Pathophysiologic basis for the medical management of portal hypertension

Endothelium dependent expression and underlying mechanisms of des-Arg⁹-bradykinin-induced B₁R-mediated vasoconstriction in rat portal vein

Endothelial dysfunction has been implicated in portal vein obstruction, a condition responsible for major complications in chronic portal hypertension. Increased vascular tone due to disruption of endothelial function has been associated with an imbalance in the equilibrium between endothelium-derived relaxing and contracting factors. Herein, we assessed underlying mechanisms by which expression of bradykinin B(1) receptor (B(1)R) is induced in the endothelium and how its stimulation triggers vasoconstriction in the rat portal vein. Prolonged in vitro incubation of portal vein resulted in time- and endothelium-dependent expression of B(1)R and cyclooxygenase-2 (COX-2). Inhibition of protein kinase C (PKC) or phosphatidylinositol 3-kinase (PI3K) significantly reduced expression of B(1)R through the regulation of transcription factors, activator protein-1 (AP-1) and cAMP response element-binding protein (CREB). Moreover, pharmacological studies showed that B(1)R-mediated portal vein contraction was reduced by COX-2, but not COX-1, inhibitors. Notably, activation of endothelial B(1)R increased phospholipase A(2)/COX-2-derived thromboxane A(2) (TXA(2)) levels, which in turn mediated portal vein contraction through binding to TXA(2) receptors expressed in vascular smooth muscle cells. These results provide novel molecular mechanisms involved in the regulation of B(1)R expression and identify a critical role for the endothelial B(1)R in the modulation of portal vein vascular tone. Our study suggests a potential role for B(1)R antagonists as therapeutic tools for diseases where portal hypertension may be involved.

Distribution of vascular endothelial growth factor receptor in hepatic arteries and veins of rats with portal hypertension

AIM: To observe the distribution of vascular endothelial growth factor receptor-1 and -2 (VEGFR-1 and -2) in both hepatic arteries and veins of rats with portal hypertension (PHT).

METHODS: Thirty male Sprague-Dawley rats, weighing 180-220 g, were randomly divided into two groups: normal control group (n = 10), and model group (n = 20). The normal control group was given normal drinking water, while the model group was given drinking water containing thioacetamide (TAA). Twelve weeks later, 12 rats who had a portal pressure > 1.57 kPa and obvious pseudolobules were selected for subsequent experiments. The distribution of VEGFR-1 and -2 in both hepatic arteries and veins of these rats was determined by immunohistochemistry.

RESULTS: VEGFR-2 expression in both hepatic arteries and veins of PHT rats significantly increased (t = 24.306, 54.776, both P < 0.05). VEGFR-1 expression in both hepatic arteries and portal veins of PHT models also significantly increased (t = 20.669, 33.210, both P < 0.05). VEGFR-2 expression in hepatic veins was markedly higher than that in hepatic arteries in PHT rats (t = 23.424, P < 0.05). There is no difference in VEGFR-1 expression between hepatic arteries and veins in PHT models (t = 1.434, P > 0.05).

CONCLUSION: VEGFR-2 can decrease the pressure of portal veins possibly by promoting the neovascularization of hepatic veins.