Estrogens stimulate proliferation of intrahepatic biliary epithelium in rats

Background & Aims: We investigated the expression of estrogen receptor (ER) α and β subtypes in cholangiocytes of normal and bile duct-ligated (BDL) rats and evaluated the role and mechanisms of estrogens in the modulation of cholangiocyte proliferation. Methods: ER-α and ER-β were analyzed by immunohistochemistry, reverse-transcription polymerase chain reaction, and Western blotting in normal and BDL rats. The effects of the ER antagonists tamoxifen and ICI 182,780 on cholangiocyte proliferation were evaluated. Results: Cholangiocytes expressed both ER-α and ER-β subtypes, whereas hepatocytes expressed only ER-α. In association with a marked cholangiocyte proliferation and with enhanced estradiol serum levels, the immunoreactivity for ER-α involved a 3-fold higher percentage of cholangiocytes in 3-week BDL than in normal rats; immunore-activity for ER-β showed a 30-fold increase. Western blot analysis showed that during BDL, the total amount of ER-β in cholangiocytes was markedly increased (5-fold), whereas that of ER-α decreased slightly (-25%). Treatment with tamoxifen or ICI 182,780 of 3-week BDL rats inhibited cholangiocyte proliferation and induced over-expression of Fas antigen and apoptosis in cholangiocytes. In vitro, 17β estradiol stimulated proliferation of cholangiocyte, an effect blocked to the same extent by tamoxifen or ICI 182,780. Conclusions: This study suggests that estrogens and their receptors play a role in the modulation of cholangiocyte proliferation

The function of alkaline phosphatase in the liver: Regulation of intrahepatic biliary epithelium secretory activities in the rat

We studied the effects of alkaline phosphatase (AP) on the secretory processes of the rat intrahepatic biliary epithelium as well as the role of the intrahepatic biliary epithelium in the uptake and biliary secretion of exogenous AP. The effects of acute and chronic administration of AP on bile secretory parameters were investigated in vivo in normal and bile duct ligated (BDL) rats and in vitro in isolated rat bile duct units (IBDU), In vivo, acute AP administration decreased bile now and biliary bicarbonate excretion and abolished secretin choleresis in BDL rats but not in normal rats. On the contrary, the AP inhibitor, levamisole, increased in BDL rat bile flow and biliary bicarbonate excretion. In vitro, basal and secretin-stimulated Cl(-)/HCO(3)(-) exchanger activity in IBDU was immediately inhibited by AP intraluminal microinjection (apical exposure) but only after a prolonged exposure to the basolateral pole. Levamisole increased the Cl(-)/HCO(3)(-) exchanger activity of IBDU, A significant basolateral uptake of AP occurs in IBDU with a progressive transport to the apical domain. AP chronic treatment increased AP and gamma-glutamyltranspeptidase (gamma-GT) activities in the intrahepatic bile ducts and hepatocyte canalicular pole, promoted enlargement of bile canaliculi, and decreased bile flow and biliary bicarbonate excretion. In conclusion, the intrahepatic biliary epithelium plays a role in the uptake and biliary secretion of serum AP. AP inhibits the secretory processes of the intrahepatic biliary epithelium and induces features of intrahepatic cholestasis after chronic administration. These findings indicate that AP plays an active role in down-regulating the secretory activities of the intrahepatic biliary epithelium

Effect of ovariectomy on the proliferative capacity of intrahepatic rat cholangiocytes

Background & Aims: We evaluated the effects of ovariectomy (OVX) and estrogen replacement treatment on cholangiocyte proliferation induced by bile duct ligation (BDL). Methods: BDL (2 weeks) was performed in ovariectomized rats and the proliferative and apoptotic activity compared with normal, with BDL control rats, and with BDL +/- OVX rats treated with 17-beta estradiol. Results: OVX induced a significant (P < 0.01) reduction of bile duct mass in BDL rats. The reduction of bile duct mass induced by OVX was associated with a decreased expression of estrogen receptor (ER)-alpha (2.5-fold) and, mainly, ER-beta (35-fold). Proliferating cellular nuclear antigen (PCNA) expression in cholangiocytes was impaired by OVX, indicating depression of proliferation, whereas terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) and Fas positivity were markedly enhanced, indicating activation of Fas-mediated apoptosis. Administration of 17-beta estradiol during BDL in OVX rats induced a normalization of bile duct mass, ER expression, cholangiocyte proliferation, and apoptosis (Fas and TUNEL) in comparison with untreated BDL rats. Conclusions: Our findings support the role of endogenous estrogens in sustaining the enhanced proliferative and secretory activities of cholangiocytes in cholestasis. On the basis of these data, the hypothesis of an estrogenic functional deficiency in chronic cholestatic liver diseases should merit careful attention