Lipoprotein binding to anionic biopolyelectrolytes and the effect of glucose on nanoplaque formation in arteriosclerosis and Alzheimer's disease.

Arteriosclerosis with its clinical sequelae (cardiac infarction, stroke, peripheral arterial occlusive disease) and vascular/Alzheimer dementia not only result in far more than half of all deaths but also represent dramatic economic problems. The reason is, among others, that diabetes mellitus is an independent risk factor for both disorders, and the number of diabetics strongly increases worldwide. More than one-half of infants in the first 6months of life have already small collections of macrophages and macrophages filled with lipid droplets in susceptible segments of the coronary arteries. On the other hand, the authors of the Bogalusa Heart Study found a strong increase in the prevalence of obesity in childhood that is paralleled by an increase in blood pressure, blood lipid concentration, and type 2 diabetes mellitus. Thus, there is a clear linkage between arteriosclerosis/Alzheimer's disease on the one hand and diabetes mellitus on the other hand. Furthermore, it has been demonstrated that distinct apoE isoforms on the blood lipids further both arteriosclerotic and Alzheimer nanoplaque formation and therefore impair flow-mediated vascular reactivity as well. Nanoplaque build-up seems to be the starting point for arteriosclerosis and Alzheimer's disease in their later full clinical manifestation. In earlier work, we could portray the anionic biopolyelectrolytes syndecan/perlecan as blood flow sensors and lipoprotein receptors in cell membrane and vascular matrix. We described extensively molecular composition, conformation, form and function of the macromolecule heparan sulfate proteoglycan (HS-PG). In two supplementary experimental settings (ellipsometry, myography), we utilized isolated HS-PG for in vitro nanoplaque investigations and isolated human coronary artery segments for in vivo tension measurements. With the ellipsometry-based approach, we were successful in establishing a direct connection on a molecular level between diabetes mellitus on the one side and arteriosclerosis/Alzheimer's disease on the other side. Application of glucose at a concentration representative for diabetics and leading to glycation of proteins and lipids, entailed a significant increase in arteriosclerotic and Alzheimer nanoplaque formation. IDLapoE4/E4 was by far superior to IDLapoE3/E3 in plaque build-up, both in diabetic and non-diabetic patients. Recording vascular tension of flow-dependent reactivity in blood substitute solution and under application of different IDLapoE isoforms showed an impaired vasorelaxation for pooled IDL and IDLapoE4/E4, thus confirming the ellipsometric investigations. Incubation in IDLapoE0/E0 (apoE "knockout man"), however, resulted in a massive flow-mediated contraction, also complemented by strongly aggregated nanoplaques. In contrast, HDL was shown to present a powerful protection against nanoplaque formation on principle, both in the in vitro model and the in vivo scenario on the endothelial cell membrane. The competitive interplay with LDL is highlighted through the flow experiment, where flow-mediated, HDL-induced vasodilatation remains untouched by additional incubation with LDL. This is due to the four times higher affinity for the proteoglycan receptor of HDL as compared to LDL. Taken together, the studies demonstrate that while simplistic, the ellipsometry approach and the endothelial-mimicking proteoglycan-modified surfaces provide information on the initial steps of lipoprotein-related plaque formation, which correlates with findings on endothelial cells and blood vessels, and afford insight into the role of lipoprotein deposition and exchange phenomena at the onset of these pathophysiologies.

Microvascular responses to (hyper-)gravitational stress by short-arm human centrifuge: arteriolar vasoconstriction and venous pooling.

