Hydrocortisone Concentrations in Post-Race Urine from Horses L.M. Ribeiro Neto 1,2 *, M.C. Salvadori 1 and H.S. Spinosa 3 1 Department of Antidoping Control, Jockey Club of Sa¬ o Paulo, Sa¬ o Paulo-SP; 2 Toxiko¨ n Assessoria Toxicolo¨ gica, Sa¬ o Paulo-SP; 3 Department of Pathology, Faculty of Veterinary Medicine, University of Sa¬ o Paulo, Sa¬ o Paulo-SP, Brazil *Correspondence:Toxiko¨ n Assessoria Toxicolo¨ gica, Rua Salvador Correa, 346, Sa¬ o Paulo-SP, 04109-070, Brazil Ribeiro-Neto, L.M., Salvadori, M.C. and Spinosa, H.S., 2000. Hydrocortisone concentrations in post-race urine from horses. Veterinary Research Communications, 24(4), 239^244 ABSTRACT As hydrocortisone is an endogenous substance, it is ¢rst necessary to establish its normal concentra- tions 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 signi¢cant in£uence of sex or time of sample collection. Keywords: chromatography, cortisol, doping, horse, hydrocortisone, urine Abbreviations: ACTH, adrenocorticotrophic hormone; HPLC-UV, high-performance liquid chromato- graphy with ultraviolet detection; i.m., intramuscular(ly) INTRODUCTION Corticosteroids are widely used for their anti-in£ammatory and anti-allergic e¡ects in human and veterinary medicine. Hydrocortisone is the main glucocorticosteroid secreted by the adrenal cortex gland and acts to limit the body's response to stress. The hot weather in Brazil may be an additional factor causing stress. As hydro- cortisone may improve a horse's performance, it is widely used in illegal medication and, being an endogenous substance, control of abuse can only be achieved through knowledge of the concentration range in biological £uids from untreated post- competition horses. High levels of hydrocortisone may indicate the administration of hydrocortisone itself or of ACTH, a peptide hormone that controls the secretion of hydrocortisone through a negative feedback mechanism (Gotzmann et al., 1995; Houghton, 1995). Misuse of hydrocortisone led the international racing authorities to set a threshold of 1.0 mg/ml in urine, in order to control the illegal use of this drug. Veterinary Research Communications, 24 (2000) 239^244 # 2000 Kluwer Academic Publishers. Printed in the Netherlands 239