bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gene‐Targeted Mice in Leukocyte Adhesion Research
Authors: LEY KLAUS 
Published: April 2008

ABSTRACTPhysiologic and inflammatory leukocyte trafficking are controlled by adhesion molecules on leukocytes and endothelial cells. These adhesion molecules can be grouped into four major families: integrins, immunoglobulinlike molecules, selectins, and glycoproteins serving as selectin ligands. The recent advent of gene‐targeting technology in embryonal stem cells has prompted the production of mutant mice that lack individual adhesion molecules or combinations thereof. Such gene‐targeted mice permit studies into the roles of adhesion molecules in acute and chronic inflammation and of the regulation and interplay between different sets of adhesion receptors in vivo. Microcirculatory studies have been indispensable to our understanding of the importance of certain adhesion molecules for different steps of leukocyte recruitment in vivo. Targeting new genes and investigating mice with combined adhesion‐molecule deficiencies will help to further clarify the molecular mechanisms of leukocyte trafficking in health and disease. This article reviews the insight gained through using adhesion molecule‐deficient mice, emphasizing the role of microcirculatory studies in this research.
Activation‐Dependent Isolation and Culture of Murine Pulmonary Microvascular Endothelium
Authors: GERRITSEN MARY E. , SHEN CHIEN‐PING , MCHUGH MARK C. , ATKINSON WILLIAM J. , KIELY JEANNE‐MARIE , MILSTONE DAVID S. , LUSCINSKAS FRANCIS W. , GIMBRONE MICHAEL A. 
Published: April 2008

ABSTRACTObjective: Establish a reproducible method for the isolation and cultivation of murine pulmonary microvascular endothelium. To this end, we exploited the localized pattern of microvascular endothelial activation induced in vivo by inflammatory stimuli to isolate a subpopulation of endothelium for in vitro study.Methods: Immunohistochemical analyses of the pulmonary vasculature of mice treated systemically with gram‐negative bacterial endotoxin (LPS) demonstrated selective expression of VCAM‐1 (CD106) in the endothelial lining of small collecting veins, venules, septal capillaries, and, infrequently, small arteries, which was not observed in control mice. Single cell suspensions prepared by enzymatic dissociation of peripheral lobular tissues dissected from the lungs of LPS‐stimulated mice were incubated with a phycoerythrin‐conjugated antimouse VCAM‐1 monoclonal antibody (MK 1.91). Cells expressing this antigen were isolated by sterile fluorescence‐activated cell sorting (FACS). Positive cell populations were collected and cultured for 1–2 weeks. When confluent, these primary cultures were further FACS enriched for endothelium, positively selecting for cells incorporating a fluorescent derivative of acetylated low density lipoprotein (Di‐I‐Ac‐LDL).Results: The resulting population of cells (mouse lung endothelial cells, MLEC) were uniformly positive for the endothelial markers von Willebrand factor, thrombomodulin, and Dil‐Ac‐LDL uptake. MLEC readily formed tube‐like structures when cultured on Matrigel and spontaneously demonstrated a sprouting phenotype on fibronectin or collagen matrices. MLEC retained responsiveness to cytokines (IL‐1α, IL‐1β, TNFα, IFNγ) up to at least eight passages from primary culture and demonstrated upregulation of E‐selectin (CD62E) and P‐selectin (CD62P) mRNA as early as 2 hr after LPS stimulation. Characteristic temporal expression patterns of cell surface E‐selectin (maximal at 4 hr and declining toward baseline by 24 hr), VCAM‐1 (maximal at 6–8 hr and remaining elevated for 24–48 hr), and ICAM‐1 (maximal at 6–8 hr and maintained at 24 hr) were observed when cultured MLEC were treated with recombinant murine TNFα or recombinant human (rh) IL‐1α or rhIL‐1β. The rolling, adhesion, and transmigration of human polymorphonuclear leukocytes was markedly increased on cytokine‐activated MLEC monolayers under defined flow conditions.Conclusion: The strategy of activation‐dependent isolation allows for the reproducible selection of a specific subset of microvascular endothelial cells for in vitro
Pulmonary Microvascular Pressure Profile During Development of Hydrostatic Edema
Authors: NEGRINI DANIELA 
Published: April 2008

