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theses

There is a well documented decline in exercise capacity, immune function, insulin sensitivity and hypothalamic-pituitary-adrenal axis function in aged horses. Aerobic training can partially reverse age-related declines in performance measures, endocrine and immune function, and insulin sensitivity in horses. The mechanisms behind the adaptive response to exercise in horses require further research. Based on the comparative literature, several mediators of energy homeostasis and adaptation to exercise were identified for investigation in whole blood and skeletal muscle of horses. Young and aged unconditioned Standardbred mares underwent an acute submaximal exercise test. Plasma cortisol, insulin and glucose concentrations were determined pre- and post-exercise. Whole blood and gluteus medius biopsies were analyzed for gene expression of inflammatory cytokines, HSP70 and HSP90 pre- and post-exercise. Skeletal muscle was also analyzed for protein content of HSP70, HSP90, AMPK, Akt and AS160 pre- and post-exercise. Exercise increased plasma cortisol concentration in both young and aged mares, with the duration of the post-exercise rise in cortisol altered in aged horses. Although the magnitude of the insulin response to exercise was not different between young and aged horses, plasma insulin was elevated sooner and declined earlier in aged mares. Subsequently, aged mares had a shorter duration of elevated plasma glucose concentration post-exercise than young mares. Exercise increased IL-β expression in whole blood of young and aged mares, with young mares having greater exercise-induced expression of IL-β. Cytokine expression was not altered in skeletal muscle, regardless of age or exercise. Young and aged horses had increased HSP70 expression in whole blood following exercise, with young horses exhibiting greater exercise-induced HSP70 expression. HSP90 expression in whole blood following exercise was increased only in young horses. HSP70 and HSP90 expression in skeletal muscle was increased following exercise in both young and aged horses, with age altering the timing of HSP70 expression. There were no changes in skeletal muscle protein content of HSP70 and HSP90; or in activation or total protein concentration of AMPK, Akt and AS160, due to exercise or age. In conclusion, mediators of energy homeostasis and the adaptive response to exercise are altered with age in horses.

ETD_5703

Ph.D.

Includes bibliographical references

by Ryan Charles Avenatti

doi:10.7282/T3FJ2F8C

ETD doctoral

The author owns the copyright to this work.