Hepatic clearance of gitoxin. Metabolism and biliary excretion by rabbit isolated liver

After in vitro perfusion of rabbit isolated liver with an emulsion of perfluorocarbon containing [3H]gitoxin, the radioactivity in the liver and in the bile was the sum of that contained in a volatile fraction (tritiated water due to metabolism of gitoxin) and that contained in a nonvolatile fraction (gitoxin and its metabolites). This fraction was divided, by differential extraction, into two groups: liposoluble (dichloromethane soluble) compounds, including unchanged gitoxin and lipophilic metabolites (amounting to 50% in the liver and to 5% in the bile), and hydrosoluble (dichloromethane insoluble) metabolites (50% in the liver, 95% in the bile). Three types of metabolites were found in the hydrosoluble fraction. One type was sensitive to beta-glucuronidase and arylsulfatase hydrolysis, a second type was insensitive to enzymatic hydrolysis but sensitive to acid hydrolysis, and a third type was insensitive to both enzymatic and acid hydrolysis. The liposoluble compounds and the conjugates sensitive to enzymatic hydrolysis were analyzed by reversed phase high performance liquid chromatography and found to comprise a wide variety of metabolites. The present study demonstrates that gitoxin uptake by the liver is followed by a fast and extensive metabolism to highly polar metabolites that are rapidly excreted into the bile.