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Query: UMLS:C0392674 (exhaustion)
 13,658 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Functional capacities in Escherichia coli cells starved for glucose were examined by comparing protein synthesis, utilization of new substrates, and maintenance of viability with the adenylate energy charge of the culture. When growth ceased because of glucose exhaustion in an E. coli culture, the energy charge dropped from 0.90 to about 0.80. During this time, the viable-cell count and the capacity for protein synthesis and for induction of new enzymes were maintained only if other substrates were available in the medium. The culture could be maintained for many hours without growth or death if glucose was added slowly; the energy charge in this case stabilized at about 0.80. A consistent transient decrease in the energy charge to around 0.80, accompanied by a decrease in protein synthesis, was also observed during the adaptation from glucose to other substrates during diauxic growth on glucose and glycerol or lactose.
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PMID:Functional capacities and the adenylate energy charge in Escherichia coli under conditions of nutritional stress. 12 11

The mode of synthesis and the regulation of fructose-1,6-bisphosphatase (Fbpase), a gluconeogenic enzyme, and phosphofructokinase (PFK), a glycolytic enzyme, were investigated in Saccharomyces cerevisiae after growth in the presence of different concentrations of glucose or various gluconeogenic carbon sources. The activity of FBPase appeared in the cells after the complete disappearance of glucose from the growth medium with a concomitant increase of the pH and no significant change in the levels of accumulated ethanol. The appearance of FBPase activity following glucose depletion was dependent upon the synthesis of protein. The FBPase PFK were present in glucose-, ethanol-, glycerol-, lactate-, or pyruvate-grown cells; however, the time of appearance and the levels of both these enzymes varied. The FBPase activity was always higher in 1% glucose-grown cells than in cells grown in the presence of gluconeogenic carbon sources. Phosphoglucose isomerase activity did not vary significantly. Addition of glucose to an FBPase and PFK synthesizing culture resulted in a complete loss, followed by a reappearance, of PFK activity. In the presence of cycloheximide the disappearance of glucose and the changes in the levels of FBPase and PFK were decreased significantly. It is concluded that S. cerevisiae exhibits a more efficient synthesis of FBPase after the exhaustion of glucose compared to the activity present in cells grown in the presence of exogenous gluconeogenic carbon sources. Two metabolically antagonistic enzymes, FBPase and PFK, are present during the transition phase, but not during the exponential phase, of growth, and the decay or inactivation of these enzymes in vivo may be dependent upon a glucose-induced protease activity.
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PMID:Biosynthesis and regulation of fructose-1,6-bisphosphatase and phosphofructokinase in Saccharomyces cerevisiae grown in the presence of glucose and gluconeogenic carbon sources. 21 20

1. In an attempt to study the intracellular location of ATP in skeletal muscle the distribution of substances which absorb light at 260 nm wave-length has been studied in isolated muscle fibres with the aid of a modified U.V.-microscope.2. U.V.-absorption in resting frog fibres was found to be higher in the I band than in the A band which confirms earlier findings. In stretched fibres (sarcomere length 2.9-3.6 mum) an absorbing substance could be seen to be concentrated in a pair of narrow lines, centred at the Z-line. The separation of the lines increased with increasing sarcomere length.3. Snake fibres, with sparse triads located at the A-I junction, displayed an absorption pattern very similar to that of frog fibres. It is concluded that it is unlikely that the absorbing substance is associated with the sarcotubular system.4. The absorption pattern of frog fibres remained unchanged during a tetanus. No clear changes could be detected after a period of stimulation, neither after single twitches nor after repeated tetani.5. In further attempts to cause exhaustion, metabolically poisoned fibres were stimulated repetitively until they went into rigor. The absorption pattern was essentially unchanged also when rigor tension started to develop.6. The characteristic absorption pattern was observed also in glycerol-extracted fibres. It was confirmed by spectrophotometry that glycerol-extraction led to the disappearance of a large amount of a substance with the spectral characteristics of ATP.7. The higher U.V.-absorption in the I band does not prove that the major part of the ATP in the fibre is concentrated here; the absorption could either be due to a minor fraction of the ATP or to RNA.
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PMID:Location of U.V.-absorbing substance in isolated skeletal muscle fibres. The effect of stimulation. 30 60

