[Vascular subendothehlium: structure and functions (author's transl)].

Two subendothelial structures, glomerular basement membrane and arterial subendothelium, were compared regarding their biochemistry and ultrastructure and their role in physiology and pathology. Filtration function of the glomerular basement membrane can be related to the presence of three layers which are superimposed on each other and which differ regarding the orientation and density of the microfibrils. The arterial subendothelium which is a mixture of amorphous material, microfibrilis, elastin and collagen, with a still unknown orientation of these components, limits the transport of many blood molecules and reinforces the endothelial barrier. A striking difference is observed in the thrombogenicity of these two structures, especially in their reactivity towards platelets. This can be related to the presence of collagen IV in the glomerular basement membrane and of collagen III in the arterial subendothelium: in both cases adhesion of platelets can be observed. The presence of platelet aggregates on the subendothelial surface may also be seen. This is probably due to the presence of collagen III which is known to be able to induce the platelet release reaction and thereby promotes aggregation.