Dietary energy source and physical conditioning affect insulin sensitivity and skeletal muscle glucose metabolism in horses
Article first published online: 8 NOV 2010
© 2010 EVJ Ltd
Equine Veterinary Journal
Special Issue: Proceedings of the 8th International Conference on Equine Exercise Physiology
Volume 42, Issue Supplement s38, pages 355–360, November 2010
How to Cite
STEWART-HUNT, L., PRATT-PHILLIPS, S., McCUTCHEON, L. J. and GEOR, R. J. (2010), Dietary energy source and physical conditioning affect insulin sensitivity and skeletal muscle glucose metabolism in horses. Equine Veterinary Journal, 42: 355–360. doi: 10.1111/j.2042-3306.2010.00255.x
- Issue published online: 8 NOV 2010
- Article first published online: 8 NOV 2010
- [Paper received for publication 09.01.10; Accepted 28.05.10]
- muscle glycogen;
- GLUT-4 protein;
- glycogen synthase;
Reasons for performing study: Starch rich (S) feeds reduce insulin sensitivity in untrained horses when compared to high fat (F) feeds, but insulin sensitivity is not affected when S or F are fed during exercise training. The effects of S vs. F on training-associated alterations in skeletal muscle glucose metabolism are unknown.
Objectives: To determine the effects of dietary energy source on training-associated changes in insulin sensitivity, skeletal muscle GLUT4 protein and hexokinase (HK) and glycogen synthase (GS) activities in horses.
Methods: After a baseline period on an all forage diet (Phase 1), horses were adapted to high starch (S) or high fat (F) diets (n = 7/group) for 6 weeks (Phase 2) and then completed 7 weeks of exercise training (Phase 3) on the same diets. To measure insulin sensitivity (SI), minimal model analysis of a frequently-sampled i.v. glucose tolerance test was performed at the end of each phase. Middle gluteal muscle biopsies to measure GLUT-4 protein content, muscle glycogen and HK and GS activities were taken before and after euglycaemic-hyperinsulinaemic clamps administered after each phase. Data were analysed by repeated measures ANOVA.
Results: In S, SI was 36% lower (P<0.05) after Phase 2 when compared to Phase 1 but was unchanged in F. After Phase 3, SI was increased (P<0.01) in S and F compared to Phase 2 and did not differ (P>0.05) between diets. Middle gluteal muscle GLUT-4 protein and post clamp HK activity were increased (P<0.05) in S after Phase 3, with higher (P<0.01) GLUT4 in S than in F. GS activities were unchanged in both diets.
Conclusions: Adaptation to S resulted in decreased SI mitigated by moderate physical conditioning. Increased GLUT-4 protein content and HK activity in S may have contributed to higher SI after training.