Autoregulation of portal circulation: a correlative study of circulation and vascular morphology

To investigate the mechanism of portal circulation and the genesis of portal hypertension, an in vivo model was made to increase portal venous flow (PVF) by forming a bypass shunt between the femoral artery to the splenic venous branch in pigs and dogs via a regulatable pump. Using this model, an autoregulatory hemodynamics of the portal circulation and corresponding morphological changes of the intrahepatic vascular system were determined. Immediately after blood flow increase (100 mL/min) to the portal vein, PVF increased to the baseline level plus bypass shunt flow. But, PVF returned to the baseline level within 1 h for both animals. Portal venous resistance (PVR) at 1 h was significantly higher than the baseline level (P < 0.05). By histometric analysis of the cross-sectional area of the portal and hepatic venous branches (CSA-PV, CSA-HV) using the biopsized liver, CSA-HV at 1 h was 27.6% of the CSA-HV of the baseline level in dog, which showed narrowing and contractive changes of the hepatic venous branches, and CSA-PV at 1 h was 36.4% of the CSA-PV of the baseline level in pig, which showed narrowing and contractive changes of the portal venous branches. It is suggested that a tone of the intrahepatic vascular system has an important role in the portal autoregulatory hemodynamics.