In cirrhosis, increased RhoA/Rho-kinase signaling and decreased nitric oxide (NO) availability contribute to increased intrahepatic resistance and portal hypertension. Hepatic stellate cells (HSCs) regulate intrahepatic resistance. 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) inhibit synthesis of isoprenoids, which are necessary for membrane translocation and activation of small GTPases like RhoA and Ras. Activated RhoA leads to Rho-kinase activation and NO synthase inhibition. We therefore investigated the effects of atorvastatin in cirrhotic rats and isolated HSCs. Rats with secondary biliary cirrhosis (bile duct ligation, BDL) were treated with atorvastatin (15 mg/kg per day for 7 days) or remained untreated. Hemodynamic parameters were determined in vivo (colored microspheres). Intrahepatic resistance was investigated in in situ perfused livers. Expression and phosphorylation of proteins were analyzed by RT-PCR and immunoblots. Three-dimensional stress-relaxed collagen lattice contractions of HSCs were performed after incubation with atorvastatin. Atorvastatin reduced portal pressure without affecting mean arterial pressure in vivo. This was associated with a reduction in intrahepatic resistance and reduced responsiveness of in situ-perfused cirrhotic livers to methoxamine. Furthermore, atorvastatin reduced the contraction of activated HSCs in a 3-dimensional stress-relaxed collagen lattice. In cirrhotic livers, atorvastatin significantly decreased Rho-kinase activity (moesin phosphorylation) without affecting expression of RhoA, Rho-kinase and Ras. In activated HSCs, atorvastatin inhibited the membrane association of RhoA and Ras. Furthermore, in BDL rats, atorvastatin significantly increased hepatic endothelial nitric oxide synthase (eNOS) mRNA and protein levels, phospho-eNOS, nitrite/nitrate, and the activity of the NO effector protein kinase G (PKG). Conclusion: In cirrhotic rats, atorvastatin inhibits hepatic RhoA/Rhokinase signaling and activates the NO/PKG-pathway. This lowers intrahepatic resistance, resulting in decreased portal pressure. Statins might represent a therapeutic option for portal hypertension in cirrhosis. (HEPATOLOGY 2007;46:242-253.)

No abstract

Prostatic α1 -adrenoceptors are known to be involved in the pathophysiology of lower urinary tract symptoms (LUTS) in patients with benign prostate obstruction (BPO). It is widely accepted that enhanced α1 -adrenergic smooth muscle contraction can contribute to bladder outlet obstruction; α1 -adrenoceptor antagonists still represent a gold standard in the treatment of LUTS. Accordingly, expression and function of α1 -adrenoceptors in the prostate have attracted large attention over the last three decades. However, recent preclinical studies have challenged our understanding of prostatic α1 -adrenoceptors. In the current review article, we summarize "modern" concepts of prostatic α1 -adrenoceptors which include novel intracellular mediators of contraction as well as non-contractile signaling and post-translational receptor regulation. Configuration of α1 -adrenoceptors with binding partners may determine its function, leading to a dynamic receptor with high functional plasticity. Cooperative regulation of different intracellular effectors (MAPK, Akt, transcription factors) by α1 -adrenoceptors, hormones or growth factors has been suggested. The prostatic α1 -adrenoceptor is no longer being regarded as an isolated, static receptor exclusively mediating prostatic smooth muscle contraction by G proteins, but a dynamic receptor interacting with other receptors within a complex network of mediators.

In liver cirrhosis, abnormal persistent extrahepatic vasodilation leads to hyperdynamic circulatory dysfunction which essentially contributes to portal hypertension. Since portal hypertension is a major factor in the development of complications in cirrhosis, the mechanisms underlying this vasodilation are of paramount interest. Extensive studies performed in cirrhotic patients and animals revealed that this vasodilation is associated on the one hand with enhanced formation of vasodilators, and on the other hand with vascular hyporesponsiveness to vasoconstrictors. The latter phenomenon has been termed "vascular hypocontractility". It is caused by a combination of different mechanisms and factors described in this review.

No abstract

The 14‐3‐3 protein family, which is present at particularly high concentrations in mammalian brain, is known to be involved in various cellular functions, including protein kinase C regulation and exocytosis. Despite the fact that most of the 14‐3‐3 proteins are cytosolic, a small but significant proportion of 14‐3‐3 in brain is tightly and selectively associated with some membranes. Using a panel of isoform‐specific antisera we find that the ε, η, γ, β, and ζ isoforms are all present in purified synaptic membranes but absent from mitochondrial and myelin membranes. In addition, the η, ε, and γ isoforms but not the β and ζ isoforms are associated with isolated synaptic junctions. When different populations of synaptosomes were fractionated by a nonequilibrium Percoll gradient procedure, the ε and γ isoforms were present and the β and ζ isoforms were absent from the membranes of synaptosomes sedimenting in the more dense parts of the gradient. The finding that these proteins are associated with different populations of synaptic membranes suggests that they are selectively expressed in different classes of neurones and raises the possibility that some or all of them may influence neurotransmission by regulating exocytosis and/or phosphorylation.

Upregulation of RhoA and Rho-kinase contributes to increased intrahepatic resistance in cirrhotic rats and to an increased sensitivity of cirrhotic livers to vasoconstrictors.

In cirrhosis, vascular hypocontractility leads to vasodilation and contributes to portal hypertension. Impaired activation of contractile pathways contributes to vascular hypocontractility. Angiotensin II type 1 receptors (AT 1 -Rs) are coupled to the contraction-mediating RhoA/Rhokinase pathway and may be desensitized by phosphorylation through G-protein-coupled receptor kinases (GRKs) and binding of ␤-arrestin-2. In the present study, we analyzed vascular hypocontractility to angiotensin II in cirrhosis. Human hepatic arteries were obtained during liver transplantation. In rats, cirrhosis was induced by bile duct ligation (BDL). Contractility of rat aortic rings was measured myographically. Protein expression and phosphorylation were analyzed by Western blot analysis. Immunoprecipitation was performed with protein A-coupled Sepharose beads. Myosin light chain (MLC) phosphatase activity was assessed as dephosphorylation of MLCs. Aortas from BDL rats were hyporeactive to angiotensin II and extracellular Ca 2؉ . Expression of AT 1 -R and G␣ q/11,12,13 remained unchanged in hypocontractile rat and human vessels, whereas GRK-2 and ␤-arrestin-2 were up-regulated. The binding of ␤-arrestin-2 to the AT 1 -R was increased in hypocontractile rat and human vessels. Inhibition of angiotensin II-induced aortic contraction by the Rho-kinase inhibitor Y-27632 was pronounced in BDL rats. Basal phosphorylation of the ROK-2 substrate moesin was reduced in vessels from rats and patients with cirrhosis. Analysis of the expression and phosphorylation of Ca 2؉ -sensitizing proteins (MYPT1 and CPI-17) in vessels from rats and patients with cirrhosis suggested decreased Ca 2؉ sensitivity. Angiotensin II-stimulated moesin phosphorylation was decreased in aortas from BDL rats. MLC phosphatase activity was elevated in aortas from BDL rats. Conclusion: Vascular hypocontractility to angiotensin II in cirrhosis does not result from changes in expression of AT 1 -Rs or G-proteins. Our data suggest that in cirrhosis-induced vasodilation, the AT 1 -R is desensitized by GRK-2 and ␤-arrestin-2 and that changed patterns of phosphorylated Ca 2؉ -sensitizing proteins decrease Ca 2؉ sensitivity. (HEPATOLOGY 2007;45:495-506.)