Hepatic capillary pressure is estimated using triple vascular occlusion method in isolated canine liver

We determined whether the triple vascular occlusion pressure (Pto), the equilibration pressure obtained when the hepatic artery, portal, and hepatic veins were occluded simultaneously, represented the capillary pressure (Pc) in isolated bivascularly blood-perfused canine livers. Effects of a bolus injection of histamine (0.1-60 micrograms), norepinephrine (NE; 1-600 micrograms), or acetylcholine (ACh; 0.01-10 micrograms) into the portal vein or the hepatic artery were also studied on vascular resistance distribution using Pto as a measure of Pc. The livers were perfused at constant flow via the portal vein and at constant pressure via the hepatic artery. Pto was compared with Pc measured using the traditional gravimetric method (Pc,i). Pto and Pc,i showed a strong correlation (Pto = -0.02 + 0.98 Pc,i; r = 0.83, P = 0.0018). With comparisons, the intercept was not significantly different from zero, and the slope was not different from 1.00, indicating that Pto accurately represented Pc. The resting postsinusoidal vascular resistance comprised 54% of the total hepatic vascular resistance (Rt). Portal or arterial injection of histamine increased predominantly hepatic venous resistance (Rhv) over portal resistance with liver weight gain. NE constricted both the portal vein and the hepatic artery in greater magnitude than the hepatic vein, as evidenced by a significant decrease in the Rhv/Rt ratio. This precapillary constriction was accompanied by a significant decrease in liver weight. In contrast, ACh contracted both portal and hepatic veins similarly without liver weight change. We conclude that Pto is an excellent estimate of Pc in isolated blood-perfused canine livers and that the hepatic vascular resistance sites in the resting states are located evenly in the pre- and postsinusoidal vessels. Intraportal or intra-arterial infusion of histamine, NE, and ACh produced characteristically different changes in hepatic vascular resistances and hepatic volume. The Pto technique could be applied in experimental research on hepatic hemodynamics.