AJP - Gastrointestinal and Liver Physiology, Vol 250, Issue 2 205-G212, Copyright © 1986 by American Physiological Society
Interaction of flow and resistance in maintenance of portal hypertension in a rat model
E. Sikuler and R. J. Groszmann
To clarify the roles that portocollateral resistance ("backward-flow"
theory) and portal flow ("forward-flow" theory) play in maintaining chronic
portal hypertension, we studied, in a rat model with prehepatic portal
hypertension, the hemodynamic changes that occur when portocollateral
resistance is reduced and high portal venous inflow is maintained. In 30
portal-hypertensive rats the constriction around the portal vein was
removed 4 days after induction of portal hypertension, 30 rats were used as
portal vein-constricted controls, and 30 additional rats were subjected to
a sham operation. The removal of the ligature constricting the portal vein
was followed by an immediate decrease in portal pressure (from 16.3 +/- 0.8
to 9.6 +/- 0.8 mmHg, P less than 0.001). Two days after the ligature
removal, hyperdynamic circulation was still evident and was characterized
by a decreased splanchnic arteriolar resistance and an increased portal
venous inflow. The coexistence of high portal venous inflow and normal
portal pressure indicates that high portal venous inflow per se is not
sufficient to produce an increase in portal pressure when it faces a
low-resistance vascular bed. We conclude that portal hypertension is
induced by the interaction of an abnormally high portal venous inflow and
high resistance offered to the flow by the portocollateral vessels. Neither
the forward-flow theory nor the backward-flow theory can be applied solely
to explain the increased portal pressure.
