3. Cumulative work was significantly reduced by ICI-118551 (6.4%, P = 0.04) and by propranolol (12.4%, P less than 0.01), whereas the reduction with atenolol (5.6%) did not reach statistical significance. 4. Atenolol and propranolol reduced peak heart rate by 23% and 29%, and peak systolic blood pressure by 9% and 11% respectively during maximal exercise. ICI-118551 caused a non-significant reduction in heart rate during submaximal exercise, with a significant reduction at maximum exercise (6% reduction), whereas systolic blood pressure was not different from placebo. Diastolic blood pressures were similar across all treatment regimens. 5. Similar glucose concentrations were obtained at baseline and at exhaustion during all treatment regimens. Lactate concentrations were comparable for any given exercise intensity irrespective of treatment regimens. Propranolol reduced lactate concentrations from the exercising muscles at maximum exercise in proportion to the reduction of maximal exercise capacity. 6. The subjective perception of fatigue was not affected by either beta 1- or beta 2-adrenoceptor blockade.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of selective beta 2-adrenoceptor blockade on serum potassium and exercise performance in normal men. 168 47

The relationship between elevated plasma ammonia (NH3) levels, fatigue development and muscle metabolism were examined in horses during a submaximal fatigue test. Eight Quarter Horse mares were intravenously infused prior to exercise with either sodium acetate (control) or ammonium acetate (AMINF), and exercised to fatigue on an 11% grade treadmill, carrying 27 kg of lead. Time to fatigue was not different (P greater than 0.05) between groups. Intramuscular NH3 and lactate increased (P less than 0.001) during exercise; however, the treatment did not (P greater than 0.05) affect either. A treatment by exercise interaction (P less than 0.01) occurred for plasma NH3. The reciprocal relationship between changes in plasma and intramuscular alanine (ala) and glutamate (glu) indicated activation of the glucose-alanine cycle. Plasma glutamine (gln) increased (P less than 0.001) during exercise; however intramuscular gln was not (P greater than 0.05) altered. The excretion of urea-N was depressed as a result of exercise while the orotic acid/creatinine ratio did not (P greater than 0.05) change. The amino acids and urinary metabolites were not (P greater than 0.05) affected by treatment. These results did not show any metabolic evidence for a role of increased plasma NH3 levels in fatigue development. However this study did provide insight into other aspects of nitrogen metabolism during exercise in the horse.
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PMID:Metabolic responses to ammonium acetate infusion in exercising horses. 168 73

Congenital malformations are the leading cause of the increased perinatal mortality in the infants of insulin-dependent diabetic mothers. The mechanisms(s) of diabetic teratologic development has yet to be defined. Hyperglycemia is known to depress aerobic metabolism in many organisms and cell lines. Reid hypothesized that exposure to hyperglycemia could result in decreased mitochondrial biogenesis in embryonic cells. Should these cells suddenly be changed to an environment of lower glucose concentration, decreased energy capabilities would exist until sufficient numbers of mitochondria could be regenerated. Such cells may not be capable of meeting temporal-spatial requirements, thereby resulting in structural abnormalities. In our study the explanted rat embryo model demonstrated that in the head-fold region hyperglycemia produced morphologic alterations of mitochondria but no difference in the number of mitochondria per cell. Specifically, embryos cultured in euglycemia demonstrated orthodox mitochondrial configuration, whereas those cultured in hyperglycemia had mitochondria in a condensed configuration. These findings were reversible. A modification of Reid's original hypothesis may provide an explanation for the mechanism of diabetic teratologic development.
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PMID:Effects of hyperglycemia on mitochondrial morphology in the region of the anterior neuropore in the explanted rat embryo model: evidence for a modified Reid hypothesis as a mechanism for diabetic teratogenesis. 175 Apr 57

