Review article: the 'mechanical pumps' and the enterohepatic circulation of bile acids--defects in coeliac disease.

Bile acid pool size is maintained relatively constant at about 3-5 g in healthy subjects by two mechanisms, enterohepatic circulation and de novo synthesis of bile acids. This latter mechanism compensates for the daily faecal loss (about 0.2-0.6 g) of bile acids, whereas the bulk of the pool is conserved by the former mechanism. The driving forces of the enterohepatic circulation are constituted by chemical pumps, including intestinal absorption and hepatic uptake, and by mechanical pumps, including gall-bladder and intestinal motility. The latter provide the main propulsive forces for bile acids to reach the site of intestinal absorption, and by contrast with the very rapid chemical pumps, mechanical pumps have storage capacity for the bile acid pool and therefore comprise the slow limb of the enterohepatic circulation. In coeliac disease, a disease classically described as a malabsorption syndrome associated with mucosal atrophy of the small intestine, both gall-bladder and small intestinal motor functions are impaired, and in this article we review the mechanisms involved in these defects, how they influence the enterohepatic circulation of bile acids, and the evidence supporting the concept that both the gall-bladder and the small intestinal motor functions represent the main factors affecting the kinetics of the enterohepatic circulation.