Differing effects of histamine and serotonin on microvascular permeability in anaesthetized rats

The mast cell: A Janus in kidney transplants

Mast cells (MCs) are innate immune cells with a versatile set of functionalities, enabling them to orchestrate immune responses in various ways. Aside from their known role in allergy, they also partake in both allograft tolerance and rejection through interaction with regulatory T cells, effector T cells, B cells and degranulation of cytokines and other mediators. MC mediators have both pro- and anti-inflammatory actions, but overall lean towards pro-fibrotic pathways. Paradoxically, they are also seen as having potential protective effects in tissue remodeling post-injury. This manuscript elaborates on current knowledge of the functional diversity of mast cells in kidney transplants, combining theory and practice into a MC model stipulating both protective and harmful capabilities in the kidney transplant setting.

Water intake releases serotonin from enterochromaffin cells in rat jejunal villi

The present study aims to investigate the roles of water intake in serotonin production and release in rat jejunum. We evaluated the changes in concentrations of serotonin in the portal vein and mesenteric lymph vessel induced by the intragastric administration of distilled water. The density of granules in enterochromaffin cells and the immunoreactivity of serotonin in the jejunal villi were investigated before and after water intake. The effects of intravenous administration of serotonin and/or ketanserin on mesenteric lymph flow and concentrations of albumin and IL-22 in the lymph were also addressed. Water intake increased serotonin concentration in the portal vein, but not in the mesenteric lymph vessel. The flux of serotonin through the portal vein was significantly larger than that through the mesenteric lymph vessel. Water intake decreased the density of granules in the enterochromaffin cells and increased the immunoreactivity of serotonin in the jejunal villi. The intravenous administration of serotonin increased significantly mesenteric lymph flow and the concentrations of albumin and IL-22; both were significantly reduced by the intravenous pretreatment with ketanserin. We showed that serotonin released from enterochromaffin cells by water intake was mainly transported through the portal vein. Additionally, serotonin in blood was found to increase mesenteric lymph formation with permeant albumin in the jejunal villi via the activation of 5-HT2 receptor.

Regulation of the glucose supply from capillary to tissue examined by developing a capillary model

A new glucose transport model relying upon diffusion and convection across the capillary membrane was developed, and supplemented with tissue space and lymph flow. The rate of glucose utilization (J util) in the tissue space was described as a saturation function of glucose concentration in the interstitial fluid (C glu,isf), and was varied by applying a scaling factor f to J max. With f = 0, the glucose diffusion ceased within ~20 min. While, with increasing f, the diffusion was accelerated through a decrease in C glu,isf, but the convective flux remained close to resting level. When the glucose supplying capacity of the capillary was measured with a criterion of J util /J max = 0.5, the capacity increased in proportion to the number of perfused capillaries. A consistent profile of declining C glu,isf along the capillary axis was observed at the criterion of 0.5 irrespective of the capillary number. Increasing blood flow scarcely improved the supplying capacity.

Sialic acids regulate microvessel permeability, revealed by novel in vivo studies of endothelial glycocalyx structure and function

Key points

We have developed novel techniques for paired, direct, real‐time in vivo quantification of endothelial glycocalyx structure and associated microvessel permeability.

Commonly used imaging and analysis techniques yield measurements of endothelial glycocalyx depth that vary by over an order of magnitude within the same vessel.

The anatomical distance between maximal glycocalyx label and maximal endothelial cell plasma membrane label provides the most sensitive and reliable measure of endothelial glycocalyx depth.

Sialic acid residues of the endothelial glycocalyx regulate glycocalyx structure and microvessel permeability to both water and albumin.

Abstract

The endothelial glycocalyx forms a continuous coat over the luminal surface of all vessels, and regulates multiple vascular functions. The contribution of individual components of the endothelial glycocalyx to one critical vascular function, microvascular permeability, remains unclear. We developed novel, real‐time, paired methodologies to study the contribution of sialic acids within the endothelial glycocalyx to the structural and functional permeability properties of the same microvessel in vivo. Single perfused rat mesenteric microvessels were perfused with fluorescent endothelial cell membrane and glycocalyx labels, and imaged with confocal microscopy. A broad range of glycocalyx depth measurements (0.17–3.02 μm) were obtained with different labels, imaging techniques and analysis methods. The distance between peak cell membrane and peak glycocalyx label provided the most reliable measure of endothelial glycocalyx anatomy, correlating with paired, numerically smaller values of endothelial glycocalyx depth (0.078 ± 0.016 μm) from electron micrographs of the same portion of the same vessel. Disruption of sialic acid residues within the endothelial glycocalyx using neuraminidase perfusion decreased endothelial glycocalyx depth and increased apparent solute permeability to albumin in the same vessels in a time‐dependent manner, with changes in all three true vessel wall permeability coefficients (hydraulic conductivity, reflection coefficient and diffusive solute permeability). These novel technologies expand the range of techniques that permit direct studies of the structure of the endothelial glycocalyx and dependent microvascular functions in vivo, and demonstrate that sialic acid residues within the endothelial glycocalyx are critical regulators of microvascular permeability to both water and albumin.

