Aspects of endothelial malfunction and function in cerebral microvessels

This review focuses upon the endothelium of the cerebral microcirculation. We will discuss the endothelium in three contexts: the interaction of endothelium with platelets; the role of endothelium as a source of mediators controlling vascular tone; and the role of endothelium in maintaining permeability barriers residing in cerebral blood vessels. With respect to the interaction of endothelium with platelets, and the role of endothelium in modulating microvascular tone, we will stress that endothelial denudation in cerebral microvessels is not required in order to initiate other platelet aggregation or the loss of endothelial mediators of tone. Minimal morphologic alterations of endothelial cells may be the only structural indication of profound loss of normal properties. It is apparent that microvascular endothelium in general, and brain microvascular endothelium in particular, possesses properties which distinguish it from endothelium of large blood vessels. The consequence of even minor damage to endothelium of brain microvessels has profound consequences leading to platelet aggregation, loss of normal control of vascular diamater, and alterations in permeability.