New insights in the physiology and molecular basis of the intestinal bile acid absorption.

Intestinal bile acid absorption is a fundamental step in the enterohepatic circulation and metabolism of these endogenous compounds. The physiology of the active, sodium coupled transport system for bile acids in the terminal ileum has been extensively studied and characterized. Structure-activity studies have elucidated the requirements for the ileal transport system, and studies with photolabile bile acid derivatives identified the putative ileal bile acid transport proteins. Characterization of the functional sites of the transport system elucidated some of the possible mechanisms which allow the interaction of bile acids and sodium ions with the ileal transporter. Considerable progress has been made during recent years, after the ileal apical and cytosolic bile acid transport proteins have been cloned and characterized. The role of point mutations in bile acid malabsorption has been studied, and the knowledge of the amino acid sequence of the transport proteins will be of help in the investigation of the transport mechanisms.