Bile acids modify alkaline phosphatase induction and bile secretion pressure after bile duct obstruction in the rat.

Bile acids induce synthesis of alkaline phosphatase by cultured hepatocytes. To test whether bile acids account for this enzyme's elevation during cholestasis, we developed an experimental model in which the content of the bile acid pool is controlled at the beginning of cholestasis. After depleting the bile acid pool by external biliary drainage, we obstructed bile flow in four groups of rats and then replenished the pool in three groups with taurocholate, taurochenodeoxycholate, or tauroursodeoxycholate, respectively, and replaced no bile acid in the fourth. Hepatic bile acid concentrations were elevated in all obstructed groups; however, the levels were higher in the groups that received bile acid replacement. Cholate was not metabolized, but both chenodeoxycholate and ursodeoxycholate were transformed to beta-muricholate. Although hepatic alkaline phosphatase activity rose in all obstructed animals, the levels achieved were higher in each group treated with bile acids than in the group that was not. Increases in plasma activities of alkaline phosphatase and 5'-nucleotidase occurred only after treatment with cholate or chenodeoxycholate. Bile secretion pressure was higher after ursodeoxycholate or no bile acid treatment but was lower after cholate or chenodeoxycholate replacement. Thus, all bile acids tested induced hepatic alkaline phosphatase to some degree, but only certain ones--those which reduced bile secretion pressure--released the enzyme into plasma. We conclude that, in the rat, the hepatic response to acute cholestasis is influenced by the composition of the intrahepatic bile acid pool and that various bile acids have significantly different effects on this response.