Effect of inflammatory stimuli on the silver staining pattern of the rat carotid endothelium

Silver nitrate stains the intercellular junctions of the endothelium and ot her cytoplasmic or membrane components. Two protocols are described for the silver staining of rat carotid endothelium that exclude the use of pressur ized fixatives and simplify the technique previously described for rat aort a. The entire surface of the carotid endothelium was examined and several p arameters (stigmata, granularity, clustering of anionic sites, transversal lines, weakening of silver lines and leukocyte adhesion) were evaluated. We studied the pattern of silver staining in two situations: (1) endothelial activation and (2) neurogenic inflammation. Endothelial activation was prod uced by the intravenous administration of a proinflammatory albumin or poly inosinic acid. Both products cause a marked increase in leukocyte adhesion concomitant with a decrease in argyrophilia and a weakness or loss of silve r lines. Neurogenic inflammation, which is mediated by substances released from sensory nerves, was induced by the intravenous administration of subst ance P or capsaicin. Both stimuli produced an increase in argyrophilia and weakness or loss of silver lines. Substance P caused a clustering of anioni c sites, whereas this phenomenon was more discrete with capsaicin. Nearly 8 0% of all examined rats (controls and inflammatory stimuli treated) showed endothelial membrane disruptions formed by clusters of cells often in the s hape of streaks aligned with the long axis of the vessel. The detection of these discontinuities is important, as loss of endothelial integrity is cen tral in the initiation of pathological events.