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Neutrophil recruitment in most tissues is limited to postcapillary venules, where E- and P-selectins are inducibly expressed by venular endothelial cells. These molecules support neutrophil rolling via binding of PSGL-1 and other ligands on neutrophils. Selectins extend ≤ 38 nm above the endothelial plasma membrane, and PSGL-1 extends to 50 nm above the neutrophil plasma membrane. However, endothelial cells are covered with an ESL composed of glycosaminoglycans that is ≥ 500 nm thick and has measurable resistance against compression. The neutrophil surface is also covered with a surface layer. These surface layers would be expected to completely shield adhesion molecules; thus, neutrophils should not be able to roll and adhere. However, in the cremaster muscle and in many other models investigated using intravital microscopy, neutrophils clearly roll, and their rolling is easily and quickly induced. This conundrum was thought to be resolved by the observation that the induction of selectins is accompanied by ESL shedding; however, ESL shedding only partially reduces the ESL thickness (to 200 nm) and thus is insufficient to expose adhesion molecules. In addition to its antiadhesive functions, the ESL also presents neutrophil arrest-inducing chemokines. ESL heparan sulfate can also bind L-selectin expressed by the neutrophils, which contributes to rolling and arrest. We conclude that ESL has both proadhesive and antiadhesive functions. However, most previous studies considered either only the proadhesive or only the antiadhesive effects of the ESL. An integrated model for the role of the ESL in neutrophil rolling, arrest, and transmigration is needed.

Objective: To establish methods for providing a comprehensive and detailed description of the spatial distribution of the vascular networks, and to reveal the spatiotemporal pattern of the yolk sac membrane vascular network during the angiogenic procedure. Methods: Addressing the limitations in the conventional local fractal analysis, an improved approach, named scanning average local fractal dimension, was proposed. This method was conducted on 6 high‐resolution vascular images of the yolk sac membrane for 3 eggs at two stages (E3 and E4) to characterize the spatial distribution of the complexity of the vascular network. Results: With the proposed method, the spatial distribution of the complexity of the yolk sac membrane vascular network was visualized. From E3 to E4, the local fractal dimension increased in 3 eggs, 1.80 ± 0.02 vs. 1.85 ± 0.02, 1.72 ± 0.03 vs. 1.83 ± 0.02, and 1.77 ± 0.03 vs. 1.82 ± 0.02, respectively. The mean local fractal dimension in the most distal area from the embryo proper was the lowest at E3 while the highest at E4. At E3, the most peaks of the local fractal dimension were located in the vein territories and shifted to artery territories at E4. Conclusions: The spatial distribution of the complexity of the yolk sac membrane vascular network exhibited diverse patterns at different stages. In addition from E3 to E4, the increment of complexity at the intersection areas between arteries and sinus terminalis was with the most advance. This is consistent with the physiologic evidence. The present work provides a potential approach for investigating the spatiotemporal pattern of the angiogenic process. [ABSTRACT FROM AUTHOR]

Reglin B, Secomb TW, Pries AR. Structural adaptation of microvessel diameters in response to metabolic stimuli: where are the oxygen sensors? Am J Physiol Heart Circ Physiol 297: H2206-H2219, 2009. First published September 25, 2009; doi: 10.1152/ajpheart.00348.2009.-- Maintenance of functional vascular networks requires structural adaptation of vessel diameters in response to hemodynamic and metabolic conditions. The mechanisms by which diameters respond to the metabolic state are not known, but may involve the release of vasoactive substances in response to low oxygen by tissue ('tissue signaling', e.g., C[O.sub.2], adenosine), by vessel walls ('wall signaling', e.g., prostaglandins, adenosine), and/or by red blood cells (RBCs) ('RBC signaling', e.g., ATP and nitric oxide). Here, the goal was to test the potential of each of these locations of oxygen-dependent signaling to control steady-state vascular diameters and tissue oxygenation. A previously developed theoretical model of structural diameter adaptation based on experimental data on microvascular network morphology and hemodynamics was used. Resulting network characteristics were analyzed with regard to tissue oxygenation (Oxdef; percentage of tissue volume with [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] < 1 Torr) and the difference between estimated blood flow velocities and corresponding experimental data [velocity error ([V.sub.err]); root mean square deviation of estimated vs. measured velocity]. Wall signaling led to Oxdef < 1% and to the closest hemodynamic similarity ([V.sub.err]: 0.60). Tissue signaling also resulted in a low oxygen deficit, but a higher [V.sub.err] (0.73) and systematic diameter deviations. RBC signaling led to widespread hypoxia (Oxdef: 4.7%), unrealistic velocity distributions ([V.sub.err]: 0.81), and shrinkage of small vessels. The results suggest that wall signaling plays a central role in structural control of vessel diameters in microvascular networks of given angioarchitecture. Tissue-derived and RBC-derived signaling of oxygen levels may be more relevant for the regulation of angiogenesis and/or smooth muscle tone. oxygen sensing; vascular diameter; angioadaptation doi: 10.1152/ajpheart.00348.2009.