We have developed novel techniques for paired, direct, real‐time in vivo quantification of endothelial glycocalyx structure and associated microvessel permeability.

Commonly used imaging and analysis techniques yield measurements of endothelial glycocalyx depth that vary by over an order of magnitude within the same vessel.

The anatomical distance between maximal glycocalyx label and maximal endothelial cell plasma membrane label provides the most sensitive and reliable measure of endothelial glycocalyx depth.

Sialic acid residues of the endothelial glycocalyx regulate glycocalyx structure and microvessel permeability to both water and albumin.

Effect of high-voltage electrical stimulation on the albumin and histamine serum concentrations, edema, and pain in acute joint inflammation of rats

BACKGROUND:

The mechanism by which high-voltage electrical stimulation (HVPC) acts on edema reduction is unknown.

OBJECTIVE:

To assess the effect of HVPC with negative polarity (-) applied to the ankle of rats with acute joint inflammation.

METHOD:

Sixty-four rats were divided into four groups (n=16): inflamed+HVPC(-), 0.03 mL application of ι-carrageenan (3%) to the tibiotarsal joint plus HVPC(-); inflamed+HVPC placebo, carrageenan application and HVPC placebo; normal+HVPC(-), HVPC application(-); and normal control, no intervention. The HVPC(-) 100 Hz at a submotor level was applied daily for 45 min on three consecutive days. The variables were pain, hind-foot volume, and serum histamine and albumin assessed before and during the 48 hours following inflammation. The variables were compared using the t test, one-way ANOVA, nested ANOVA for repeated measures, and the post hoc Bonferroni test. Analysis of covariance was applied to adjust the effects of HVPC(-) by measurements of pain, inflammation, albumin, and histamine at 24 h, and the final weight was compared to the other groups. The significance level was set at p<0.05.

RESULTS:

There were no differences between the inflamed+HVPC(-) and inflamed+HVPC placebo groups in terms of pain or edema (p>0.05). Albumin was reduced in the groups that received the intervention, but there was no differences between them. There was only a 24 hour increase in histamine with the normal+HVPC(-) (p=0.0001) and inflamed+HVPC placebo groups (p=0.01) compared to the normal control group.

CONCLUSIONS:

The results of the present study suggest that HVPC(-) with the parameters employed did not reduce pain or edema and did not change serum albumin or histamine levels,, which indicates the inability of this resource to have a positive effect when treating treat acute joint inflammation.

Brain-derived microparticles induce systemic coagulation in a murine model of traumatic brain injury

Traumatic brain injury (TBI) is associated with coagulopathy, although it often lacks 2 key risk factors: severe bleeding and significant fluid resuscitation associated with hemorrhagic shock. The pathogenesis of TBI-associated coagulopathy remains poorly understood. We tested the hypothesis that brain-derived microparticles (BDMPs) released from an injured brain induce a hypercoagulable state that rapidly turns into consumptive coagulopathy. Here, we report that mice subjected to fluid percussion injury (1.9 ± 0.1 atm) developed a BDMP-dependent hypercoagulable state, with peak levels of plasma glial cell and neuronal BDMPs reaching 17 496 ± 4833/μL and 18 388 ± 3657/μL 3 hours after TBI, respectively. Uninjured mice injected with BDMPs developed a dose-dependent hyper-turned hypocoagulable state measured by a progressively prolonged clotting time, fibrinogen depletion, and microvascular fibrin deposition in multiple organs. The BDMPs were 50 to 300 nm with intact membranes, expressing neuronal or glial cell markers and procoagulant phosphatidylserine and tissue factor. Their procoagulant activity was greater than platelet microparticles and was dose-dependently blocked by lactadherin. Microparticles were produced from injured hippocampal cells, transmigrated through the disrupted endothelial barrier in a platelet-dependent manner, and activated platelets. These data define a novel mechanism of TBI-associated coagulopathy in mice, identify early predictive markers, and provide alternative therapeutic targets.

Myocardial gene transfer: routes and devices for regulation of transgene expression by modulation of cellular permeability

Heart diseases are major causes of morbidity and mortality in Western society. Gene therapy approaches are becoming promising therapeutic modalities to improve underlying molecular processes affecting failing cardiomyocytes. Numerous cardiac clinical gene therapy trials have yet to demonstrate strong positive results and advantages over current pharmacotherapy. The success of gene therapy depends largely on the creation of a reliable and efficient delivery method. The establishment of such a system is determined by its ability to overcome the existing biological barriers, including cellular uptake and intracellular trafficking as well as modulation of cellular permeability. In this article, we describe a variety of physical and mechanical methods, based on the transient disruption of the cell membrane, which are applied in nonviral gene transfer. In addition, we focus on the use of different physiological techniques and devices and pharmacological agents to enhance endothelial permeability. Development of these methods will undoubtedly help solve major problems facing gene therapy.

