Metabolism of lethocholate in healthy man. I. Biotransformation and biliary excretion of intravenously administered lithocholate, lithocholylglycine, and their sulfates.

The metabolism of intravenously injected radiolabeled lithocholate, lithocholylglycine, and their 3alpha-sulfate esters was characterized in healthy subjects. Lithocholate radioactivity was excreted rapidly and predominantly in bile; the excreted radioactivity had the chromatographic properties of glycine and taurine conjugates of lithocholate, of which 60% were sulfated. Lithocholylglycine also was excreted rapidly and predominantly in bile, and 60% of excreted radioacitvity was sulfated. Sulfolithocholate radioactivity was only partially conjugated (about 60%) in association with biliary excretion. Sulfolithocholylglycine was excreted unchanged in bile. Neither sulfated derivative showed appreciable excretion in urine, although both were excreted more slowly in bile than unsulfated free or conjugated lithocholate. The data suggest that unconjugated lithocholate which is absorbed is completely conjugated and partially sulfated before excretion which occurs exclusively in bile. Since sulfation is not complete, some unsulfated lithocholate is always present in bile. This conjugated but unsulfated lithocholate, if reabsorbed, would be again partially sulfated during its next enterohepatic circulation. Thus, the end result of these biotransformations would be for absorbed lithocholate to be excreted in bile mostly, but not entirely as the sulfated conjugates.