Diversity of bile acids in the fetus and newborn infant.

The bile acids found in the fetus and newborn are more numerous and diverse than has generally been appreciated. The four conventional bile acids, cholic, chenodeoxycholic, deoxycholic, and lithocholic acids, are found. In addition, however, stereoisomers of the conventional bile acids, bile acids with functional groups at different positions or in greater number than found in conventional bile acids, and "short-chain" and "long-chain" bile acids are found. The site of origin, pathways of synthesis, metabolism, and excretory routes of these unconventional bile acids are largely unknown. Their effects on the function of the liver and other tissues have not yet been established. It is uncertain which of these compounds is peculiar to the fetus and newborn, and which will be found in normal or abnormal adults. This review is an early look at a field bound to advance rapidly in the next several years.