Felodipine, a dihydropyridine calcium-channel antagonist, significantly reduces systolic and diastolic blood pressure (BP) in patients with hypertension and has been associated with beneficial hemodynamic effects in patients with chronic stable angina pectoris or congestive heart failure (CHF). In hypertensive patients, felodipine does not appear to significantly affect glomerular filtration rate, creatinine clearance, glucose tolerance, or plasma lipoprotein concentrations. Studies comparing felodipine with other agents as monotherapy in mild to moderate hypertension have demonstrated felodipine to be at least as efficacious as hydrochlorothiazide (HCTZ) and HCTZ plus amiloride hydrochloride in combination. Comparisons of felodipine with other agents as adjuncts to beta-blocker or diuretic therapy have shown felodipine to be at least as effective as HCTZ, propranolol hydrochloride, prazosin hydrochloride, and nifedipine. Evaluations of patients with chronic stable angina are limited, and additional studies are needed before felodipine can be recommended for the routine management of angina pectoris. Similarly, additional studies are essential to delineate the role of felodipine, if any, in the management of CHF. In the management of hypertension, felodipine 5-40 mg/d significantly reduces systolic and diastolic BP. Although some patients may be controlled throughout the entire dosing interval when felodipine is administered bid, many patients will require more frequent dosing to obtain adequate BP control. Adverse effects associated with felodipine are similar to those of other dihydropyridine calcium-channel antagonists and include peripheral edema, headache, dizziness, flushing, and fatigue. A potentially clinically important drug interaction was observed when felodipine was administered concomitantly with theophylline aminopropanol; significant decreases in theophylline concentrations were noted. In summary, felodipine appears to be safe and effective for the management of hypertension when used alone or in combination with other antihypertensive agents. The efficacy of felodipine in the management of chronic stable angina pectoris and CHF requires further investigation.
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PMID:Felodipine: a new dihydropyridine calcium-channel antagonist. 176 37

The internal space of the antheridium in Chara vulgaris L. is filled with the PAS-positive mucilage which is of pectic nature. Morphometric and cytophotometric measurements on the semithin sections indicate that the concentration and amount of PAS-positive polysaccharides: 1) increase during the time of antheridial growth accompanying the phase of antheridial filament divisions, 2) these parameters have the maximum after spermatid formation and at the beginning of their differentiation, i.e. spermiogenesis, 3) both concentration and amount of this substance decrease at the end of spermiogenesis. A decrease in mucilage concentration is also observed in the young antheridia after 3 days of continuous darkness. The results suggest that PAS-positive mucilagenous material is a nutritive substance, accumulated in the first phase of antheridial development and utilized mainly in spermiogenesis. These substances may also be used up in the young antheridia during the lack of energy supply. The autoradiographic studies with the use of a 3H-glucose and 3H-galactose mixture seem to confirm these suggestions.
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PMID:Cytochemical studies on the antheridial mucilage and changes in its concentration and amount during the spermatogenesis in Chara vulgaris L. 179 40

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

Although fats and protein contribute to energy demands of exercise, carbohydrate, principally glycogen, is the preferred fuel for muscular activity. Because of its limited storage, depletion of muscle glycogen has been shown to be one factor responsible for fatigue and exhaustion during prolonged exercise. Thus, dietary carbohydrate plays a key role in exercise performance and training. When the athlete's diet is low in carbohydrate, little glycogen is resynthesized between training sessions, leaving the individuals with low muscle glycogen and a state of chronic fatigue. The most sensitive period for glycogen resynthesis is within the first few hours after exercise. Optimal recovery from an exhaustive exercise bout depends on a reasonably rich carbohydrate diet soon after the exercise. Such feedings serve to replenish carbohydrate stores in both liver and muscles. Exertional hypoglycemia can occur when liver glucose output falls below the rate of muscle glucose uptake. Though this seldom occurs in well-fed and highly trained individuals, sugar feedings during long-term exercise has been shown to enhance performance. Thus, the important role of dietary carbohydrate before, during and after endurance activities is well established, whereas our understanding of the nutritional needs for protein and fat remain unclear.
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PMID:Carbohydrate for athletic training and performance. 181 89