ABSTRACTObjective: To measure, in intact closed chest, the pressure in the pulmonary microvasculature during transition to mild interstitial edema.Methods: In anesthetized spontaneously breathing rabbits, the pulmonary artery and left atrium were cannulated. Pleural windows were prepared to view the superficial pulmonary microvascular network through the intact parietal pleura. After intravenous infusion of 96.4 ± 12.3 ml of saline at a rate of 0.5 ml/kg h, the hydraulic pressure in the pulmonary microvessels (15–240 μm in diameter) were measured using glass pipettes driven through the pleural window and connected to a servonull system.Results: After saline, plasma protein concentration decreased from 6 ± 1 to 4.8 ± 0.5 g/dl; pulmonary arterial and left atrial pressures averaged 22.3 ± 6.4 and 2.3 ± 2 cm H2O in control and 23.1 ± 4.2 and 4.2 ± 2 cm H2O after infusion. After saline loading, 16.4% of total pressure drop occurred from pulmonary artery to 80‐μm arterioles, 60.3% in 30–80‐μm arterioles, 6.9% from 30‐μm arterioles to 30‐μm venules and 16.4% in the downstream segment.Conclusions: Mild interstitial edema induced, with respect to control, constriction of small arterioles and capillary recruitment to maintain a low capillary pressure. Hence, in initial edema, pulmonary circulation prevents further fluid filtration, acting like an intrinsic safety factor to delay development of severe edema.
Heterogeneity of Red Blood Cell Velocity in Skeletal Muscle Decreases with Increased Flow
Authors: TYML KAREL , CHENG LINONG 
Published: April 2008

ABSTRACTObjective: Effective material exchange between blood and tissue depends on the heterogeneity of microvascular flow. The objective was to address inconsistencies between intravital studies regarding this dependency. We tested the hypothesis that heterogeneity of red blood cell velocity (VRBC) in capillary beds varies with the strength of metabolic stimulus and with capillary bed geometry.Methods: We used videomicroscopy to measure VRBC in a bed of 10–24 capillaries at the surface of extensor digitorum longus (EDL) muscle in anesthetized rats. The coefficient of variation (CV = standard deviation/mean; an index of spatial heterogeneity) was computed in the same bed before and after (i) 1, 2, 4, or 8 Hz supramaximal muscle contraction or (ii) adenosine superfusion (10−7–10−3 M). Beds with or without arteriolar—venular capillary shunts were used.Results: Although control VRBC differed between beds (shunt: 232 μm/s; no shunt: 130 μm/s), the percentage increases in postcontraction VRBC did not (range: 111–326%). In both beds, control CV varied greatly (overall range: 28–117%) and 2–8 Hz muscle contractions reduced CV significantly by 25%. Similar results were obtained for adenosine. In confirmatory experiments using the rat cremaster muscle, contractions (4 Hz) and adenosine (10−4 M) also reduced CV. Based on all data, CV = 63–0.022 VRBC (r = 0.82, P < 0.001).Conclusions: The heterogeneity of VRBC decreased with metabolic stress, regardless of capillary bed geometry. We propose that both the large variability in control CV and the relatively shallow dependence of CV on velocity could be responsible for the present inconsistencies between intravital studies.
Microvascular Architecture and Exchange in Synovial Joints
Authors: LEVICK J. R. 
Published: April 2008

