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Effect of tryptophan and of glucose on exercise capacity of horses.
Abstract: We hypothesized that central fatigue may have a role in limiting the endurance capacity of horses. Therefore, we tested the effect of infusing tryptophan and/or glucose on endurance time and plasma concentrations of free tryptophan and other substrates thought to affect tryptophan uptake into the brain of seven mares (3-4 yr of age, 353-435 kg) that ran on a treadmill at 50% of maximal O2 consumption to fatigue. With use of a counterbalanced crossover design, the horses were infused with tryptophan (100 mg/kg in saline solution) or a similar volume of saline solution (placebo) before exercise. During exercise, horses received infusions of glucose (2 g/min, 50% wt/vol) or a similar volume of saline. Thus the treatments were 1) tryptophan and glucose (T & G), 2) tryptophan and placebo (T & P), 3) placebo and glucose (P & G), and 4) placebo and placebo (P & P). Mean heart rate, hematocrit, and concentration of plasma total solids before and during exercise were similar for all trials. Mean time to exhaustion was reduced (P < 0.05) for T & P and T & G compared with P & P [86.1 +/- 6.9 and 87.1 +/- 6.8 vs. 102.3 +/- 10.3 (SE) min], whereas endurance for P & G (122.4 +/- 11.9 min) was greater than for all other trials (P < 0.05). Compared with nontryptophan trials, during the tryptophan trials plasma prolactin increased (P < 0.05) nearly threefold before exercise and almost twofold early in exercise. Muscle glycogen concentrations were reduced (P 0.05) concentrations of plasma free fatty acids or ratios of branched-chain amino acids to free tryptophan. In conclusion, tryptophan infusion reduced endurance time, which was consistent with the central fatigue hypothesis. The failure of glucose infusion to alleviate the effects of tryptophan and the absence of significant muscle glycogen reduction in the tryptophan trials suggest that the early onset of fatigue in the tryptophan trials is not due to a lack of readily available substrate.
Publication Date: 1998-09-08 PubMed ID: 9729551DOI: 10.1152/jappl.1998.85.3.807Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.
This study investigated the effects of infusing tryptophan, glucose, or both on the endurance capacity of horses, following the hypothesis that central fatigue could limit endurance capacity. The findings suggest that tryptophan infusion reduces endurance time, consistent with the central fatigue hypothesis, while glucose infusion did not mitigate the effects of tryptophan, leading to an early onset of fatigue not due to a lack of available substrate.
Study Design and Experimentation Process
- Seven mares were made to run on a treadmill at 50% of their maximal oxygen consumption until they felt fatigued. The experiment was carried out under different conditions where the horses were infused with either tryptophan, glucose, both, or neither (acting as a placebo).
- The treatment categories were tryptophan and glucose (T & G), tryptophan and placebo (T & P), placebo and glucose (P & G), and placebo and placebo (P & P). The administration of these treatments was done using a counterbalanced crossover design to limit bias and ensure the accuracy of results.
- Measurements of heart rate, hematocrit (proportion of blood that is made up of red blood cells), and plasma total solids concentration were taken before and during exercise. These parameters were found to be similar across all trials, signifying that only the treatments varied within the experiment.
Findings and Conclusion
- The mean time to exhaustion was found to be reduced when horses were only given the tryptophan treatments (T & P and T & G), as compared to placebo and placebo (P & P) trials.
- The endurance time was significantly higher when horses received the glucose placebo (P & G) treatment compared to all other conditions.
- In the tryptophan trials, plasma prolactin levels increased significantly before the start of exercise and early during the exercise phase, and muscle glycogen concentrations were reduced in the placebo trials (P & G and P & P).
- The infusion of glucose did not affect the concentrations of plasma free fatty acids or the ratios of branched-chain amino acids to free tryptophan.
- The results suggest that infusion of tryptophan reduces endurance time, supporting the central fatigue hypothesis. The early onset of fatigue in tryptophan trials was not due to a lack of readily available substrate, as indicated by the fact that glucose infusion did not alleviate the effects of tryptophan.