The purpose of this study was to test the hypothesis that increased availability of fatty acids could increase endurance by slowing the rate of glycogen depletion. Rats were given corn oil by stomach tube, and 3 h later an injection of heparin was given to raise their plasma free fatty acids (FFA). The rats with raised FFA were able to run approximately 1 h longer than otherwise comparable control animals before becoming exhausted (181 +/- 8 vs. 118 +/- 8 min, P less than 0.001). At the point of exhaustion, both groups were hypoglycemic and had low muscle glycogen concentrations. The fall in blood glucose occurred less rapidly in the animals with raised FFA; these rats also had significantly higher blood glycerol and beta-hydroxybutyrate concentrations than the controls. Glycogen concencentration decreased less rapidly in all three types of skeletal muscle and in liver in the animals with raised FFA than in the controls. We conclude that increased availability of fatty acids delays the development of exhaustion in rats subjected to prolonged running. It appears likely that the carbohydrate-sparing effect of fatty acids is largely responsible for the increase in endurance.
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PMID:Effects of increased plasma fatty acids on glycogen utilization and endurance. 59 76

The importance of autonomic nervous activity for the pancreatic hormonal response to exercise in man was studied. 7 men ran at 58% of V(O2)max (determined without administration of drugs) to exhaustion during alpha-adrenergic blockade with phentolamine (P), during parasympathetic blockade with atropine (A), or without drugs (C). At rest phentolamine increased the plasma concentrations of both insulin and norepinephrine. During exercise norepinephrine concentrations increased and were in P experiments 3 times the concentrations in C experiments. Insulin always declined during exercise but in P experiments never decreased below basal levels. At identical times neither glucagon nor glucose differed significantly in the different expts. Thus during exercise alpha-adrenergic blockade increased insulin concentrations but did not diminish the glucagon response. Nor was this response increased when beta-receptor stimulation in P experiments was intensified by the particularly high catecholamine concentrations. The concentrations of FFA, glycerol and lactate were highest in P experiments and identical in A and C experiments. These findings indicate that during prolonged moderate exercise in man insulin secretion is depressed by stimulation of alpha-adrenergic receptors whereas glucagon secretion is not influenced by adrenergic receptors. Stimulation of beta-adrenergic receptors enhances lipolysis but neither lipolysis nor pancreatic hormonal secretion is influenced by cholinergic activity during exercise.
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PMID:Catecholamines and pancreatic hormones during autonomic blockade in exercising man. 59 18

Blood samples were taken from 15 horses before and after a 50-mile ride to examine the changes occurring in some biochemical constituents. There was a significant (P less than 0.05) decrease in plasma potassium, calcium and magnesium concentrations and a rise in inorganic phosphate but there was no alteration in plasma sodium, chloride or protein levels or change in haematocrit. After the ride there was a highly significant (P less than 0.01) fall in blood glucose corresponding with increased lipolysis and a rise in plasma free fatty acids (P less than 0.001) and glycerol (P less than 0.001). There was a modest increase in blood lactate and a rise in plasma creatine phosphokinase. The results of this preliminary investigation are discussed in relation to the problem of exhaustion in horses during endurance rides.
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PMID:Biochemical changes in horses during a 50-mile endurance ride. 65 49

1. Seven healthy male volunteers performed intermittent exercise (15 sec work--15 sec rest) at a high work load for 60 min and six subjects performed continuous exercise at an equally high load to exhaustion, which occurred after 4--6 min. 2. Muscle biopsies were obtained from the lateral portion of the quadriceps muscle before intermittent exercise and after the end of a work period and the end of the subsequent rest period at 5, 15, 30 and 60 min of exercise, as well as before, immediately after and about 15, 30, 60 and 180 sec after continuous exercise. 3. The reduction in glycogen content was smaller and glucose-6-phosphate, glycerol-1-phosphate, lactate and malate contents were lower after both work and rest periods in intermittent compared with continuous exercise, indicating a lower rate of glycolysis. 4. ATP and CP levels had decreased at the end of work periods in intermittent exercise but increased to slightly below basal in the subsequent rest periods. A still larger decrease in ATP and CP levels was found after continuous exercise to exhaustion and a progressive increase occurred over the 3 min of recovery. 5. In each rest period during intermittent exercise citrate levels increased to reach above basal. They increased also in the recovery phase after continuous exercise, although more slowly. 6. The findings support the assumption that ATP, CP and citrate act as regulatory factors of glycolysis in human muscle by retarding certain rate limiting steps. The increase in G-6-P/F-1-6-P2 ratio in rest periods of intermittent intense exercise and in the recovery phase of continuous intense exercise suggests that glycolysis is retarded at the phosphofructokinase reaction. 7. The factors mentioned may therefore contribute to the relative increase in lipid utilization during intense intermittent compared to continuous exercise.
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PMID:Regulation of glycolysis in intermittent exercise in man. 70 3

