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

Sustained exercise to fatigue elicits no major differences either in plasma amino acid levels or in brain 5-hydroxytryptamine (5-HT) metabolism between sedentary and endurance-trained animals. Furthermore, 11 weeks of endurance training did not influence the maximal activity of the enzyme monoamine oxidase in the brain areas which were studied. In both sedentary and endurance-trained rats, sustained running to fatigue caused an increase in the plasma concentration ratio of free tryptophan/other large neutral amino acids and an increase in the concentration of tryptophan in the six brain areas that were studied. The increase was similar in the different regions of the brain and averaged 36%. Exercise caused an increase in the levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the brain stem (14 and 44% respectively) and hypothalamus (16 and 17% respectively) and an increase in the level of 5-HIAA in the hippocampus (21%) and striatum (28%). Exercise also caused an increase in the level of dopamine in the brain stem (56%) and hypothalamus (46%) and of nor adrenaline in the striatum (59%). Since the levels of 5-HT and dopamine were both increased in the brain stem and hypothalamus, it is possible that these changes may play important roles in the central effects of exercise, including both physical and mental fatigue and effects on mood.
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PMID:Effect of sustained exercise on plasma amino acid concentrations and on 5-hydroxytryptamine metabolism in six different brain regions in the rat. 247 2

The authors studied whether the fatiguing effects of eating lunch are greater for carbohydrate-rich meals than for other meals, and related the time course of behavioral change to plasma glucose, insulin, and amino acids. On different occasions, in counterbalanced order, normal women (N = 7) fasted overnight, ate a standard breakfast, and at lunch either continued to fast or ate a high-carbohydrate, low-protein meal; a hedonically similar meal containing both carbohydrate and protein; or a high-protein, low-carbohydrate meal. Meals were isocaloric and equated for fat content. Only the carbohydrate meal significantly increased fatigue, which could not be attributed to hypoglycemia because plasma glucose remained elevated. Fatigue began approximately, when the carbohydrate meal elevated the plasma tryptophan ratio but ended even though the ratio remained elevated. Fatigue after a high-carbohydrate lunch could not be explained by reactive hypoglycemia or sweet taste, and could partially be explained by the hypothesis that fatigue parallels an elevation of the tryptophan ratio.
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PMID:Psychobiological effects of carbohydrates. 256 98

The uremic syndrome is multifactorial, and affects most tissues and organs. Disturbances in protein and amino acid metabolism may play important roles, especially in chronic uremia, either directly or by production of toxic metabolites, with resultant negative nitrogen (N) balance, muscle wasting, reduced protein synthesis, and characteristically abnormal intracellular free amino acid concentrations. There are also grossly abnormal amino acid levels in the plasma of uremic patients, e.g., increases in conjugated amino acids, high levels of several nonessential and low levels of essential amino acids. The ratios of tyrosine/phenylalanine and of valine/glycine are decreased. The low tryptophan levels may contribute to encephalopathy as a result of an imbalance in neurotransmitter synthesis. Citrulline is found in excess; the explanation is unresolved. There are elevated concentrations of the sulfur-containing amino acids: cystine, taurine, cystathionine, and homocysteine. Excess of the latter is implicated in the atherogenesis of renal failure. Disturbed metabolism and interorgan exchange of amino acids in the uremic state explains some of the abnormalities in tissue and plasma concentrations of individual amino acids. Enzymatic defects are involved in the disturbed metabolism of branched chain amino acids (BCAA), with possible antagonism among them, which impairs growth and amino acid utilization. Carbohydrate intolerance, associated with insensitivity of peripheral tissues to insulin and hyperinsulinemia, elicits decreased plasma BCAA. Protein synthesis rates in normal and pathological conditions are more closely related to the intracellular amino acid pool than to plasma amino acid levels. Concentrations of individual amino acids in the plasma pool are poor indicators of their intracellular concentrations. Muscle contains the largest pool of protein and free amino acids in the body. In chronic renal failure patients, the intracellular concentrations of valine, threonine, lysine, and carnosine are low. With low protein diets and in hemodialysis, serine, tyrosine, and taurine often are also low. The low taurine may be related to fatigue and to uremic cardiomyopathies. The commonly used amino acid supplements generally fail to correct the intracellular amino acid deficits. A "New Formula" has been developed to correct these intracellular amino acid abnormalities, and to supplement a low protein diet. It provides more valine than leucine, increased tyrosine and threonine, and less histidine, leucine, isoleucine, lysine, methionine, and phenylalanine than in formulas customarily used for patients with chronic renal failure. It is uncertain whether other ap
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PMID:Amino acid metabolism in uremia. 267 58

Carbohydrate craving can cause weight gain in affected people and is present in women with premenstrual syndrome (PMS) and persons with seasonal affective disorder (SAD). The neurotransmitter serotonin regulates carbohydrate intake; its precursor, tryptophan, enhances serotonin release. Animal studies have shown that serotonergic drugs decrease carbohydrate consumption. Three studies of the eating patterns of over 150 obese subjects have shown that carbohydrate craving occurred at specific times, that is, at 4 p.m. and 9 p.m. A serotonergic drug (D-fenfluramine) has been shown to decrease carbohydrate consumption by 40%. Further dietary and pharmacological studies of PMS and SAD are needed to determine serotonin's involvement with symptoms of depressed mood, increased fatigue, and carbohydrate craving.
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PMID:Carbohydrate craving, mood changes, and obesity. 304 10