Cite This Article
APA
Farris JW, Hinchcliff KW, McKeever KH, Lamb DR, Thompson DL.
(1998).
Effect of tryptophan and of glucose on exercise capacity of horses.
J Appl Physiol (1985), 85(3), 807-816.
https://doi.org/10.1152/jappl.1998.85.3.807 Publication
Researcher Affiliations
- School of Physical Activity and Educational Services, College of Veterinary Medicine, The Ohio State University, Columbus, Ohio 43210, USA.
MeSH Terms
- Animals
- Blood Glucose / metabolism
- Blood Proteins / metabolism
- Body Weight / physiology
- Diet
- Fatty Acids, Nonesterified / blood
- Female
- Glucose / pharmacology
- Glycogen / metabolism
- Heart Rate / physiology
- Hematocrit
- Horses / physiology
- Muscle, Skeletal / metabolism
- Oxygen Consumption / drug effects
- Physical Endurance / drug effects
- Physical Exertion / drug effects
- Prolactin / blood
- Time Factors
- Tryptophan / pharmacology
Citations
This article has been cited 16 times.- Acri G, Testagrossa B, Piccione G, Arfuso F, Giudice E, Giannetto C. Central and Peripheral Fatigue Evaluation during Physical Exercise in Athletic Horses by Means of Raman Spectroscopy. Animals (Basel) 2023 Jul 5;13(13).
- Ma H, Yao S, Bai L, Bai S, Liu G. The effects of rumen-protected tryptophan (RPT) on production performance and relevant hormones of dairy cows. PeerJ 2022;10:e13831.
- Jansson A, Gunnarsson VÞ, Ringmark S, Ragnarsson S, Söderroos D, Ásgeirsson E, Jóhannsdóttir TR, Liedberg C, Stefánsdóttir GJ. Increased body fat content in horses alters metabolic and physiological exercise response, decreases performance, and increases locomotion asymmetry. Physiol Rep 2021 Jun;9(11):e14824.
- Ferlazzo A, Cravana C, Fazio E, Medica P. The different hormonal system during exercise stress coping in horses. Vet World 2020 May;13(5):847-859.
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- Perrier JF, Rasmussen HB, Jørgensen LK, Berg RW. Intense Activity of the Raphe Spinal Pathway Depresses Motor Activity via a Serotonin Dependent Mechanism. Front Neural Circuits 2017;11:111.
- Connysson M, Muhonen S, Jansson A. Road transport and diet affect metabolic response to exercise in horses. J Anim Sci 2017 Nov;95(11):4869-4879.
- Cotel F, Exley R, Cragg SJ, Perrier JF. Serotonin spillover onto the axon initial segment of motoneurons induces central fatigue by inhibiting action potential initiation. Proc Natl Acad Sci U S A 2013 Mar 19;110(12):4774-9.
- Lustgarten MS, Price LL, Logvinenko T, Hatzis C, Padukone N, Reo NV, Phillips EM, Kirn D, Mills J, Fielding RA. Identification of serum analytes and metabolites associated with aerobic capacity. Eur J Appl Physiol 2013 May;113(5):1311-20.
- Alberghina D, Giannetto C, Piccione G. Peripheral serotoninergic response to physical exercise in athletic horses. J Vet Sci 2010 Dec;11(4):285-9.
- Hadjicharalambous MP, Kilduff LP, Pitsiladis YP. Brain serotonergic and dopaminergic modulators, perceptual responses and endurance exercise performance following caffeine co-ingested with a high fat meal in trained humans. J Int Soc Sports Nutr 2010 May 27;7:22.
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- Reemtsma FP, Giers J, Horstmann S, Stoeckle SD, Gehlen H. Concentration Changes in Plasma Amino Acids and Their Metabolites in Eventing Horses During Cross-Country Competitions. Animals (Basel) 2025 Jun 22;15(13).
- Park T, Yoon J, Yun Y, Unno T. Comparison of the fecal microbiota with high- and low performance race horses. J Anim Sci Technol 2024 Mar;66(2):425-437.
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