Track 15. Microcirculat ion 15.1 Hemodynamics and Angiogenesis/Angioadaptation $623

were defined and systolic and diastolic blood pressure as well as maximum and minimum artery diameter were assessed beat to beat. Peterson elastic modulus, compliance and beta index were calculated to represent arterial stiffness. Beat to beat variations in stiffness values were expressed in the form of coefficient of variation (CV%). In addition, spectral analysis was performed for systolic blood pressure and maximum artery diameter. The mean CV% was 9.4% for Peterson elastic modulus, 8.7% for compliance and 8.1% for beta index. Spectral analysis showed a variable coherence be- tween systolic blood pressure and maximum artery diameter. Mean coherence in the low frequency band (0.04q3.15 Hz) correlated negatively with stiffness variation in Peterson elastic modulus ( r=-0.72, P<0.05) and compliance (r= -0.74, P <0.05). We found a remarkable beat to beat variability in arterial stiffness, which may be attributed to the physioloical variations of blood pressure and artery diameter. As compared with the traditional method, beat to beat assessment enables calculation of averaged stiffness values irrespective of short term variations and, thus, may provide more reliable information regarding arterial properties.

7648 Mo-Tu, no. 86 (P66) Endocytos is and degradat ion o f LDL-Cholesterol in human endothel ia l cells under shear stress: a Forster-type resonance energy transfer (FRET) s tudy

M. Traor61 , A. Kadi 1 , S. Fawzi-Grancher 1 , D. Dumas 1 , L. Marchal 1 , R. Sun 2, J.-E Stoltz 1 , S. Muller 1 . 1Bioengineering, LEMTA-UMR 7563 CNRS, Facult~ de M6decine, Vandoeuvre-les-Nancy, France, 2Research Institute of Clinical Medical Sciences, China-Japan Friendship Hospital, Beijing, China

Studies of the pathogenesis of atherosclerosis suggest that several steps are involved [3], such as lipid accumulation in the artery wall resulting from transendothelial uptake of LDLCholesterol, followed by LDL oxidation and uptake by monocytes/macrophages and smooth muscle proliferation. In this work, we studied the effect of shear stress on the kinetics of internaliza- tion of native LDL, ox-LDL and LDL cholesterol in an endothelial cell line. This study was performed by using Confocal microscopy and FRET method with two carbocyanine dyes (1,1 '-dioctadecyl-3,3,3/,31-tetramethylindoCarboCyanine perchlorate (DiO) as donor and 3,3~-dioctadecyloxacarbocyanine perchlorate (Dil) as receptor). FRET allows to follow the degradation of the double labelled LDL-cholesterol (Dil and DiO). Cells were incubated with a culture medium in static conditions or subjected to a laminar flow under a Confocal Laser Scanning Microscope (SP2 Leica, Germany). Results show that: (1) it was possible to evaluate the kinetics of LDL endocytosis in living cells, (2) shear stress and oxydation enhanced LDL uptake and induced changes in the kinetic of degradation. Regarding all available data, we conclude that confocal microscopic study and FRET could be useful methods to establish the basic and clinical studies of LDL uptake in atherosclerosis. However, further studies need to be performed to elucidate the molecular mechanism by which shear stress modulates the expression of LDL. Acknowledgments: This work was supported in part by a grant of AFCRST (Paris) PRA B03-08, the Region of Lorraine and ARC for FRET and confocal multiphoton microscopy.

Track 15

Microcirculation

15.1 Hemodynamics and Angiogene- sis/Angioadaptation 4632 Mo-Tu, no. 1 (P66) Mathematical models o f capi l lary sprouts in develop ing microvascular networks S.R. Pop 1 , S.L. Waters 1 , G. Richardson 1 , L. Lucas 2, C.A. Mitchell 2, O.E. Jensenl. 1 School of Mathematical Sciences, University of Nottingham, Nottingham, UK, 2School of Biomedical Sciences, University of Ulster, Coleraine, UK

Recent experiments using in vivo microscopy have demonstrated that blind- ended capillary sprouts can arise transiently during angiogenesis in wound healing. Sprout formation appears to be an important intermediate step in the growth and formation of new blood vessels from an existing microvascular network. To complement existing models of blood flow in capillary networks, we develop here new models for the flow of plasma and red blood cells in blind-ended capillary sprouts; cells can be trapped within a sprout although

plasma may leak through the sprout's walls. In our model a sprout is assumed to be axisymmetric but to have axially nonuniform radius. A pressure drop between the sprout's entrance and the surrounding interstitium is imposed. Starling's law is used to model transmural flux of plasma under hydrostatic and osmotic pressure differences. Red blood cells are excluded from very narrow sprouts; we model such sprouts using lubrication theory, showing how the wall's permeability and shape influence the flow of plasma within the sprout. We model red blood cells stacked inside larger sprouts as either a porous or a poroelastic medium; here too the sprout's slender geometry is used to develop simplified models that relate the plasma flux to the imposed pressure drop across the sprout. We report the dependence of flux on sprout geometry and compare results with experiment. This work was funded by EPSRC grant G R/T 19605/01.