Adenosine triphosphate (ATP) is the sole fuel for muscle contraction. During near maximal intense exercise the muscle store of ATP will be depleted in < 1s, therefore, to maintain normal contractile function ATP must be continually resynthesized. During intense exercise (from approximately 75% VO2 max to near maximal workloads) this is achieved principally by the oxidation of carbohydrate and the anaerobic utilisation of phosphocreatine (PCr) and carbohydrate. The relative contribution of carbohydrate oxidation to total energy provision decreases, while that from anaerobic utilization increases. During prolonged intense exercise (approximately 75% VO2 max), the oxidation of glucose derived from skeletal muscle and liver glycogen stores is the primary pathway for ATP resynthesis. It is widely accepted that the availability of carbohydrate limits performance during this type of exercise as the point of exhaustion has been shown to be closely related to the depletion of muscle and liver glycogen stores. It is probable that carbohydrate depletion results in the inability of skeletal muscle to maintain the required rate of ATP resynthesis and therefore, the work intensity must be reduced for exercise to continue. During short lasting near maximal exercise (0-30 s), the anaerobic utilization of muscle PCr and glycogen will fuel muscle contraction. Evidence is available to indicate that fatigue during this type of exercise is related to the inability of type II fibres to maintain the required very high rate of ATP resynthesis. This has been suggested to result from a rapid depletion of type II fibre PCr stores and an insufficiency of the glycogenolytic rate to compensate for the fall in ATP production when the PCr store is depleted. In this situation the force generation has to decrease due to insufficient energy supplies.
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PMID:Skeletal muscle energy metabolism and fatigue during intense exercise in man. 184 55

We hypothesized that when plasma glucose availability is maintained by carbohydrate (CHO) ingestion, trained cyclists can utilize plasma glucose at very high rates during the later stages of prolonged exercise (10). To test this hypothesis, a well-trained male cyclist was studied during exercise to fatigue at 70% VO2max when ingesting glucose throughout exercise. A primed continuous infusion of [U-13C]glucose was begun after 60 min of exercise to measure rates of plasma glucose appearance (Ra), disappearance (Rd), and oxidation (R(ox)). Ra and Rd rose progressively throughout exercise, peaking at 6.85 and 6.99 mmol/min, respectively, at fatigue (i.e., 133 min). Most (93%) of this glucose was oxidized; during the final 30 min of exercise, R(ox) averaged 6.10 mmol/min and accounted for approximately half of total CHO oxidation. These results support the hypothesis that trained cyclists can oxidize plasma glucose at very high rates during the later stages of prolonged exercise when fed CHO.
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PMID:Plasma glucose kinetics in a well-trained cyclist fed glucose throughout exercise. 184 2

The effect of carbohydrate (CHO) ingestion on metabolic responses to exercise has been investigated. Subjects cycled at approximately 70% of maximal oxygen uptake to fatigue [135 +/- 17 (+/- SE) min] on the first occasion (control, CON) and at the same work load and duration on the second occasion but with addition of ingestion of CHO during the exercise. Biopsies were taken from the quadriceps femoris muscle before and after exercise. The sum of the hexose monophosphates (HMP), as well as lactate and alanine, in muscle was higher after CHO exercise (P less than or equal to 0.05, P less than or equal to 0.05, and P less than or equal to 0.01, respectively). Acetylcarnitine increased during exercise but was not significantly different between treatments after exercise (CON, 6.6 +/- 1.7; CHO, 10.0 +/- 1.2 mmol/kg dry wt; P = NS). The sum of the tricarboxylic acid cycle intermediates (TCAI; citrate + malate + fumarate) was increased during exercise and was higher after CHO exercise (2.34 +/- 0.32 vs. 1.68 +/- 0.17 mmol/kg dry wt; P less than or equal to 0.05). IMP was less than 0.1 mmol/kg dry wt at rest and increased to 0.77 +/- 0.26 (CON) and 0.29 +/- 0.11 mmol/kg dry wt (CHO) (P less than or equal to 0.05) during exercise. It was recently found that during prolonged exercise there is initially a rapid and large expansion of TCAI and glycogenolytic intermediates in human muscle followed by a continuous decline in TCAI and glycogenolytic intermediates [K. Sahlin, A. Katz, and S. Broberg. Am. J. Physiol. 259 (Cell Physiol. 28): C834-C841, 1990].(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Carbohydrate supplementation attenuates IMP accumulation in human muscle during prolonged exercise. 185 60


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