Analysis of microvascular permeability to macromolecules by video-image digital processing

Endothelial barrier dysfunction in systemic inflammation is mediated by soluble VE-cadherin interfering VE-PTP signaling

Breakdown of endothelial barrier integrity determines organ dysfunction and outcome of patients with sepsis. Increased levels of soluble vascular endothelial (VE)-cadherin fragments (sVE-cadherin) have previously been linked with inflammation-induced loss of endothelial barrier function. We provide evidence for a causative role of sVE-cadherin to induce loss of endothelial barrier function. In patients with sepsis, sVE-cadherin levels were associated with organ dysfunction and the need for volume resuscitation. Similarly, LPS-induced systemic inflammation in rats with microvascular dysfunction was paralleled by augmented sVE-cadherin levels. Newly generated recombinant human sVE-cadherin (extracellular domains EC1-5) induced loss of endothelial barrier function in both human microvascular endothelial cells in vitro and in rat mesenteric microvessels in vivo and reduced microcirculatory flow. sVE-cadherinEC1-5 disturbed VE-cadherin-mediated adhesion and perturbed VE-protein tyrosine phosphatase (VE-PTP)/VE-cadherin interaction resulting in RhoGEF1-mediated RhoA activation. VE-PTP inhibitor AKB9778 and Rho-kinase inhibitor Y27632 blunted all sVE-cadherinEC1-5-induced effects, which uncovers a pathophysiological role of sVE-cadherin via dysbalanced VE-PTP/RhoA signaling.

Interleukin-8 Secreted by Glioblastoma Cells Induces Microvascular Hyperpermeability Through NO Signaling Involving S-Nitrosylation of VE-Cadherin and p120 in Endothelial Cells

Glioblastoma is a highly aggressive brain tumor, characterized by the formation of dysfunctional blood vessels and a permeable endothelial barrier. S-nitrosylation, a post-translational modification, has been identified as a regulator of endothelial function. In this work we explored whether S-nitrosylation induced by glioblastoma tumors regulates the endothelial function. As proof of concept, we observed that S-nitrosylation is present in the tumoral microenvironment of glioblastoma in two different animal models. Subsequently, we measured S nitrosylation and microvascular permeability in EAhy296 endothelial cells and in cremaster muscle. In vitro, conditioned medium from the human glioblastoma cell line U87 activates endothelial nitric oxide synthase, causes VE-cadherin- S-nitrosylation and induces hyperpermeability. Blocking Interleukin-8 (IL-8) in the conditioned medium inhibited S-nitrosylation of VE-cadherin and hyperpermeability. Recombinant IL-8 increased endothelial permeability by activating eNOS, S-nitrosylation of VE-cadherin and p120, internalization of VE-cadherin and disassembly of adherens junctions. In vivo, IL-8 induced S-nitrosylation of VE-cadherin and p120 and conditioned medium from U87 cells caused hyperpermeability in the mouse cremaster muscle. We conclude that eNOS signaling induced by glioma cells-secreted IL-8 regulates endothelial barrier function in the context of glioblastoma involving S-nitrosylation of VE-cadherin and p120. Our results suggest that inhibiting S-nitrosylation may be an effective way to control and/or block damage to the endothelial barrier and prevent cancer progression.

Sphingosine-1-Phosphate Receptor-1 Agonist Sew2871 Causes Severe Cardiac Side Effects and Does Not Improve Microvascular Barrier Breakdown in Sepsis

BACKGROUND

Endothelial barrier dysfunction is a hallmark in the pathogenesis of sepsis. Sphingosine-1-phosphate (S1P) has been proposed to be critically involved in the maintenance of endothelial barrier function predominately by activating S1P receptor-1 (S1P1). Previous studies have shown that the specific S1P1 agonist SEW2871 improves endothelial barrier function under inflammatory conditions. However, the effectiveness of SEW2871 and potential side effects remained largely unexplored in a clinically relevant model of sepsis. Therefore, this study aimed to evaluate the effects of SEW2871 in the Colon ascendens stent peritonitis (CASP) model.

METHODS

Polymicrobial sepsis was induced in Sprague-Dawley rats using CASP model that enabled the monitoring of macro-hemodynamic parameters. Twelve hours after surgery, animals received either SEW2871 or sodium chloride. Mesenteric endothelial barrier function was evaluated 24 h after sepsis induction by intravital microscopy. Organ pathology was assessed in lungs. S1P levels, blood gas analyses, and blood values were measured at different time points. In parallel the effect of SEW2871 was evaluated in human dermal microvascular endothelial cells.

RESULT

In vitro SEW2871 partially stabilized TNF-α-induced endothelial barrier breakdown. However, in vivo SEW2871 caused severe cardiac side effects in septic animals leading to an increased lethality. Sepsis-induced endothelial barrier dysfunction was not attenuated by SEW2871 as revealed by increased FITC-albumin extra-vasation, requirement of intravasal fluid replacement, and pulmonary edema. Interestingly, Sham-operated animals did not present any side effects after SEW2871 treatment.

