Stereospecific reduction of 3- and 7-oxo groups of oxocholanic acids in isolated perfused rat liver.

The metabolism of 3- and 7-oxo groups of oxocholanic acids was studied in isolated perfused rat liver. The metabolites in bile were determined enzymatically using 3 alpha- and 7 alpha-hydroxysteroid dehydrogenases. The 3-oxo group of all the oxocholanic acids tested (dehydrocholate, glycodehydrocholate, taurodehydrocholate, 3,7-dioxocholanate, 3,12-dioxocholanate and tauro-7,12-dihydroxy-3-oxocholanate) was reduced stereospecifically to 3 alpha-hydroxy metabolites. On the other hand the 7-oxo group was excreted partially unchanged (30% of the dose) and partially as 7 alpha-hydroxy metabolites (6-10% of the dose). The remainder of the 7-oxo group was concluded to have been reduced to 7 beta-hydroxy metabolites. These results indicate that the 7-oxo group of oxocholanic acids is reduced predominantly to 7 beta-hydroxy metabolites in rats rather than to 7 alpha-hydroxy metabolites as found in man.