title: Sensitivity to endothelin-1 is decreased in isolated livers of endothelial constitutive nitric oxide synthase knockout mice.
abstract: BACKGROUND
  Hepatic sinusoidal resistance is regulated by vasoactive factors including endothelin-1 (ET-1) and nitric oxide (NO). In the absence of NO, vasoconstrictor response to endothelin is expected to predominate. Therefore, we hypothesized sensitivity to endothelin to be increased in mice lacking the endothelial cell NO synthase gene. Response of vascular resistance to endothelin was assessed in the in situ perfused liver of endothelial constitutive nitric oxide synthase (ecNOS) knockout and wild type mice. Livers were also harvested for RNA and protein isolation for quantitative PCR and Western blotting, respectively. The expression of endothelin receptors, isoenzymes of NO synthase, heme-oxygenase and adrenomedullin was quantified.
  
  
  RESULTS
  Endothelin increased hepatic vascular resistance in a dose-dependent manner in both strains; however, this increase was significantly less in ecNOS knockout mice at physiologic concentrations. Expression of heme-oxygenases and adrenomedullin was similar in both groups, whereas inducible nitric oxide synthase (iNOS) protein was not detectable in either strain. mRNA levels of pre-pro-endothelin-1 and ETB receptor were comparable in both strains, while mRNA for ETA receptor was decreased in ecNOS knockouts.
  
  
  CONCLUSIONS
  Livers of ecNOS knockout mice have a decreased sensitivity to endothelin at physiologic concentrations; this is associated with a decreased expression of ETA receptors, but not with other factors, such as iNOS, ETB receptors, adrenomedullin or heme-oxygenase. Further studies targeting adaptive changes in ETA receptor distribution and/or intracellular signaling downstream of the receptor are indicated.
authors.affiliation: Department of Clinical Pharmacology, University of Berne, Murtenstrasse 35, 3010 Berne, Switzerland. andrea.de-gottardi@alumni.uni-heidelberg.de
authors.forename: Andrea
authors.initials: A
authors.lastname: De Gottardi
authors.forename: Erwin
authors.initials: E
authors.lastname: Biecker
authors.forename: Abraham
authors.initials: A
authors.lastname: Koshy
authors.forename: Dieter
authors.initials: D
authors.lastname: Bohler
authors.forename: Sidney
authors.initials: S
authors.lastname: Shaw
authors.forename: Hans
authors.initials: H
authors.lastname: Sägesser
authors.forename: Jürg
authors.initials: J
authors.lastname: Reichen