Portal-systemic spill-over of bile acids: a study of mechanisms using ursodeoxycholic acid.

Portal-systemic spill-over of unconjugated ursodeoxycholic acid (UDCA) was assessed in ten healthy subjects, six patients with mild chronic liver disease and eight patients with cirrhosis. Following oral administration of UDCA (1.5 mg/kg body weight), serum concentrations of unconjugated UDCA were measured during 2 h using a capillary gas-liquid chromatographic method. Peak time of UDCA varied from 15 to 30 min, but was not significantly different in the three groups studied. Peak concentration was increased up to two-fold in patients with mild, and up to three-fold in patients with cirrhotic liver disease. Since, in addition, plasma disappearance rate (k) was markedly impaired in cirrhotics (1.7 +/- SD 0.5%/min, compared to 2.8 +/- 0.6 in healthy controls), the calculated area under the curve (AUC) was on the average five-fold that in controls. In two healthy and four cirrhotic subjects, the data obtained after oral administration were compared with those after i.v. loading with the same UDCA dose. The k-values after the two routes of administration were practically identical. Calculated systemic availability was 50% in normals, 78-87% in cirrhotics, 90 and 136% in two patients with surgical porta-caval shunt. It is concluded that the portal-systemic spill-over of UDCA in patients with liver disease is increased primarily due to portal-systemic shunting. Since in the normal liver hepatic extraction of conjugated, endogenous bile acids is greater than 80%, diminished first-pass elimination is expected to augment systemic concentrations even more, particularly when measured after a meal.