6502 Mo-Tu, no. 2 (P66) An endothelial mechanism for control o f capi l lary f low speed

N.M. Scheidler 1 , S.S. Shin 1 , C.D. Bertram 2, EA. Delano 1 , G.W. Schmid- SchSnbein 1 . 1Department of Bioengineering and The Whitaker Institute of Biomedical Engineering, University of California San Diego, La Jolla, USA, 2 Graduate School of Biomedical Engineering, The University of New South Wales, Sydney, Australia

Vascular endothelial cells in larger blood vessels respond to fluid shear stress with morphological restructuring and intracellular signaling. But no exploration of capillary endothelium exists. We hypothesize that the endothelial cells in true capillaries with a single file of blood cells respond to fluid shear by morphological restructuring. We developed a model of fluid shear-dependent control mechanism assuming that the cross-sectional areas of the lumen are adjusted such that reduction of fluid shear stress serves to enlarge the capillary lumen and an increase of fluid shear stress on capillary endothelium stimulates narrowing of the lumen. The capillary lumen enlarges along longer capillary pathways from terminal arterioles to venules and narrows along shorter pathways. The shear control mechanism leads to minimization of the spatial dispersion of red cell speeds in a network of skeletal muscle capillaries. The model predicts that at capillary bifurcations the sum of the cross-sections of the inflow vessels and outflow vessels are about equal, a fact that is supported by experimental evidence. Furthermore, suppression of the fluid shear control mechanisms by nitric oxide suppression leads to a dramatic increase in the spatial variation of the capillary red cell speed in skeletal muscle capillaries. These results suggest that besides the ability of arterioles and venules to control microvascular flow via smooth muscle, capillaries per se may have an independent mechanism that relies on fluid shear stress. Shear stress may serve to adjust lumen diameters and consequently the cell speed in capillaries. Supported by HL 43026 and 10881.

5600 Mo-Tu, no. 3 (P66) Effect of hypoxia on micro-vessel format ion in vi t ro

I. Yoneyama 1 , A. Ueda 1 , H. Kajiwara 2, M. Tsuchiya 2, K. Kokubo 3, H. Kobayashi 3, M. Ikeda 1 , K. Tanishita 1 . 1Keio University, Kanagawa, Japan, 2yamate Scientific Co. Ltd., Tokyo, Japan, 3 Kitasate University, Kanagawa, Japan

It is necessary to have vascular network in the reconstructed tissue to supply the oxygen and other nutritious substances to the individual cell. The control of 3D microvessel formation is critical for regeneration medicine and tissue engineering because vessels are essential for the formation and maintenance of organ function. Here we focused on the capability of hypoxia for the enhance- ment of vascular network formation of endothelial cells (ECs) in the 3D manner. ECs are seeded on type I collagen gel and cultured in hypoxia (5% 02) without growth factors. As a results, ECs in hypoxia formed longer and deeper three- dimensional networks than those in normoxia. Hypoxia significantly induces ECs penetration into underlying collagen gel and forming the 3D capillary like network. We observed the 3D morphology of the network in detail by confocal laser scanning microscopy. Network formation in the hypoxia condition not only spread widely but also penetrate to deeper position in underlying collagen gel. We also confirmed that hypoxia solely induces the 3D network formation by ECs in vitro. We should note that the hypoxia promotes many genes expression of ECs. It is concluded that the hypoxia enables to form three-dimensional vessel network along with growth factors.

5098 Mo-Tu, no. 4 (P66) Remodel l ing o f the complete circle o f Wil l is in male Wistar rats M. Vorstenbosch, A. Schepens-Franke, B. Hillen, J. Kooloos. Department ef Anatomy, UMC St Radbeud, Nijmegen, The Netherlands

Introduct ion: Vascular occlusions can jeopardise cerebral perfusion, provok- ing strokes and ischemic attacks. Besides leptomeningeal anastomoses, the