[Pathogenic significance of bile acids (author's transl)]

Because of their amphiphilic properties, bile acids have important physiological functions. However, they can also be pathogenetically active. Some recent findings on the biochemistry and enterohepatic circulation of bile acids are presented. In contrast to the adult liver where the only primary bile acids formed are cholic- and chenodeoxycholic acid, the foetal liver is able to synthesise a variety of "atypical" bile acids. Under certain circumstances, a retrograde differentiation is possible in the adult. The very effective transport systems in gut and in the sinusoidal and canalicular membrane of the liver cell limit the bile acids almost exclusively to the enterohepatic circulation. During transport in blood, through biomembranes and in the liver cytosol, bile acids are bound to carrier proteins. The carrier has been detected using photoaffinity labelling. Following biotransformation (sulphation and glucuronidation) pathogenetically active bile acids can be converted into derivatives which can be rapidly eliminated. Disturbances of these mechanisms result in functional defects and diseases. The pathological significance of bile acids in hepato-biliary diseases is represented with regard to the cholestatic and proliferative effect of individual bile acids. The significance of bile acids in chologenic diarrhea, steatorrhea and enteral hyperoxaluria are presented as examples of the pathogenetic effects of bile acids on the gut. In these diseases it is possible to recognise the specific effects of certain bile acids on the colon mucosa. Recent studies have demonstrated that bile acids are possibly of pathogenetic significance in the case of epidemiologically proven relationship between colon carcinoma and high fat, high cholesterol and low fibre diets.