Liver cytosol protein binding may be not responsible for hepatic uptake of biliary contrast agents

The interaction of five intravenous and one oral biliary contrast agents with soluble proteins of rat liver cytosol was investigated in order to clarify if cytosol protein binding might be responsible for the previously reported accumulation of all six compounds by the liver. While nearly all of the investigated compounds did interact with cytosol proteins, no correlation between the extent of the cytosol protein binding and the hepatic accumulation was found. Therefore, the results do not support the theory of an important role of the cytosol protein binding for the hepatic uptake of biliary contrast agents. Preliminary results, however, suggest that binding to membranous components of the rat liver could be responsible for the saturable accumulation of the contrast agents by the liver.