Residues and metabolism of 19-nortestosterone laurate in steers

The illegal use of 19-nortestosterone( 19NT; 4-estren-17 beta-ol-3-one; nan drolone) and its esters in livestock, for growth promotion purposes, has be en widely reported in the European Union. The target residues for surveilla nce of abuse in bovine urine and bile samples are 17 alpha- and 17 beta-19N T, although this choice of target residues is not based on in vivo radiotra cer biotransformation data. In this study, four steers were administered [H -3(2)]- and [H-2(3)] 17 beta-19NT laurate (2 mg kg(-1) body mass) by intram uscular injection and blood, urine, faeces and bile samples were taken for 30 d until slaughter, after which tissues were sampled for total residue an alysis. Total plasma radiolabelled residues reached a maximum of 56.3 +/- 1 5.9 pmol ml(-1) at 36 h and were still appreciable (13.3 +/- 1.6 pmol ml(-1 )) 30 d after treatment. Throughout the study period, total residue concent rations in bile (about 2-16 nmol ml(-1)), urine and faeces (0.5-3 nmol ml(- 1) or g(-1)) were higher than in other tissues sampled at slaughter. At sla ughter there was evidence of residue accumulation in pigmented eye tissue ( 33.1 +/- 6.1 pmol g(-1)) and in white (13.3 +/- 3.4 pmol g(-1)) and black h air (28.9 +/- 8.9 pmol g(-1)). Evaluation of radio-HPLC profiles of urine a nd bile extracts generally indicated that 19NT and 19NT laurate residues we re present in relatively small amounts among a complex mixture of metabolit es. GC-MS analysis of glucuronidase-hydrolysed bile extracts indicated that the major metabolites were 5 beta-estrane-3 alpha,17 alpha-diol, 5 alpha-e strane-3 beta,17 alpha-diol, 5 beta-estran-3 alpha-ol-17-one (norandrostero ne) and estra-1,3,5(10)-triene-3,17 alpha-diol (17 alpha-estradiol).