PRELIMINARY-STUDY OF THE METABOLISM OF 17-ALPHA-METHYLTESTOSTERONE INHORSES UTILIZING GAS-CHROMATOGRAPHY - MASS-SPECTROMETRIC TECHNIQUES

Little is known about the metabolism of 17 alpha-alkyl anabolic steroi ds in horses. In this study, the metabolism of 17 alpha-methyltestoste rone is investigated by oral administration of a (1 + 1) mixture of th e steroid and its deuteriated analogue. Both compounds were synthesize d from dehydroisoandrosterone (DHA), using a Grignard reaction followe d by an Oppenauer oxidation. Post-administration urine extracts were a nalysed by gas chromatography-mass spectrometry (GC-MS) using both ele ctron impact (EI) and chemical ionization (CI), Interpretation of the data was facilitated by observation of the fragment ions present in th e mass spectra. Notably, the D-ring fragment ions were indicative of 1 5- or 16-hydroxylation, where 16-hydroxy metabolites showed ion pairs at mit 218/221 and at mit 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 wer e partial and complete reduction of the 3-oxo-4-ene group, 15-hydroxyl ation, 16-hydroxylation, 17-epimerization and hydroxylation at at leas t 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 r esult in improved effectiveness of confirmatory analytical procedures for 17 alpha-alkyl anabolic steroids.