In vitro biotransformation of anabolic steroids in canines

Forensic drug testing of anabolic steroids in racing animals is required be cause of the potential for steroid abuse. Often when the metabolic products of an administered compound have not been identified, the analysis and ver ification of the administered compound is difficult. The objective of this study was to qualitatively identify the in vitro phase I biotransformation products of anabolic steroids that have a high potential for abuse in canin es. The investigated steroids included testosterone, methyltestosterone, mi bolerone and boldenone. Steroid biotransformation products were generated u sing beagle liver microsomes and analysed by high performance liquid chroma tography (HPLC)/mass spectrometry (MS) with an electrospray ionization sour ce. Characterization of steroid metabolites was based on HPLC retention, UV and mass spectra. The major testosterone metabolites were identified as an drostenedione and 6 beta- and 16 alpha-hydroxytestosterone. 6 beta-Hydroxym ethyltestosterone was identified as a major metabolite in the methyltestost erone microsomal incubations. Several mibolerone metabolites were identifie d as monohydroxylated mibolerones as well as an oxidized mibolerone metabol ite. Boldenone metabolites were identified as monohydroxylated boldenones, oxidized boldenone, and testosterone. This information should assist in the determination of anabolic steroid use in canines through the correlation o f the urinary metabolites to the administered drug.