Control of the misuse of testosterone in castrated horses based on an international threshold in plasma.

Testosterone is an endogenous steroid produced primarily in the testes. Trace levels of testosterone are found in urine samples from geldings, as testosterone is also secreted by the adrenal. An international threshold of free and conjugated testosterone in urine (20 ng/mL) was adopted by the International Federation of Horseracing Authorities (IFHA) in 1996 for controlling testosterone misuse in geldings. In view of the recent popularity of using blood in doping control testing, it is necessary to establish a threshold for testosterone in gelding plasma. A liquid chromatography-mass spectrometry (LC/MS) method was developed for quantifying low levels of free testosterone in gelding plasma. Based on a population study of 152 post-race plasma samples, the mean ± SD concentration of plasma testosterone was determined to be 14.7 ± 6.8 pg/mL. Normal distribution could be obtained after square-root or cube-root transformation, resulting in respective tentative thresholds of 49 or 55 pg/mL (corresponding to a risk factor of less than 1 in 10 000). A rounded-up threshold of 100 pg/mL of free testosterone in plasma was proposed. Based on the administration of Testosterone Suspension 100 to six geldings, the same average detection time of 14 days was observed in either plasma or urine using the proposed plasma threshold and the existing international urine threshold. The maximum detection time was 18 days in plasma and 20 days in urine. The results demonstrated the proposed plasma threshold is effective in controlling the misuse of testosterone in geldings. Similar results were subsequently obtained in Europe, and this proposed threshold was adopted by IFHA in October 2013.

Evidence of purinergic neurotransmission in isolated, intact horse sweat glands.

BACKGROUND: Fluid secretion by sweat glands in response to heat and exercise is underpinned by increases in intracellular calcium. In horses, this is primarily via ß2-adrenoceptors, but studies in equine sweat gland cell lines have indicated a possible role for purinergic agonists. Knowledge of equine sweating stimulus-secretion mechanisms in intact glands from healthy animals would allow future comparison to determine whether these mechanisms are affected in equine anhidrosis. HYPOTHESIS/OBJECTIVES: To determine whether purinergic agonists can induce changes in intracellular calcium in intact, freshly isolated equine sweat glands. ANIMALS: Eleven healthy thoroughbred horses from the Hong Kong Jockey Club were used in this study. METHODS: Freshly isolated equine sweat glands were loaded with the calcium-sensitive fluorescent dye fura-2 AM, and changes in intracellular calcium were recorded before, during and after stimulation by purinergic agonists. RESULTS: Purinergic agonists ATP and UTP generated significant increases in intracellular calcium. CONCLUSIONS AND CLINICAL IMPORTANCE: The results show that it is possible to investigate stimulus-secretion coupling mechanisms by fluorescence imaging in equine sweat glands that have been isolated from fresh skin samples. Such isolated glands retain functional ß2-adrenoceptors and P2Y purinergic receptors that couple to a calcium-signalling pathway. Using isolated, intact sweat glands therefore offers a very useful model for the further study of secretory processes in equine sweat glands, and using this experimental approach could facilitate a better understanding of how these mechanisms are affected in equine anhidrosis.