Browsing by Author "PIZARRO, M"

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    ADAPTIVE REGULATION OF HEPATIC BILE-SALT TRANSPORT - EFFECTS OF ALLOXAN DIABETES IN THE RAT
    (W B SAUNDERS CO, 1991) ICARTE, MA; PIZARRO, M; ACCATINO, L
    The hepatic transport of bile salts appears to be adaptively regulated by changes in the bile salt pool size and in the flux of bile salt through the liver. The maximum secretory rate of taurocholate increases or decreases when the bile salt pool size is modified by either oral feeding of cholate or taurocholate (up-regulation) or prolonged bile salt depletion through a biliary fistula (down-regulation), respectively. It is not known whether adaptive regulation of hepatic bile salt transport operates under conditions in which the bile salt pool size is modified by endogenous changes in bile acid metabolism. Because experimental diabetes mellitus is associated with alterations in the synthesis of bile acids and total bile salt pool size and composition in the rat, we examined the effects of diabetes mellitus induced by alloxan (5 mg/100 gm body weight, intravenously) and insulin treatment on hepatic bile salt transport and relate the changes to bile salt pool size variations. At 3 days after alloxan injection (DIAB-3 group) both taurocholate maximum secretory rate and pool size were significantly decreased, whereas they were restored to normal values after 6 days of diabetes (DIAB-6 group). Insulinopenic diabetes for 14 days (DIAB-14 group) and for 24 days (DIAB-24 group) resulted in a marked increase of basal bile salt secretory rate (secondary to an increased contribution of cholate conjugates) and an enhanced taurocholate maximum secretory rate compared with control rates (147% and 188% increase, respectively) and with a group (PHARM-control) that received alloxan but did not develop detectable glycosuria (224% and 286% increase, respectively). In contrast, sulfobromophthalein maximum secretory rate was not significantly modified in 14-day diabetic rats compared with control rats. In addition, diabetic rats demonstrated a significant reduction of the bile salt-independent fraction of bile flow. Insulin treatment (3 units/100 gm body wt/day) in diabetic rats from day 0 (alloxan injection) to day 14 (INS-14 group) and from day 14 to day 24 after alloxan administration (INS-24 group) normalized basal bile salt secretion, taurocholate maximum secretory rate and the bile salt-independent fraction of bile flow. Bile salt pool size was significantly greater in DIAB-14 and DIAB-24 groups than in the control group (172% and 216% greater, respectively) and the PHARM-control group (246% and 309% greater, respectively). Insulin treatment prevented, in the INS-14 group, and reversed, in the INS-24 group, the increase of bile salt pool. Cholestyramine administration (5% wt/wt in the diet) to diabetic rats from day 0 (alloxan injection) to day 14 (CHOL-14 group) and from day 14 to day 24 after alloxan administration (CHOL-24 group) prevented and reversed, respectively, bile salt pool and taurocholate maximum secretory rate increase without modifying the hyperglycemia.
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    ADAPTIVE-CHANGES OF HEPATIC BILE-SALT TRANSPORT IN A MODEL OF REVERSIBLE INTERRUPTION OF THE ENTEROHEPATIC CIRCULATION IN THE RAT
    (1993) ACCATINO, L; HONO, J; KOENIG, C; PIZARRO, M; RODRIGUEZ, L
    The reversibility and time course of the adaptive changes in hepatic bile salt transport related to modifications of the bile salt enterohepatic circulation and bile salt pool size have not been previously studied. For this reason a model of reversible interruption of entero-hepatic circulation was characterized in unrestrained rats, which allowed the study of changes in hepatic bile salt transport following bile salt pool depletion and subsequent restoration by either the de novo synthesis of bile acids or i.v. administration of exogenous taurocholate. Rats subjected to biliary drainage for 24 h through a transduodenal common bile duct cannula, followed by removal of the cannula and restoration of the enterohepatic circulation were studied at 24, 48 and 72 h. Neither light and electron microscopy examination nor plasma biochemical parameters showed evidence of necrosis, fibrosis, cholestasis or inflammatory changes. Maximum taurocholate secretory rate decreased to 50% following 24-h bile salt depletion. After restoration of the enterohepatic circulation maximum taurocholate secretory rate progressively increased to normal values at 72 h, following the normalization of the bile salt pool size, which had a similar composition compared with controls. The same effect was obtained when the native bile salt pool was substituted with exogenous taurocholate. Thus, adaptive down-regulation of hepatic bile salt transport capacity is a reversible process, related to restoration of entero-hepatic circulation and normalization of bile salt pool size.
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    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.