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

An investigation was undertaken to demonstrate whether therapeutic treatmen t with ACTH raises hydrocortisone (cortisol) levels in horse urine above th e limit (1000 ng/ml) established by the International Conference of Racing Authorities with the aim of controlling the abuse of cortisol and ACTH in e quine sports. ACTH (200 iu) was administered i.m. to 3 Thoroughbred horses; urine and blood samples were collected at intervals afterwards and analyse d by an immunoenzymatic system (ELISA) and HPLC-MS, To ascertain post exerc ise cortisol levels in untreated horses, 101 urine and 103 serum samples we re taken from horses immediately after racing and analysed by ELISA, The pe ak urine level of cortisol, detected 8 h after ACTH administration, was aro und 600 ng/ml using either ELISA or HPLC-MS. The peak serum cortisol concen tration was found to be around 250 ng/ml by ELISA, but consistently less by HPLC-MS. Mean cortisol levels in post race horses were 135.1 +/- 72.1 ng/m l in urine and 90.1 +/- 41.7 ng/ml in serum. sigh levels of the metabolite 20 beta-dihydrocortisol in urine and the cortisol precursor 11 beta-desoxyc ortisol in serum were found. The latter showed high cross-reactivity with c ortisol on ELISA. In our experiment, treatment with ACTH 200 iu i.m. did no t raise urinary cortisol levels above the 1000 ng/ml threshold proposed by the ICRA.