PURPOSE: We hypothesized that lower body microvessels are particularly challenged during exposure to gravity and hypergravity leading to failure of resistance vessels to withstand excessive transmural pressure during hypergravitation and gravitation-dependent microvascular blood pooling. METHODS: Using a short-arm human centrifuge (SAHC), 12 subjects were exposed to +1Gz, +2Gz and +1Gz, all at foot level, for 4 min each. Laser Doppler imaging and near-infrared spectroscopy were used to measure skin perfusion and tissue haemoglobin concentrations, respectively. RESULTS: Pretibial skin perfusion decreased by 19% during +1Gz and remained at this level during +2Gz. In the dilated area, skin perfusion increased by 24 and 35% during +1Gz and +2Gz, respectively. In the upper arm, oxygenated haemoglobin (Hb) decreased, while deoxy Hb increased with little change in total Hb. In the calf muscle, O2Hb and deoxy Hb increased, resulting in total Hb increase by 7.5 ± 1.4 and 26.6 ± 2.6 µmol/L at +1Gz and +2Gz, respectively. The dynamics of Hb increase suggests a fast and a slow component. CONCLUSION: Despite transmural pressures well beyond the upper myogenic control limit, intact lower body resistance vessels withstand these pressures up to +2Gz, suggesting that myogenic control may contribute only little to increased vascular resistance. The fast component of increasing total Hb indicates microvascular blood pooling contributing to soft tissue capacitance. Future research will have to address possible alterations of these acute adaptations to gravity after deconditioning by exposure to micro-g.

[Physiological basis of the microcirculation: vascular adaptation]. / Physiologische Grundlagen der Mikrozirkulation: vaskuläre Adaptation.

The microcirculation is the functional "business end" of the cardiovascular system. In vessels with diameters below about 300 µm processes including the regulation of perfusion, exchange processes and relevant components of the immune system are localised. A large number of individual mechanisms are involved, including micro-rheology, the endothelial surface layer, vascular permeability, endothelial function, regulation of smooth muscle tone, leukocyte endothelial interaction, vascular adaptation and angiogenesis. The present article focusses mainly on the role of vascular adaptation. Much more than in large vessels, the microcirculation is characterised by constant adaptation to haemodynamic and metabolic signals. In reaction to changes in parenchymal demand, changes of the diameter of existing vessels (by changes in tone or by structural remodelling) as well as generation of new vessels (angiogenesis) or the pruning of vessels are elicited. These mechanisms are part of the so-called "angioadaptation" which is of great clinical relevance for the pathophysiological consequences of hypertension and age-related macular degeneration.

Intussusceptive angiogenesis: pillars against the blood flow.

Adaptation of vascular networks to functional demands needs vessel growth, vessel regression and vascular remodelling. Biomechanical forces resulting from blood flow play a key role in these processes. It is well-known that metabolic stimuli, mechanical forces and flow patterns can affect gene expression and remodelling of vascular networks in different ways. For instance, in the sprouting type of angiogenesis related to hypoxia, there is no blood flow in the rising capillary sprout. In contrast, it has been shown that an increase of wall shear stress initiates the splitting type of angiogenesis in skeletal muscle. Otherwise, during development, both sprouting and intussusception act in parallel in building the vascular network, although with differences in spatiotemporal distribution. Thereby, in addition to regulatory molecules, flow dynamics support the patterning and remodelling of the rising vascular tree. Herewith, we present an overview of angiogenic processes with respect to intussusceptive angiogenesis as related to local haemodynamics.

Differential expression of VEGFA, TIE2, and ANG2 but not ADAMTS1 in rat mesenteric microvascular arteries and veins.

Microvessels respond to metabolic stimuli (e.g. pO(2)) and hemodynamic forces (e.g. shear stress and wall stress) with structural adaptations including angiogenesis, remodeling and pruning. These responses could be mediated by differential gene expression in endothelial and smooth muscle cells. Therefore, rat mesenteric arteries and veins were excised by microsurgery, and mRNA expression of four angioadaptation-related genes was quantified by real time duplex RT-PCR in equal amounts of total RNA, correlated to two different house keeping genes (beta-actin, GAPDH). The results show higher expression of VEGFA, TIE2, and ANG2 in arteries than in veins, but equal expression of ADAMTS1. Higher availability of VEGFA mRNA in endothelial cells of arteries shown here could contribute to the maintenance of mechanically stressed blood vessels and counteract pressure-induced vasoconstriction.

An imaging spectroscopy approach for measurement of oxygen saturation and hematocrit during intravital microscopy.