Spatio-temporal development of the endothelial glycocalyx layer and its mechanical property in vitro

The endothelial glycocalyx is a thin layer of polysaccharide matrix on the luminal surface of endothelial cells (ECs), which contains sulphated proteoglycans and glycoproteins. It is a mechanotransducer and functions as an amplifier of the shear stress on ECs. It controls the vessel permeability and mediates the blood-endothelium interaction. This study investigates the spatial distribution and temporal development of the glycocalyx on cultured ECs, and evaluates mechanical properties of the glycocalyx using atomic force microscopy (AFM) nano-indentation. The glycocalyx on human umbilical vein endothelial cells (HUVECs) is observed under a confocal microscope. Manipulation of the glycocalyx is achieved using heparanase or neuraminidase. The Young's modulus of the cell membrane is calculated from the force-distance curve during AFM indentation. Results show that the glycocalyx appears predominantly on the edge of cells in the early days in culture, e.g. up to day 5 after seeding. On day 7, the glycocalyx is also seen in the apical area of the cell membrane. The thickness of the glycocalyx is approximately 300 nm-1 μm. AFM indentation reveals the Young's modulus of the cell membrane decreases from day 3 (2.93 ± 1.16 kPa) to day 14 (0.35 ± 0.15 kPa) and remains unchanged to day 21 (0.33 ± 0.19 kPa). Significant difference in the Young's modulus is also seen between the apical (1.54 ± 0.58 kPa) and the edge (0.69 ± 0.55 kPa) of cells at day 7. By contrast, neuraminidase-treated cells (i.e. without the glycocalyx) have similar values between day 3 (3.18 ± 0.88 kPa), day 14 (2.12 ± 0.78 kPa) and day 21 (2.15 ± 0.48 kPa). The endothelial glycocalyx in vitro shows temporal development in the early days in culture. It covers predominantly the edge of cells initially and appears on the apical membrane of cells as time progresses. The Young's modulus of the glycocalyx is deduced from Young's moduli of cell membranes with and without the glycocalyx layer. Our results show the glycocalyx on cultured HUVECs has a Young's modulus of approximately 0.39 kPa.

Microvascular fluid exchange and the revised Starling principle

Microvascular fluid exchange (flow J(v)) underlies plasma/interstitial fluid (ISF) balance and oedematous swelling. The traditional form of Starling's principle has to be modified in light of insights into the role of ISF pressures and the recognition of the glycocalyx as the semipermeable layer of endothelium. Sum-of-forces evidence and direct observations show that microvascular absorption is transient in most tissues; slight filtration prevails in the steady state, even in venules. This is due in part to the inverse relation between filtration rate and ISF plasma protein concentration; ISF colloid osmotic pressure (COP) rises as J(v) falls. In some specialized regions (e.g. kidney, intestinal mucosa), fluid absorption is sustained by local epithelial secretions, which flush interstitial plasma proteins into the lymphatic system. The low rate of filtration and lymph formation in most tissues can be explained by standing plasma protein gradients within the intercellular cleft of continuous capillaries (glycocalyx model) and around fenestrations. Narrow breaks in the junctional strands of the cleft create high local outward fluid velocities, which cause a disequilibrium between the subglycocalyx space COP and ISF COP. Recent experiments confirm that the effect of ISF COP on J(v) is much less than predicted by the conventional Starling principle, in agreement with modern models. Using a two-pore system model, we also explore how relatively small increases in large pore numbers dramatically increase J(v) during acute inflammation.

Systemic vascular leakage associated with dengue infections - the clinical perspective

Vascular leakage is the most serious complication of dengue infection. However, despite considerable progress in understanding the immunological derangements associated with dengue, the pathogenic mechanisms underlying the change in vascular permeability remain unclear. Lack of suitable model systems that manifest permeability characteristics similar to human vascular endothelium has seriously impeded research in this area. Similarly, limited knowledge of the factors regulating intrinsic microvascular permeability in health, together with limited understanding of the alterations seen in disease states in general, has also hampered progress. Fortunately considerable advances have been made in the field of endothelial biology in recent years, especially following appreciation of the crucial role played by the endothelial surface glycocalyx, acting in concert with underlying cellular structures, in regulating fluid flow across the microvasculature. We review what is known about vascular leakage during dengue infections, particularly in relation to current knowledge of vascular physiology, and discuss potential areas of research that may help to elucidate the complex nature of this singular phenomenon in the future.