The goals of this study were to determine the time course and spatial dependence of structural diameter changes in the mouse gracilis artery after a redistribution of blood flow and to compare the observations with predictions of computational models for structural adaptation. Diameters were measured 1,2, 7, 14, 21, 28, and 56 days after resection of one of the two blood supplies to the artery. Overall average diameter, normalized with respect to diameters in untreated vessels, increased slightly during the first 7 days, then increased more rapidly, reaching a peak around day 21, and then decreased. This transient increase in diameter was spatially nonuniform, being largest toward the point of resection. A previously developed theoretical model, in which diameter varies in response to stimuli derived from local metabolic and hemodynamic conditions, was extended to include effects of time-delayed remodeling stimuli in regions of reduced perfusion. Predictions of this model were consistent with observed diameter changes, including the transient increase in diameters near the point of resection, when a remodeling stimulus with a time delay of ~7 days was included. The results suggest that delayed stimuli significantly influence the dynamic characteristics of vascular remodeling resulting from reduced blood supply. metabolic response; shear stress; vessel wall conduction; adaptation; computational model

Endothelial NOS is main mediator for shear stress-dependent angiogenesis in skeletal muscle after prazosin administration. Am J Physiol Heart Cite Physiol 287: H2300-H2308, 2004. First published July 1, 2004; doi:10.1152/ajpheart.00065. 2004.--The increase of wall shear stress in capillaries by oral administration of the [[alpha].sub.1]-adrenergic receptor antagonist prazosin induces angiogenesis in skeletal muscles. Because endothelial nitric oxide synthase (eNOS) is upregulated in response to elevated wall shear stress, we investigated the relevance of eNOS for prazosin-induced angiogenesis in skeletal muscles. Prazosin and/or the NOS inhibitor [N.sup.[omega]]-nitro-L-arginine methyl ester (L-NAME) were given to C57BL/6 wild-type mice and eNOS-knockout mice for 14 days. The capillary-to-fiber (C/F) ratio and capillary density (CD; no. of capillaries/[mm.sup.2]) were determined in frozen sections from extensor digitorum longus (EDL) muscles of these mice. Immunoblotting was performed to quantify eNOS expression in endothelial cells isolated from skeletal muscles, whereas VEGF (after precipitation with heparin-agarose) and neuronal NOS (nNOS) concentrations were determined in EDL solubilizates. In EDL muscles of C57BL/6 mice treated for 14 days, the C/F ratio was 28% higher after prazosin administration and 11% higher after prazosin and L-NAME feeding, whereas the CD increased by 21 and 13%, respectively. The C/F ratio was highest after day 4 of prazosin treatment and decreased gradually to almost constant values after day 8. Prazosin administration led to elevation of eNOS expression. VEGF levels were lowest at day 4, whereas nNOS values decreased after day 8. In EDL muscles of eNOS-knockout mice, no significant changes in C/F ratio, CD, or VEGF and nNOS expression were observed in response to prazosin administration. Our data suggest that the presence of eNOS is essential for prazosin-induced angiogenesis in skeletal muscle, albeit other signaling molecules might partially compensate for or contribute to this angiogenic activity. Furthermore, subsequent remodeling of the capillary system accompanied by sequential downregulation of VEGF and nNOS in skeletal muscle fibers characterizes shear stress-dependent angiogenesis. angiogenesis; skeletal muscle; endothelial nitric oxide synthase

Interaction of albumin with the endothelial cell surface. Am J Physiol Heart Circ Physiol 283: H398-H405, 2002. First published March 7, 2002; 10.1152/ajpheart.00558.2001.--Endothelial cells (EC) are covered with cell-borne proteoglycans and glycoproteins. Blood plasma proteins (e.g., albumin) adsorb to this glycocalyx forming a complex endothelial surface layer (ESL). We determined the molecular mobility of albumin by electron spin resonance (ESR) in the presence and absence of ECs to analyze interactions with the ESL. Albumin was spin labeled with 5- or 12-4,4-dimethyloxazolidine-N-oxyl (DOXYL)-stearic acid yielding information on the mobility of the molecular surface (5-DOXYL) or the entire protein (12-DOXYL). EC cultures grown on glass coverslips were immersed in labeled albumin and placed in the temperature-regulated cavity of an ESR spectrometer. Alternatively, ECs were labeled and then exposed to native albumin. At 37[degrees]C, rotational correlation times determined by modified saturation transfer ESR (ST-ESR) were 26 and 48 ns for 5-DOXYL- and 12-DOXYL-labeled albumin, respectively. Presence of ECs increased rotational correlation time values for 5-DOXYL-stearic acid to 37 ns but not for 12-DOXYLstearic acid. Albumin was able to completely take up the label from labeled EC within 2 min. The present study shows that modified ST-ESR can be used to determine the mobility of biological macromolecules interacting with cellular surfaces. Reduction in albumin surface mobility in the presence of EC at unchanged mobility of protein proper and fast removal of labeled fatty acids from EC membranes indicate rapid transient interactions between albumin surface and ESL but no rigid incorporation of albumin into a macromolecular network that would interfere with its transport function for poorly water-soluble substances. electron spin resonance; molecular mobility; endothelial surface layer

The relationship between the endothelial surface layer and the microvascular turbulence resistance in blood vessels were investigated through analysis of the results of heparinase microinfusion in mesenteric network of arteries in rats. Results obtained have shown the possible role of the concentration of plasma proteins in the composition of macromolecular glycocalyx protein lining the endothelium through increasing the colloid oncotic pressure.

The hemodynamic effects of apparent diameter irregularity on vascular flow hindrance in microvascular networks were analyzed in the rat mesentery to characterize the impact of diameter variability on segmental flow. Quantitative analysis of the diameter of vessel segments in the rat microvascular network indicated the presence of variable local shear stress which was induced by surface irregularities. Furthermore, axial diameter variability was characterized as a general property of microvessels.