OBJECTIVE: Oxygen supply and partial pressure are key determinants of tissue metabolic status and are also regulators of vascular function including production of reactive oxygen species, vascular remodeling, and angiogenesis. The objective of this study was to develop an approach for the determination of oxygen saturation and hematocrit for individual microvessels in trans- and epi-illumination intravital microscopy. METHODS: A spectral approach was used, taking advantage of the availability of commercial imaging systems that allow digital recording of intravital images at a number of predetermined wavelengths within a relatively short time. The dependence of validity and precision of saturation measurements on critical experimental variables (reference spectra, number and selection of wavelengths, exposure time, analysis area, analysis model) was evaluated. In addition, a software approach for two-dimensional analysis of images was developed. RESULTS: Exposure times per wavelength of about 200 ms and use of up to 50 wavelengths evenly spaced from 500 to 598 nm allow automatic discrimination of microvessels from tissue background (segmentation) with reliable determination of oxygen saturation (in trans- and epi-illumination) and hematocrit (in transillumination). CONCLUSIONS: The present imaging spectroscopy approach allows detailed assessment of oxygen transport and other functional parameters at the microcirculatory level.

Normal endothelium.

In recent decades, it has become evident that the endothelium is by no means a passive inner lining of blood vessels. This 'organ' with a large surface (approximately 350 m2) and a comparatively small total mass (approximately 110 g) is actively involved in vital functions of the cardiovascular system, including regulation of perfusion, fluid and solute exchange, haemostasis and coagulation, inflammatory responses, vasculogenesis and angiogenesis. The present chapter focusses on two central aspects of endothelial structure and function: (1) the heterogeneity in endothelial properties between species, organs, vessel classes and even within individual vessels and (2) the composition and role of the molecular layer on the luminal surface of endothelial cells. The endothelial lining of blood vessels in different organs differs with respect to morphology and permeability and is classified as 'continuous', 'fenestrated' or 'discontinuous'. Furthermore, the mediator release, antigen presentation or stress responses of endothelial cells vary between species, different organs and vessel classes. Finally there are relevant differences even between adjacent endothelial cells, with some cells exhibiting specific functional properties, e.g. as pacemaker cells for intercellular calcium signals. Organ-specific structural and functional properties of the endothelium are marked in the vascular beds of the lung and the brain. Pulmonary endothelium exhibits a high constitutive expression of adhesion molecules which may contribute to the margination of the large intravascular pool of leucocytes in the lung. Furthermore, the pulmonary microcirculation is less permeable to protein and water flux as compared to large pulmonary vessels. Endothelial cells of the blood-brain barrier exhibit a specialised phenotype with no fenestrations, extensive tight junctions and sparse pinocytotic vesicular transport. This barrier allows a strict control of exchange of solutes and circulating cells between the plasma and the interstitial space. It was observed that average haematocrit levels in muscle capillaries are much lower as compared to systemic haematocrit, and that flow resistance of microvascular beds is higher than expected from in vitro studies of blood rheology. This evidence stimulated the concept of a substantial layer on the luminal endothelial surface (endothelial surface layer, ESL) with a thickness in the range of 0.5-1 microm. In comparison, the typical thickness of the glycocalyx directly anchored in the endothelial plasma membrane, as seen in electron micrographs, amounts to only about 50-100 microm. Therefore it is assumed that additional components, e.g. adsorbed plasma proteins or hyaluronan, are essential in constituting the ESL. Functional consequences of the ESL presence are not yet sufficiently understood and acknowledged. However, it is evident that the thick endothelial surface layer significantly impacts haemodynamic conditions, mechanical stresses acting on red cells in microvessels, oxygen transport, vascular control, coagulation, inflammation and atherosclerosis.

Shear stress modulates the expression of thrombospondin-1 and CD36 in endothelial cells in vitro and during shear stress-induced angiogenesis in vivo.

Binding of thrombospondin-1 (TSP-1) to the CD36 receptor inhibits angiogenesis and induces apoptosis in endothelial cells (EC). Conversely, matrix-bound TSP-1 supports vessel formation. In this study we analyzed the shear stress-dependent expression of TSP-1 and CD36 in endothelial cells in vitro and in vivo to reveal its putative role in the blood flow-induced remodelling of vascular networks. Shear stress was applied to EC using a cone-and-plate apparatus and gene expression was analyzed by RT-PCR, Northern and Western blot. Angiogenesis in skeletal muscles of prazosin-fed (50 mg/l drinking water; 4 d) mice was assessed by measuring capillary-to-fiber (C/F) ratios. Protein expression in whole muscle homogenates (WMH) or BS-1 lectin-enriched EC fractions (ECF) was analyzed by Western blot. Shear stress downregulated TSP-1 and CD36 expression in vitro in a force- and time-dependent manner sustained for at least 72 h and reversible by restoration of no-flow conditions. In vivo, shear stress-driven increase of C/F in prazosin-fed mice was associated with reduced expression of TSP-1 and CD36 in ECF, while TSP-1 expression in WMH was increased. Down-regulation of endothelial TSP-1/CD36 by shear stress suggests a mechanism for inhibition of apoptosis in perfused vessels and pruning in the absence of flow. The increase of extra-endothelial (e.g. matrix-bound) TSP-1 could support a splitting type of vessel growth.