Edemagenic gain and interstitial fluid volume regulation

Under physiological conditions, interstitial fluid volume is tightly regulated by balancing microvascular filtration and lymphatic return to the central venous circulation. Even though microvascular filtration and lymphatic return are governed by conservation of mass, their interaction can result in exceedingly complex behavior. Without making simplifying assumptions, investigators must solve the fluid balance equations numerically, which limits the generality of the results. We thus made critical simplifying assumptions to develop a simple solution to the standard fluid balance equations that is expressed as an algebraic formula. Using a classical approach to describe systems with negative feedback, we formulated our solution as a "gain" relating the change in interstitial fluid volume to a change in effective microvascular driving pressure. The resulting "edemagenic gain" is a function of microvascular filtration coefficient (K(f)), effective lymphatic resistance (R(L)), and interstitial compliance (C). This formulation suggests two types of gain: "multivariate" dependent on C, R(L), and K(f), and "compliance-dominated" approximately equal to C. The latter forms a basis of a novel method to estimate C without measuring interstitial fluid pressure. Data from ovine experiments illustrate how edemagenic gain is altered with pulmonary edema induced by venous hypertension, histamine, and endotoxin. Reformulation of the classical equations governing fluid balance in terms of edemagenic gain thus yields new insight into the factors affecting an organ's susceptibility to edema.

Postinfectious irritable bowel syndrome: a long-term consequence of bacterial gastroenteritis

Irritable bowel syndrome (IBS) is a commonly diagnosed disease characterized by gastrointestinal symptoms that may be associated with psychological illness and emotional problems. The prevalence rate worldwide for IBS ranges from 10 to 20% and is higher for women than for men. IBS imposes a substantial financial burden on both patients and employers because of increased medical costs and decreased work productivity. Recent studies indicate that inflammatory processes involving the gastrointestinal tract are strongly correlated with IBS. Acute bacterial gastroenteritis has been linked with the onset of symptoms in approximately 15% of patients diagnosed with IBS; these cases have been called postinfectious IBS. Organisms commonly associated with postinfectious IBS include the foodborne pathogens Campylobacter, Escherichia coli, Salmonella, and Shigella. The pathologic changes associated with postinfectious IBS are likely due to inflammatory reactions induced by the infecting organisms. Postinfectious IBS should be recognized as a potential long-term consequence of foodborne gastroenteritis.

Catheter-mediated subselective intracoronary gene delivery to the rabbit heart: introduction of a novel method

BACKGROUND

Recent studies suggest that gene therapy using replication-deficient adenoviruses will benefit treatment of cardiovascular diseases including heart failure. A persistent hurdle is the effective and reproducible delivery of a transgene to the myocardium with minimal iatrogenic morbidity. In this study, we sought to design a relatively non-invasive percutaneous gene delivery system that would maximize cardiac transgene expression and minimize mortality after intracoronary adenovirus injection.

METHODS

Adult rabbits received a left circumflex coronary artery (LCx) infusion of 5x10(11) total viral particles of an adenovirus containing the marker transgene beta-galactosidase (Adeno-betaGal) via either a continuous infusion method utilizing an oxygenated, normothermic, physiologic pH Krebs solution driven by a Langendorff apparatus (n=12) or a timed bolus and set concentration at a constant infusion rate to the LCx (n=12). Six rabbits underwent global transgene delivery via an invasive method involving intraventricular delivery and aortic root cross-clamping. The efficacy of transgene expression via these three distinct delivery methods was determined in the left ventricle at 5 days by histological staining and colorimetric quantification assay.

RESULTS

While the open-chest, aortic cross-clamping method provides the highest level of gene expression throughout the heart, the morbidity of this procedure is clinically prohibitive. Percutaneous LCx delivery of Adeno-betaGal using the Langendorff apparatus was associated with the lowest morbidity and mortality while still supporting significant myocardial gene expression.

CONCLUSIONS

Percutaneous delivery of an adenovirus solution using a continuous infusion of oxygenated Krebs solution via a Langendorff apparatus appears to be a gene delivery modality offering the best compromise of gene expression and clinical utility to maximize any potential therapeutic outcome.

