Pattern and distribution of intrahepatic lymph vessels in the rat.

The pattern and distribution of intrahepatic lymph vessels were examined by light and electron microscopy in rat livers fixed by perfusion through the portal vein. Lymph vessels were found in the connective tissue of the larger portal canals, where they coursed in close association with branches of the hepatic artery. The smallest portal canals contained no lymphatics. Of the portal canals that lacked a lymphatic, over 50% also lacked an arterial component. Direct connections between the lymphatic lumen and the spaces of Disse or Mall were not observed but lymphatics were found close to Mall's space, separated by only a sparse connective tissue space containing a few collagen fibrils. Lymphatics were neither seen within the parenchyma, nor associated with intercalated (sublobular) veins. Cross-sectional area (223.2 +/- 48.7 micron2 SEM), maximum diameter (20.5 +/- 2.0 microns), volume density (0.00098 +/- 0.00046 micron3/micron3) and profile density (1.8 +/- 0.3 lymphatics per 1 mm2) of hepatic lymph vessels were determined by stereological measurement by a computer-based image analyzer. These data were used to estimate the rate of lymph formation in the liver. It was concluded that 1) initial lymphatics probably originate in the portal canals; 2) the concept that fluid in the space of Disse can be regarded as the principal source of fluid-forming hepatic lymph is questioned, since initial lymphatics appear to be separated from the space of Disse by hepatocytes and the space of Mall; and 3) the rate of lymph formation in the liver of the rat is approximately 0.06-0.08 microliter/min/cm2 of lymphatic endothelium.