Microvascular blood viscosity in vivo and the endothelial surface layer.

The apparent viscosity of blood in glass tubes declines with decreasing diameter (Fåhraeus-Lindqvist effect) and exhibits a distinctive minimum at 6-7 microm. However, flow resistance in vivo in small vessels is substantially higher than predicted by in vitro viscosity data. The presence of a thick endothelial surface layer (ESL) has been proposed as the primary cause for this discrepancy. Here, a physical model is proposed for microvascular flow resistance as a function of vessel diameter and hematocrit in vivo; it combines in vitro blood viscosity with effects of a diameter-dependent ESL. The model was developed on the basis of flow distributions observed in three microvascular networks in the rat mesentery with 392, 546, and 383 vessel segments, for which vessel diameters, network architecture, flow velocity, and hematocrit were determined by intravital microscopy. A previously described hemodynamic simulation was used to predict the distributions of flow and hematocrit from the assumed model for effective blood viscosity. The dependence of ESL thickness on vessel diameter was estimated by minimizing deviations of predicted values for velocities, flow directions, and hematocrits from measured data. Optimal results were obtained with a layer thickness of approximately 0.8-1 microm for 10- to 40-microm-diameter vessels and declined strongly for smaller diameters, with an additional hematocrit-dependent impact on flow resistance exhibiting a maximum for approximately 10-microm-diameter vessels. These results show that flow resistance in vivo can be explained by in vitro blood viscosity and the presence of an ESL and indicate the rheologically effective thickness of the ESL in microvessels.

Estimation of the left ventricular relaxation time constant tau requires consideration of the pressure asymptote.

The left ventricular isovolumic pressure decay, obtained by cardiac catheterization, is widely characterized by the time constant tau of the exponential regression p(t)=Pomega+(P0-Pomega)exp(-t/tau). However, several authors prefer to prefix Pomega=0 instead of coestimating the pressure asymptote empirically; others present tau values estimated by both methods that often lead to discordant results and interpretation of lusitropic changes. The present study aims to clarify the relations between the tau estimates from both methods and to decide for the more reliable estimate. The effect of presetting a zero asymptote on the tau estimate was investigated mathematically and empirically, based on left ventricular pressure decay data from isolated ejecting rat and guinea pig hearts at different preload and during spontaneous decrease of cardiac function. Estimating tau with preset Pomega=0 always yields smaller values than the regression with empirically estimated asymptote if the latter is negative and vice versa. The sequences of tau estimates from both methods can therefore proceed in reverse direction if tau and Pomega change in opposite directions between the measurements. This is exemplified by data obtained during an increasing preload in spontaneously depressed isolated hearts. The estimation of the time constant of isovolumic pressure fall with a preset zero asymptote is heavily biased and cannot be used for comparing the lusitropic state of the heart in hemodynamic conditions with considerably altered pressure asymptotes.

Control of blood vessel structure: insights from theoretical models.

Blood vessels are capable of continuous structural adaptation in response to changing local conditions and functional requirements. Theoretical modeling approaches have stimulated the development of new concepts in this area and have allowed investigation of the complex relations between adaptive responses to multiple stimuli and resulting functional properties of vascular networks. Early analyses based on a minimum-work principle predicted uniform wall shear stress in all segments of vascular networks and led to the concept that vessel diameter is controlled by a feedback system based on responses to wall shear stress. Vascular reactions to changes in transmural pressure suggested feedback control of circumferential wall stress. However, theoretical simulations of network adaptation showed that these two mechanisms cannot, by themselves, lead to stable and realistic network structures. Models combining reactions to fluid shear stress, circumferential stress, and metabolic status of tissue, with propagation of stimuli upstream and downstream along vascular segments, are needed to explain stable and functionally adequate adaptation of vascular structure. Such models provide a basis for predicting the response of vascular segments exposed to altered conditions, as, for example, in vascular grafts.