Plasma from women with severe pre-eclampsia increases microvascular permeability in an animal model in vivo

Pre-eclampsia results in oedema, hypertension and proteinuria, and is associated with increased vascular permeability. A number of studies have pointed to the existence of a circulating macromolecule that induces this endothelial dysfunction. To test whether this circulating factor could increase vascular permeability, we have measured the effect of dialysed human plasma from pregnant women with mild or severe pre-eclampsia (pre-eclamptic toxaemia). Plasma was collected from patients with mild or severe pre-eclampsia and from normotensive women. Plasma was dialysed against frog Ringer's solution using a 12-14 kDa molecular-mass cut-off dialysis tubing. pi c (colloid osmotic pressure) was measured with a modified Hansen oncometer. Lp (hydraulic conductivity) and sigma (oncotic reflection coefficient) were measured in individually perfused frog mesenteric microvessels using the Landis-Michel technique during perfusion with dialysed plasma. Perfusion of vessels with normal plasma or plasma from patients with mild pre-eclampsia did not alter either Lp or sigma. However, plasma from patients with severe pre-eclampsia resulted in a 3.8+/-0.3-fold increase in Lp and a reduction in sigma from 0.96+/-0.03 to 0.80+/-0.11. There was a significant correlation between the change in sigma and the change in Lp, suggesting that the increase in permeability was due to an increase in pore size in these vessels. A circulating macromolecule in human plasma in severe pre-eclampsia is therefore able to increase vascular permeability in an animal model. The nature of the circulating macromolecule is not known, except that it is, or is bound to, a molecule greater than 12 kDa.

PAF- and bradykinin-induced hyperpermeability of rat venules is independent of actin-myosin contraction

We tested the hypothesis that acutely induced hyperpermeability is dependent on actin-myosin contractility by using individually perfused mesentery venules of pentobarbital-anesthetized rats. Venule hydraulic conductivity (Lp) was measured to monitor hyperpermeability response to the platelet-activating factor (PAF) 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine or bradykinin. Perfusion with PAF (10 nM) induced a robust transient high Lp [24.3 +/- 1.7 x 10-7 cm/(s.cmH2O)] that peaked in 8.9 +/- 0.5 min and then returned toward control Lp [1.6 +/- 0.1 x 10-7 cm/(s.cmH2O)]. Reconstruction of venular segments with the use of transmission electron microscopy of serial sections confirmed that PAF induces paracellular inflammatory gaps. Specific inhibition of myosin light chain kinase (MLCK) with 1-10 microM 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7) failed to block the PAF Lp response or change the time-to-peak Lp. ML-7 reduced baseline Lp 50% at 40 min of pretreatment. ML-7 also increased the rate of recovery from PAF hyperpermeability measured as the decrease of half-time of recovery from 4.8 +/- 0.7 to 3.2 +/- 0.3 min. Inhibition of myosin ATPase with 5-20 mM 2,3-butanedione 2-monoxime also failed to alter the hyperpermeability response to PAF. Similar results were found using ML-7 to modulate responses. These experiments indicate that an actin-myosin contractile mechanism modulated by MLCK does not contribute significantly to the robust initial increase in permeability of rat venular microvessels exposed to two common inflammatory mediators. The results are consistent with paracellular gap formation by local release of endothelial-endothelial cell adhesion structures in the absence of contraction by the actin-myosin network.

Structural mechanisms of acute VEGF effect on microvessel permeability

To investigate the ultrastructural mechanisms of acute microvessel hyperpermeability by vascular endothelial growth factor (VEGF), we combined a mathematical model (J Biomech Eng 116: 502-513, 1994) with experimental data of the effect of VEGF on microvessel hydraulic conductivity (L(p)) and permeability of various-sized solutes. We examined the effect of VEGF on microvessel permeability to a small solute (sodium fluorescein, Stokes radius 0.45 nm), an intermediate solute (alpha-lactalbumin, Stokes radius 2.01 nm), and a large solute [albumin (BSA), Stokes radius 3.5 nm]. Exposure to 1 nM VEGF transiently increased apparent permeability to 2.3, 3.3, and 6.2 times their baseline values for sodium fluorescein, alpha-lactalbumin, and BSA, respectively, within 30 s, and all returned to control within 2 min. On the basis of L(p) (DO Bates and FE Curry. Am J Physiol Heart Circ Physiol 271: H2520-H2528, 1996) and permeability data, the prediction from the model suggested that the most likely structural changes in the interendothelial cleft induced by VEGF would be a approximately 2.5-fold increase in its opening width and partial degradation of the surface glycocalyx.

Reduced blood-to-tissue albumin movement after plasmapheresis

We tested the hypothesis that a decrease in the blood-to-tissue movement of albumin contributes to the recovery of plasma albumin and plasma volume after acute plasma protein depletion (plasmapheresis). Awake and unrestrained male Sprague-Dawley rats (220-320 g) fitted with jugular catheters were plasmapheresed, and plasma volume, plasma albumin, and total plasma protein content were measured at 1, 5, 24, and 48 h postplasmapheresis. Plasma volume recovered to baseline within 1 h (4.6 +/- 0.42 vs. 4.7 +/- 0.46 mL/100 g body weight (bw), remained at baseline from 5 h to 24 h but increased to 5.5 + 0.57 mL/100 g bw at 48 h (P < 0.05). Plasma albumin and total protein content recovered rapidly but remained below baseline levels at 1 h (10.05 +/- 0.98 vs. 12.33 +/- 1.29 and 19.75 +/- 1.75 vs. 24.73 +/- 2.56 mg/100 g bw, respectively). Plasma protein content retumed to baseline by 5 h of recovery. Tissue uptake of I125-labeled albumin decreased in the heart, skin, skeletal muscle, and small Intestines of plasmapheresed rats (P < 0.05). These data support the hypothesis that a reduction in albumin efflux from the vascular space contrlbutes to the recovery of plasma albumin and total protein content during plasma volume recovery and eventual expansion after plasmapheresis.

