We have developed an in-vitro system for studying the dynamic response of vascular endothelial cells to controlled levels of fluid shear stress. Cultured monolayers of bovine aortic endothelial cells are placed in a cone-plate apparatus that produces a uniform fluid shear stress on replicate samples. Subconfluent endothelial cultures continuously exposed to 1-5 dynes/cm2 shear proliferate at a rate comparable to that of static cultures and reach the same saturation density (congruent to 1.0-1.5 X 10(5) cells/cm2). When exposed to a laminar shear stress of 5-10 dynes/cm2, confluent monolayers undergo a time-dependent change in cell shape from polygonal to ellipsoidal and become uniformly oriented with flow. Regeneration of linear "wounds" in confluent monolayer appears to be influenced by the direction of the applied force. Preliminary studies indicate that certain endothelial cell functions, including fluid endocytosis, cytoskeletal assembly and nonthrombogenic surface properties, also are sensitive to shear stress. These observations suggest that fluid mechanical forces can directly influence endothelial cell structure and function. Modulation of endothelial behavior by fluid shear stresses may be relevant to normal vessel wall physiology, as well as the pathogenesis of vascular diseases, such as atherosclerosis.

The flow between a shallow rotating cone and a stationary plate has been investigated using flow visualization, hot-film heat-transfer probes, and measurements of the torque required to rotate the cone against the retardation of the viscous fluid that fills the device. Theory appropriate to these experiments is also presented.An expansion of the Navier–Stokes equations is performed for small values of the single parameter $\tilde{R} = r^2\omega\alpha^2/12\nu $. (Here r is the local radius, ω the angular velocity of the cone, α([Lt ] 1) is the angle between the cone and plate, and v is the fluid kinematic viscosity.) The measurements at low rotational speeds describe a simple linear velocity profile as predicted for the laminar flow of a Newtonian fluid. At larger rotational speeds, strong secondary flows are observed. There is agreement between the laminar theory and the measured streamline angles and shear stresses for values of $\tilde{R} < 0.5$. Turbulence is observed for $\tilde{R} \gtrsim 4$.

Abstract. The relationships between fluid shear stress, a physiologically relevant mechanical force in the circulatory system, and pinocytosis (fluid-phase endocytosis) were investigated in cultured bovine aortic endothelial cells using a specially designed apparatus. Continuous exposure to steady shear stresses ( 1-15 dyn/cm2) in laminar flow stimulated time-and amplitude-dependent increases in pinocytotic rate which returned to control levels after several hours. pendent and shows accommodation, (c) certain patterns of fluctuation in shear stress result in sustained elevation of pinocytotic rate, and (d) shear stresses can modulate endothelial pinocytosis independent of growth stimulation. These findings are relevant to (i) transendothelial transport and the metabolism of macromolecules in normal endothelium and (ii) the role ofhemodynamic factors in the localization of atherosclerotic lesions in vivo.

This apparatus subjects cultured cell specimens to controlled levels of fluid shear stress in vitro. The cone-plate geometry permits long term (≳7 days) investigation of the effects of external fluid forces on living cells.