Analysis of development of atherosclerosis based on the relationship between blood velocity profiles in vascular branch and the structure of endothelial cell

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To analyze mechanisms of development and localization of atherosclerosis, we investigated the relationship between detailed blood velocity profiles in vascular branch and the structure of vascular endothelial cell. Using a 20MHz ultrasound pulsed Doppler velocimeter and a high-resolution echo ultrasound device, we studied in vivo hemodynamics at the origin of the renal artery measuring the velocity profiles and bifurcation geometry of left renal artery. The velocity pattern near the cranial wall at renal ostia, at which atherosclerosis lesions are prone to be developed, are characterized by low time-averaged shear rate, flow separation, and time-varying flow oscillation. To evaluate the possible contribution of blood flow pattern to the structure of endothelial cell in the renal artery, we investigated the structure of endothelial cells at different site of the left renal artery using a confocal laser scanning microscope. F-actin and DNA in nuclei were stained with rhodamine phalloidin and bisBenzimide, respectively. On the cranial side wall immediately distal to the origin of the renal artery, where blood flow showed recirculation and bi-directional oscillation, the shapes of endothelial cells and nuclei were relatively round. The cell orientation was not uniform. On the wall four-vascular diameters distal to the origin of the renal artery, where blood flow had a parabolic forward-velocity profile, endothelial cells and nuclei were elongated and were oriented to the flow direction. Also the number of stress fibers in the endothelial cell increased, and those stress fibers were also oriented to the flow direction. In conclusion, there were significant differences in the structure of endothelial cells in the proximal and distal regions of the renal artery. The unique blood flow pattern in the proximal region is thus likely to cause atherogenesis by modifying endothelial structure.