Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Microbial metabolism wikipedia , lookup
Citric acid cycle wikipedia , lookup
Adenosine triphosphate wikipedia , lookup
Oxidative phosphorylation wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Fatty acid metabolism wikipedia , lookup
Biochemistry wikipedia , lookup
Close this window to return to IVIS www.ivis.org Proceedings of the 5th European Equine Nutrition & Health Congress April. 15-16, 2011 Waregem, Belgium Next EENHC Congress: 6th European Equine Nutrition & Health Congress: Feeding for Gastrointestinal Health Mar. 1-2, 2013- Ghent , Belgium Reprinted in IVIS with the permission of the Scientific Committee of the European Equine Health & Nutrition Congress: http://www.equine-congress.com/ Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS Energy metabolism of the performance horse Ingrid Vervuert Institute of Animal Nutrition, Nutrition Diseases and Dietetics, Faculty of Veterinary Medicine, University of Leipzig, Germany E-mail: [email protected] Introduction The superior athletic ability of horses is closely related to their high maximal aerobic capacity, large intramuscular energy stores (glycogen), high mitochondrial volume in muscle, the ability to increase oxygen-carrying capacity of blood at the onset of exercise (splenic contraction), efficient thermoregulation and the efficiency of gait (Hinchcliff & Geor 2008). The great athletic ability of the equine is summarized by selected variables in Table 1. Table 1: Selected physiological parameters in the equine and human athlete (adapted from Gäbel 2010) Parameter Rest Intensive Increase exercise rate Horses Heart rate (bpm) 30 210-250 7-8 Stroke volume (L) 1.0 1.7 1.7 Respiratory minute volume (L/min) 30 240-425 8-13 Haemoglobin (g/dl) 13 17-24 1.3-1.6 2-4 160-220 40-110 VO2 max (ml O2/kg/min) Humans Heart rate (bpm) 45 190-200 4.2-4.4 Stroke volume (L) 0.1 0.2 2 Respiratory minute volume (L/min) 4.5 38-40 8-9 4 50-90 13-23 VO2 max (ml O2/kg/min) VO2 max = maximal oxygen consumption The energy expenditure of exercised horses rises due to the energy cost of the work of the skeletal muscles, respiratory apparatus and cardiovascular system (Martin-Rosset 2008). Herby, oxygen consumption is supposed to be the best criterion of energy expenditure. In horses, the rate at which oxygen consumption can increase with the onset of exercise is superior (40-110-fold increase within 60 seconds, Table 1). The rapid increases in ventilation, cardiac output and haemoglobin allow for the rapid VO2, implying that the oxygen dependent processes for energy production within the muscle are able to utilize the O2. However, intensive exercise in horses, particularly when performed in hot and humid conditions will result in the depletion of the energy stores like liver and 23 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS muscle glycogen (Hyyppä et al. 1997) and in excessive water and electrolyte losses (Coenen 2005). These changes impair exercise capacity and result in cardiorespiratory and metabolic alterations contributing to fatigue (Hodgson & Rose 1994). The supply, uptake and utilization of substrates for the production of energy are integral components for the ability to carry out physical exercise. The primary sources for energy production in the exercising horse are carbohydrates and fats and, to a much lesser degree, protein (Hiney & Potter 1996). The extent to which each fuel is utilized depends on several factors, including the intensity and duration of exercise, the availability of fuels, and the influence of hormones. Energy for muscular work Muscular contraction results from the transformation of chemical energy into mechanical energy. The conversion of chemical energy into the mechanical energy of muscular movement requires the provision of adenosine triphosphate (ATP) which is the substrate utilized by the contracting muscle: myosin ATPase ATP + H2O ADP + Pi and kinetic energy ADP = adenosine diphosphate However, endogenous ATP stores within the muscles are very limited (~22-28 mmol/kg dry matter) and provide only energy for a few seconds (Hodgson 1985). To continue muscle contraction, ATP must be continuously resynthesised. The regeneration of ATP is achieved by two metabolic pathways which can be basically divided into 1) Anaerobic (without oxygen) phosphorylation and 2) Oxidative (aerobic) phosphorylation. Anaerobic phosphorylation Phosphocreatine reaction Creatine phosphate and ADP are the substrates for this reaction: creatine kinase Phosphocreatine + ADP creatine + ATP Endogenous phosphocreatine stores within the muscles are limited (58-62 mmol/kg dry matter) and provide only a restricted amount of ATP (Table 2). It is postulated that phosphocreatine reaction is of importance during the initial stages of high intensity exercise and during jumping (Snow 1991). Myokinase reaction ATP can be synthesized from ADP, and this reaction is catalyzed by myokinase. myokinase 2 ADP ATP + AMP 24 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS AMP = adenosine monophosphate This rapid reaction provides energy during severe exercise and maintains the muscle ATP: ADP ratio. Glycolysis ATP is regenerated from circulating glucose and glycogen stores. In a multiple step pathway, 2 ATP molecules result from the glycolytic pathway per glucose (Table 2). The production of lactate is a possible end stage of this anaerobic pathway. Oxidative phosphorylation The major energy source in muscle cells is the oxidation of free fatty acids and glucose, and to lesser extent amino acids like alanine. The oxidative phosphorylation pathway needs oxygen (aerobic pathway) provided by the circulation. The regeneration of ATP requires a series of complex steps requiring specific enzymes (Krebs cycle, ß oxidation of fatty acids, electron transport chain). During aerobic phosphorylation fuel is used efficiently (Table 2) but this pathway is a slower process than anaerobic metabolism with a rate limited by oxygen transport. Table 2: Overview over substrate utilisation and resulting ATP production during exercise Energy source Substrate Pathway Outcome ATP/mol Immediate response to exercise Muscle ATP anaerobic 1 Phosphocreatine anaerobic 1 Glycogen anaerobic 2 Blood Glucose anaerobic 2 Slow response to exercise Muscle Glycogen Liver Glucose aerobic 36-38 Blood Amino acids Muscle Liver Fatty acids aerobic ~140 Blood Triglycerides Adipose tissue Integration of anaerobic and aerobic pathways At the onset of exercise energy is primarily derived from the anaerobic pathways. At maximal short lasting exercise speeds, energy must be predominately generated by anaerobic pathways (Figure 1). Herby glycogen serves as the major fuel source, resulting in an accumulation of lactate (McMiken 1983, Table 3). However, within ~60 sec after the onset of exercise, there is a clear shift to aerobic metabolism (Figure 1). 25 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS Anaerobic contribution Aerobic contribution 100 90 % of total energy 80 70 60 50 40 30 20 10 0 400 m 1000 m Quarter Horse Race 1600 m 3200 m Thoroughbred Race 1600 m 2400 m Standardbred Race 2.Tag 80 km Ritt Cross country Endurance Figure 1: Energy partitioning during different types of exercise (adapted from Eaton 1994) 26 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS Table 3: Maximal lactate concentrations after different types of exercise (adapted from Pösö et al. 2008) Type of exercise Distance (km) Peak plasma lactate (mmol/L) Endurance rides 80 - 100 0.50 ± 0.2 Standardbred races 2.1 24.5 ± 0.7 Thoroughbred races 1.1 – 3.8 33.0 ± 1.9 Three-day event (cross country) 6.2 19.1 ± 4.2 Showjumping 9.00 ± 0.9 Polo 9.20 ± 1.2 At low to moderate exercise intensities, the oxidation of fatty acids provides the major source of energy. At moderate to high aerobic exercise intensities, the oxidation of fatty acids decreases and the oxidation of carbohydrates