The inhibitory effects of high molecular levan on transport across the vascular wall stimulated by histamine.

Administration of levan to mice and rats inhibited the passage of intravenously injected trypan blue into the area of skin injected with histamine. In the mouse, the optimal dose of levan was about 5 mg/25 g body weight; higher doses, on the other hand, enhanced diffusion. In the rat, the inhibitory effect was directly related to the dose of levan, the optimal dose being five times higher than for mice. Treatment of rats with levan caused a marked reduction in the uptake and transport of colloidal carbon. In normal and histamine- or turpentine-injected cremaster muscles, treatment with levan prevented carbon from being adsorbed and endocytosed by the endothelial cells. Levan itself was frequently attached to the lumenal surface of endothelial cells, or less frequently was enclosed within pinocytic vesicles. Occasionally, transport across the interendothelial junction was also seen, but the impression gained was that the frequency and extent of patent junctions were reduced in animals receiving phlogistic stimuli and treated with levan. Carbon particles were generally aggregated in the central zone of vessels and were seldom seen near the endothelial cells, within endothelial cells or within any open junctions, presumably because of the coating effect of levan. With partly depolymerised levan, carbon particles were found in endothelial cells and intercellular spaces, but at lower concentrations than in non-levanised control animals. It is suggested that levan acts by altering the rheologic patterns in the microcirculation, by modifying the surface of endothelial cells and by influencing their behaviour, and, finally, by changing the constitution of the ground substance and basement lamina.