ABSTRACTThe microcirculation of the synovial lining of joints displays many fascinating adaptations to function. One primary function is to supply nutrients to the avascular cartilage, whose chondrocytes are metabolically active but are relatively vast distances from the nearest capillary (> 1 cm in the center of a human knee). Exchange is facilitated by a high density of fenestrated capillaries situated very close to the synovial surface (an arrangement disrupted in rheumatoid synovium) with fenestrations preferentially oriented toward the joint cavity. Even so, diffusion alone is too slow to supply central chondrocytes with glucose. The problem is solved by the synovial microcirculation generating intra‐articular fluid (synovial fluid) that transports glucose by convection during joint movement. Synovial fluid is a plasma ultrafiltrate into which hyaluronan has been secreted, and it also serves to lubricate the joint.The joint cavity offers unusually easy access to the interstitial side of the microcirculation because the synovial cell layer is discontinuous, with an interstitial matrix between capillary and joint cavity. This allows the experimental study of the effect of the extravascular Starling “forces” (hydraulic and colloid osmotic pressure) on fluid exchange. One unexpected outcome has been the finding that a substantial part of the hydraulic resistance to fluid transport between blood and joint cavity resides in the series interstitial layer rather than in the capillary wall. Another is that, under appropriate boundary conditions (joint angle, etc.) fluid can simultaneously filter into the cavity in some regions (synovium directly overlying capillaries) and out of the cavity into subsynovium in other regions (synovium in the mesh space between capillaries) to produce a turnover of synovial fluid.
Autoradiographic Assessment of Blood Flow Heterogeneity in the Hamster Heart
Authors: STAPLETON DWIGHT D. , MOFFETT TYLER C. , RASKIN DENIS G. , BASSINGTHWAIGHTE JAMES B. 
Published: April 2008

ABSTRACTObjective: Provide regional flow measurement in the hearts of small mammals using a new, higher‐resolution technique based on the deposition of a molecular marker.Methods: We determined the instantaneous extraction and retention of the “molecular microsphere” radiolabeled desmethylimipramine in retrogradely perfused hamster hearts. In a separate series of experiments, autoradiography was used to measure regional myocardial deposition densities in hamster hearts of about 0.5 g with spatial area resolution of 16 × 16 μm.Results: Radiolabeled desmethylimipramine is almost 100% extracted during a single transcapillary passage and is retained in the tissue for many minutes. Autoradiographic images demonstrated a spatial flow heterogeneity with standard deviations of 31 ± 4% of the mean flow (N = 5) in 16 × 16 × 20‐μm3 voxels. This is equivalent to the projections made using fractal relationships from cruder observations obtained with microspheres in the hearts of baboons, sheep, and rabbits.Conclusion: Autoradiography using a molecular deposition marker provides quantitative information on myocardial flow heterogeneities with resolution at the size of cardiac myocytes. Because the regions resolved are smaller than the volume of regions supplied by single arterioles, the results must slightly exaggerate the true heterogeneity of regional flows.
The Role of Mechanical Stresses in Microvascular Remodeling
Authors: Skalak Thomas C. , Price Richard J. 
Published: April 2008

ABSTRACTThe microvasculature is an extremely adaptable structure that is capable of architectural and functional adjustments in response to multiple biochemical and mechanical stimuli. Inadequate or inappropriate adjustments often result in pathophysiology. Recent work has brought increasing recognition of the importance of microvascular remodeling in widespread disease states such as hypertension, tumor growth, diabetes, and progressive coronary artery occlusion. Much work has been done to characterize the cells and molecules with putative roles in microvascular remodeling, but little is known regarding the mechanotransduction processes that might link hemodynamic stresses such as wall shear stress and circumferential wall stress to structural and functional changes in vivo. Two primary approaches have been employed: in vitro studies that use cultured cells and allow molecular biologic analysis of signaling pathways and gene expression; and in vivo experiments aimed at understanding vessel adaptations in the intact tissue. This article reviews the structural adaptations exhibited by microvessels and the information available from in vitro and in vivo approaches. The formation of new arterioles in intact tissues is examined in detail as an example of integrative work, and the prospects for new technologies are discussed. This is a time of great opportunity for bidirectional exchange between basic in vitro advances and in vivo experimentation. This exchange will be essential in generating new understanding of the role of mechanical stresses in microvascular remodeling.
Conservation of Flow Demonstrated Using the Two‐Slit Velocimeter and Cross Correlator in Epiilluminated Surface Microvessels of the Mouse Brain
Authors: Rosenblum William I. 
Published: April 2008

