Tissue Residues and Metabolism of Narasin in Chicken

Abstract

Chickens were fed 50 ppm [14C]narasin rations. After 5 days, the chickens were sacrificed, and tissues were taken for assay. Tissues were assayed for total radioactivity by solubilization and liquid scintillation counting. The mean residue concentrations of narasin equivalents were 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 chromatography (LC). Radioactivity in fat was isolated and assayed by high-performance liquid chromatography/electrospray-mass spectrometry/liquid scintillation counting (HPLC/ESMS/LSC). The radioactivity in fat was characterized as being predominately parent narasin. Excreta samples were also collected for isolation, quantification, and characterization of narasin and its metabolites. Fifteen metabolites and parent narasin were characterized from the excreta of chickens using HPLC/ESMS/LSC. These metabolites were predominately di- and trihydroxylated narasin and di- and trihydroxylated narasin B. These hydroxylated metabolites represented almost 50% of the total radioactivity in excreta. The chromatographic distribution and relative magnitude of radioactivity from liver and excreta were similar, suggesting that excreta metabolites are the same as those found in liver. Keywords: Narasin; residues; metabolites; mass spectrometry