Residues of nortestosterone esters at injection sites. Part 1. Oral bioavailability

Injectable esters of 17 beta-19-nortestosterone (beta-NT) have been used il legally for growth promotion in European Union (EU) cattle production. Ther e are no data on oral bioavailability of free P-NT from P-NT esters. Adult non-pregnant female Landrace pigs (n = 4) were fitted with jugular vein can nulae and were treated as follows with an appropriate 'flushing out' period between each treatment: an intravenous bolus of beta-NT at 0.1 mg kg(-1) b ody weight (NTiv), 300 mg nortestosterone phenylpropionate (NTPP) in oil of arachis administered per. os (NTPPoil) and 300 mg NTPP in aqueous suspensi on administered per os (NTPPaq). Blood samples were taken for up to 24 h an d analysed for free beta-NT by enzyme immunoassay. Calculation of the area under the plasma time concentration curve (AUC), allowed absolute bioavaila bility estimations for both oral treatments. Mean bioavailability of beta-N T following NTPPaq was 0.35% (range 0.25-0.41%) compared to 2.25% (range 0. 86-2.85%) for NTPPoil. Mean +/- standard error of mean time of maximum plas ma concentration (T-mas) of free beta-NT occurred earlier (2.3 +/- 0.6 h) w ith NTPPoil compared to NTPPaq (10.3 +/- 1.03 h) and the maximum plasma con centration (C-max) was also greater for NTPPoil compared to NTPPaq (36.1 +/ - 6.49 vs. 3.2 +/- 0.31 mu g 1(-1)). It is concluded that the presence of a rachis oil enhances the absorption of NTPP. Notwithstanding the possible ef fects that cooking and other food processing may have on such injection sit e residues, extrapolation of these results to man suggests that consumption of NTPP-containing injection sites may result in peak plasma concentration s of free beta-NT which are significantly greater than those observed follo wing injection of NT esters.