Plasma,Urinary and Biliary Residues in Cattle Following Intramuscular Injection of Nortestosterone Laurate

The synthetic androgen 19-nortestosterone (-NT) has been used illegally as a growth promoter in cattle production in the European Union. Elimination of -NT and its metabolites in plasma, urine and bile was studied in three cattle with cannulated gallbladders following intramuscular injection at a single site of 500 mg of the laurate ester (NTL) containing 300.5 mg -NT. Using enzyme immunoassay quantification, plasma Cmax of free -NT was 0.5±0.15 g/L (mean±SEM). Concentrations of free -NT in plasma were consistently greater than the assay limit of quantification (0.12 g/L) for 32.7±13.42 days. Mean residence time for free -NT in plasma was 68.5±20.75 days. Following sample preparation by immunoaffinity chromatography, high-resolution GC-MS was used to quantify -NT and -NT in urine and bile. -NT was detected irregularly in urine from two of the three animals post injection. The principal metabolite present in the urine, -NT, was detected for 160.3±22.67 days post injection. Cmax for -NT in urine was 13.7±5.14 g/L. Mean urinary AUC0–183 days for -NT was 845.7±400.90 (g h)/L.In bile, -NT was the only metabolite detected for 174.3±8.67 days post treatment. Cmax for -NT in bile was 40.8±12.70 g/L and mean biliary AUC0–183 days for -NT was 1982.6±373.81 (g h)/L. Concentrations of -NT in bile samples were greater than those in urine samples taken at the same time. The mean ratio of biliary:urinary AUC0–183 days was 3.0±0.72. It is concluded that bile is a superior fluid for detection of -NT following injection of NTL, owing to the longer period during which residues may be detected after administration.