Gastroenterology

Gastroenterology

Volume 130, Issue 3, March 2006, Pages 838-854
Gastroenterology

Basic-liver, pancreas, and biliary tract
Defective RhoA/Rho-Kinase Signaling Contributes to Vascular Hypocontractility and Vasodilation in Cirrhotic Rats

https://doi.org/10.1053/j.gastro.2005.11.029Get rights and content

Background & Aims: 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 α1-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.

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Animals

For our experiments, male Sprague–Dawley rats with an initial body weight of 180 to 200 g were used and divided into 2 groups. One group (n = 109) underwent bile duct ligation (BDL) as previously described.21 The rats of the other group (n = 118) were sham operated and served as controls. In these rats, the common bile duct was exposed by median laparotomy, but no ligation or resection was performed. In both groups of rats, BDL and sham-operated rats, experiments were carried out after 5 weeks.

Hypocontractility of Isolated Aortic Rings

Contraction of aortic rings from BDL rats induced by the α1-adrenergic receptor agonist methoxamine (10 μmol/L) was reduced on average by 51% compared with contraction of aortic rings from sham-operated rats (Figure 2A), demonstrating the typical hypocontractility of aortic smooth muscle in cirrhosis. Preincubation of the aortic rings with the NOS inhibitor L-NAME (200 μmol/L) increased the contraction in both groups. However, the increase was similar in both groups (Figure 2A). Thus, aortic

Discussion

Vasodilation because of an impaired response to vasoconstrictors is one of the main features of hemodynamic changes occurring in cirrhosis.34 The reasons for this hypocontractility have been the topic of many investigations but are still discussed controversially.9, 10, 35, 36, 37, 38, 39, 40, 41, 42 Vasoconstrictor-induced contraction of vascular smooth muscle is not only mediated by the PLC/IP3 pathway but also in large parts by the RhoA/Rho-kinase pathway.14, 16, 18 Here, evidence is

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    Supported by grants of the Deutsche Forschungsgemeinschaft (HE 2402/5-1) and the Ernst und Berta Grimmke-Stiftung.

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