Metabolism of digitoxin in the isolated perfused rat liver. Effect of spironolactone pretreatment.

Livers from either control or spironolactone-treated rats were perfused for a 90-min period with 30% rat blood and 3H-digitoxin. At several time periods throughout perfusation, bile was collected and a sample of blood was removed from the perfusate. Extractions were performed on both blood and bile to determine amount of polar and nonpolar metabolites at 60 min. Polar metabolites were cleaved with beta-glucuronidase and high-pressure liquid chromatography was used to separate the resultant nonpolar metabolites from blood and bile cleaved with beta-glucuronidase. Biliary excretion and perfusate disappearance of 3H-digitoxin were significantly increased in livers taken from spironolactone-pretreated animals. Both polar and nonpolar metabolites in bile were significantly increased in pretreated animals. The majority of polar metabolites produced by livers from both treated and nontreated animals were readily cleaved with beta-glucuronidase. Both biliary excretion and metabolic pattern, obtained from these studies in an isolated perfused rat liver, mimic those seen in the intact rat. Thus, the isolated perfused rat liver can be used as a model for in vivo studies of cardiac glycoside metabolism.