The purpose of the studies is to isolate, identify and characterize Delta 6-lithocholenic acid (Delta 6-LC) as a significant metabolite of chemodeoxycholic acid (cheno) and ursodeoxycholic acid (urso). Specifically, the project has the following aims: (1) To isolate Delta 6-LC both in vitro in fecal incubations and in vivo in the colon as a bacterial metabolite of cheno and urso. The 14C-and 2H2 labeled precursors will be used and the methabolities analyzed by thin-layer chromatography (TLC), gas liguid chromatography (GLC), mass spectometry (MS) and nuclear resonance. (2) To study the intestinal absorption and the hepatic biotransformation of 14C- and 2H2-Delta 6-LC in vivo. After i.v. injection and small intestinal infusion of the compounds, duodenal bile, feces and urine will be collected and the metabolites identified by TLC, GLC and MS. (3) To study the colonic bacterial biotransformation of 14C- and 2H2-Delta 6-LC in vitro and in vivo. These studies also encompass in vitro isotope dilution studies in which trace amounts of 14C-Delta 6-LC are incubated in a fecal medium with unlabeled cheno and urso, respectively, in order to determine the role of Delta 6-LC as an intermediate in the interconversion of cheno and urso. The biotransformation products are analyzed by TLC, GLC, and MS. (4) To determine the fecal Delta 6-LC excretion in healthy subjects. The importance and health-relatedness of the studies are evidenced by preliminary findings by the P.I. which indicate Delta 6-LC to occur as a significant intestinal bacterial metabolite of both cheno and urso. The studies will (a) enhance the understanding of the metabolism of both cheno and urso which represent physiologically as well as therapeutically important bile acids in man and (b) provide the basis for a comprehensive exploration of the physiological as well as potentially toxic and carcinogenic effects of cheno and its metabolites during their enterophepatic circulation. In particular, the fundamental information gained and these studies will provide the basis for in-depth studies of the role of Delta 6-LC as a potential carcinogen or co-carcinogen in the development of colon and liver cancer.