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  • Author or Editor: Maria E. Everts x
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Abstract

Objective—To investigate the effects of moderate short-term training on K+ regulation in plasma and erythrocytes during exercise and on skeletal muscle Na+,K+-ATPase concentration in young adult and middle-aged horses.

Animals—Four 4- to 6-year-old and four 10- to 16-yearold Dutch Warmblood horses.

Procedure—The horses underwent a 6-minute exercise trial before and after 12 days of training. Skeletal muscle Na+,K+-ATPase concentration was analyzed in gluteus medius and semitendinosus muscle specimens before and after the 12-day training period. Blood samples were collected before and immediately after the trials and at 3, 5, 7, and 10 minutes after cessation of exercise for assessment of several hematologic variables and analysis of plasma and whole-blood K+ concentrations.

Results—After training, Na+,K+-ATPase concentration in the gluteus medius, but not semitendinosus, muscle of middle-aged horses increased (32%), compared with pretraining values; this did not affect the degree of hyperkalemia that developed during exercise. The development of hyperkalemia during exercise in young adult horses was blunted (albeit not significantly) without any change in the concentration of Na+,K+-ATPase in either of the muscles. After training, the erythrocyte K+ concentration increased (7% to 10%) significantly in both groups of horses but did not change during the exercise trials.

Conclusions and Clinical Relevance—In horses, the activation of skeletal muscle Na+,K+-ATPase during exercise is likely to decrease with age. Training appears to result in an increase in Na+,K+-ATPase activity in skeletal muscle with subsequent upregulation of Na+,K+-ATPase concentration if the existing Na+,K+-ATPase capacity cannot meet requirements. (Am J Vet Res 2005;66:1252–1258)

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in American Journal of Veterinary Research

Abstract

Objective—To investigate whether training for show jumping that is commenced early after birth affects the characteristics of equine locomotory muscle.

Animals—19 Dutch Warmblood horses.

Procedures—Horses were assigned to a trained or not trained (control) group. After weaning, training (free jumping [2 d/wk] that was alternated with a 20-minute period of exercise in a mechanical rotating walker [3 d/wk]) was started and continued until horses were 3 years old. Fiber type composition (determined from myosin heavy chain [MyHC] content), fiber area, diffusion index (area supplied by 1 capillary), citrate synthase activity, and Na+,K+-ATPase content were assessed in gluteus medius muscle specimens collected at 0.5, 1, 2, and 3 years.

Results—Developmental changes included an increase in MyHC fiber type IIa and a decrease in type IIad; increases in fiber area, diffusion index, and citrate synthase activity; and a decrease in Na+,K+-ATPase content. The MyHC fiber type I and type IId were detected in high and low proportions, respectively. Training increased Na+,K+-ATPase content, but did not affect other variables.

Conclusions and Clinical Relevance—In horses, show jumping training at an early age resulted in increased Na+,K+-ATPase content of the deep portions of the gluteus medius muscle. The lack of training effects on the other muscle characteristics can partly be explained by the fact that an appropriate (aerobic) fiber type composition was already established at training commencement. These data also suggested that the developmental changes in equine muscle represent sufficient adaptation to meet the demands of this specific training.

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in American Journal of Veterinary Research

Abstract

Objective—To determine whether postnatal development of oxidative capacity and capillary supply of skeletal muscle is affected by various movement regimens in horses.

Animals—35 foals.

Procedures—Dutch Warmblood foals were allocated into 3 groups (box stall rest, box stall rest with training, and free pasture exercise). Training comprised an increasing number of gallop sprints from 1 week after birth to 22 weeks of age. From 22 to 48 weeks, the 3 groups were combined and allowed to exercise freely. Capillary supply (diffusion index [ie, area supplied by 1 capillary]), citrate synthase (CS) activity, and succinate dehydrogenase (SDH) activity were measured in biopsy specimens of deep gluteus medius muscle.

Results—During the first 22 weeks, diffusion index increased in all 3 groups (the training and pasture groups had a smaller increase, compared with the box stall rest group), total SDH activity increased in the training and pasture groups and decreased in the box stall rest group, and CS activity decreased in all groups. The effect of the various movement regimens on the diffusion index remained after the groups were combined.

Conclusions and Clinical Relevance—Withholding of exercise had a negative effect on the capillary supply (ie, diffusion index increased) that remained after box stall rest was discontinued and on oxidative capacity. Box stall rest with training prevented the negative effects and eventually had the same positive effect as pasture exercise.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To investigate the effects of acute exercise and long-term training on Na+,K+-ATPase content, mRNA isoforms, and protein concentration in equine muscle.

Animals—6 Standardbreds.

Procedures—Horses performed a bout of exercise on a treadmill before and after 18 weeks of combined interval and endurance training. Muscle biopsy specimens were obtained from vastus lateralis muscle (VLM) and pectoralis descendens muscle (PDM) before and after exercise. The Na+,K+-ATPase content, mRNA isoforms, and protein concentrations were determined by use of [3H]ouabain binding, real-time PCR assay, and western blotting, respectively.

Results—6 Na+,K+-ATPase mRNA isoforms were present in equine muscle, but only A2 and B1 proteins were detected. Exercise before training resulted in increases of mRNA isoforms A1, A2, A3, and B2 in VLM and A1 and B3 in PDM. Training increased resting values for mRNA isoforms A3 and B1 in VLM and B3 in PDM. The Na+,K+-ATPase, [3H]ouabain binding, and proteins of mRNA A2 and B1 increased in VLM, whereas in PDM, only A2 protein increased as a result of training. After training, effects of strenuous exercise on mRNA expression were no longer detectable.

Conclusions and Clinical Relevance—Equine muscle contained all Na+,K+-ATPase mRNA isoforms, but only A2 and B1 proteins could be detected. Expression of these isoforms changed as a result of strenuous exercise and long-term training, representing an adaptive response. Determination of Na+,K+-ATPase gene expression may be relevant for understanding alterations in excitability during neuromuscular diseases.

Full access
in American Journal of Veterinary Research