Effect of tryptophan and of glucose on exercise capacity of horses

Farris, James W.; Hinchcliff, Kenneth W.; McKeever, Kenneth H.; Lamb, D. R.; Thompson, Donald L.

doi:10.1152/jappl.1998.85.3.807

Cited by 83 publications

(52 citation statements)

References 42 publications

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“…Several physiological effects have been reported for l-tryptophan, mainly in the veterinary medicine field (e.g., horses, oxen or sheep) with regard to its nutritional value, such as its effects on physical abilities (19). The present study demonstrated that co-administration of l-tryptophan with glucose increased the energy expenditure without any exercise (Fig.…”

Section: Discussionsupporting

confidence: 70%

L-Tryptophan Suppresses Rise in Blood Glucose and Preserves Insulin Secretion in Type-2 Diabetes Mellitus Rats

Inubushi

Kamemura

Oda

et al. 2012

J Nutr Sci Vitaminol

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Summary Ample evidence indicates that a high-protein/low-carbohydrate diet increases glucose energy expenditure and is beneficial in patients with type-2 diabetes mellitus (T2DM). The present study was designed to investigate the effects of l-tryptophan in T2DM. Blood glucose was measured by the glucose dehydrogenase assay and serum insulin was measured with ELISA in both normal and hereditary T2DM rats after oral glucose administration with or without l-d-tryptophan and tryptamine. The effect of tryptophan on glucose absorption was examined in the small intestine of rats using the everted-sac method. Glucose incorporation in adipocytes was assayed with [ 3 H]-2-deoxy-d-glucose using a liquid scintillation counter. Indirect computer-regulated respiratory gas-assay calorimetry was applied to assay energy expenditure in rats. l-Tryptophan suppressed both serum glucose and insulin levels after oral glucose administration and inhibited glucose absorption from the intestine. Tryptamine, but not l-tryptophan, enhanced insulin-stimulated [ 3 H]-glucose incorporation into differentiated adipocytes. l-Tryptophan increased glucose-associated energy expenditure in rats in vivo. l-Tryptophan-rich chow consumed from a young age preserved the secretion of insulin and delayed the progression of T2DM in hereditary diabetic rats. The results suggested that l-tryptophan suppresses the elevation of blood glucose and lessens the burden associated with insulin secretion from b-cells.

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Section: Discussionsupporting

confidence: 70%

L-Tryptophan Suppresses Rise in Blood Glucose and Preserves Insulin Secretion in Type-2 Diabetes Mellitus Rats

Inubushi

Kamemura

Oda

et al. 2012

J Nutr Sci Vitaminol

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“…The origin and importance of this elevation in glucose concentration for exercise performance is not clear, but endurance during both maximal (Lacombe et al, 2001) and sub-maximal (Farris et al, 1998) exercise is improved by glucose infusion, indicating that high blood glucose availability could improve performance. Alterations in glucose metabolism (both in tissue uptake and release from the liver) are likely to occur in horses on forage-only diets, based on the low insulin levels observed here and earlier , and might be the reason for the elevated glucose levels during exercise.…”

Section: Discussionmentioning

confidence: 99%

A forage-only diet alters the metabolic response of horses in training

Jansson

Lindberg

2012

Animal

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Most athletic horses are fed a high-starch diet despite the risk of health problems. Replacing starch concentrate with high-energy forage would alleviate these health problems, but could result in a shift in major substrates for muscle energy supply from glucose to short-chain fatty acids (SCFA) due to more hindgut fermentation of fibre. Dietary fat inclusion has previously been shown to promote aerobic energy supply during exercise, but the contribution of SCFA to exercise metabolism has received little attention. This study compared metabolic response with exercise and lactate threshold (V La4 ) in horses fed a forage-only diet (F) and a more traditional high-starch, low-energy forage diet (forage-concentrate diet -FC). The hypothesis was that diet F would increase plasma acetate concentration and increase V La4 compared with diet FC. Six Standardbred geldings in race training were used in a 29-day change-over experiment. Plasma acetate, non-esterified fatty acids (NEFA), lactate, glucose and insulin concentrations and venous pH were measured in samples collected before, during and after a treadmill exercise test (ET, day 25) and muscle glycogen concentrations before and after ET. Plasma acetate concentration was higher before and after exercise in horses on diet F compared with diet FC, and there was a tendency ( P 5 0.09) for increased V La4 on diet F. Venous pH and plasma glucose concentrations during exercise were higher in horses on diet F than diet FC, as was plasma NEFA on the day after ET. Plasma insulin and muscle glycogen concentrations were lower for diet F, but glycogen utilisation was similar for the two diets. The results show that a high-energy, forage-only diet alters the metabolic response to exercise and, with the exception of lowered glycogen stores, appears to have positive rather than negative effects on performance traits.

