Functional units in rainbow trout (Salmo gairdneri) liver: I. Arrangement and histochemical properties of hepatocytes.

The architectural arrangement and selected histochemical properties of hepatocytes in the rainbow trout (Salmo gairdneri Richardson) were examined. Light and transmission electron microscopic (TEM) examination following fixation by portal venous perfusion revealed a tubular arrangement of hepatocytes. Lobules, as defined in the adult mammal, were absent. Biliary epithelial cells associated with bile preductules and ductules were a prominent feature of trout liver. Patterns and location of reaction products for glucose-6-phosphatase (G-6-Pase), glucose-6-phosphate dehydrogenase (G-6-PDH), and magnesium-dependent adenosine triphosphatase (ATPase), enzymes preferentially distributed in mammalian liver, were demonstrated in trout liver. A slightly heavier staining pattern for G-6-Pase was seen around presumptive portal venules but all other enzyme reaction patterns were uniform throughout the liver parenchyma. Following ATPase localization, four sizes of biliary passageways (canaliculi, bile preductules, ductules, and ducts) were visualized. Maximum glycogen retention was achieved with freeze-drying and glycolmethacrylate embedding and with this method intense, uniform glycogen staining was observed in all areas of the liver. Companion TEM examinations revealed large depots of glycogen within hepatocytes. The results are important for interpretation and description of the effects of toxic/carcinogenic alteration on trout liver.