Macromolecular transport across arterial and venous endothelium in rats. Studies with Evans blue-albumin and horseradish peroxidase.

Abstract

Atherosclerotic lesions are characterized by llpid Infiltration in regions wtth high rates of endothellal cell turnover. The present investigation was designed to elucidate the route of macromolecular transport across vascular endothelium. The aorta and vena cava of male Sprague-Dawley rats were perfusion-flxed after the intravenous in|ection of Evans-blue albumin (EBA) or horseradish peroxidase (HRP). Fluorescence microscopic examination of en face preparation of the aorta stained with hematoxylln allowed the Identification of endothellal cells that underwent mitosis, together with the localization and quantification of fluorescent spots for EBA leakage. The HRP specimens were subjected to histochemicai treatment, and HRP leakage was seen as brown spots under the light microscope. Sliver nitrate stain was added In both EBA and HRP studies to outline cell boundaries and to visualize stigmata, stomata, and dead cells. In the aorta, almost every dividing cell showed Junctional leakage to albumin and HRP, with clustering of leaky spots around the branch orifices. Time-dependent studies showed gradual increases In the diameter and number of these heterogeneously sized leaky spots, which finally fused to sizes corresponding to the "blue areas" for EBA or "brown areas" for HRP. Compared wtth arteries, veins had fewer mltotlc cells, but more dead cells and diffuse dye-staining areas, Indicating a more rapid transport of macromolecules. The leaky spots In the artery were associated mainly with mltotic cells, dead cells, and stigmata, whereas those In the vein occurred primarily at regions with dead cells. These results suggest that the preferential association of the enhanced transport of macromolecules with mttosls In the arterial as compared to venous endothelium and the differential behavior In transmural transport between arteries and veins may form the basis for the predilection of atherosclerosis in arteries.

Mechanotransduction and endothelial cell homeostasis: the wisdom of the cell

“…Our experimental studies have provided evidence that EC mitosis (12,44) and death (42) are associated with the leakage of macromolecules such as LDL and albumin on an individual cell basis. Studies performed in a number of laboratories, including our own, have shown that these events of accelerated EC turnover occur primarily in areas with disturbed blood flow, e.g., arterial branch points (15,43,60,72). Electron microscopic studies have identified the widening of the intercellular junctions around ECs that are undergoing mitosis or dying and the leakage of the macromolecular tracer horseradish peroxidase (9,27).…”

“…30), and there is evidence that sustained, but not transient, activation of JNK is associated with apoptosis (26). Therefore, cyclic stretch without a clear direction, such as that seen in branch points of the arterial tree, would cause a higher frequency of apoptosis (15) and a greater vulnerability to atherogenesis compared with the straight part of the arterial tree, where the cyclic stretch due to the pulsatile pressure is primarily uniaxial in the circumferential direction.…”

Transport in rat vessel walls. I. Hydraulic conductivities of the aorta, pulmonary artery, and inferior vena cava with intact and denuded endothelia

“…One of the first issues that one must address to develop an understanding of the mass transport in these vessels is whether such transport is driven by diffusion and/or convection. In previous mass transport studies of the aorta, rats were injected with a macromolecular tracer, such as horseradish peroxidase (HRP), and were killed after different circulation times (11,35). In an examination of the animals' aortas en face, HRP was found to traverse the endothelium in rare localized spots, rather than uniformly.…”

A theory for water and macromolecular transport in the pulmonary artery wall with a detailed comparison to the aorta

“…Stemerman (52) found that macromolecules cross the aortic endothelium in focal spots, not uniformly. Aortic endothelial cells (ECs) in the M phase of mitosis (37,38), ECs in the process of dying and/or sloughing of neighboring dying cells (36), or those containing stigmata (9) temporarily allow easily detectable macromolecules of different sizes, e.g., Evans blue albumin conjugate, horseradish peroxidase (HRP), and Lucifer yellow-low density lipoprotein, through their junctions (7). In rat aorta, the average HRP leak frequency is ϳ1/(2,000 -6,000) cells (7, 36 -38) and leak duration is ϳ1 h (9).…”

“…In rat aorta, the average HRP leak frequency is ϳ1/(2,000 -6,000) cells (7, 36 -38) and leak duration is ϳ1 h (9). Chuang et al (9) injected rats with HRP, killed them at various circulation times up to 4 min, examined aortic spots en face, and observed very rapid spot grown, with spot diameters ϳ30 m to Ͼ200 m in 4 min. Tompkins (61) injected 125 I-LDL into four squirrel monkeys, killed them 30 min later, harvested numerous vessels, sectioned the vessels extensively, and placed the sections on photographic film.…”