AGE-RELATED-CHANGES IN THE BILIARY BILE-ACID COMPOSITION OF BOVIDS

The biliary bile acid composition of 12 tribes of bovids (66 species, 168 animals) was determined by highperformance liquid chromatography a nd mass spectrometry. In adult animals, the biliary bile acids were co njugated with taurine or glycine and consisted mostly (>90%) of three bile acids: cholic acid (CA), chenodeoxycholic acid (CDCA), and deoxyc holic acid (DCA). Biliary bile acid composition did not vary among spe cies, and was identical in male and female bovids. Within each species , there were consistent changes in biliary bile acid composition with age. Three steady-state stages could be distinguished: (1) the fetal s tage, when bile acid input is from placental transfer from the mother as well as biosynthesis (from cholesterol) by the newborn liver (45 +/ - 12% CA; 50 +/- 11% CDCA; 5 +/- 4% DCA (mean +/- SD)); (2) the infant stage, when bile acid input is solely from biosynthesis by the infant liver (80 +/- 6% CA; 20 +/- 6% CDCA; 0.5 +/- 0.7% DCA); and (3) the a dult stage, when bile acid input is not only from biosynthesis by the adult liver but also from intestinal absorption of DCA, formed by bact erial 7-dehydroxylation of CA (75 +/- 12% CA: 6 +/- 7% CDCA; 19 +/- 9% DCA). The transition from the infant stage to the adult stage, indica ting the development of an anerobic cecum, occurred before weaning. Th ese three stages of biliary bile acid composition are likely to be pre sent in other placental vertebrates, including most primates, in whom a cecum containing an anerobic flora develops after birth; the functio nal implications of these changes are discussed.