Factors influencing muscle fibre composition in the horse

Guy, Paul Scott (1978) Factors influencing muscle fibre composition in the horse. PhD thesis, University of Glasgow.

Abstract

1) Horse skeletal muscle was found to consist of three distinct fibre types. a) A high myosin ATPase activity at pH 9.4, high oxidative, high glycolytic capacity fibre (FTH). b) A high myosin ATPase activity at pH 9.4, low oxidative, high glycolytic capacity fibre (FT). c) A low myosin ATPase activity at pH 9.4, high oxidative, low glycolytic capacity fibre (ST). 2) Most dog skeletal muscle examined also contained these fibre types but identification was more difficult. Some mongrels had an unusual fibre type profile, with only two types being distinguished, one having high oxidative, high myosin ATPase at pH 9.4 activity and the other having low oxidative, low myosin ATPase at pH 9.4 activity. 3) In the muscles examined in the horse, fibre type percentages were similar in both deep and superficial regions of the muscle. In the gluteus medius variation within a muscle and between contralateral muscles was small for enzyme activities, glycogen and protein. Triglyceride variation was much larger and results were impossible to interpret. 4) The percentages of the three fibre types in the horse varied from muscle to muscle, being generally lower in the fore limb muscles. This variation between muscles was not as great in the dog. 5) In the gluteus medius muscle of the horse, the fastest breed had the highest percentage of high myosin ATPase activity at pH 9.4 fibres. This relationship was less obvious in-the other muscles examined. 6) The greyhound dog had the highest percentage of high myosin ATPase activity at pH 9.4 in all of the muscles examined when compared to the foxhound and cross-bred mongrel. This percentage reached 100% in the deltoideus of several of the greyhounds. 7) In the horse, the Quarterhorse had the largest Lactate Dehydrogenase and Aldolase activities and the lowest Citrate Synthase and 3-Hydroxyacyl CoA Dehydrogenase activities indicating a high capacity for anaerobic metabolism. Similarly, the breeds best suited to endurance exercise had the highest capacity for aerobic metabolism. The donkey, in general, had the lowest enzyme activities. 8) In the dog, greyhound muscle was highest in aerobic and glycolytic carbohydrate metabolism enzyme activities. The mongrel had higher activities in fatty acid oxidation enzymes. 9) During a training programme involving both aerobic and anaerobic work, the activity of several enzymes increased progressively but at different rates, with an approximately twofold increase in Aldolase, Lactate Dehydrogenase, Alanine Aminotransferase, Aspartate Aminotransferase, Citrate Synthase and 3-Hydroxy-acyl CoA Dehydrogenase and a 30% increase in Creatine Phosphokinase. When the isoenzyme content of Lactate Dehydrogenase was examined, an increase in the percentage of the H subunit was found. When the relative activity of the subunits were determined, an increase in both subunits occurred. Hexokinase Glycogen Synthetase Glycerol-3-Phosphate Dehydrogenase and protein were unaffected by training. Glycogen increased by about 33% with training. 10) There was a significant increase in the percentage of FTH fibres at the expense of both the percentage of ST and FT fibres after ten weeks training. 11) A decrease in the activity of those enzymes which increased with training occurred after five weeks detraining. By ten weeks detraining, the activity of those enzymes had increased again to values above those at the end of training. Enzymes which were unchanged with training were similarly unaffected by detraining. Glycogen remained elevated above pre-training levels after ten weeks detraining. 12) Glycogen depletion occurred in horse skeletal muscle after both maximal and sub-maximal exercise. The beta1, beta2 adrenoreceptor blocker dl propranolol (0.2 mg.kg-1) decreased the rate of glycogen depletion during maximal exercise. During submaximal exercise, glycogen depletion was unaffected by dl propranolol (0.2 mg.kg-1) the biologically inactived propranolol (0.2 mg,kg-1 ) or the beta1 blocker dl metoprolol (0.2 mg.kg-1).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: D H Snow
• Keywords: Veterinary science, Animal sciences
• Date of Award: 1978
• Depositing User: Enlighten Team
• Unique ID: glathesis:1978-73785
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73785