No abstract

The three-dimensional structure of endothelial cells in the hepatic sinusoids of the rat was studied by application of light- and electron microscopy on Golgi-impregnated specimens. A number of endothelial cells could thus be individually delineated throughout the hepatic lobules. The cytoplasm, showing heavy silver deposits, consists of two distinct areas, a thick and thin portion. The thick portion, issuing from the region of the perikaryon, branches and tapers toward the cell periphery. The thin portion, occupying the remainder of the cytoplasm, consists largely of highly fenestrated sieve plates. Some intralobular variation can be noted; the thick portion of the endothelial cells is well developed in the periportal zone, while the cells in the centrilobular zone are relatively rich in thin portions. In addition, the area of distribution of an individual endothelial cell is larger in the centrilobular sinusoids than in the periportal zone. Some endothelial cells also possess unique cytoplasmic processes projecting into the intercellular space between hepatocytes and connecting the sinusoidal walls of neighboring sinusoids. These processes may anchor the endothelial cells to the hepatic plates.

OK-432, a streptococcal preparation, induced a marked increase in the number of rodcored vesicles in pit cells (natural killer cells) of the rat liver. OK-432 enhanced also the liver-associated natural killer activity. OK-432 injected intravenously was incorporated into lysosomes ofKupffer cells. Kupffer cells and pit cells were increased in their number and were in wide contact with each other. Prominent Golgi complex and many rodcored vesicles characterized the actively secreting pit cells. No obvious morphological changes were detected in dense granules in pit cells. It is suggested that the increment of rod-cored vesicles induced by OK-432 is responsible for the augmentation of the liverassociated natural killer activity.

The pit cells are one of the constituent cell types of the liver and are characterized by their characteristic granules and 'rod-cored vesicles.' In previous studies (7), we demonstrated their existence in the liver, spleen, and peripheral blood of rats, and described their close relationship with lymphocytes.

During anoxic liver perfusion, numerous blebs were formed that protruded from hepatocytes, and their contents were released into the sinusoidal lumen. Cytosolic enzymes such as the cytoplasmic isozyme of aspartate aminotransferase and lactate dehydrogenase leaked into the perfusate after a lag of about 60 min, which was the time required for the formation of blebs. The leakage pattern of the enzymes was