Endothelial Permeability in Inflammation
The electron microscopic studies of N. Simionescu and collaborators17–19 have clearly shown that the endothelium in the three basic segments of the microcirculation—arterioles, capillaries, and venules—differs in terms of ultrastructure and permeability. Segmental differences are obvious also in the inflammatory response. Indeed, those chemical mediators that increase microvascular permeability do so by affecting selectively the permeability of the venules; this was established by using a method that selectively marks leaky segments of the microcirculation, namely vascular labeling.13 A clue to this selectivity for the venules was provided by Heltianu et al. 5 who showed that the endothelium of these vessels is especially rich in histamine receptors. Another difference between capillary and venular endothelium is that the latter is able to contract in vivo under the stimulus of inflammatory mediators7; rather than reducing the caliber of the vessel, this contraction produces gaps between the endothelial cells, allowing the escape of fluid.7,14
KeywordsCarbon Black Histamine Receptor Vascular Leakage Capillary Leakage Glass Sphere
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