A single bout of high-intensity exercise modulates the expression of vitamin D receptor and vitamin D-metabolising enzymes in horse skeletal muscle.
Authors: Puangthong Chanikarn, Sukhong Patskit, Saengnual Pattrawut, Srikuea Ratchakrit, Chanda Metha
Journal: Equine veterinary journal
Summary
# Editorial Summary Vitamin D's role in equine skeletal muscle adaptation remains poorly understood, particularly following intense exercise when muscle remodelling occurs. Chanikarn and colleagues investigated how a single high-intensity exercise bout affects vitamin D receptor (VDR) and metabolising enzyme expression in gluteus medius muscle samples from six healthy ponies, alongside measurements of skeletal muscle stem cell (SMSC) activity, serum 25(OH)D levels, blood lactate and creatine kinase. VDR and the SMSC marker Pax7 showed significant upregulation immediately post-exercise alongside elevated blood lactate and CK, suggesting coordinated activation of the vitamin D system during acute muscle stress; however, whilst CYP27B1 (the enzyme activating vitamin D) correlated with serum 25(OH)D2 levels, both decreased significantly in the 1–3 weeks following exercise, whereas the inactivating enzyme CYP24A1 remained unchanged. These findings indicate that high-intensity work triggers vitamin D system engagement as part of the muscle repair response, but the subsequent reduction in circulating active vitamin D and CYP27B1 expression may signal compromised vitamin D metabolism during recovery—a pattern worth monitoring in performance horses, particularly if repeated intense training cycles deplete functional vitamin D status and impair the SMSC-mediated adaptation process that depends on this nutrient.
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Practical Takeaways
- •High-intensity exercise triggers vitamin D system activation in skeletal muscle; monitor vitamin D status in performance horses undergoing intense training as deficiency may impair muscle repair capacity
- •Post-exercise serum 25(OH)D2 reductions suggest compromised vitamin D metabolism after intense work; consider supplementation strategies for horses in heavy work to support muscle recovery
- •The vitamin D system appears involved in muscle stem cell activation and repair processes; adequate vitamin D nutrition may be important for optimizing recovery in competition and training programmes
Key Findings
- •High-intensity exercise significantly upregulated Pax7 and VDR protein expression immediately post-exercise, correlating with elevated blood lactate and serum CK levels
- •Serum 25(OH)D2 level reduced significantly immediately post-exercise and at 1 and 3 weeks post-exercise, correlating with CYP27B1 protein expression changes
- •CYP24A1 protein expression remained unchanged throughout the study period despite exercise-induced muscle damage
- •The findings suggest an association between skeletal muscle stem cell activity and vitamin D system activation in response to exercise-induced muscle injury in horses