Vasopressin regulates the growth of the biliary epithelium in polycystic liver disease

The neurohypophysial hormone arginine vasopressin (AVP) acts by three distinct receptor subtypes: V1a, V1b, and V2. In the liver, AVP is involved in ureogenesis, glycogenolysis, neoglucogenesis and regeneration. No data exist about the presence of AVP in the biliary epithelium. Cholangiocytes are the target cells in a number of animal models of cholestasis, including bile duct ligation (BDL), and in several human pathologies, such as polycystic liver disease characterized by the presence of cysts that bud from the biliary epithelium. In vivo, liver fragments from normal and BDL mice and rats as well as liver samples from normal and ADPKD patients were collected to evaluate: (i) intrahepatic bile duct mass by immunohistochemistry for cytokeratin-19; and (ii) expression of V1a, V1b and V2 by immunohistochemistry, immunofluorescence and real-time PCR. In vitro, small and large mouse cholangiocytes, H69 (non-malignant human cholangiocytes) and LCDE (human cholangiocytes from the cystic epithelium) were stimulated with vasopressin in the absence/presence of AVP antagonists such as OPC-31260 and Tolvaptan, before assessing cellular growth by MTT assay and cAMP levels. Cholangiocytes express V2 receptor that was upregulated following BDL and in ADPKD liver samples. Administration of AVP increased proliferation and cAMP levels of small cholangiocytes and LCDE cells. We found no effect in the proliferation of large mouse cholangiocytes and H69 cells. Increases were blocked by preincubation with the AVP antagonists. These results showed that AVP and its receptors may be important in the modulation of the proliferation rate of the biliary epithelium

Functional Characterization of the Arginine Vasotocin 4 Receptor (VT4R) in Sensory Circumventricular Organs of the Chicken Gallus gallus

Past studies have shown that the avian vasotocin 4 receptor (VT4R), homologous to the mammalian arginine vasopressin receptor 1a (V1aR/AVPR1A) is involved in immobilization stress. It was not known, however, whether the receptor is also associated with osmotic stress, and if so, what brain regions may be involved. Four treatment groups of chicks were used for the study. One group was subjected to 1h immobilization stress and two groups were administered intraperitoneal injection of 3 M NaCl or 0.15 M NaCl. One additional group served as controls. After 1 h, blood samples were taken for the determination of plasma levels of arginine vasotocin and corticosterone by radioimmunoassay. Chick brains were sampled for immunohistochemistry utilizing an antibody, anti-VT4R, and for real time RT-PCR. Plasma corticosterone (CORT) concentrations were significantly increased in the immobilized group (p \u3c 0.01) and hypertonic saline group (p \u3c 0.01) compared with controls. Plasma arginine vasotocin (AVT) concentrations were significantly increased (p \u3c 0.01) in hypertonic saline birds and immobilized birds compared with controls. Intense staining of the VT4R in the organum vasculosum of the lamina terminalis (OVLT) and subseptal organ (SSO) of both treatment groups showed marked morphological changes compared to controls. AT1AR mRNA, TRPV1 mRNA, and VT4R mRNA levels were increased in SSO in hypertonic saline birds, while these genes were increased in OVLT in acute immobilization stressed birds. The CRH-R1 mRNA genes were decreased in hypertonic saline birds, while increased in acute immobilization stressed birds. These results strongly suggest that physical stress affect the vasotocinergic system in the SSO to regulate the water balance through VT4R, while psychogenic stress causes change in VT4R expressed in the OVLT for the classical activation of the HPA. Taken together, results provide evidence that both osmotic challenge and psychological stress affect the vasotocinergic system via the VT4R in two avian sensory circumventricular organs