Effects of short-term training on insulin sensitivity and skeletal muscle glucose metabolism in standardbred horses.
BACKGROUND
Increased insulin sensitivity occurs after a period of exercise training, but the mechanisms underlying this training-associated increase in insulin action have not been investigated.


OBJECTIVE
To examine the effects of short-term endurance training (7 consecutive days) and a subsequent period of inactivity (5 days) on whole body insulin sensitivity and GLUT-4 protein and the activities of glycogen synthase (GS) and hexokinase (HK) in skeletal muscle. It was hypothesised that training would increase insulin sensitivity in association with increased GLUT-4 protein and activities of GS and HK, but that these changes would be transient, returning to baseline after 5 days of inactivity.


METHODS
Seven mature Standardbred horses completed training consisting of 7 consecutive days of 45 min of treadmill exercise at a speed that elicited 55% of pretraining maximal aerobic capacity (VO2peak). Insulin sensitivity was determined by rate of glucose disposal (M) during the last 60 min of a 120 min euglycaemic-hyperinsulinaemic clamp (EHC) performed before (-2 days) and at 1 and 6 days following training. VO2peak was measured before (UT) and after (TR) training and the period of inactivity (IA).


RESULTS
Training resulted in a 9% increase in mean VO2peak (P<0.05) that was maintained following inactivity (IA). Mean M values were more than 2-fold higher (P<0.05) in TR than in UT. Mean M was also higher (P<0.05) in IA when compared to UT. GLUT-4 protien abundancewas more than 10-fold higher in TR and IA (P<0.001) than in UT. Pre-EHC GS activity and GS fractional velocity were increased (P<0.05) in TR when compared to UT and IA. Pre-EHC HK activity was increased (P<0.05) in IA when compared to UT and TR. Muscle glycogen was 66% lower (P<0.05) in TR than in UT and IA.


CONCLUSIONS
Short-term training resulted in increases in whole body insulin sensitivity, and GLUT-4 protein content and glycogen synthase activity in skeletal muscle. The enhancements in insulin sensitivity, GLUT-4 protein and glycogen synthase activity were still evident after 5 days of inactivity.


CONCLUSIONS
Insulin resistance in equids has been associated with obesity and predisposition to laminitis. Regular physical activity may mitigate risk of these conditions via enhancement of insulin sensitivity and/or control of bodyweight.
Stewart-Hunt
L
L
Department of Biomedical Science and Pathobiologyt, University of Guelph, Guelph, Ontario NIG 2W1, Canada.
Geor
R J
RJ
McCutcheon
L J
LJ
D000818:Animals; D019540:Area Under Curve; D005260:Female; D005947:Glucose / Q000378:metabolism*; D015309:Glucose Clamp Technique / Q000662:veterinary; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D006593:Hexokinase / Q000378:metabolism; D006736:Horses / Q000097:blood / Q000378:metabolism / Q000502:physiology*; D007328:Insulin / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D013997:Time Factors
D051275:Glucose Transporter Type 4; D007328:Insulin; D006006:Glycogen Synthase; D006593:Hexokinase; D005947:Glucose