account for >50% of the amount of substrate utilized (Pösö et al. 2008, Figure 2). Energy expenditure (%) Fat 100 90 80 70 60 50 40 30 20 10 0 Glycogen Glucose 30 60 Exercise intensity (% VO2 max) Figure 2: Estimated relative contributions of fat, plasma glucose and muscle glycogen expenditure in horses during different type of exercise (adapted from Pösö et al. 2008) to energy Metabolic properties of muscle fiber types During exercise, metabolites and oxygen reach skeletal muscle fibers and muscular contraction results from the transformation of chemical energy into mechanical energy. Muscle fibers show significant differences in their morphologic, physiologic and biochemical properties within and between muscles. These differences represent the basis for the classification of fiber types. Muscle fibers have been differentiated either histochemically (staining reaction for myosin ATPase) into type I and type II myofibers (Rivero et al. 2008) or 27 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS immunohistochemically (based on antibodies directed against myosin heavy chain isoforms, Valberg 2008), hereby type 1, type 2a and 2x myofibers are most commonly found in the equine limb muscles. The different physiological and metabolic properties are illustrated in Table 4 and 5. Metabolic properties of muscle fiber types in horses (immunohistochemically differentiation, adapted from Valberg 2008) Type 1 Type 2a Type 2x Speed of contraction Slow Intermediate Fast Fatigue resistance High Intermediate Low Oxidative capacity High Intermediate Low Fat content High Intermediate Low Glycolytic capacity Low High High Glycogen content Low High High Table 4: Table 5: Metabolic properties of muscle fiber types in horses (histochemically differentiation, adapted from Rivero et al. 2008) Type I Type IIA Type IIAx Type IIaX Type IIX Speed of Slow Fast Intermediate Intermediate Very fast contraction Fatigue High Intermediate Intermediate Intermediate Low resistance Oxidative High High to Intermediate Intermediate Low capacity intermediate Fat content High Intermediate Glycolytic Relative High Intermediate Intermediate High capacity low Glycogen Relative High High content low Fiber-type composition varies extremely between muscles depending largely on function. For example, forelimb musculature consist of postural type I fibers, while propulsive muscles of the hindlimbs contain a high proportion of fasttwitch type II fibers (Rivero et al. 2008). Additionally, performance is highly correlated with selected muscle characteristics. Endurance capacity is linked to high percentages of type I and IIA fibers and high activities of oxidative enzymes, whereas sprint capacity is related to high percentages of type II fibers (Essén-Gustavsson 2008, Rivero et al. 2008). Sources of energy The major stored fuels for energy production during exercise occur in the form of carbohydrates and fats and to a lesser extent of proteins. The fat stores represent herby the largest nutrient reserve whereas the carbohydrate stores are limited. However, most studies in exercising horses have focussed on glycogen stores, whereas only a few studies have addressed muscle triglyceride or protein stores. 28 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS Glycogen stores In horses, resting muscle glycogen stores varied around 550-650 mmol/kg dry matter (Pösö et al. 2008), whereas in humans, resting muscle glycogen stores are significant lower (300-400 mmol/kg dry matter, Hultman & Greenhaff 1993). Following any type of exercise, glycogen stores within muscle and liver decline. The extent of the decrease will depend on the intensity and duration of exercise (Figure 3). During short-term intensive exercise, muscle glycogen stores may be depleted by 20-35%. Prolonged exercise results in the greatest depletion of muscle glycogen. For example, during endurance rides in the order of 100 km, muscle glycogen can decline between 50 and 100% (Hodgson & Rose 1994). However after cessation of exercise, the rate of glycogen repletion is much lower than in other animal species and in the human athlete. Following complete glycogen depletion, complete repletion may take up to 92 h. In general, it is concluded that glycogen resynthesis is a limiting step in recovery after a strenuous competition exercise. before exercise after exercise Glucose (mmol/kg DM) 700 600 500 400 300 200 100 0 100 km 80 km Cross country 4 x 620 m 800 m 2000 m Figure 3: Decline in muscle glycogen concentrations (expressed in glucose mmol/kg dry matter) during different types of exercise in horses (adapted from Hodgson & Rose 1994) Fat stores The different fat depots like skeletal muscle or adipose tissue store triglycerides, with the largest storage capacity in the adipose tissue. The triglyceride content in the skeletal muscle varied between 7-128 mmol/kg dry matter with large breed related differences (Essén-Gustavsson 2008). It is supposed that triglyceride stores are used to a great extent during prolonged exercise (Essén-Gustavsson 2008), but obviously without depletion of muscle fat even during endurance rides (Snow et al. 1991). Interestingly, high pre-exercise muscle levels of triglycerides before exercise seems to favourite the utilisation of muscle triglycerides during exercise (Essén-Gustavsson 2008). However, the higher utilisation of muscle triglyceride stores does not necessarily reflect a better exercise performance. It is 29 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS reported that those endurance horses with a greater depletion of muscle glycogen stores and a lower reduction of muscle triglycerides were among the best during a 50 km ride compared to those horses that finished the competition at lower speeds (Table 6). The largest store of triglycerides is the adipose tissue. Fatty acids (hydrolysis of triglycerides in glycerol and fatty acids) are efficiently mobilised from the adipose tissue into the bloodstream during exercise, and those fatty acids may be utilised for ATP production in the muscle rather than intramuscular triglycerides stores. However, the role of muscle triglycerides stores and their contribution to fat oxidation in energy metabolism during exercise is still open. Table 6: Muscle (M. gluteus) glycogen and triglyceride reduction of horses after a 50 km endurance ride (adapted from Essén-Gustavsson 2008) Racing times (min) 209-231 237-287 Glycogen reduction (mmol/kg DM) 313 ± 118 115 ± 103 Triglyceride reduction (mmol/kg DM) 13 ± 12 37 ± 31 Protein stores It has been shown that exercise induces changes in the amino acid profile in blood and muscle. An increase in branched-chain amino acids (BCAA) such as leucine, isoleucine, and valine is observed during prolonged sub-maximal exercise in horses (Pösö et al. 1991, Vervuert et al. 2005) which may have been due to increased output by the liver, where proteolysis has been shown to accelerate during exercise (Dohm et al. 1987). Furthermore, it is supposed that certain amino acids are oxidised for energy production in the muscle (Strüder et al. 1996), although the contribution of protein to energy expenditure in horses during exercise remains open (approximating to a maximum of 10-16 %). Take home message Energy demands increase with exercise, the extent being dependent on the type and duration of exercise. Maintenance of muscular work during exercise requires the provision of ATP which is the substrate utilized by the contracting muscle. As endogenous ATP stores are very limited, carbohydrates, fats and, to a much lesser degree, protein are utilized for ATP production. The aerobic pathway to regenerate ATP is the most efficient way but this pathway is a slower process than the anaerobic metabolism. At the onset of exercise and during high speed exercise energy is primarily derived from the anaerobic pathways, herby muscle glycogen serves as the major fuel source. The production of lactate is a possible end stage of this anaerobic pathway. 