Hydrocortisone concentrations in post-race urine from horses

Area of Science:

• Equine Sports Medicine
• Analytical Chemistry
• Pharmacology

Background:

• Hydrocortisone is an endogenous substance, requiring baseline concentration data for regulatory control in racing animals.
• Establishing normal physiological levels is crucial for monitoring drug use in equine sports.
• International thresholds exist for hydrocortisone, necessitating local data for accurate interpretation.

Purpose of the Study:

• To determine hydrocortisone concentrations in post-race urine samples from horses competing in Brazil.
• To compare these findings with established international thresholds for hydrocortisone.
• To investigate potential influences of sex and race timing on hydrocortisone levels.

Main Methods:

• Urine samples were collected from horses participating in races in Brazil.
• High-Performance Liquid Chromatography with Ultraviolet detection (HPLC-UV) was used for hydrocortisone analysis.
• Data were analyzed based on concentration ranges, sex, and time of sample collection (afternoon/evening).

Main Results:

• A wide variation in urinary hydrocortisone concentrations was observed (mean 93 +/- 69 ng/ml).
• The majority of horses (91%) exhibited levels between 0-150 ng/ml; only 1% exceeded 500 ng/ml.
• No statistically significant effect of horse sex or time of race (afternoon vs. evening) on hydrocortisone levels was found.

Conclusions:

• The study established reference ranges for hydrocortisone in Brazilian racehorses, showing predominantly low levels.
• Findings suggest that most observed hydrocortisone levels fall well below international thresholds, indicating low prevalence of illicit use.
• Sex and race timing do not significantly impact hydrocortisone concentrations in this population.