Microcirculation of hepatic nodules from diethylnitrosamine-treated rats

The microcirculation of nodules (0.5 to 10 mm in diameter) from diethylnitrosamine-treated rats was studied in perfused livers. Microlight guides were placed on nodules and surrounding tissue on the capsular surface of the liver to measure fluorescence due to fluorescein-dextran (12 microM), a dye confined to the vascular space, infused via the hepatic artery and portal vein separately or simultaneously. The fluorescence increase due to fluorescein-dextran infusion via the artery and vein simultaneously was used to compare vascular space in nodules with that of surrounding tissue. The vascular space of nodules less than 1 mm in diameter was only about one-half as large as that of surrounding tissue. In contrast, in nodules 1 to 2 mm in diameter, the vascular space was similar to values from surrounding tissue. This was largely due to an increase in the fluid entering via the artery. As nodules grew from 2 to 10 mm in diameter, the vascular space decreased as a function of nodule size to 40% of surrounding tissue. The sum of fluorescence increases due to fluorescein-dextran infused via the artery and vein separately always equalled values obtained from simultaneous infusions. From these measurements, the fraction of vascular fluid observed by the microlight guide that entered the liver via the artery was calculated. In tissue surrounding nodules, fluid entering from the artery was 19% of the total, a value approximating the fraction of fluid pumped into the liver via the artery (25%). The percentage of fluid in the nodule that entered the liver via the hepatic artery increased progressively to 100% of the total as nodules grew from 2 to 10 mm in diameter. Thus, nodules become increasingly dependent on the hepatic artery and less dependent on blood supply via the portal vein as they grow.