Abstract

The metabolism of testosterone (<TEX>$17{\beta}$</TEX>-hydroxy-androst-4-en-3-one) was confirmed in horse after a single intramuscular administration of testosterone cypionate (750 mg). Solvent extracts of urine obtained with enzymatic hydrolysis and methanolysis were analyzed by GC/MS after oxime t-butyldimethylsilyl (oxime-TBDMS) derivatization. The structures of four urinary metabolite after testosterone administration in horse were determined based on EI mass spectra and <TEX>$5{\alpha}$</TEX>-androstane-<TEX>$3{\beta}$</TEX>, <TEX>$17{\alpha}$</TEX>-diol and <TEX>$5</TEX><TEX>{\alpha}$</TEX>-androstane-<TEX>$3{\beta}$</TEX>-ol-17-one as major was confirmed with authentic standard. Also the concentrations of <TEX>$5{\alpha}$</TEX>-androstane-<TEX>$3{\beta}$</TEX>, <TEX>$17{\alpha}$</TEX>-diol, <TEX>$5{\alpha}$</TEX>-androstane-<TEX>$3{\beta}$</TEX>, <TEX>$17{\beta}$</TEX>-diol, dehydroepiandrosterone (DHEA), <TEX>$5{\alpha}$</TEX>-androstane-<TEX>$3{\beta}$</TEX>-ol-17-one and testosterone were determined in the urine of normal subjects and the urine after administration. The recovery and detection limit in the most drugs were 86.3~94.7% and 1~3 ppb, respectively. Correlation coefficients for calibration were in the range of 0.984~0.999. Excretion profile of testosterone presents the rapid and large increasement up to maximum values at days 5 after administration and the slow regression. The relative ratios of testosterone, its metabolites over DHEA were determined for indication of testosterone administration in horse doping.