The vascular occlusion methods for determination of hepatic vasoconstriction sites

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We determined whether the triple vascular occlusion pressure (P_<to>), the equilibration pressure obtained when the hepatic artery, portal and hepatic veins were occluded simultaneously, represented the capillary pressure (P_c) in isolated bivascularly blood-perfused canine livers. Effects of a bolus injection of histamine (0.1-60mug), norepinephrine (NE,1-600mug), acetylcholine (ACh, 0.01-10mug) or platelet-activating factor (PAF,0.01-30mug) into the portal vein or the hepatic artery were also studied on vascular resistance distribution using P_<to> as a measure of P_c. The livers were perfused at constant flow via portal vein and at constant pressure via hepatic artery. P_<to> was compared with P_c measured using the traditional gravimetric method (P_<c, i>). P_<to> and P_<c, i> showed a strong correlation (P_<to>=-0.02+0.98 P_<c, 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 tha … More t P_<to> accurately represented P_c. The resting postsinusoidal vascular resistance comprised of 54% of the total hepatic vascular resistance (R_t). Portal or arterial injection of histamine increased predominantly hepatic venous resistance (R_<hv>) over portal resistance with liver weight gain. NE constricted both portal vein and hepatic artery in greater magnitude than hepatic vein, as evidenced by a significant decrease in the R_<hv>/R_t ratio. This precapillary constriction was accompanied by a significant decrease in liver weight. In contrast, ACh and PAF contracted both portal and hepatic veins similarly without liver weight change. We conclude that P_<to> is an excellent estimate of the capillary pressure 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 intraarterial infusion of histamine, norepinephrine acetylcholine and platelet-activating factor produced characteristically different changes in hepatic vascular resistances and hepatic volume. P_<to> could be applied in experimental research on hepatic hemodynamics. Less