Defective RhoA/Rho-kinase signaling contributes to vascular hypocontractility and vasodilation in cirrhotic rats.
OBJECTIVE
Portal hypertension is associated with arterial hypotension and vascular hypocontractility, which persists despite elevated plasma levels of vasoconstrictors. We investigated the role of the RhoA/Rho-kinase pathway in vascular smooth muscle hypocontractility of rats with secondary biliary cirrhosis.


METHODS
Aortic expressions of RhoA and Rho-kinase were analyzed in sham-operated and BDL rats by reverse-transcription polymerase chain reaction (RT-PCR) and immunoblots. Activation of aortic RhoA was examined by pull down of guanosine triphosphate (GTP)-RhoA and membrane translocation of RhoA. Rho-kinase activity was assessed as phosphorylation of its substrate, moesin. Contractility of isolated aortic rings was determined myographically. The hemodynamic effect of the Rho-kinase inhibitor (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide (Y-27632) was determined in vivo by measuring changes in mean arterial pressure and systemic vascular resistance (SVR) (microspheres).


RESULTS
Contraction of aortic rings from BDL rats was impaired in response to the alpha(1)-adrenergic receptor agonist methoxamine but not to high molar KCl. Aortic expression of RhoA was unchanged in cirrhotic rats, whereas Rho-kinase was down-regulated posttranscriptionally. Methoxamine-induced activation of RhoA as well as basal and methoxamine-induced phosphorylation of moesin were strongly reduced in aortas from cirrhotic rats. Aortic rings from cirrhotic rats precontracted with methoxamine showed an increased sensitivity to relaxation with Y-27632. The drop in SVR induced by Y-27632 was larger in cirrhotic rats than in sham-operated rats.


CONCLUSIONS
An impaired vascular activation of RhoA and a down-regulation of Rho-kinase might contribute to vasodilation and vascular hypocontractility in BDL-induced cirrhosis.
Hennenberg
Martin
M
Department of Internal Medicine I, University of Bonn, Bonn, Germany.
Biecker
Erwin
E
Trebicka
Jonel
J
Jochem
Kerstin
K
Zhou
Qi
Q
Schmidt
Martina
M
Jakobs
Karl H
KH
Sauerbruch
Tilman
T
Heller
Jörg
J
D000577:Amides / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D008106:Liver Cirrhosis, Experimental / Q000503:physiopathology*; D008297:Male; D008840:Microfilament Proteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology*; D014661:Vasoconstriction; D014664:Vasodilation / Q000187:drug effects; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000502:physiology*
D000577:Amides; D047908:Intracellular Signaling Peptides and Proteins; D008840:Microfilament Proteins; D011725:Pyridines; D012333:RNA, Messenger; C108830:Y 27632; C071058:moesin; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein