A histochemical study on the distribution of injected canine intestinal alkaline phosphatase in rat liver.

After intravenous administration to rats, the distribution of injected canine intestinal alkaline phosphatase in the liver was studied morphologically by means of histochemical and cytochemical methods on liver sections and pellets of homogenized livers. The interference of various sugars, sugar polymers and glycoproteins with the receptor-bound injected enzyme was investigated in rat liver sections. Injected canine intestinal alkaline phosphatase, being an asialoglycoprotein, is captured by the galactose-specific lectin present on the plasma membrane of the hepatocytes and can be displaced by incubation with galactose-containing sugars and proteins. The enzyme is subsequently taken up by a process of "adsorptive endocytosis" and was found first in a plasma membrane fraction and later in a pellet enriched in lysosomes. This hepatic handling of the enzyme predominantly occurs in the area around the central vein (zone 3 of Rappaport). This is the first evidence for zonal heterogeneity in hepatic disposition of an asialoglycoprotein.