PRESINUSOIDAL AND PROXIMAL INTRASINUSOIDAL CONFLUENCE OF HEPATIC-ARTERY AND PORTAL-VEIN IN RAT-LIVER - FUNCTIONAL EVIDENCE BY ORTHOGRADE AND RETROGRADE BIVASCULAR PERFUSION

The site of confluence of the artery and the portal vein in the liver still appears to be controversial. Anatomical studies suggested a pres inusoidal or an intrasinusoidal confluence in the first, second or eve n final third of the sinusoids. The objective of this investigation wa s to study the problem with functional biochemical techniques. Rat liv ers were perfused through the hepatic artery and simultaneously either in the orthograde direction from the portal vein to the hepatic vein or in the retrograde direction from the hepatic vein to the portal vei n. Arterial how was linearly dependent on arterial pressure between 70 cm H2O and 120 cm H2O at a constant portal or hepatovenous pressure o f 18 cm H2O. An arterial pressure of 100 cm H2O was required for the m aintenance of a homogeneous orthograde perfusion of the whole parenchy ma and of a physiologic ratio of arterial to portal how of about 1:3. Glucagon was infused either through the artery or the portal vein and hepatic vein, respectively, to a submaximally effective ''calculated'' sinusoidal concentration after mixing of 0.1 nmol/L. During orthograd e perfusions, arterial and portal glucagon caused the same increases i n glucose output. Yet during retrograde perfusions, hepatovenous gluca gon elicited metabolic alterations equal to those in orthograde perfus ions, whereas arterial glucagon effected changes strongly reduced to b etween 10% and 50%. Arterially infused trypan blue was distributed hom ogeneously in the parenchyma during orthograde perfusions, whereas it reached clearly smaller areas of parenchyma during retrograde perfusio ns. Finally, arterially applied acridine orange was taken up by all pe riportal hepatocytes in the proximal half of the acinus during orthogr ade perfusions but only by a much smaller portion of periportal cells in the proximal third of the acinus during retrograde perfusions. Thes e findings suggest that in rat liver, the hepatic artery and the porta l vein mix before and within the first third of the sinusoids, rather than in the middle or even last third.