ABSTRACTObjective: To validate the use of two‐slit velocimetry in an epiilluminated microvascular bed by demonstrating conservation of flow and to compare this validation with that provided by the literature for transilluminated beds.Methods: The brain surface vessels of mice were epiilluminated with a mercury lamp and observed with a Leitz Ultrapak objective (22X) and dipping cone. The internal diameters were measured with an ocular micrometer. The Instrumentation for Physiology and Medicine (IPM) velocimeter and cross correlator were used to measure red blood cell (RBC) velocity at the centerline of 17 different microvascular branch points. The velocity in the feeding arteriole and each branch or in the tributaries and draining venule were used, together with the respective diameters, to calculate flow in each vessel. Findings in the arterioles and venules were combined, because the results were the same in either set of vessels.Results: Flow in the main vessel (nl/sec) = 0.97 (sum of flow in branches or tributaries) +2. The correlation coefficient was 0.95. The relationship was not significantly different from an ideal slope of unity. However, in individual bifurcations the sum of flows in branches or tributaries deviated by as much as 40% from predicted values.Conclusions: On the average, conservation of flow was present. The deviations from conservation at individual bifurcations were similar to those reported by others who utilized transilluminated beds. Thus, when conservation of flow is the validating criterion, the two‐slit technique used with epiillumination is not less valid than when used with transillumination.
Transvascular and Interstitial Migration of Neutrophils in Rat Mesentery
Authors: Ohashi K. L. , Tung D. K.‐L. , Wilson J. , Zweifach B. W. , Schmid‐Schönbein G. W. 
Published: April 2008

ABSTRACTObjective: The consequential implications of the leukocyte‐endothelial cell adhesion reaction, as well as the subsequent migratory activity of the leukocytes within the interstitium proper, are currently known only in general phenomenological terms. Our objective was to carry out a detailed quantitative analysis of transendothelial and interstitial migration.Method: We incorporated several new features, such as the video recording of time‐lapse photography in conjunction with the time history of individual leukocytes under the influence of representative stimulators and inhibitors. The mesentery was suffused with the chemical activator N‐formyl‐met‐leu‐phe (fMLP, 5 ± 10−8 M) and histamine (10−6 M) for periods up to 3 h. This leads to an attachment of neutrophils preferentially to the walls of small postcapillary venules followed by migration into the adjacent interstitium.Results: The time interval between the initial neutrophil adhesion to the luminal side of the venules and their first appearance on the abluminal side of the venule wall was about 25 min. The time interval for the actual physical migration across the endothelium was only about 1‐2 min. There was an initial increase in the number of neutrophils migrating across the wall per unit time after the application of fMLP. However, this effect then gradually decreased over the course of 1 h. In the extravascular tissue, the neutrophils appeared to migrate along random pathways with an average trajectory away from the venular wall. When histamine (1 μM) was applied topically in conjunction with fMLP, the overall migratory flux across the venular wall increased, although the cells migrated comparatively short distances into the interstitium. After pretreatment with phalloidin (25 μg/kg), an actin cross‐linking agent, neutrophil adhesion and migration in response to fMLP stimulation was reduced. The mast cell stimulator 48/80 (25 mg/ml) resulted in rapid degranulation, which was accompanied by an insignificant increase in neutrophil diapedesis. After fMLP stimulation there was reduced neutrophil emigration in the presence of mast cell inhibitors, such as lodoxamide (1 μg/kg) and ketotifin (1 μg/kg).Conclusions: Our results demonstrate that both the endothelial cells and interstitial mast cells are involved in the rate of transvascular migration of leukocytes across postcapillary venules and into the interstitium.
Regulation of the Gene‐Encoding Angiotensin II Receptor in Vascular Tissue
Authors: Wang Donna H. , Du Yong , Yao Aqing 
Published: April 2008

ABSTRACTSpecific angiotensin (Ang)‐dependent mechanisms significantly contribute to vascular development and function, and to the pathophysiology of hypertension. The effects of Ang II are mediated by binding to specific receptors. The focus of most studies has been changes in vascular function and structure in response to Ang II. Relatively little is known regarding the molecular basis of changes in the vascular Ang II receptor. We have recently found that, without altering blood pressure, Ang II infusion at a dose of 25 ng · kg · min−1 decreases expression of the gene‐encoding Ang II type 1 (AT1) receptor in both the aorta and resistant arteries. This suggests that exogenous Ang II negatively regulates AT1 mRNA expression in these tissues. Furthermore, hypertension induced by reduced renal mass plus high salt intake upregulates AT1 mRNA expression in the hypertrophied aorta and heart. In this model, the reduction of Ang II formation by captopril without decreasing blood pressure prevents the increase in AT1 mRNA in the aorta but not in the heart. This suggests that the regulation of AT1 gene expression in the heart may be pressure‐dependent while there is an Ang II‐dependent mechanism operant in the aorta. The precise tissue‐specific control mechanisms for AT1 gene expression remain to be defined.
A New Method for Blood Velocimetry in the Microcirculation
Authors: Hitt Darren L. , Lowe Mary L. , Tincher Juvena R. , Watters J. Michael 
Published: April 2008

