Ultrastructural changes of endothelium associated with thrombocytopenia

In a study of the relationship between thrombocytopenia and increased vascular fragility, changes in the endothelium of capillaries and postcapillary venules of the tongue were examined by electron microscopy. Adult male albino rabbits (4 kg) were maintained thrombocytopenic (platelets less than 20,000/cu mm) up to 24 hr by one to three injections of guinea pig antirabbit platelet serum. Within 6 hr the normal projections and folds of the lumenal surface of the endothelial surface were largely effaced. In addition, the endothelium became thinner. In places, pores and membranous diaphragms were observed. Endothelial junctions appeared normal. Identical findings were observed if rabbits were made thrombocytopenic by administration of intraperitoneal busulfan. Intravenously administered Thorotrast was observed in endothelial cells and in the extravascular spaces within 3 min after injection into thrombocytopenic animals, while it was seen only intravascularly in control rabbits. With the spontaneous restoration of circulating platelets, the endothelium reverted to normal.