Acylcarnitine ester utilization by the hindlimb of warmblood horses at rest and following low intensity exercise and carnitine supplementation.

BACKGROUND: Acylcarnitines play an important role in fuel metabolism in skeletal muscle.

OBJECTIVE: To assess acylcarnitine ester utilization by the hindlimb of horses at rest and following low intensity exercise and carnitine supplementation.

ANIMALS AND METHODS: Acylcarnitine ester uptake by the hindlimb was investigated using the arteriovenous difference technique. Blood from six warmblood mares (mean age 12 ± 3 (SD) years and weighing 538 ± 39 kg) was collected simultaneously from the transverse facial artery and from the caudal vena cava. Food was withheld for 12 hours prior to exercise. Exercise comprised a standardized treadmill protocol consisting of 5 minutes of walk, 20 minutes of trot and thereafter another 5 minutes of walk. At the end of the first exercise day, three horses were given carnitine supplementation (100 mg/kg bodyweight), whereas the other horses received saline. The next day the exercise was repeated and blood samples collected similarly. Free carnitine and acylcarnitines were analyzed as their butyl ester derivatives in heparinized plasma by electrospray tandem mass spectrometry. Statistical analysis was performed using a general linear mixed model.

RESULTS: C3-carnitine, C6-carnitine and C14:1-carnitine showed the largest average extraction by the hindlimb at rest and C3-carnitine, C5:1-carnitine and C16-carnitine immediately after low-intensity exercise. Carnitine supplementation significantly increased free carnitine, C5-carnitine and C8-carnitine extraction.

CONCLUSION: Carnitine supplementation altered the extraction of acylcarnitines by the hindlimb in horses exercising at low intensity.

CLINICAL IMPORTANCE: Findings might aid in optimizing performance and myopathy prevention of the equine athlete.