Endotoxin increases both protein and fluid microvascular permeability in cat skeletal muscle

OBJECTIVE

To evaluate effects of lipopolysaccharide (endotoxin) on protein and fluid permeability in a whole organ skeletal muscle preparation.

DESIGN

Controlled, prospective laboratory study.

SETTING

University research laboratory.

SUBJECTS

Eleven adult male cats.

INTERVENTIONS

The study was performed on the autoperfused and denervated calf muscles of the cat hindlimb placed in a fluid-filled plethysmograph. The endotoxin-induced change in the osmotic reflection coefficient for albumin was used as a measure of alteration in protein permeability of the microvascular wall, and the simultaneous change in capillary filtration coefficient was used as a measure of alteration in fluid permeability. Endotoxin as a bolus infusion (1 mg/kg iv) was given to six cats, and another five cats given only the vehicle (NaCl) were used as control.

MEASUREMENTS AND MAIN RESULTS

Arterial blood flow, arterial and venous blood pressures, total vascular resistance, and tissue volume changes were measured continuously. The ratio between the osmotic reflection coefficients for albumin on two occasions (before and about 1.5 hr after endotoxin infusion) was calculated from the Starling fluid equilibrium equation. This was performed by measurement of the maximum absorption rate from an isovolumetric state by an intravenous bolus infusion of 20% human albumin (0.6 g/kg) and the capillary filtration coefficient. Albumin concentrations were measured before and after the albumin infusion to correct for effects of difference in plasma volume on the induced increase in colloid osmotic pressure. We found that the osmotic reflection coefficient for albumin was reduced by 30% (p <.05), and the capillary filtration coefficient was increased by 31% (p <.05) by endotoxin. No changes were seen in the vehicle experiments.

CONCLUSION

Endotoxin causes a significant increase in both protein and fluid microvascular wall permeability. These effects may explain the marked leakage of plasma to the interstitium that is often seen in critically ill patients with sepsis and systemic inflammatory response syndrome.

Contribution of F-actin to barrier properties of the blood-joint pathway

OBJECTIVES

Because fibroblast filamentous actin (F-actin) influences cutaneous interstitial matrix swelling pressure (5), we investigated whether F-actin in fibroblast-derived synoviocytes influences the hydraulic permeability of the trans-synovial interstitial pathway. The study also tested whether F-actin in fenestrated synovial endothelium contributes to the blood-joint barrier in vivo.

METHODS

The clearance of Evans blue-albumin (EVA) from plasma into the knee joint cavity was determined in joint infused with F-actin disrupting cytochalasin D (1-200 microM), latrunculin B (100 microM) or vehicle in anesthetized rabbits. The hydraulic permeability of the lining was determined as the slope relating net trans-synovial flow Q(s) to intra-articular pressure P(j). Synovium was examined histologically after i.v. Monastral blue to assess endothelial leakiness.

RESULTS

EVA permeation in vivo was increased up to 25-fold by cytochalasin (p = 0.0002, ANOVA), with an EC(50) of 23 microM (95% confidence limits 13-43 microM). Washout quickly reversed the increase. Latrunculin had a similar effect. F-actin disruption switched Q(s) from drainage (control) to filtration into the cavity at low P(j) in vivo and raised the conductance Q(s)/dP(j) by 2.13 (p = 0.001, ANOVA). Circulatory arrest abolished these effects. Monastral blue revealed numerous endothelial leaks.

CONCLUSIONS

F-actin is crucial to the barrier function of fenestrated endothelium in situ. No significant effect of synoviocyte F-actin on matrix permeability was detected.

Measurement of hydraulic conductivity of single perfused Rana mesenteric microvessels between periods of controlled shear stress

