title: Desensitization of G-protein-coupled receptors induces vascular hypocontractility in response to norepinephrine in the mesenteric arteries of cirrhotic patients and rats.
abstract: BACKGROUND
  The increased beta-arrestin-2 and its combination with G-protein-coupled receptors (GPCRs) lead to GPCRs desensitization. The latter may be responsible for decreased contractile reactivity in the mesenteric arteries of cirrhotic patients and rats. The present study is to investigate the machinery changes of alpha-adrenergic receptors and G proteins and their roles in the contractility of mesenteric arteries of cirrhotic patients and animal models.
  
  
  METHODS
  Patients with cirrhosis due to hepatitis B and cirrhotic rats induced by CCl4 were studied. Mesenteric artery contractility in response to norepinephrine was determined by a vessel perfusion system. The contractile effect of G protein-coupled receptor kinase-2 (GRK-2) inhibitor on the mesenteric artery was evaluated. The protein expression of the alpha1 adrenergic receptor, G proteins, beta-arrestin-2, GRK-2 as well as the activity of Rho associated coiled-coil forming protein kinase-1 (ROCK-1) were measured by Western blot. In addition, the interaction of alpha1 adrenergic receptor with beta-arrestin-2 was assessed by co-immunoprecipitation.
  
  
  RESULTS
  The portal vein pressure of cirrhotic patients and rats was significantly higher than that of controls. The dose-response curve to norepinephrine in mesenteric arteriole was shifted to the right, and EC50 was significantly increased in cirrhotic patients and rats. There were no significant differences in the expressions of the alpha1 adrenergic receptor and G proteins in the cirrhotic group compared with the controls. However, the protein expressions of GRK-2 and beta-arrestin-2 were significantly elevated in cirrhotic patients and rats compared with those of the controls. The interaction of the alpha1 adrenergic receptor and beta-arrestin-2 was significantly aggravated. This interaction was significantly reversed by GRK-2 inhibitor. Both the protein expression and activity of ROCK-1 were significantly decreased in the mesenteric artery in patients with cirrhosis compared with those of the controls, and this phenomenon was not shown in the cirrhotic rats. Norepinephrine significantly increased the activity of ROCK-1 in normal rats but not in cirrhotic ones. Norepinephrine significantly increased ROCK-1 activity in cirrhotic rats when GRK-2 inhibitor was used.
  
  
  CONCLUSIONS
  beta-arrestin-2 expression and its interaction with GPCRs are significantly upregulated in the mesenteric arteries in patients and rats with cirrhosis. These upregulations result in GPCR desensitization, G-protein dysfunction and ROCK inhibition. These may explain the decreased contractility of the mesenteric artery in response to vasoconstrictors.
authors.affiliation: Department of Surgery, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200127, China. zhiyongwu@gmail.com
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Jiang-Yong
authors.initials: JY
authors.lastname: Sang
authors.forename: De-Jun
authors.initials: DJ
authors.lastname: Liu
authors.forename: Jun
authors.initials: J
authors.lastname: Qin
authors.forename: Yan-Miao
authors.initials: YM
authors.lastname: Huo
authors.forename: Jia
authors.initials: J
authors.lastname: Xu
authors.forename: Zhi-Yong
authors.initials: ZY
authors.lastname: Wu
mesh_terms: D000328:Adult; D000818:Animals; D019390:Arrestins / Q000378:metabolism; D002251:Carbon Tetrachloride; D004305:Dose-Response Relationship, Drug; D005260:Female; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D006509:Hepatitis B / Q000150:complications; D006801:Humans; D008103:Liver Cirrhosis / Q000378:metabolism* / Q000503:physiopathology / Q000821:virology; D008106:Liver Cirrhosis, Experimental / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D008875:Middle Aged; D009638:Norepinephrine / Q000494:pharmacology*; D017082:Portal Pressure / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; D054460:rho-Associated Kinases / Q000378:metabolism
chemical_list: C000605254:ARRB2 protein, human; C000605257:Arrb2 protein, rat; D019390:Arrestins; D047428:Protein Kinase Inhibitors; D018340:Receptors, Adrenergic, alpha-1; D014662:Vasoconstrictor Agents; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; D002251:Carbon Tetrachloride; C515851:ROCK1 protein, human; C578418:ROCK1 protein, rat; D054460:rho-Associated Kinases; C496567:GRK2 protein, human; C496569:Grk2 protein, rat; D054769:G-Protein-Coupled Receptor Kinase 2; D009638:Norepinephrine