Hydrocortisone concentrations in post-race urine from horses.

As hydrocortisone is an endogenous substance, it is first necessary to establish its normal concentrations so as to be able to control its use in racing animals. This study was designed to establish the hydrocortisone concentrations in post-race urine samples of horses racing in Brazil and also to evaluate the results in relation to the international threshold set for this drug. Urine samples were analysed by HPLC-UV. The results were evaluated according to the concentration range as well as sex and time of sample collection (afternoon or evening races). The results showed a high degree of variation in the concentrations of hydrocortisone in the urine (93 +/- 69 ng/ml). The maximum concentration observed was 646 ng/ml, although only a few horses (around 1%) showed levels within the range 500-650 ng/ml, 91% being in the range 0-150 ng/ml. The data suggested a normal distribution curve. Statistical analysis showed no significant influence of sex or time of sample collection.