A new method for the determination of hydraulic conductivity in individually perfused microvessels in vivo is described. A vessel is cannulated at both ends with glass micropipettes and the fluid filtration rate across the vessel wall measured from the velocities of red cells when the pressure in the micropipettes is balanced. Hydraulic conductivity measured using this double-cannulation method (2.6 (+/- 0.9) x 10(-7) cm s(-1) cmH(2)O(-1)) was not significantly different from that measured using a previously described technique in the same vessel (2.4 (+/- 0.9) x 10(-7) cm s(-1) cmH(2)O(-1) using the Landis-Michel method). Shear stress on the vessel wall was controlled by changing the difference between the inflow and outflow pressures during periods of perfusion. The volume flow through the vessel, calculated from red cell velocity either in the vessel or in the pipette, was linearly proportional to this pressure difference. Higher flow rates could only be calculated from red cell velocities in the micropipette. There was no relationship between the imposed shear stress and intervening measurements of hydraulic conductivity (r = 0.029). This novel technique has advantages over the Landis-Michel method, which include the control of outflow resistance, the measurement of shear stress under conditions of controlled pressure, the elimination of compression damage to the vessel (since vessel occlusion is not necessary) and assessment of hydraulic conductivity over the same length of vessel throughout the experiment. The measurement of solute concentrations by indwelling micropipette electrodes and the collection of perfusate for analysis are other possibilities.

Restoration of deficient membrane proteins in the cardiomyopathic hamster by in vivo cardiac gene transfer

BACKGROUND

One of the most important problems in developing in vivo cardiac gene transfer has been low transfection efficiency. A novel in vivo technique was developed, tested in normal hamsters, and the feasibility of restoring a deficient structural protein (delta-sarcoglycan) in the cardiomyopathic (CM) hamster evaluated.

METHODS AND RESULTS

Adenoviral (AdV) vectors encoding either the lacZ gene or delta-sarcoglycan gene were constructed. Hypothermia was achieved in hamsters by external body cooling to a rectal temperature of 18 to 25 degrees C. Through a small thoracotomy, the ascending aorta and the main pulmonary artery were occluded with snares, and cardioplegic solution containing histamine was injected into the aortic root; viral constructs were delivered 3 to 5 minutes later followed by release of the occluders and rewarming. Four days later, homogeneous beta-galactosidase expression was detected throughout the ventricles of the normal hearts (average 77.3+/-9.0% [SEM] of left ventricular myocytes). At 1 and 3 weeks after transfection, immunostaining showed extensive restoration of delta-sarcoglycan as well as alpha- and beta-sarcoglycan proteins to the myocyte membranes, despite loss of beta-galactosidase expression at 3 weeks. Also, at 3 weeks after gene transfer, there was significantly less progression of left ventricular dysfunction assessed as percent change in fractional shortening compared with controls.

CONCLUSIONS

This study demonstrates the feasibility of high efficiency in vivo myocardial gene transfer and shows application in improving the level of a deficient cardiac structural protein and cardiac function in CM hamsters. The approach should be useful for assessing effects of expressing other genes that influence the structure or function of the normal and failing heart.

Influence of tilapia mast cell lysate on vascular permeability

Kinetics of vascular permeability was determined by measuring the amount of Evans blue leaked into the tilapia mast cell (tMC)-lysate injection site. Injection with tMC lysate enhanced the vascular permeability. The response consisted of three distinct phases, the first started immediately after the injection, the second started at about 2 h, reaching its maximum at 4 h, and the third response started at 12 h and continued for more than 24 h. Heating of the tMC lysate at 100 degrees C for 10 min had no effect on the first response, while the second response was significantly reduced by heating at 50 degrees C for 10 min. The tMCs seem to have two kinds of factors that enhance vascular permeability. The tMC lysate induced Ca2+ uptake by cultured tilapia endothelial cells, indicating that tMC products directly activate the endothelial cells and increase vascular permeability similar to products of mammalian mast cells. These results indicate that with respect to influence on vascular permeability tilapia mast cells resemble the mast cells of mammals.

Dextran, gelatin, and hydroxyethyl starch do not affect permeability for albumin in cat skeletal muscle

OBJECTIVE

To evaluate the effects of the three commercially available colloid solutions, 6% dextran 70, 6% hydroxyethyl starch (HES) 200/0.5, and 3.5% urea-linked gelatin on permeability for human albumin in a skeletal muscle in vivo model by evaluating their effects on the reflection coefficient for albumin.

DESIGN

Controlled laboratory study.

SETTING

University research laboratory.

SUBJECTS

Eighteen adult cats.

INTERVENTIONS

The autoperfused and denervated calf muscles of the cat hindlimb were placed in a plethysmograph. The transvascular fluid absorption induced by an increase in the colloid osmotic pressure following a fixed intravenous bolus of human albumin was analyzed, first before start of, and then during an intra-arterial infusion to, the muscle preparation of the synthetic colloid to be analyzed. Capillary filtration coefficient as a measure of microvascular fluid permeability (conductance) was analyzed before and after start of the synthetic colloid.

MEASUREMENTS AND MAIN RESULTS

Arterial blood flow, arterial and venous blood pressures, total vascular resistance, tissue volume changes, capillary filtration coefficient, and plasma volume were measured before and during the colloid infusion. According to the Starling fluid equilibrium, the ratio between the reflection coefficients for albumin on two occasions (before and after infusion of the synthetic colloid) can be calculated from the maximum osmotic absorption rates induced by a fixed intravenous bolus infusion of albumin and from the capillary filtration coefficients. Obtained data were adjusted for different plasma volume at the two occasions. We found that none of the three synthetic colloids analyzed had any significant effect on the reflection coefficient for albumin.

