CYTOCHEMICAL STUDIES OF RABBIT AORTIC CELLS IN TISSUE CULTURE

Abstract

The enzymatic activities of acid and alkaline phosphatase, adenosine triphosphatase, carboxyl esterase and succinic dehydrogenase as well as the lipid, cholesterol and acid mucopolysaccharide content in three types of cells cultured from normal and cholesterol-fed rabbit aortae were studied. Although enzymatic activities varied from cell to cell in the same culture, there was good evidence that "endothelial" type III cells had more activity than the other two cell types. With normal aging enzymatic activity seemed to diminish in all three cell types. Giant cells were usually more active. Degenerated cells also had somewhat increased enzymatic activity. However, type I and II cells always had considerably less activity than type III cells, regardless of their origin, age or shape. Type III cells exhibited intense activity in acid phosphatase; moderate activity in esterase and in succinic dehydrogenase; and weak or almost negligible activity in alkaline phosphatase and adenosine triphosphatase. In "fibroblastic," type I or II cells all these enzymatic activities were weak or negligible. No differences of enzymatic activity were seen between cells from normal and atherosclerotic aorta but for the esterase activity which was highest in type III cells from plaques. With the exception of carboxyl esterase activity which seemed to be slightly higher in the type III cells from atherosclerotic aorta, cells of different origin did not differ in enzymatic activity. Some type I or II cells changed their shape and became round (9), but these round cells did not exhibit stronger enzymatic activities than the spindle forms. On the other hand, large size or differently shaped type III cells retained their greater activity. Thus, greater activity of type III cells was not due to shrinking of the cytoplasm and subsequent condensation of the cell. Studies of other enzyme systems are under way. Very preliminary results indicate that "endothelial" cells yield considerably higher (G. Nadi) cytochrome-c oxidase than other cells. "Endothelial" or type III cells contained more lipid and acid mucopolysaccharide than "intermediate" or type I cells and "fibroblastic" or type II cells. "Endothelial" our type III cells from atherosclerotic plaques contained cholesterol in their cytoplasm while none of the cells from normal aorta did. Type III cells are metabolically the most active cells cultured form the aortic wall. Their activity may play a major role in the development of the atherosclerotic plaques. Morphologic and functional characteristics of these cells led to the suggestion that they may be endothelial cells or, possibly, macrophages. The fact that only type III cells from atherosclerotic aorta contain much cholesterol and that they appear in larger numbers than cells from normal aorta is held supportive evidence that they are endothelial cells. Results with cells in tissue cultures were compared with reports on histochemical findings in aortae.