30 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS References Coenen, M., 2005. Exercise and stress. Impact on adaptive processes involving water and electrolytes. In: Advances in Equine Nutrition III. J.D. Pagan (editor). Nottingham University Press, Hampshire, UK, 265-288. Dohm, G.L.; Tabscott, E.B.; Kasperek, G.J., 1987. Protein degradation during exercise and recovery. Med. Sci. Sports Exerc. Suppl. 189, 166-171. Eaton, M.D., 1994. Energetics and performance. In: The athletic horse. Principles and practice of equine sports medicine, Hodgson, D.R., Rose, R.J. (eds.), Saunders, Philadelphia, 49-62. Essén-Gustavsson, B., 2008. Triglyceride storage in the skeletal muscle. In: Nutrition of the exercising horse, Saastamoinen, M.T., Martin-Rosset, W. (eds.), EAAP publication No. 125, Wageningen Academic publishers, 3142. Gäbel, G., 2010. Physiologische Grundlagen der körperlichen Belastung. LBH: Proceedings, 5. Leipziger Tierärztekongress, Band 1, 119-123. Hinchcliff, K.W., Geor, R.J. 2008. The horse as an athlete: a physiological overview. In: Equine Exercise Physiology, Hinchcliff, K.W., Geor, R.J., Kaneps, A.J. (eds.), Saunders Elsevier, Philadelphia, 2-11. Hodgson, D.R. and R.J. Rose, 1994. The athletic horse. Principles and practice of equine sports medicine. Saunders, Philadelphia, PA, USA. Hiney, K.M., Potter, G.D., 1996. A review of recent research on nutrient and metabolism in the athletic horse. Nutr. Res. Reviews 9, 149-173. Hodgson, D.R. 1985. Energy considerations during exercise. Equine Practice 1, 447-460. Hultman, E., Greenhaff, P.L., 1993. Ernährung und Energiereserven. In: Shepard, , R.J., Astrand, P.O. (eds.), Ausdauer im Sport, Deutsche Ärzte Verlag, 137-144. Hyyppä, S., L.A. Räsänen, Pösö, A.R., 1997. Resynthesis of glycogen in skeletal muscle from standardbred trotters after repeated bouts of exercise. Am. J. Vet. Res. 58, 162-166. Martin-Rosset, W., 2008. Energy requirements and allowances of exercising horses. In: Nutrition of the exercising horse, Saastamoinen, M.T., MartinRosset, W. (eds.), EAAP publication No. 125, Wageningen Academic publishers, 103-138. McMiken, D.F., 1983. An energetic basis of equine performance. Equine Vet. J. 15, 123-133. Pösö, A.R., Essen-Gustavsson, B., Lindholm, A., Persson, S.G.B., 1991. Exerciseinduced changes in muscle and plasma amino acid levels in the Standardbred horse. In: Persson, S.G.B.; Lindholm, A.; Jeffcott, L.B. (eds.). Equine Exercise Physiology 3, ICEEP Publications, Davis, California, 9296. Pösö, A.R., Hyyppä, S, Geor, R.J., 2008. Metabolic responses to exercise and training. In: In: Equine Exercise Physiology, Hinchcliff, K.W., Geor, R.J., Kaneps, A.J. (eds.), Saunders Elsevier, Philadelphia, 248-272. Rivero, J.L.L., Piercy, R.J., 2008. Muscle physiology: responses to exercise and training. In: Equine Exercise Physiology, Hinchcliff, K.W., Geor, R.J., Kaneps, A.J. (eds.), Saunders Elsevier, Philadelphia, 30-80. 31 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium Reproduced in IVIS with the permission of the Scientific Committee of the EENHC Close window to return to IVIS Snow, D.H. 1991. Fatigue and exhaustion in the horse. Austr. Equine Vet. 9, 108111. Strüder, K.H., Hollmann, W., Platen, P., Duperly, J., Fischer, H.G., Weber, K., 1996. Alterations in plasma free tryptophan and large neutral amino acids do not affect perceived exertion and prolactin during 90 min of treadmill exercise. Int. J. Sports Med. 17, 73-79. Valberg, S.J., 2008. Skeletal muscle function. In: Clinical biochemistry of domestic animals, Kaneko, J.J., Harvey, J.W., Bruss, M.L. (eds.), Academic press, California, 459-484 Vervuert I, Coenen M, Watermülder E., 2005. Metabolic responses to oral tryptophan supplementation before exercise in horses. J. Anim. Physiol. Anim. Nutr. (Berl).89(3-6), 140-145. 32 Proceedings of the 5th European Equine Nutrition & Health Congress (EENHC), 2011 - Waregem, Belgium