Hepatic microvascular pressure during anaphylactic shock in anesthetized rats

ObjectiveHepatic venoconstriction plays a significant role in anaphylactic hypotension in anesthetized rats. The purpose of this study is to determine whether the primary site of anaphylactic venoconstriction in the liver venous circulation occurs prior to or distal to the sinusoidal capillaries. We also determined whether the hepatic blood volume is increased during anaphylactic hypotension.MethodsWe measured, using a servo-null micropipette pressure-measuring system, the hepatic venular transmural pressure (Pμhv) at the liver surface of anesthetized rats sensitized with the antigen of ovalbumin (1 mg). We also measured the liver lobe thickness, using the ultrasonic crystal dimension measuring system. Anaphylactic hypotension was induced by an intravenous injection of 0.6 mg ovalbumin.ResultsWhen the antigen was injected, the systemic arterial pressure decreased profoundly from 118 ± 9 to 45 ± 4 mm Hg, which was accompanied by an increase in Ppv and Pμhv: Pμhv only transiently increased from 3.1 ± 0.9 to 8.8 ± 1.5 cmH2O at 1 min and then rapidly returned to the baseline within 2 min, when Ppv continued to increase and reached the peak of 36 ± 7 cmH2O at 3.5 min after antigen. This greater increase in Ppv-to-Pμhv gradient than that in Pμhv-to-Pcv gradient after antigen indicated that the constriction of the portal veins and the sinusoids much predominates over that of the hepatic veins. Along with this hepatic pre- and sinusoidal constriction, the liver lobe thickness significantly decreased by 4% after antigen.ConclusionPre-sinusoidal constriction during anaphylactic shock in anaesthetized rats increased the portal venous pressure while the hepatic venular pressure only increased slightly and transiently. This predominant pre-sinusoidal constriction is accompanied by a decrease in liver volume.