Metabolic studies of 1-testosterone in horses.

1-Testosterone (17β-hydroxy-5α-androst-1-en-3-one), a synthetic anabolic steroid, has been described as one of the most effective muscle-building supplements currently on the market. It has an anabolic potency of 200 as compared to 26 for testosterone. Apart from its abuse in human sports, it can also be a doping agent in racehorses. Metabolic studies on 1-testosterone have only been reported for human in the early seventies, whereas little is known about its metabolic fate in horses. This paper describes the studies of in vitro and in vivo metabolism of 1-testosterone in horses, with the aim of identifying the most appropriate target metabolites to be monitored for controlling the misuse or abuse of 1-testosterone in racehorses. Six in vitro metabolites, namely 5α-androst-1-ene-3α,17β-diol (T1a), 5α-androstane-3β,17β-diol (T2), epiandrosterone (T3), 16,17-dihydroxy-5α-androst-1-ene-3-one (T4 & T5), and 5α-androst-1-ene-3,17-dione (T6), were identified. For the in vivo studies, two thoroughbred geldings were each administered orally with 800 mg of 1-testosterone by stomach tubing. The results revealed that the parent drug and eight metabolites were detected in urine. Besides the four in vitro metabolites (T1a, T2, T3, and T5), four other urinary metabolites, namely 5α-androst-1-ene-3β,17α-diol (T1b), 5α-androst-1-ene-3β,17β-diol (T1c), 5α-androstane-3α,17α-diol (T7) and 5α-androstane-3β,17α-diol (T8) were identified. This study shows that the detection of 1-testosterone administration is best achieved by monitoring the parent drug, which could be detected for up to 30 h post-administration.