EFFECTS OF DRUGS WHICH INFLUENCE RENAL TRANSPORT-SYSTEMS ON THE URINARY-EXCRETION OF THE BETA(2)-ADRENOCEPTOR AGONIST CLENBUTEROL AND THE ANABOLIC-STEROIDS ETHINYLESTRADIOL AND METHYLTESTOSTERONE

The aim of this study was to determine whether the illegal application of clenbuterol, ethinylestradiol and methyltestosterone in cattle as growth promoters can be concealed by co-treatment with drugs that affe ct urinary excretion. Six male veal calves were fed with 0.8 mu g clen buterol kg(-1) of body weight (BW), 3.5 mu g ethinylestradiol kg(-1) o f body weight (BW), 3.5 mu g ethinylestradiol kg(-1) BW and 35 mu g me thyltestosterone kg(-1) BW together twice daily for 28 days. At the ei ghth day of clenbuterol, ethinylestradiol and methyltestosterone treat ment each calf was additionally fed either with probenecid, para-amino hippuric acid, trimethoprim, famotidine or cimetidine at three differe nt doses which were increased in weekly intervals. During the treatmen t 24 h-urine and blood samples (once daily) were obtained and analysed for clenbuterol, ethinylestradiol and methyltestosterone by specific enzyme immunoassay. By high performance liquid chromatography/enzyme i mmunoassay it was determined whether these drugs or their metabolites interfered with the immunological detection of the growth promoters. C lenbuterol, ethinylestradiol and methyltestosterone could be detected in plasma and urine throughout the whole experiment. Co-treatment with probenecid led to a five-fold reduction in urinary excretion of ethin ylestradiol and co-treatment with trimethoprim led to a three-fold red uction in urinary excretion of clenbuterol. None of the drugs reduced urinary excretion of the growth promoters to concentrations below the limit of detection. The detection of these three growth promoters in u rine samples from calves which were co-treated with the drugs tested i n this study can thus not be prevented.