Browsing by Author "SOLIS, N"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    ASSOCIATION OF CANALICULAR MEMBRANE ENZYMES WITH BILE-ACID MICELLES AND LIPID AGGREGATES IN HUMAN AND RAT BILE
    (ELSEVIER SCIENCE BV, 1995) ACCATINO, L; PIZARRO, M; SOLIS, N; KOENIG, CS
    This study was undertaken to gain insights into the characteristics of the polymolecular association between canalicular membrane enzymes, bile acids, cholesterol and phospholipids in bile and into the cellular mechanisms whereby the enzymes are secreted into bile. With this purpose, we studied the distribution of bile acids, cholesterol, phospholipids, proteins and representative canalicular membrane enzymes (alkaline phosphatase, 5'-nucleotidase and gamma-glutamyl transpeptidase), which can be considered specific marker constituents, in bile fractions enriched in phospholipid-cholesterol lamellar structures (multilamellar and unilamellar vesicles) and bile acid-mixed micelles. These fractions were isolated by ultracentrifugation from human hepatic bile, normal rat bile and bile of rats treated with diosgenin, a steroid that induces a marked increase in biliary cholesterol secretion, and were characterized by density, lipid composition and transmission electron microscopy. These studies demonstrate that alkaline phosphatase, T-nucleotidase and gamma-glutamyl transpeptidase are secreted into both human and rat bile where they are preferentially associated with bile acid-mixed micelles, suggesting a role for bile acids in both release of these enzymes and lipids from the canalicular membrane and solubilization in bile. In addition, heterogeneous association of these enzymes with nonmicellar, lamellar structures in human and rat bile is consistent with the hypothesis that processes independent of the detergent effects of bile acids might also result in the release of specific intrinsic membrane proteins into bile.
  • Thumbnail Image
    Item
    ENHANCED BILIARY-EXCRETION OF CANALICULAR MEMBRANE ENZYMES IN ESTROGEN-INDUCED AND OBSTRUCTIVE CHOLESTASIS, AND EFFECTS OF DIFFERENT BILE-ACIDS IN THE ISOLATED-PERFUSED RAT-LIVER
    (MUNKSGAARD INT PUBL LTD, 1995) ACCATINO, L; FIGUEROA, C; PIZARRO, M; SOLIS, N
    Backgrounds/Aims: Canalicular membrane enzymes are normally released into bile by partially known processes. This study was undertaken to investigate whether hepatocellular cholestasis induced in rats by ethynylestradiol or obstructive cholestasis produced by complete biliary obstruction for 24 h is associated with an increased release of alkaline phosphatase and gamma-glutamyl transpeptidase into bile, and to clarify hen: this process is affected by different bile acids.
  • Thumbnail Image
    Item
    ENHANCED BILIARY-EXCRETION OF CANALICULAR MEMBRANE ENZYMES IN ETHYNYLESTRADIOL-INDUCED CHOLESTASIS - EFFECTS OF URSODEOXYCHOLIC ACID ADMINISTRATION
    (PERGAMON-ELSEVIER SCIENCE LTD, 1995) ARRESE, M; PIZARRO, M; SOLIS, N; KOENIG, C; ACCATINO, L
    Cholestasis is associated with a marked increase in the release of canalicular membrane enzymes into bile. This phenomenon has been related to an increased lability of these canalicular membrane integral proteins to the solubilizing effects of secreted bile salts. To further characterize the effects of oral ursodeoxycholic acid (UDCA) administration on ethynylestradiol (EE)-induced cholestasis, the influence of this bile acid on changes in biliary excretion of membrane-bound enzymes was investigated Bile flow, basal bile salt and biliary lipid secretory rates, the maximum secretory rate of taurocholate TC SRm), and the biliary excretion of the canalicular membrane-bound ectoenzymes alkaline phosphatase (ALP) and gamma-glutamyl transpeptidase (GGT) were measured in rats after EE and/or UDCA administration. The activities of ALP, GGT and Na+,K+-ATPase in purified isolated canalicular and sinusoidal membrane fractions and the ultrastructure of hepatic acinus, including histochemical studies of ALP distribution, were also examined. EE significantly reduced bile flow, bile salt and biliary lipid secretory rates, and TC SRm, and caused dilatation and loss of microvilli at the canalicular pole of hepatocytes. Biliary excretion of ALP increased 2-fold, whereas biliary excretion of GGT was unchanged. The relationship