Preliminary study of the metabolism of 17 alpha-methyltestosterone in horses utilizing gas chromatography-mass spectrometric techniques

Abstract

Little is known about the metabolism of 17 alpha-alkyl anabolic steroids in horses. In this study, the metabolism of 17 alpha-methyltestosterone is investigated by oral administration of a (1 + 1) mixture of the steroid and its deuteriated analogue. Both compounds were synthesized from dehydroisoandrosterone (DHA), using a Grignard reaction followed by an Oppenauer oxidation. Post-administration urine extracts were analysed by gas chromatography--mass spectrometry (GC-MS) using both electron impact (IE) and chemical ionization (CI). Interpretation of the data was facilitated by observation of the fragment ions present in the mass spectra. Notably, the D-ring fragment ions were indicative of 15- or 16-hydroxylation, where 16-hydroxy metabolites showed ion pairs at m/z 218/221 and at m/z 231/234 while 15-hydroxy compounds gave the 231/234 ion pair alone. Unaltered D-rings showed fragment ions at m/z 143/146. The data showed that the main phase 1 metabolic processes were partial and complete reduction of the 3-oxo-4-ene group, 15-hydroxylation, 16-hydroxylation, 17-epimerization and hydroxylation at at least two other undetermined sites, postulated as the 6 and 11 positions. Phase 2 metabolism, in the form of glucuronide and sulfate formation, was also common. The information provided by this investigation will result in improved effectiveness of confirmatory analytical procedures for 17 alpha-alkyl anabolic steroids.