TISSUE RESIDUES AND METABOLISM OF NARASIN IN CHICKEN

Chickens were fed 50 ppm [C-14]narasin rations. After 5 days, the chic kens were sacrificed, and tissues were taken for assay. Tissues were a ssayed for total radioactivity by solubilization and liquid scintillat ion counting. The mean residue concentrations of narasin equivalents w ere 0.32 ppm in liver, 0.12 ppm in fat, 0.08 ppm in skin/fat, 0.04 ppm in kidney, and <0.04 ppm in muscle. Liver radioactivity was isolated by liquid-liquid extractions and preparative silica liquid chromatogra phy (LC). Radioactivity in fat was isolated and assayed by high-perfor mance liquid chromatography/electrospray-mass spectrometry/liquid scin tillation counting (HPLC/ESMS/LSC). The radioactivity in fat was chara cterized as being predominately parent narasin. Excreta samples were a lso collected for isolation, quantification, and characterization of n arasin and its metabolites. Fifteen metabolites and parent narasin wer e characterized from the excreta of chickens using HPLC/ESMS/LSC. Thes e metabolites were predominately di- and trihydroxylated narasin and d i- and trihydroxylated narasin B. These hydroxylated metabolites repre sented almost 50% of the total radioactivity in excreta. The chromatog raphic distribution and relative magnitude of radioactivity from liver and excreta were similar, suggesting that excreta metabolites are the same as those found in liver.