Deterministic nonlinear characteristics of in vivo blood flow velocity and arteriolar diameter fluctuations.

We have performed a nonlinear analysis of fluctuations in red cell velocity and arteriolar calibre in the mesenteric bed of the anaesthetized rat. Measurements were obtained under control conditions and during local superfusion with NG-nitro-L-arginine (L-NNA, 30 microM) and tetrabutylammonium (TBA, 0.1 mM), which suppress NO synthesis and block Ca2+ activated K+ channels (KCa), respectively. Time series were analysed by calculating correlation dimensions and largest Lyapunov exponents. Both statistics were higher for red cell velocity than diameter fluctuations, thereby potentially differentiating between global and local mechanisms that regulate microvascular flow. Evidence for underlying nonlinear structure was provided by analysis of surrogate time series generated from the experimental data following randomization of Fourier phase. Complexity indices characterizing time series under control conditions were in general higher than those derived from data obtained during superfusion with L-NNA and TBA.

In situ analysis of coronary terminal arteriole diameter responses: technical report of a new experimental model.

INTRODUCTION: To date, investigation of coronary arteriole vasomotor activity has been limited to arterioles >30- 40 microm. Here, we introduce a new experimental model to allow for in situ microscopy of terminal coronary arterioles. METHODS: Rat hearts were perfused in a closed loop system (priming volume 20 ml) which was placed on a computer-controlled microscope stage. FITC-dextran and tetrodotoxin (TTX, 50 microM) were added. Tilting of the microscope by 90 degrees allowed for visual access to the ventricular surface. Arterioles were identified by the flow direction of fluorescent beads (1 microm). Images were recorded on video tape, and arteriole diameters were measured offline. Stability of the preparation and maintenance of coronary flow reserve were analyzed. Responses of coronary flow and arteriole diameters to the vasodilators papaverine and Na-nitroprusside were recorded. RESULTS: In TTX-arrested control hearts coronary flow and terminal arteriole diameters were stable for 2 h. Administration of papaverine and Na-nitroprusside increased coronary flow from 6.4 +/- 0.7 to 13.3 +/- 1.3 ml/min, decreasing coronary resistance by 52 +/- 3%. Terminal coronary arteriole diameters increased from 12.0 +/- 0.9 to 13.6 +/- 1.0 microm, decreasing hindrance of this vessel segment by 45 +/- 11%. CONCLUSION: Preservation of coronary terminal arteriolar tone and adequate responsiveness to vasodilators in the TTX-arrested isolated heart were demonstrated. Thus, this model may serve to complement our understanding of coronary microvascular control mechanisms by extending observations to the terminal arteriolar bed.

Structural response of microcirculatory networks to changes in demand: information transfer by shear stress.

Matching blood flow to metabolic demand in terminal vascular beds involves coordinated changes in diameters of vessels along flow pathways, requiring upstream and downstream transfer of information on local conditions. Here, the role of information transfer mechanisms in structural adaptation of microvascular networks after a small change in capillary oxygen demand was studied using a theoretical model. The model includes diameter adaptation and information transfer via vascular reactions to wall shear stress, transmural pressure, and oxygen levels. Information transfer is additionally effected by conduction along vessel walls and by convection of metabolites. The model permits selective blocking of information transfer mechanisms. Six networks, based on in vivo data, were considered. With information transfer, increases in network conductance and capillary oxygen supply were amplified by factors of 4.9 +/- 0.2 and 9.4 +/- 1.1 (means +/- SE), relative to increases when information transfer was blocked. Information transfer by flow coupling alone, in which increased shear stress triggers vascular enlargement, gave amplifications of 4.0 +/- 0.3 and 4.9 +/- 0.5. Other information transfer mechanisms acting alone gave amplifications below 1.6. Thus shear-stress-mediated flow coupling is the main mechanism for the structural adjustment of feeding and draining vessel diameters to small changes in capillary oxygen demand.