between biliary excretion of ALP or GGT and bile salt secretion (units of enzyme activity secreted per nanomole of bile salt) was greater in EE-treated rats compared with controls (2.1- and 1.5-fold greater for ALP and GGT, respectively), indicating that in EE-induced cholestasis more enzyme was released into bile per nanomole of bile salt. Na+,K+-ATPase activity in sinusoidal membrane fraction was reduced significantly, whereas ALP activity increased in both membrane fractions in EE-treated rats. The histochemical distribution of ALP in the acinus showed a strong reaction in acinar zone 3 and at both the canalicular and sinusoidal membranes. Oral administration of UDCA prevented EE-induced bile secretory failure by normalizing bile flow, bile salt and biliary phospholipid secretory rates, and TC SRm. UDCA also prevented the EE-induced changes in the biliary excretion of enzymes. On the contrary, UDCA did not modify either the enzyme activity in isolated membrane fractions or the morphological or ALP histochemical changes associated with EE administration. These data indicate that in BE-induced cholestasis changes occur at the canalicular membrane, enabling this portion of the plasma membrane to be more susceptible to the solubilizing effect of bile salt, and that oral administration of UDCA prevents bile secretory failure and changes in the biliary excretion of ALP and GGT in EE-treated rats.
  • No Thumbnail Available
    Item
    POSTCHOLESTATIC ALKALINE-PHOSPHATASE ACTIVITY AFTER RELIEF OF BILE-DUCT OBSTRUCTION IN THE RAT
    (W B SAUNDERS CO, 1993) WIELANDT, AM; PIZARRO, M; SOLIS, N; ARRESE, M; ACCATINO, L
    The effects of obstructive cholestasis on the activity of alkaline phosphatase have been extensively studied in serum and liver tissue. However, very little is known about the activity of this enzyme in the postcholestatic condition after relief of the biliary obstruction. The purpose of this study has been to characterize alkaline phosphatase activity in serum, liver and bile in the postcholestatic period and to relate it to changes in bile acid secretory rate. Serum activity and biliary secretory rates of alkaline phosphatase were markedly increased in rats subjected to a reversible obstructive cholestasis for 24 hr or 48 hr and progressively declined along the postcholestatic period to values not significantly different from those of control rats within 48 hr. A significant direct linear relationship between the biliary secretory rates of enzyme activity and bile salts was apparent both in cholestatic groups and in the control groups. The slope of the regression line (units of alkaline phosphatase secreted per micromole of bile salts) was 1.5-fold to 3-fold higher in cholestatic animals. Remarkably, a positive y-intercept of regression lines suggested that a significant fraction of the enzyme was secreted independently of bile salts; this fraction was 18-fold and 34-fold greater in 24-hr and 48-hr cholestatic rats, respectively, compared with that in controls. Sodium taurocholate administered intravenously, either as a bolus or as an infusion at increasing submaximal rates, resulted in parallel increases of bile salt and alkaline phosphatase secretory rates into bile. The enzyme activity secreted per micromole of taurocholate was significantly greater in cholestatic than in control rats. In the liver tissue, increased homogenate and canalicular membrane alkaline phosphatase activity in 24-hr cholestatic rats progressively decreased to reach control values 48 hr after relief of biliary obstruction. This study demonstrates that a marked increase of alkaline phosphatase secretion into bile occurs in the postcholestatic condition. It presents further evidence for bile acid dependency of this process and demonstrates that more enzyme is secreted per micromole of bile salt in the postobstructive condition, probably related to the increased enzyme content in the liver and to an increased lability of the canalicular membrane enzyme to the solubilizing effect of secreted bile acids in cholestatic rats. In addition, this study suggests that alkaline phosphatase might be normally secreted into bile by another process independent of bile salts, which appears to be quantitatively more important in cholestatic than in control rats.