Pathogenesis of Portal Hypertension: Extrahepatic Mechanisms

Chronic liver diseases, including hepatic cirrhosis, chronic hepatitis, alcoholic liver disease, and hepatocellular carcinoma, are one of the commonest causes of death and liver transplantation in adults worldwide. They are accompanied by profound disturbances that are not limited to the intrahepatic circulation, but involve also the splanchnic and systemic vascular beds. These hemodynamic disturbances are responsible for the development of portal hypertension, the most frequent and severe of cirrhosis. This syndrome is characterized by a pathological increase of blood pressure in the portal vein and concomitant increases in splanchnic blood flow and portosystemic collateral vessel formation. Increased blood flow in splanchnic organs draining into the portal vein augments in turn the portal venous inflow. Such increased portal venous inflow perpetuates and exacerbates portal pressure elevation and determines the formation of ascites during chronic liver disease. In addition, portosystemic collateral vessels include the gastroesophageal varices, which are particularly prone to rupture causing massive gastroesophageal bleeding. Collateral vessels are also responsible for other major consequences of chronic liver disease, including portosystemic encephalopathy and sepsis. Extrahepatic mechanisms are clearly of major importance for disease progression and aggravation of the portal hypertensive syndrome. Accordingly, most of the therapies currently used in portal hypertension do not act inside the liver but they actually target the increased splanchnic blood flow. This paper reviews the consequences of the splanchnic circulatory abnormalities in portal hypertension and the complex signals capable of increasing vasodilatation, hyporesponsiveness to vasoconstrictors and angiogenesis in the splanchnic vascular bed and the portosystemic collateral circulation in this pathological setting.