In an effort to assess the effects of caffeine ingestion on metabolism and performance during prolonged exercise, nine competitive cyclists (two females and seven males) exercised until exhaustion on a bicycle ergometer at 80% of Vo2 max. One trial was performed an hour after ingesting decaffeinated coffee (Trial D), while a second trial (C) required that each subject consume coffee containing 330 mg of caffeine 60 min before the exercise. Following the ingestion of caffeine (Trial C), the subjects were able to perform an average of 90.2 (SE +/- 7.2) min of cycling as compared to an average of 75.5 (SE +/- 5.1) min in the D Trial. Measurements of plasma free fatty acids, glycerol and respiratory exchange ratios evidenced a greater rate of lipid metabolism during the caffeine trial as compared to the decaffeinated exercise treatment. Calculations of carbohydrate (CHO) metabolism from respiratory exchange data revealed that the subjects oxidized roughly 240 g of CHO in both trials. Fat oxidation, however, was significantly higher (P less than 0.05) during the C Trial (118 g or 1.31 g/min) than in the D Trial (57 g or 0.75 g/min). On the average the participants rated (Perceived Exertion Scale) their effort during the C Trial to be significantly (P less than 0.05) easier than the demands of the D treatment. Thus, the enhanced endurance performance observed in the C Trial was likely the combined effects of caffeine on lipolysis and its positive influence on nerve impulse transmission.
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PMID:Effects of caffeine ingestion on metabolism and exercise performance. 72 3

Seven men ran at 60% of individual maximal oxygen uptake to exhaustion during beta-adrenergic blockade with propranolol or without drugs. After propranolol administration the increases during exercise in plasma glucagon and epinephrine concentrations as well as the decrease in plasma glucose concentrations were faster than in control experiments. When euglycemia was maintained by glucose infusion during beta-adrenergic blockade, glucagon and epinephrine responses to exercise, although not abolished, were markedly reduced. The diminution of the exercise-induced decline in glucose concentrations correlated significantly with the diminution of the glucagon as well as the epinephrine responses. Thus decreased glucose concentrations may significantly enhance the secretion of glucagon and epinephrine during prolonged exercise in man. Since the diminution of the glucagon response produced by glucose infusion was not accompanied by significant alterations in the levels of nonesterified fatty acid (NEFA) and glycerol, increased glucagon secretion does not seem to be a major determinant of lipolysis during exercise in man. During glucose infusion, glycogen utilization rates in muscle (n = 4) tended to decrease, whereas carbohydrate combustion rate and concentrations of norepinephrine, insulin, alanine, and lactate were unchanged.
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PMID:Glucose-induced decrease in glucagon and pinephrine responses to exercise in man. 86 12

Seven men ran at 60% of individual maximal oxygen uptake to exhaustion during beta-adrenergic blockade with propranolol (P), during lipolytic blockade with nicotinic acid (N), or without drugs (C). The total work times (83 +/- 9 (P), 122 +/- 8 (N), 166 +/- 10 (C) min, mean and SE) differed significantly. Epinephrine rose progressively above preexercise levels (0.06 +/- 0.01 ng/ml); at exhaustion concentrations in P experiments (2.15 +/- 0.41) were larger than in N (1.08 +/- 0.31) and C (0.72 +/- 0.28) experiments. Norepinephrine increased consistently while insulin decreased. After an initial decrease glucagon concentrations increased progressively in parallel with declining plasma glucose and were at exhaustion always three times preexercise values. Thus beta-adrenergic blockade did not diminish the glucagon response. Nor was this response increased when alpha-receptor stimulation in P experiments was intensified. Carbohydrate combustion was smaller and NEFA and glycerol concentrations in serum larger during C experiments. Alanine concentrations were never raised at exhaustion. Accordingly, neither stimulation of adrenergic receptors nor NEFA and alanine concentrations are major determinants for the exercise-induced glucagon secretion in man. It is suggested that decreased glucose availability enhances the secretion of glucagon and epinephrine during prolonged exercise.
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PMID:Glucagon and plasma catecholamines during beta-receptor blockade in exercising man. 93 21


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