Functional implications of structural differences between consecutive segments of microvascular endothelium.

Abstract

Structural and functional data which can be ascribed to consecutive segments of the microvascular bed are reviewed and tentatively correlated. Compared to the knowledge of endothelial cells in general, little is known about segmental variations of the microvascular endothelium. The gradient in microvascular permeability has been quantified by single capillary techniques. The results conform to structural data on endothelial tight junctions which indicate that pathways through the junctions occur with increasing frequency towards the venous end of the microvascular bed. A number of compounds mediate gap formation in venular endothelium presumably via endothelial surface-receptors. It has been demonstrated that receptors to histamine are preferentially located at the luminal surface of venular endothelium. Immunocytochemical localization of metabolic activities of microvascular endothelium in situ has started; thus it has been shown that specific antibodies to xanthine oxidase bind only to endothelium of true capillaries.