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

During long-distance exercise, branched-chain amino acid (BCAA) catabolism could lead to an increase in the blood tryptophan/BCAA ratio and an early onset of 'central fatigue'. Based on these considerations, we studied the modifications of blood serum BCAA and tryptophan (Try) levels in 30 endurance horses competing in rides varying in distance from 20 to 72 km. From all horses, blood samples were drawn just before and just after the end of the ride. Samples were analysed for their leucine (Leu), valine (Val), isoleucine (Iso) and Try levels. Data were processed by anova, using sampling moment and ride as factors, and by LSD post hoc test. Significant differences were recorded among the different distance rides for Leu, Val, Iso, Try, Try/BCAA ratio; the same trend was recorded between samples taken at the start and the end of the race for Val and Leu. The main effect observed was an increase of BCAA levels for all rides, except the 72-km ride; for Try, a significant increase was present in all races, except the 50-km ride. The Try/BCAA ratio decreased in 20- and 50-km races and increased in the others. These data confirm that long-distance exercise involves a mobilization of BCAA. The utilization of BCAA seems to be important in prolonged exercise: in the 72-km ride, we observed a decrease in BCAA blood serum levels, while a major role of Try was indicated by its increase, resulting in a rise of the Try/BCAA ratio.
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PMID:Blood serum branched chain amino acids and tryptophan modifications in horses competing in long-distance rides of different length. 1505 43

Fatigue during prolonged exercise has traditionally been attributed to the occurrence of a "metabolic end point", where muscle glycogen concentrations are depleted, plasma glucose concentrations are reduced, and plasma free fatty acid levels are elevated. But there exists also a "central fatigue hypothesis" which is based on the increase in the concentration of brain serotonin (5-Hydroxytryptamine or 5-HT) during exercise. However, the physiological mechanisms for central fatigue are largely unexplored, therefore we designed several experiments where central serotonergic activity was manipulated. These animal and human experiments showed that although brain neurotransmission had significantly increased, the supplementation with L-TRP did not lead to premature fatigue. In human studies we used several reuptake inhibitors in order to modify brain activity during exercise. These results clearly showed that time trial performance could not be influenced, but that during prolonged exercise the brain activity can be influenced, as measured by the peripheral hormones.
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PMID:Exercise, fatigue, neurotransmission and the influence of the neuroendocrine axis. 1520 69

The level of tryptophan and 5-hydroxyindoleacetic acid were measured in the brain (striatum) of rats on tryptophan-deficient diet and tryptophan-enriched diet. We measured concentrations of tryptophan and 5-hydroxyindoleacetic acid in striatum by using microdialysis and HPLC methods. The extracellular level of tryptophan and 5-hydroxyindoleacetic acid concentration in the striatum of a tryptophan-reduced rats was decreased by about 50% compared with a tryptophan-enriched diet. In the tryptophan-reduced condition, the rats an increased the running time of more than 100 min, compared with those on a tryptophan-enriched diet. These results suggest the tryptophan and 5-hydroxytryptamine in the central nervous system are involved in fatigue.
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PMID:The effect of tryptophan deficiency in the brain on rat fatigue levels: a rat model of fatigue reduction. 1520 70

The role of increased hypothalamic tryptophan (TRP) availability on thermoregulation and rates of core temperature increase and heat storage (HS) during exercise was studied in normal untrained rats running until fatigue. The rats were each anesthetized with 2.5% tribromoethanol (1.0 ml kg(-1) ip) and fitted with a chronic guiding cannula attached to the right lateral cerebral ventricle 1 week prior to the experiments. Immediately before exercise, they were randomly injected through these cannulae with 2.0 microl of 0.15 M NaCl (SAL; n=6) or 20.3 microM L-TRP solution (n=7). Exercise consisted of running on a treadmill at 18 m min(-1) and 5% inclination until fatigue. Body temperature was recorded before and during exercise with a thermistor probe implanted into the peritoneal area. Rates of core temperature increase (HR, degrees C min(-1)) and heat storage (HSR, cal min(-1)) were calculated. TRP-treated rats showed a rapid increase in body temperature which was faster than that observed in the saline-treated group during the exercise period. The TRP group also showed a higher rate of core temperature increase and HS. TRP-treated rats that presented higher HR and HSR also fatigued much earlier than saline-treated animals (16.8+/-1.1 min TRP vs. 40+/-3 min SAL). This suggests that the reduced running performance observed in TRP-treated rats is related to increased HR and HSR induced by intracerebroventricular injection of TRP in these animals.
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PMID:Intracerebroventricular tryptophan increases heating and heat storage rate in exercising rats. 1521 65

There are two major aspects focused in the present work. The first one concerns the tryptophan: a cerebral serotonin precursor aminoacid that alters serotonin and its relation to the offer of nutrients (carbohydrates, proteins and aminoacids). As an essential aminoacid it can be modulated through diet, having its physiological and behavioral effects changed, as it can be learned in the present study. The second aspect is related to the precocious fatigue during sports and activities of short and long duration and its relation with the serotoninergic cerebral function. What causes this precocious fatigue and how it is developed is yet largely unknown. The present work reviews the mechanism involved in the "central fatigue hypothesis" and the offer of carbohydrates and aminoacids as a strategy to retard this effect during physical activity.
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PMID:[Serotoninergic system and its implications on physical exercise]. 1564 Aug 76

