The role of bile acids in the biliary secretion of alkaline phosphatase was studied. Rats with external bile fistulae were drained for 4 hr. After 2 hr, bile acid secretion fell progressively. Alkaline phosphatase secretion also decreased progressively during the period of drainage, suggesting that secretion of the two components was related. Each rat was then given an i.v. infusion of the taurine conjugate of either cholate, chenodeoxycholate, or ursodeoxycholate. Alkaline phosphatase secretion increased in a dose-dependent manner as bile acid secretion was varied over and beyond the physiologic range. Each bile acid affected alkaline phosphatase secretion differently: given at 0.5 mumoles per min per 100 gm, tauroursodeoxycholate caused a 3-fold, taurocholate a 14-fold, and taurochenodeoxycholate a 75-fold increase in enzyme secretion. To determine if these findings might represent elution of canalicular enzyme by bile acids, isolated liver surface membranes were incubated with the bile acids. Like the findings in vivo, taurochenodeoxycholate was strongest and tauroursodeoxycholate weakest in removing alkaline phosphatase from the membrane. Differential centrifugation of liver surface membranes after exposure to bile acids and ultracentrifugation of bile showed that more than half of the enzyme released by the action of bile acids did not sediment at 100,000 g and, thus, could be considered soluble. These results document bile acid-dependent secretion of alkaline phosphatase in rat bile and suggest that the process involves solubilization of both membrane fragments and free enzyme from membranes lining the biliary space.

Alkaline Phosphatase↗

PubMedDate not supplied

Similarities and differences between models of extrahepatic biliary obstruction and complete biliary retention without obstruction in the rat.

Biliary obstruction in the rat causes known biochemical and morphological abnormalities. These abnormalities might be caused simply by retention of biliary constituents or might require other factors such as high biliary pressure, interruption of the normal flux of fluid, ions, and other biliary constituents through the hepatocyte and/or changes in intracellular concentrations, binding, and distribution of biliary constituents. We studied a choledochocaval (CC) fistula rat model characterized by complete biliary retention without bile stasis. CC fistula animals were compared with biliary obstructed rats over a 46-hr period. Bile flow and bile acid excretion rate reached high levels by hour 5 and remained high in CC fistula rats. Urinary bile acid excretion, shrinkage of the rapidly exchangeable bile acid pool, and serum bile acid and bilirubin concentrations were equivalent in the two models. Serum cholesterol concentration was higher and serum alkaline phosphatase and 5'-nucleotidase activities lower in obstructed rats. The percentage of beta-muricholate rose and the percentage of cholate decreased in bile acid from obstructed rats. This was associated with increased microsomal 6 beta-hydroxylase activity. Bile acid composition and microsomal 6 beta-hydroxylase activity changed little in CC fistula rats. Morphological examination revealed greater damage in obstructed rat livers. These data indicate that factors other than simple retention of biliary constituents contribute to the abnormalities observed in extrahepatic biliary obstruction.

Alkaline Phosphatase↗

PubMedDate not supplied

Studies of the intestinal metabolism of oral gold.

In order to understand some of the unique toxic/therapeutic properties of the orally administered gold containing compound auranofin, the intestinal metabolism of gold was studied in 4 normal subjects. A triple lumen intestinal perfusion apparatus was used to measure intestinal flux using a non-absorbable radiolabelled marker dilution technique. Over a short (50 cm) segment of proximal small bowel, substantial disappearance of gold was observed; the findings, however, were most consistent with a loose, reversible adsorption onto the enteric cell surface rather than true trans-mucosal absorption. There was no evidence for an entero-hepatic recirculation of gold in these subjects or in 4 additional patients with rheumatoid arthritis studied in a similar manner.

Administration, Oral↗