ABSTRACTWe describe a simple new method for computing two‐dimensional velocity vector fields of blood flows in microvascular networks. This method, known as optical flow, requires a time sequence of two or more images obtained by a process such as conventional videomicroscopy. There is no need to distinguish individual cells provided clear variations in the light intensity levels are present in the images. The result of the computation reveals the velocity distribution in the microvascular network and the geometry of the blood vessels. Although various implementations of the optical flow technique exist, we have found that the spatial correlation algorithm of Anandan performs best for microcirculatory flows. This report is an introduction to the application of optical flow to the microcirculation and provides instructions on how to obtain and run the codes.
Control Mechanisms of Retinal Vein Pressure: Evaluation in the Cat Using an In Situ Infusion Micropipette
Authors: Attariwala R. , Glucksberg M. R. 
Published: April 2008

ABSTRACTObjective: Previous work in our laboratory has shown that retinal vein pressure is significantly greater than intraocular pressure in the cat. Our purpose here is to evaluate the potential of an active mechanism being responsible for the control of vein pressure in the cat retina.Methods: A double‐lumen, concentric barrel micropipette assembly designed for operation within the eye of a spontaneously breathing anesthetized cat was developed. The micropipette, initially filled with hypertonic saline for use with a servonull pressure measuring system, was used to determine intravascular pressure. With the tip of the micropipette still situated in the lumen of the vessel the solution in the micropipette was exchanged for papaverine, a potent smooth muscle dilator. Following vasodilation in the distal portion of a major retinal vein, the papaverine was exchanged for hypertonic saline and intravascular pressures were measured in the dilated vessel.Results: Microinjection of papaverine caused visible dilation of the major retinal vein downstream from the site of microinjection. This indicates a relaxation of the smooth muscle yet papaverine caused no change in measured retinal vein pressure.Conclusions: Vein pressure in the cat retina is maintained above intraocular pressure by mechanisms other than active control. A passive high‐resistance segment resides somewhere within the optic nerve possibly within the lamina cribosa or prelaminar region.
Theoretical Studies of Steady‐State Transcapillary Exchange in Countercurrent Systems
Authors: Wang W. , Parker K. H. , Michel C. C. 
Published: April 2008

ABSTRACTObjective: As a first step in modeling microvascular exchange in the renal medulla, we developed mathematical models to explore the effects of blood flow, permeability, and anatomical arrangement of microvessels on the steady‐state distribution of solute in the blood and the interstitial fluid (ISF).Methods: Single capillaries and countercurrent capillary loops were used to model microvessels that were surrounded by a secretory epithelium over either the whole or part of the capillary length. Solute concentration in the vessels and the ISF were derived analytically. We also derived approximate solutions that ignored axial diffusion of solute.Results: The full and approximate solutions were in good agreement with data based on measurements in the renal medulla. Model results revealed that concentration in the ISF falls rapidly with distance beyond the region of solute secretion and equilibrates with the concentration in capillaries, even with countercurrent exchange between the two limbs of the capillary loop. The ratio of the product of the permeability and area to the flow of the afferent limb, γ1, is an important parameter. When γ1 > 4, countercurrent exchange in a capillary loop facilitates a greater ISF concentration gradient than with a single capillary. Changes in flow also have a greater effect on this gradient.Conclusion: The model of countercurrent exchange presented here not only demonstrates the sensitivity of interstitial concentration gradients of solute to flow through capillary loops but also reveals the importance of the absolute value of γ1 in determining the magnitude and direction of these gradients.