There is much more seasonal difference in higher latitudes than in lower latitudes. In a significant portion of the population of the northern United States, the shorter days of fall and winter precipitate a syndrome that can consist of depression, fatigue, hypersomnolence, hyperphagia, carbohydrate craving, weight gain, and loss of libido. If these symptoms persist in the winter, abate as the days grow longer, and disappear in the summer, the diagnosis of seasonal affective disorder (SAD) can be made. Many hypotheses exist regarding the biochemical mechanisms behind the predisposition toward this disease, including circadian phase shifting, abnormal pineal melatonin secretion, and abnormal serotonin synthesis. Although the mechanism(s) behind this disease is not fully known, one treatment appears to address each of the theories. Light therapy is a natural, non-invasive, effective, well-researched method of treatment for SAD. Various light temperatures and times of administration of light therapy have been studied, and a combination of morning and evening exposure appears to offer the best efficacy. Other natural methods of treatment have been studied, including L-tryptophan, Hypericum perforatum (St. John's wort), and melatonin.
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PMID:Epidemiology, etiology, and natural treatment of seasonal affective disorder. 1577 58

BACKGROUND: The serotonergic system is associated with numerous brain functions, including the resetting of the mammalian circadian clock. The synthesis and metabolism of 5-HT in the brain increases in response to exercise and is correlated with high levels of blood-borne tryptophan (TRP). The present investigation was aimed at testing the existence of a daily rhythm of TRP and 5-HT in the blood of athletic horses. METHODS: Blood samples from 5 Thoroughbred mares were collected at 4-hour intervals for 48 hours (starting at 08:00 hours on day 1 and finishing at 4:00 on day 2) via an intravenous cannula inserted into the jugular vein. Tryptophan and serotonin concentrations were assessed by HPLC. Data analysis was conducted by one-way repeated measures analysis of variance (ANOVA) and by the single cosinor method. RESULTS: ANOVA showed a highly significant influence of time both on tryptophan and on serotonin, in all horses, on either day, with p values < 0.0001. Cosinor analysis identified the periodic parameters and their acrophases (expressed in hours) during the 2 days of monitoring. Both parameters studied showed evening acrophases. CONCLUSION: The results showed that serotonin and tryptophan blood levels undergo nycthemeral variation with typical evening acrophases. These results enhance the understanding of the athlete horse's chronoperformance and facilitate the establishment of training programs that take into account the nycthemeral pattern of aminoacids deeply involved in the onset of central fatigue.
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PMID:Central fatigue and nycthemeral change of serum tryptophan and serotonin in the athletic horse. 1586 Jan 31

The serotonergic hypothesis for depression in Parkinson's disease (PD) states that the reduced cerebral serotonergic activity that occurs in PD constitutes a biological risk factor for depression. The aim of our study was to assess the serotonergic hypothesis of depression in PD patients using an experimental approach. In a double-blind, randomized order, placebo-controlled crossover design, the response on the Profile of Mood States (POMS) questionnaire to acute tryptophan depletion (ATD) was studied in 15 PD nondepressed patients and 15 control subjects, without a prior personal or family history of depression. PD patients had lower (worse) baseline scores on the sadness, fatigue and vigor subscales of the POMS, in both ATD and the placebo condition, but not on the tension and anger subscales. There was however neither a significance between group effect, nor significance within-group effect due to ATD. We could find no evidence of a specific serotonergic vulnerability of PD patients for depression. Therefore, our results do not support the serotonergic hypothesis for depression in PD.
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PMID:The serotonergic hypothesis for depression in Parkinson's disease: an experimental approach. 1620 79

An account of the tryptophan (Trp)-5-hydroxytryptamine (5-HT)-central fatigue theory is provided and an explanation of how oral administration of BCAAs can decrease fatigue on the basis of this theory is given. The rate-limiting step in the synthesis of 5-HT is the transport of Trp across the blood-brain barrier. This transport is influenced by the fraction of Trp available for transport into the brain and the concentration of the other large neutral amino acids, including the BCAAs, which are transported via the same carrier system. During endurance exercise, there is an uptake of Trp by the brain, suggesting that this may increase the synthesis and release of 5-HT in the brain. Oral intake of BCAAs may reduce this uptake and also brain 5-HT synthesis and release, thereby delaying fatigue. Other hypotheses for the effect of BCAAs on central fatigue are included.
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PMID:Branched-chain amino acids and central fatigue. 1636 97

Several factors have been identified to cause peripheral fatigue during exercise, whereas the mechanisms behind central fatigue are less well known. Changes in the brain 5-hydroxytryptamine (5-HT) level is one factor that has been suggested to cause fatigue. The rate-limiting step in the synthesis of 5-HT is the transport of tryptophan across the blood-brain barrier. This transport is influenced by the fraction of tryptophan available for transport into the brain and the concentration of the other large neutral amino acids, including the BCAAs (leucine, isoleucine, and valine), which are transported via the same carrier system. Studies in human subjects have shown that the plasma ratio of free tryptophan (unbound to albumin)/BCAAs increases and that tryptophan is taken up by the brain during endurance exercise, suggesting that this may increase the synthesis of 5-HT in the brain. Ingestion of BCAAs increases their concentration in plasma. This may reduce the uptake of tryptophan by the brain and also 5-HT synthesis and thereby delay fatigue. Accordingly, when BCAAs were supplied to human subjects during a standardized cycle ergometer exercise their ratings of perceived exertion and mental fatigue were reduced, and, during a competitive 30-km cross-country race, their performance on different cognitive tests was improved after the race. In some situations the intake of BCAAs also improves physical performance. The results also suggest that ingestion of carbohydrates during exercise delays a possible effect of BCAAs on fatigue since the brain's uptake of tryptophan is reduced.
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PMID:A role for branched-chain amino acids in reducing central fatigue. 1642 44


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