Hydrocortisone levels in the urine and blood of horses treated with ACTH.

This study focused on determining if the therapeutic use of a hormone, ACTH, raises cortisol levels in horses’ urine above the established limit set by the International Conference of Racing Authorities. The researchers administered ACTH to Thoroughbred horses, collected samples, analyzed them, and found the cortisol levels remain below the threshold.

Study Objective

• The research aimed to investigate whether therapy with ACTH (Adrenocorticotropic hormone), could raise the concentration of cortisol in horse urine above the 1000 ng/ml limit, a threshold established by the International Conference of Racing Authorities.

Study Methodology

• ACTH was administered to three Thoroughbred horses (200 iu, intramuscular injection).
• Urine and blood samples were collected at different intervals following treatment.
• These samples were analyzed using an immunoenzymatic system (ELISA) and High-Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS).
• For comparison, the cortisol levels in untreated horses after exercise were assessed by collecting and analyzing 101 urine samples and 103 serum samples.

Study Findings

• The highest cortisol level in the urine (the peak level), which was detected 8 hours following ACTH administration, was about 600 ng/ml as per both the ELISA and HPLC-MS results.
• The peak concentration of cortisol in the blood serum was approximately 250 ng/ml as per the ELISA results, although HPLC-MS consistently recorded a lesser value.
• The average cortisol level in post-race horses was 135.1±72.1 ng/ml in urine and 90.1±41.7 ng/ml in serum.
• High levels of 20beta-dihydrocortisol, a metabolite of cortisol, were found in the urine while 11beta-desoxycortisol, a cortisol precursor, was detected in the serum. The latter showed high cross-reactivity with cortisol on ELISA.

Conclusion

• The study concluded that the therapeutic dosage of ACTH (200 iu, intramuscular) did not elevate urinary cortisol levels beyond the threshold limit of 1000ng/ml, a benchmark set by the International Conference of Racing Authorities.