Case-control exercise challenge study on the pathogenesis of high serum gamma-glutamyl transferase activity in racehorses.
Authors: Mann Sabine, Abuelo Angel, Stokol Tracy, Wakshlag Joseph J, Bayly Warwick, Reed Steven, Gandy Jeff, Ramsay Joshua David, Divers Thomas J
Journal: Equine veterinary journal
Summary
Elevated serum gamma-glutamyl transferase (GGT) activity in racing Thoroughbreds and Standardbreds has been linked to exercise intolerance, yet the underlying mechanisms remain poorly understood. Researchers conducted a case-control study comparing seven actively racing horses with persistently high GGT activity (≥50 IU/L without liver disease) to matched controls of similar age and training intensity, collecting blood samples before exercise and at 15 and 120 minutes post-exercise, alongside baseline micronutrient profiling and advanced metabolomic analysis via liquid chromatography-mass spectrometry. High GGT cases demonstrated significantly elevated baseline total glutathione, taurocholic acid (indicating altered bile acid metabolism), cortisol and cholesterol concentrations, alongside dysregulated oxylipids and isoprostanes—yet notably, these biomarker differences did not change in response to the exercise challenge itself. The findings suggest that high GGT activity in racehorses reflects chronic alterations in glutathione recycling and subclinical cholestasis rather than an acute post-exercise metabolic crisis, pointing towards enhanced hepatic glutathione turnover as a compensatory response to underlying oxidative or biliary stress. For practitioners, this implies that persistently elevated GGT in racehorses warrants investigation of resting metabolic status—including antioxidant capacity, bile acid handling and chronic stress markers—rather than attributing the elevation solely to exercise-induced hepatocellular injury.
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Practical Takeaways
- •High GGT activity in racing Thoroughbreds and Standardbreds may indicate altered glutathione metabolism rather than primary liver disease; baseline metabolic profiling could help identify affected horses earlier
- •Exercise response patterns differed between high GGT and normal GGT horses, suggesting the syndrome represents maladaption rather than an acute exercise-induced response
- •Veterinarians should monitor resting cortisol, glutathione, and bile acid concentrations in competition horses showing persistently elevated GGT, as these may indicate systemic stress or cholestasis
Key Findings
- •High GGT racehorses had elevated baseline total glutathione, taurocholic acid, cortisol, and cholesterol compared to controls
- •Specific oxylipid and isoprostane mediators were altered in high GGT cases at baseline
- •No significant case-dependent biomarker changes occurred immediately after exercise or at 120 minutes post-exercise
- •Altered glutathione metabolism and mild cholestasis may underlie the high GGT syndrome in racehorses