Rheology of the microcirculation.

The main function of the microvasculature is the controlled exchange of materials with surrounding tissues. This necessitates a large vessel surface established by a high number of vessels with small diameters and thus an inherently high individual resistance to flow. The hydrodynamic resistance of a microvascular network with given angioarchitecture depends on the apparent viscosity of blood flowing in the microvessels. Apparent viscosity declines with decreasing diameter (the Fahraeus-Lindqvist effect) and is minimal at diameters of about 5-7 micrometers due to the optimal alignment of red cells with the flow. In vivo, a number of additional phenomena influence blood rheology and network hemodynamics. The distribution of blood flow and red cell flux within networks is influenced by the mechanics of red cell motion at individual diverging bifurcations (phase-separation effect). Furthermore, recent studies have revealed the presence of a thick endothelial surface layer ( approximately 0.5 micrometers) on the luminal surface of microvessels which is attached to the endothelial glycocalyx. This layer modulates flow resistance and may be relevant for a number of other processes such as inflammatory responses and blood coagulation. Information on microvascular rheology can be used to develop mathematical models of network hemodynamics and vascular adaptation to the local environment (angioadaptation), to investigate the complex interrelated mechanisms which establish and maintain functionally adequate microvascular networks.

OPS imaging of human microcirculation: a short technical report.

Despite the pivotal role of microcirculation in numerous diseases, techniques for the direct assessment of human microcirculation are limited. A new approach based on orthogonal polarization spectral (OPS) imaging (Cytoscan microscope) allows noninvasive observation of human microcirculation in all accessible tissue surfaces. Limitations remain: application of pressure with the instrument affects blood flow, lateral movement of tissue precludes continuous investigation of a given microvascular region, and blood flow velocities above 1 mm/s cannot be measured. We addressed these problems by (a) constructing an attachment to the probe, preventing direct contact of the instrument with the observed tissue area and allowing fixation of the tissue, and (b) implementing a double-flash spatial correlation technique extending the measuring range for blood flow velocities up to approximately 40 mm/s. The modified approach was tested in vitro and in vivo. Velocity readings correlated well with velocities of an external standard (r(2) = 0.99, range 1.9-33.8 mm/s). Pulsatile flow patterns synchronous with heart rate with maximal velocities of about 10 mm/s could be detected in arterioles of the human sublingual mucosa. The modified instrument may prove useful to investigate the microcirculation in the context of research, diagnosis and therapy control.

Blood flow and red blood cell deformation in nonuniform capillaries: effects of the endothelial surface layer.

OBJECTIVE: A theoretical model is used to examine the mechanics of red blood cell (RBC) motion in nonuniform capillaries. The model includes effects of the endothelial surface layer (ESL), which is a layer of macromolecules adjacent to the endothelium and which impedes plasma flow. METHODS: The motion of an RBC traversing a capillary with diameter varying sinusoidally between 5.4 microm and 7.4 microm is simulated numerically. The ESL is assumed to be 0.7-microm wide and deformable. Axisymmetric RBC shapes are assumed. Lubrication theory is used to analyze the motion of plasma around the RBC and through the ESL. RESULTS: In a nonuniform capillary with no ESL, moving RBCs undergo large transient deformations and predicted flow resistance is substantially higher than in a uniform capillary with the same mean diameter. The presence of a deformable ESL reduces the transient fluid shear stresses and deformations experienced by RBCs traversing a nonuniform capillary. With an ESL, the increase in flow resistance resulting from nonuniformity is less than twofold versus three- to fourfold with no ESL in vessel geometries with the same ESL-free luminal region. CONCLUSIONS: The presence of the ESL reduces the impact of capillary irregularity on flow resistance and may protect RBCs traversing irregular capillaries from damage due to large, rapidly fluctuating external stresses.

Cariporide (HOE 642) attenuates leukocyte activation in ischemia and reperfusion.

