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Comparison of the effects of injections of nortestosterone phenyipropionate at single and multiple sites in cattle on the detection of its residues in plasma, urine and bile
  1. J. D. G. McEvoy, MVB, PhD, MRCVS1,
  2. C. E. McVeigh, ONC1,
  3. W. J. McCaughey, MA, MSc, MVB, PhD, MRCVS1 and
  4. D. G. Kennedy, BSc, PhD1
  1. 1 Residues Department, Department of Agriculture for Northern Ireland, Veterinary Sciences Division, Stoney Road, Stormont, Belfast BT4 3SD

Abstract

The synthetic androgen 17β-19-nortestosterone (β-NT) has been used illegally as a growth promoter in cattle production in the European Union. The elimination of β-NT and its metabolites in plasma and urine was studied in cattle which had received intramuscular injections of its phenylpropionate ester (NTP) at either single or multiple sites at a dose rate of 1 mg/kg bodyweight. In both groups, the plasma concentrations of β-NT, measured by enzyme immunoassay, were consistently greater than the assay's limit of quantification (0.24 ng/ml) during days 1 to 7 of the study. The mean (sd) maximum plasma concentration (Cmax) was significantly greater in the multiply injected animals (4.4 [0.48] v 2.7 [0.15] ng/ml), but other prasma pharmacokinetic parameters, AUC, CL, T1/2β, Tmax and MRT, were not significantly different in the two groups. The equivalent urinary concentrations exceeeded the limit of quantification of the assay (4.5 ng/ml) for up to 24 days after injection. In a second study, the biliary concentrations of β-NT and its 17α-epimer (α-NT) were measured by gas chromatography-high resolution mass spectrometry after cattle were injected intramuscularly at either single or multiple sites with NTPP. Only α-NT was detected in bile for up to 62 days after injection at concentrations above the limit of quantification of the assay (0.7 ng/ml). It is concluded that in some animals, intramuscular injections of NTPP at several sites may decrease the period after injection during which free β-NT and its metabolites are detectable in plasma and urine. After the injection of NTPP, α-NT was detected in bile for longer than it was detected in plasma or urine.

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