Bile acids extracted from the urine of a healthy volunteer who excreted 7 beta-hydroxylated bile acids were fractionated to nonamidated, glycine-conjugated, taurine-conjugated, and sulfated bile acid fractions. The chemical conjugation types of the 7 beta-hydroxylated bile acids were then determined by treatment with several enzymes and by capillary column gas chromatography. Large amounts of 3 alpha,7 beta,12 alpha-trihydroxycholanoic acid were present as nonamidated and nonconjugated bile acids, while 3 beta,7 beta-dihydroxycholanoic acid formed nonamidated bile acid N-acetylglucosaminide. In addition, ursodeoxycholic acid formed both glycine-conjugated bile acid and glycine-conjugated bile acid N-acetylglucosaminide. Bile acid N-acetylglucosaminides were hydrolyzed by solvolysis.
The effects on bile acid and sterol transformation of clostridia (fusiform bacteria), the dominant intestinal bacteria in rodents (ca. 10(10) counts per g wet feces) were examined in Wistar rats. After inoculation of clostridia into germ-free rats and into rats previously inoculated solely with Escherichia coli, most of the endogenous bile acids were deconjugated, and cholic acid and chenodeoxycholic acid were 7alpha-dehydroxylated to deoxycholic acid and lithocholic acid, respectively. Tauro-beta-muricholic acid, another major bile acid in rats, was deconjugated, but only part of it (ca. 30%) was transformed into hyodeoxycholic acid. Cholesterol and sitosterol were also reduced to coprostanol and sitostanol, respectively. Escherichia coli transformed neither bile acids nor sterols. These data suggest that clostridia play an important role in the formation of secondary bile acids and coprostanol in rats.
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