CONCLUSION

An effect on albumin microvascular permeability of the synthetic colloids dextran 70, HES 200/0.5, and urea-linked gelatin could not be shown by a method analyzing their effect on the reflection coefficient for albumin.

Flow modulates the transport of K+ through the walls of single perfused mesenteric venules in anaesthetised rats

1. We have investigated the effects of varying flow velocity (U) upon permeability to potassium ions (PK) of single perfused mesenteric venules in anaesthetised rats. PK was estimated using a development of the single bolus microperfusion technique at chosen flow velocities in the range of 300 to 6000 microm s-1. 2. In an initial study on 12 vessels, there was a strong positive correlation between PK and U. This was described by the relation: PK = 0.0053U + 8.86, where PK and U are both expressed in micrometres per second (microm s-1). 3. The addition of the nitric oxide (NO) synthase inhibitors (20 micromol l-1) N G-monomethyl-L-arginine (L-NMMA) and N G-nitro L-arginine (L-NNA) to the superfusate abolished the positive correlation between PK and U. The addition of D-NNA (20 micromol l-1) did not change the relation between PK and U where the median value for the slope of the relation was 57.7 (+/- 58.7 interquartile (IQR)) x 10-4 (n = 4). The addition of L-arginine (200 micromol l-1) restored the relation between PK and U where the slope of the relation was increased from 3.9 (+/- 16.3 IQR) x 10-4 to 69.2 (+/- 13.5 IQR) x 10-4 (n = 7). 4. The addition of the guanylate cyclase inhibitor LY83583 (10 micromol l-1) abolished the positive correlation between PK and U (n = 6). 5. Our data suggest that the flow modulates the potassium permeability through the walls of single perfused rat mesenteric venules via a NO-cGMP-dependent process.

Microvascular permeability

This review addresses classical questions concerning microvascular permeabiltiy in the light of recent experimental work on intact microvascular beds, single perfused microvessels, and endothelial cell cultures. Analyses, based on ultrastructural data from serial sections of the clefts between the endothelial cells of microvessels with continuous walls, conform to the hypothesis that different permeabilities to water and small hydrophilic solutes in microvessels of different tissues can be accounted for by tortuous three-dimensional pathways that pass through breaks in the junctional strands. A fiber matrix ultrafilter at the luminal entrance to the clefts is essential if microvascular walls are to retain their low permeability to macromolecules. Quantitative estimates of exchange through the channels in the endothelial cell membranes suggest that these contribute little to the permeability of most but not all microvessels. The arguments against the convective transport of macromolecules through porous pathways and for the passage of macromolecules by transcytosis via mechanisms linked to the integrity of endothelial vesicles are evaluated. Finally, intracellular signaling mechanisms implicated in transient increases in venular microvessel permeability such as occur in acute inflammation are reviewed in relation to studies of the molecular mechanisms involved in signal transduction in cultured endothelial cells.

The chronic effect of vascular endothelial growth factor on individually perfused frog mesenteric microvessels

1. Hydraulic conductivity (Lp) of the wall of perfused microvessels has previously been shown to be chronically increased 24 h after a 10 min perfusion with vascular endothelial growth factor (VEGF). In order to investigate this further, Lp and the effective oncotic pressure difference (f3DeltaPi) acting across the vessel walls was measured before exposure to VEGF and 24 h later after the mesentery had been replaced in the abdominal cavity. 2. Acute 10 min perfusion with VEGF did not chronically change f3DeltaPi despite chronically increasing Lp 6.8 +/- 1.2-fold. This suggests that pathways formed 24 h after perfusion with VEGF which increase hydraulic conductivity of the capillary walls have the same reflection coefficient as those present before VEGF. 3. Acute 10 min perfusion with VEGF significantly increased the diameter of vessels after 24 h by 48 +/- 13%. To determine whether this was due to changes in the compliance of the vessel wall, the distensibility of microvessels was measured before and 24 h after perfusion with VEGF. The distensibility was increased 45 +/- 15% by VEGF but this was not great enough to account for the increase in diameter. 4. The chronic increase in Lp could be attenuated by inhibition of nitric oxide synthase with L-NAME. In addition, the chronic increase in permeability was correlated with the acute response to VEGF (r = 0.71, P < 0.01) suggesting that the acute and chronic changes may be related. 5. These results show that VEGF chronically increases Lp without affecting the oncotic reflection coefficient. This may be due to reduced pore path length, or increased small pore numbers, which are properties of fenestrated capillaries. They also show that VEGF increases microvascular distensibility and diameter.