The gamma-crystallin fractions II, III and IV from calf eye lens were treated with the thiol-specific fluorescent probe 2-(4'-maleimidylanilino)naphthalene-6-sulfonate (MIANS), in order to determine the reactivity of the seven (gamma-II) or six (gamma-III, gamma-IV) cysteine residues. Two classes of reactive cysteines were distinguished by variations in fluorescence intensity with increasing molar excess of the probe, and approximately three cysteines were nonreactive in each gamma-crystallin. From the position of the emission maximum, it is apparent that MIANS-labeled cysteines of gamma-IV are in the least hydrophobic environment. Fluorescence energy transfer was observed from tryptophan to MIANS-labeled cysteines in both gamma-II and gamma-III crystallins, with efficiencies of 86% and 89%, respectively, but not in gamma-IV crystallin. We suggest that the spatial arrangements and microenvironments of cysteine residues of gamma-crystallins are sufficiently different from each other to account for the variations in fluorescence characteristics of the MIANS-labeled proteins and the lack of energy transfer in gamma-IV crystallins.
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PMID:Structure and stability of gamma-crystallins. II. Differences in microenvironments and spatial arrangements of cysteine residues. 381 5

The neurotransmitter precursors tryptophan and tyrosine are present in a variety of foods. In order to document possible effects of tryptophan and tyrosine on human behavior, single oral doses of these substances and matched placebos were administered to 20 men in a double-blind, crossover study. Various tests of mood state and performance were then administered. Tryptophan increased subjective fatigue and decreased self-ratings of vigor and alertness, but did not impair performance on any of the tests. Tyrosine produced no effects in our young population compared with placebo, but did decrease reaction time relative to tryptophan. It may be concluded that tryptophan has significant sedative-like properties, but unlike other sedatives may not impair performance.
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PMID:The effects of dietary neurotransmitter precursors on human behavior. 402 6

We examined the behavioral effects of the dietary constituents tryptophan and tyrosine on human mood, sensorimotor performance and pain sensitivity. Tryptophan and tyrosine are neurotransmitter precursors present in varying amount in protein-containing foods. Tryptophan (50 mg/kg) increased subjective drowsiness and fatigue but unlike many hypnotics did not impair sensorimotor performance. Tryptophan also decreased human pain sensitivity in a manner that was more specific than certain analgesic drugs.
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PMID:Mood, performance, and pain sensitivity: changes induced by food constituents. 676 30

One of the most important food components for the ability to concentrate is protein because certain amino acids are precursors of neurotransmitters, e.g. serotonin from tryptophan. There is a close relation between tryptophan content in the diet, serotonin biosynthesis in the brain and food intake. While lack of carbohydrates causes a symptomatic hypoglycemia which leeds to decreases in different functions and performances (e.g. memory and concentration, orientation, critical evaluation of environmental influences), glucose load does not mean an increased performance. In this respect dietary fats and minerals have not been investigated, some vitamins, e.g. thiamin, influence the functions of the nervous system. With coffee and caffeine containing beverages a drop of performance can be compensated for only a short time at the expense of energy reserves. Under the moderate influence of alcohol the function of nervous cells is markedly affected. In connection with medicine this negative effect is aggravated. After coffee and alcohol consumption events are subjectively experienced on quite a different level than can be objectively measured; misleading estimations are the consequence. A high meal frequency with small meals stimulates the serotonin biosynthesis and seems to reduce fatigue.
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PMID:[Nutrition and capacity for concentration in automobile drivers]. 685 55

1. An increased uptake of tryptophan in the brain may increase serotoninergic activity and recently has been suggested to be a cause of fatigue during prolonged exercise. The present study, therefore, investigates whether ingestion of tryptophan or the competing branched-chain amino acids (BCAAs) affect performance. Ten endurance-trained male athletes were studied during cycle exercise at 70-75% maximal power output, while ingesting, ad random and double-blind, drinks that contained 6% sucrose (control) or 6% sucrose supplemented with (1) tryptophan (3 g l-1), (2) a low dose of BCAA (6 g l-1) or (3) a high dose of BCAA (18 g l-1). 2. These treatments greatly increased the plasma concentration of the respective amino acids. Using the kinetic parameters of transport of human brain capillaries, BCAA supplements were estimated to reduce brain tryptophan uptake at exhaustion by 8-12%, while tryptophan ingestion caused a 7- to 20-fold increase. Exercise time to exhaustion was not different between treatments (122 +/- 3 min). 3. The data suggest that manipulation of tryptophan supply to the brain either has no additional effect upon serotoninergic activity during prolonged exhaustive exercise or that manipulation of serotoninergic activity functionally does not contribute to mechanisms of fatigue.
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PMID:Ingestion of branched-chain amino acids and tryptophan during sustained exercise in man: failure to affect performance. 747 39

The mechanisms of central fatigue are largely unexplored, but the central fatigue hypothesis suggests that increased brain serotonin (5-HT) can cause a deterioration in sport and exercise performance. There is now convincing evidence that exercise-induced increases in the plasma free tryptophan (f-TRP)/branched-chain amino acids (BCCA) ratio are associated with increased brain 5-HT and the onset of fatigue during prolonged exercise. Furthermore, when drugs are administered to alter brain 5-HT, they have the predicted effects on exercise performance. The influence of nutritional manipulations of f-TRP/BCCA on performance is less well established. The effects of BCCA supplementation on exercise performance are mixed, and the published studies often suffer from methodological flaws. Alternatively, dramatic reductions in f-TRP/BCCA and enhanced performance accompany carbohydrate feedings during prolonged exercise. However, it is difficult to distinguish between the effects of carbohydrate feedings on mechanisms that reside in the brain versus the muscles themselves.
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PMID:Carbohydrates, branched-chain amino acids, and endurance: the central fatigue hypothesis. 755 Feb 56


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