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“…Human subjects that perform an intense motor task are faster exhausted after intake of a 5-HT 1A receptor agonist (14) or a selective serotonin reuptake inhibitor (15). In animals, injection of the 5-HT precursor tryptophan in the blood or directly in the CNS accelerates the exhaustion occurring during motor activity (16,17). Moreover, the time to exhaustion is decreased by serotonin receptor agonists and increased by serotonin antagonists (18).…”

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confidence: 99%

Serotonin spillover onto the axon initial segment of motoneurons induces central fatigue by inhibiting action potential initiation

Cotel

Exley

Cragg

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

133

141

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Motor fatigue induced by physical activity is an everyday experience characterized by a decreased capacity to generate motor force. Factors in both muscles and the central nervous system are involved. The central component of fatigue modulates the ability of motoneurons to activate muscle adequately independently of the muscle physiology. Indirect evidence indicates that central fatigue is caused by serotonin (5-HT), but the cellular mechanisms are unknown. In a slice preparation from the spinal cord of the adult turtle, we found that prolonged stimulation of the raphespinal pathway-as during motor exercise-activated 5-HT 1A receptors that decreased motoneuronal excitability. Electrophysiological tests combined with pharmacology showed that focal activation of 5-HT 1A receptors at the axon initial segment (AIS), but not on other motoneuronal compartments, inhibited the action potential initiation by modulating a Na + current. Immunohistochemical staining against 5-HT revealed a high-density innervation of 5-HT terminals on the somatodendritic membrane and a complete absence on the AIS. This observation raised the hypothesis that a 5-HT spillover activates receptors at this latter compartment. We tested it by measuring the level of extracellular 5-HT with cyclic voltammetry and found that prolonged stimulations of the raphe-spinal pathway increased the level of 5-HT to a concentration sufficient to activate 5-HT 1A receptors. Together our results demonstrate that prolonged release of 5-HT during motor activity spills over from its release sites to the AIS of motoneurons. Here, activated 5-HT 1A receptors inhibit firing and, thereby, muscle contraction. Hence, this is a cellular mechanism for central fatigue.movement | spike genesis | input-output gain | movement control P rolonged physical activity leads to motor fatigue (1, 2). The force produced by muscles decreases in part because of the lack of glycogen (3) in the muscle and/or failures at the neuromuscular junctions (4). In addition to this well-described muscle fatigue, motor fatigue also involves an element originating in the CNS (5-8). This "central fatigue" is characterized by a decreased ability to contract the muscle fibers adequately during a motor activity and is observed independently of the muscle fatigue (6). It is often studied during maximal voluntary contractions (5, 6, 9). Nevertheless, it is also present during weak physical contraction (1,2,8,(10)(11)(12). Central fatigue secures rotation of motor units (13) and prevents hyperactivity of muscles (6). Elements of central fatigue involve the cortex (6), and the spinal cord at the level of motoneurons (MNs) (5).The cellular mechanisms responsible for a decrease of the activity of MNs remain unknown. However, evidence suggests that central fatigue correlates with increased levels of serotonin (5-HT) in the CNS. Human subjects that perform an intense motor task are faster exhausted after intake of a 5-HT 1A receptor agonist (14) or a selective serotonin reuptake inhibitor (15). In animals, inject...

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Effect of tryptophan and of glucose on exercise capacity of horses

Cited by 83 publications

References 42 publications

L-Tryptophan Suppresses Rise in Blood Glucose and Preserves Insulin Secretion in Type-2 Diabetes Mellitus Rats

L-Tryptophan Suppresses Rise in Blood Glucose and Preserves Insulin Secretion in Type-2 Diabetes Mellitus Rats

A forage-only diet alters the metabolic response of horses in training

Serotonin spillover onto the axon initial segment of motoneurons induces central fatigue by inhibiting action potential initiation

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