In vitro metabolism of the anabolic drug zeranol.

The anabolic drug zeranol, which is employed for livestock breeding was studied for its metabolic fate in vitro using isolated microsomal preparations from bovine liver, uterus, and muscle. Diethylstilbestrol and 17 beta-estradiol were investigated simultaneously for comparison. The structure of the zeranol metabolite was examined by means of TLC as well as GC-MS analysis. A sensitive color reaction after two-dimensional TLC described earlier for zeranol determination in veal samples is proposed for the detection of the zeranol metabolite zearalanone and the mycotoxin zearalenone. The estrogenic activity of the three mycoestrogens, understood as their binding capacity to the cytoplasmic estrogen receptor protein from bovine uterus, is measured using the estrogen receptor test. The data suggest that zeranol is biotransformed in vitro to a less active estrogen which has a marked similarity to the mycotoxin zearalenone. Further investigations are necessary to quantitate the biotransformation in vitro as well as to evaluate the toxicity of the drug metabolite.