BINDING OF C-14 FURAZOLIDONE METABOLITES TO THE MUSCULAR AND HEPATIC PROTEINS OF TROUT

A high level of C-14 was found to bind irreversibly with the liver pro teins of rainbow trout (Oncorhyncus mykiss) exposed to 135 mg/kg bodyw eight of C-14-labelled furazolidone (C-14-FZ) in fish feed daily for 1 0 days. After the cessation of C-14-FZ treatment, hepatic protein-boun d C-14 in trout stayed high for at least 30 days. The chemical identit y of protein-bound C-14 remained to be elucidated. However, a part of the protein-bound C-14 in the liver and muscle could be released as 3- amino-2-oxazolidinone by acid hydrolysis. The formation of protein-bou nd C-14 in the liver was investigated further with trout dosed intrave nously with different C-14-FZ doses at 10 degrees C or with 5 mg/kg FZ at different water temperatures. C-14 binding to the liver proteins w as found to increase with increasing FZ dose or water temperature. Res ults of these studies indicate that protein-bound C-14 in the muscle a nd liver of trout is related to the formation of reactive intermediate s from FZ. However, additional studies on the identities of the protei n-bound FZ residues are required before they can serve as useful bioma rkers to monitor FZ exposure in farm fish.