Metabolic studies of mesterolone in horses
Abstract
Mesterolone (1alpha-methyl-5alpha-androstan-17beta-ol-3-one) is a synthetic anabolic androgenic steroid (AAS) with reported abuses in human sports. As for other AAS, mesterolone is also a potential doping agent in equine sports. Metabolic studies on mesterolone have been reported for humans, whereas little is known about its metabolic fate in horses. This paper describes the studies of both the in vitro and in vivo metabolism of mesterolone in racehorses with an objective to identify the most appropriate target metabolites for detecting mesterolone administration. In vitro biotransformation studies of mesterolone were performed by incubating the steroid with horse liver microsomes. Metabolites in the incubation mixture were isolated by liquid-liquid extraction and analysed by gas chromatography-mass spectrometry (GC-MS) after acylation or silylation. Five metabolites (M1-M5) were detected. They were 1alpha-methyl-5alpha-androstan-3alpha-ol-17-one (M1), 1alpha-methyl-5alpha-androstan-3beta-ol-17-one (M2), 1alpha-methyl-5alpha-androstane-3alpha,17beta-diol (M3), 1alpha-methyl-5alpha-androstane-3beta,17beta-diol (M4), and 1alpha-methyl-5alpha-androstane-3,17-dione (M5). Of these in vitro metabolites, M1, M3, M4 and M5 were confirmed using authentic reference standards. M2 was tentatively identified by mass spectral comparison to M1. For the in vivo metabolic studies, Proviron (20 tablets x 25 mg of mesterolone) was administered orally to two thoroughbred geldings. Pre- and…
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