An ultrastructural characterization of the endothelial cell in the rat liver sinusoid under normal and various experimental conditions, as a contribution to the distinction between endothelial and Kupffer cells.

The fenestrated endothelial lining of rat liver sinusoids has been described elsewhere (90). The continuity of this fenestrated lining with a certain cell permitted identification of the latter as an endothelial cell (90–92). Among other criteria, the morphology and dynamics of the vacuolar apparatus before and after injection of colloidal Thorotrast particles, the morphological specializations of the endoplasmic reticulum, and the presence of a sphaeridium (nuclear body) serve to characterize the liver sinusoidal endothelial cell and to distinguish it from the Kupffer cell. The endothelial cells could be recognized easily in all livers studied under both normal and experimental conditions, e.g., partial hepatectomy, Thorotrast or Zymosan injections, and splenectomy. No transitional stages between endothelial and Kupffer cells, bearing one or more characteristic features of both cells, were observed. It is therefore concluded that the present data do not support the hypothesis that endothelial cells can develop into Kupffer cells.