Determination of the exogenous character of testosterone in bovine urine by gas chromatography-combustion-isotope ratio mass spectrometry

A new approach was developed in order to control testosterone abuse in anim al production. A gas chromatographic-combustion-isotope ratio mass spectrom etric (GC-C-IRMS) method was used to distinguish the exogenous character fr om the endogenous character of the main metabolites of testosterone (epites tosterone and etiocholanolone) in cattle urine. This method is based on a c omparison between the carbon isotope ratio (C-13/C-12) of testosterone meta bolites and those of testosterone endogenous precursors. After urinary ster oid purification, extracts were acetylated with acetic anhydride and inject ed into the GC-C-IRMS system. In order to validate the method, testosterone enanthate was administered to a 4 year old cow. The C-13/C-12 isotope rati os of testosterone exogenous metabolites appeared to be significantly diffe rent to the C-13/C-12 precursor ratios and were detected until 3 weeks afte r the anabolic administration. These preliminary results appear to be promi sing for the difficult control of natural hormones in livestock.