The focal location of atherosclerosis in the vascular tree is correlated with local variations in shear stress. We developed a method to induce defined variations in shear stress in a straight vessel segment of a mouse. To this end, a cylinder with a tapered lumen was placed around the carotid artery, inducing a high shear stress field. Concomitantly, regions of low shear stress and oscillatory shear stress were created upstream and downstream of the device, respectively. This device was used in mice transgenic for an

The activity of endothelial nitric oxide synthase (eNOS) is subject to complex transcriptional and posttranslational regulation including the association with several proteins and variations in subcellular distribution. In the present study we describe a transgenic mouse model expressing eNOS fused to green fluorescent protein (GFP), which allows the study of localization and regulation of eNOS expression. We tested the functionality of eNOS in the eNOS-GFP mice. Expression of eNOS was restricted to the endothelial lining of blood vessels in various tissues tested, without appreciable expression in non-endothelial cells. Activity of the enzyme was confirmed by assaying the conversion of L-arginine to L-citrulline. NO production in isolated vessels was increased in transgenic mice when compared to non-transgenic control animals (4.88 ؎ 0.59 and 2.48 ؎ 0.47 mol/L NO, respectively, P < 0.005). Both the mean aortic pressure and the pulmonary artery pressure were reduced in eNOS-GFP mice (both ϳ30%, P < 0.05). Plasma cholesterol levels were also slightly reduced (ϳ20%, P < 0.05). In conclusion, eNOS-GFP mice express functional eNOS and provide a unique model to study regulation of eNOS activity or eNOS-mediated vascular events, including response to ischemia, response to differences in shear stress, angiogenesis and vasculogenesis, and to study the subcellular distribution in relation with functional responses to these events.

Background-Low wall shear stress (WSS) increases neointimal hyperplasia (NH) in vein grafts and stents. We studied the causal relationship between WSS and NH formation in stents by locally increasing WSS with a flow divider (Anti-Restenotic Diffuser, Endoart SA) placed in the center of the stent. Methods and Results-In 9 rabbits fed a high-cholesterol diet for 2 months to induce endothelial dysfunction, 18 stents were implanted in the right and left external iliac arteries (1 stent per vessel). Lumen diameters were measured by quantitative angiography before and after implantation and at 4-week follow-up, at which time, macrophage accumulation and interruption of the internal elastic lamina was determined. Cross sections of stent segments within the ARED (SϩARED), outside the ARED (S[minus]ARED), and in corresponding segments of the contralateral control stent (SCTRL) were analyzed. Changes in WSS induced by the ARED placement were derived by computational fluid dynamics. Computational fluid dynamics analysis demonstrated that WSS increased from 0.38 to 0.82 N/m 2 in the SϩARED immediately after ARED placement. This augmentation of shear stress was accompanied by (1) ARED, and SCTRL), and (3) a reduced inflammation score and a reduced injury score. Increments in shear stress did not change the relationship between injury score and NH or between inflammation score and NH. Conclusions-The newly developed ARED flow divider significantly increases WSS, and this local increment in WSS isaccompanied by a local reduction in NH and a local reduction in inflammation and injury. The present study is therefore the first to provide direct evidence for an important modulating role of shear stress in in-stent neointimal hyperplasia. Key Words: shear stress Ⅲ restenosis Ⅲ stents Ⅲ cells Ⅲ inflammation A lthough stents are responsible for a clear reduction in the restenosis rate, 1 stents exacerbate the normal proliferative reaction because of a variety of factors related to stent design. 2 In addition to conventional risk factors for stent restenosis, the restored level of blood flow seems to be a crucial factor in the development of neointimal hyperplasia (NH). 3 It has been postulated that wall shear stress (WSS) is an important causative factor. Indeed, other studies 4 have demonstrated that low WSS is associated with and even predicts NH in either bypass graft or stents. However, these earlier studies could not exclude the possibility that other factors in addition to WSS explained the observations. This hypothesis is not unrealistic, because it is known that the strain and lipid distribution are different in inner and outer curves of blood vessels. 5,6 In view of the above-mentioned arguments, we devised an experiment to evaluate the role of shear stress on NH with a more direct approach. To that end, we induced a local augmentation in WSS with a new device, the AntiRestenotic Diffuser (ARED) flow divider (Figure 1; European patent number EP0989830), which is positioned in 1 of the 2 stents placed at similar locations in...

These results indicate the feasibility of contrast harmonic intravascular ultrasound as a new technique for vasa vasorum imaging.

Background-Atherosclerosis is considered an inflammatory disease. Recent studies provided evidence for a predominant upstream location of plaque inflammation. The present study introduces a novel technique that evaluates the underlying mechanism of this spatial organization. Methods and Results-In hypercholesterolemic rabbits, atherosclerosis of the infrarenal aorta was induced by a combination of endothelial denudation and a high-cholesterol diet (2% cholesterol for 2 months). At the time of death, aortic vessel segments were dissected and reconstructed with a new technique that preserved the original intravascular ultrasound-derived lumen geometry. This enabled us to study the spatial relation of histological markers like macrophages, smooth muscle cells, lipids, gelatinolytic activity, and oxidized low-density lipoprotein. Results showed a predominant upstream localization of macrophages and gelatinase activity. Colocalization studies indicated that gelatinase activity was associated with macrophages and smooth muscle cells. Further analysis revealed that this was caused by subsets of smooth muscle cells and macrophages, which were associated with oxidized low-density lipoprotein accumulation. Conclusions-Upstream