Electron microscopic characteristics of plant peroxidase transport pathways in the microcirculatory bed of the rabbit peritoneum

The dynamics of exogenic peroxidase transfer from blood into the roots of the rabbit mesenteric lymphatic system have been studied by means of electron microscopic methods in combination with the trasser technique. Light optic identification of the vascular segments and selection of samples for electron microscopic analysis make it possible to reveal certain differences in the pathways of protein transport via the walls of the blood capillaries and venules. The vesicular transport is the only means for peroxidase to be transferred via the walls of the mesenteric blood capillaries. The time for transendothelial transfer of the marker is more than 10 min. In the venules the vesicular transport of protein does not differ from that in the capillaries, however, the predominant leakage of peroxidase from blood into the interstitium is performed through open interendothelial contacts. The hemato-interstitial transport via the intercellular clefts takes less than 3 min. For transferring protein from the interstitium into the lumen of the lymphatic capillaries and postcapillaries, the vesicular mechanism is used, and to a less extent--the open intercellular contacts. A suggestion is made that the term "open contact" should be understood in functional meaning and this means should be considered as an intercellular pathway for transporting molecules of a definite size.