UNLABELLED: Cariporide (HOE 642) ameliorates myocardial ischemia/reperfusion (I/R) injury, by the well established reduction of cytosolic [Ca(2+)] in cardiac myocytes through inhibition of Na(+)/H(+) exchange. However, postischemic inflammation also contributes to I/R injury. We tested the hypothesis that cariporide also modulates the inflammatory response. The effect of cariporide on L-selectin expression by human leukocytes in vitro and leukocyte adhesion and emigration in the reperfused rat cremaster muscle in vivo were studied. The rat cremaster muscle was exteriorized for intravital videomicroscopy, induction of ischemia (90 min), and reperfusion (90 min). Eleven rats were pretreated with cariporide (9 mg/kg body weight IV) whereas 11 rats received saline. Leukocyte adhesion was quantified offline. Human venous blood was incubated with cariporide (3 micromol/L) or saline, stimulated with formyl- methionine-leucine-phenylalanine (10(-10)-10(-6) mol/L), and granulocyte L-selectin expression was analyzed by flow cytometry. Cariporide reduced leukocyte rolling and adhesion by approximately 35% and 45%, respectively, after 30 min of reperfusion. Leukocyte extravasation was decreased by approximately 85% after 90 min. Cariporide increased L-selectin shedding at each formyl-methionine-leucine-phenylalanine concentration, reducing the 50% effective dose from 9.95 to 4.68 nmol/L. Thus, cariporide may ameliorate I/R injury not only by the known reduction of cytosolic [Ca(2+)] in cardiomyocytes, but also by attenuating leukocyte-dependent inflammatory responses. Promotion of L-selectin shedding from activated leukocytes may present a mechanism underlying this newly detected effect. IMPLICATIONS: This study provides evidence that inhibition of Na(+)/H(+) exchange by cariporide (HOE 642) attenuates the postischemic inflammatory response. Leukocyte adhesion and emigration, assessed by in vivo microscopy, were markedly reduced in rat cremaster muscle, possibly because of increased L-selectin shedding of activated leukocytes as demonstrated by flow cytometry.

Structural adaptation of vascular networks: role of the pressure response.

Structural reductions in vessel luminal diameters in response to elevated pressure may play a role in the elevation of peripheral resistance generally observed in hypertension. In the present study, a theoretical model is used to simulate the effect of increased driving pressure on flow resistance in microvascular networks. The angioarchitecture (lengths and diameters of all segments, topology) of microvascular networks (n=6) in the rat mesentery was recorded by intravital microscopy. The model simulation of vascular adaptation in response to local wall shear stress, transmural pressure, and tissue PO(2) was used to predict changes in network pressure drop and flow resistance for a given change of driving pressure (DeltaP). For DeltaP increasing from 15% to 190% of the normotensive value, a 3.3-fold increase in flow resistance was observed (structural autoregulation). If vascular reactivity to pressure was suppressed, the resistance increase was abolished. Suppressing pressure sensitivity also led to a rise in mean capillary pressure at normal driving pressure from 23.8+/-7.3 mm Hg to 34+/-6.9 mm Hg. These results indicate that low capillary pressure levels as well as structural autoregulation depend on vascular responses to circumferential wall stress (corresponding to pressure). This tendency of peripheral vascular beds to increase flow resistance for a given increase of bulk flow or driving pressure may amplify and stabilize blood pressure elevation in the development of hypertension.

Structural adaptation of microvascular networks: functional roles of adaptive responses.

Terminal vascular beds continually adapt to changing demands. A theoretical model is used to simulate structural diameter changes in response to hemodynamic and metabolic stimuli in microvascular networks. Increased wall shear stress and decreased intravascular pressure are assumed to stimulate diameter increase. Intravascular partial pressure of oxygen (PO(2)) is estimated for each segment. Decreasing PO(2) is assumed to generate a metabolic stimulus for diameter increase, which acts locally, upstream via conduction along vessel walls, and downstream via metabolite convection. By adjusting the sensitivities to these stimuli, good agreement is achieved between predicted network characteristics and experimental data from microvascular networks in rat mesentery. Reduced pressure sensitivity leads to increased capillary pressure with reduced viscous energy dissipation and little change in tissue oxygenation. Dissipation decreases strongly with decreased metabolic response. Below a threshold level of metabolic response flow shifts to shorter pathways through the network, and oxygen supply efficiency decreases sharply. In summary, the distribution of vessel diameters generated by the simulated adaptive process allows the network to meet the functional demands of tissue while avoiding excessive viscous energy dissipation.