CONCLUSION

Our study demonstrates that the application of SEW2871 causes severe cardiac side effects and cannot attenuate the inflammation-induced endothelial barrier breakdown in a clinically relevant sepsis model, suggesting that the time point of administration and the pro-inflammatory milieu play a pivotal role in the therapeutic benefit of SEW2871.

Endothelial cAMP deactivates ischemia-reperfusion-induced microvascular hyperpermeability via Rap1-mediated mechanisms

Approaches to reduce excessive edema due to the microvascular hyperpermeability that occurs during ischemia-reperfusion (I/R) are needed to prevent muscle compartment syndrome. We tested the hypothesis that cAMP-activated mechanisms actively restore barrier integrity in postischemic striated muscle. We found, using I/R in intact muscles and hypoxia-reoxygenation (H/R, an I/R mimic) in human microvascular endothelial cells (HMVECs), that hyperpermeability can be deactivated by increasing cAMP levels through application of forskolin. This effect was seen whether or not the hyperpermeability was accompanied by increased mRNA expression of VEGF, which occurred only after 4 h of ischemia. We found that cAMP increases in HMVECs after H/R, suggesting that cAMP-mediated restoration of barrier function is a physiological mechanism. We explored the mechanisms underlying this effect of cAMP. We found that exchange protein activated by cAMP 1 (Epac1), a downstream effector of cAMP that stimulates Rap1 to enhance cell adhesion, was activated only at or after reoxygenation. Thus, when Rap1 was depleted by small interfering RNA, H/R-induced hyperpermeability persisted even when forskolin was applied. We demonstrate that 1) VEGF mRNA expression is not involved in hyperpermeability after brief ischemia, 2) elevation of cAMP concentration at reperfusion deactivates hyperpermeability, and 3) cAMP activates the Epac1-Rap1 pathway to restore normal microvascular permeability. Our data support the novel concepts that 1) different hyperpermeability mechanisms operate after brief and prolonged ischemia and 2) cAMP concentration elevation during reperfusion contributes to deactivation of I/R-induced hyperpermeability through the Epac-Rap1 pathway. Endothelial cAMP management at reperfusion may be therapeutic in I/R injury.NEW & NOTEWORTHY Here, we demonstrate that 1) stimulation of cAMP production deactivates ischemia-reperfusion-induced hyperpermeability in muscle and endothelial cells; 2) VEGF mRNA expression is not enhanced by brief ischemia, suggesting that VEGF mechanisms do not activate immediate postischemic hyperpermeability; and 3) deactivation mechanisms operate via cAMP-exchange protein activated by cAMP 1-Rap1 to restore integrity of the endothelial barrier.

S-nitrosylation regulates VE-cadherin phosphorylation and internalization in microvascular permeability

The adherens junction complex, composed mainly of vascular endothelial (VE)-cadherin, β-catenin, p120, and γ-catenin, is the main element of the endothelial barrier in postcapillary venules.S-nitrosylation of β-catenin and p120 is an important step in proinflammatory agents-induced hyperpermeability. We investigated in vitro and in vivo whether or not VE-cadherin isS-nitrosylated using platelet-activating factor (PAF) as agonist. We report that PAF-stimulates S-nitrosylation of VE-cadherin, which disrupts its association with β-catenin. In addition, based on inhibition of nitric oxide production, our results strongly suggest that S-nitrosylation is required for VE-cadherin phosphorylation on tyrosine and for its internalization. Our results unveil an important mechanism to regulate phosphorylation of junctional proteins in association with S-nitrosylation.

Phosphodiesterase 4 inhibition dose dependently stabilizes microvascular barrier functions and microcirculation in a rodent model of polymicrobial sepsis

BACKGROUND

Breakdown of microvascular endothelial barrier functions contributes to disturbed microcirculation, organ failure, and death in sepsis. Increased endothelial cAMP levels by systemic application of phosphodiesterase 4 inhibitors (PD-4-I) have previously been demonstrated to protect microvascular barrier properties in a model of systemic inflammation (systemic inflammatory response syndrome) suggesting a novel therapeutic option to overcome this problem. However, in a clinically relevant model of polymicrobial sepsis long-term effects, immunomodulatory effects and effectivity of PD-4-I to stabilize microvascular barrier functions and microcirculation remained unexplored.

METHODS

We induced polymicrobial sepsis using the colon ascendens stent peritonitis (CASP) model in which we performed macrohemodynamic and microhemodynamic monitoring with and without systemic intravenous application of different doses of PD-4-I rolipram in Sprague-Dawley rats over 26 h.

RESULTS

All animals with CASP showed clinical and laboratory signs of sepsis and peritonitis. Whereas macrohemodynamic adverse effects were not evident, application of PD-4-I led to stabilization of endothelial barrier properties as revealed by reduced extravasation of fluorescein isothiocyanate-albumin. However, only low-dose application of 1 mg/kg body weight per hour of PD-4-I improved microcirculatory flow in the CASP model, whereas high-dose therapy of 3 mg/kg BW per hour PDI-4-I had adverse effects. Accordingly, sepsis-induced acute kidney injury and lung edema were prevented by PD-4-I treatment. Furthermore, PD-4-I showed immunomodulatory effects as revealed by decreased interleukin 1α (IL-1α), IL-1β, IL-12, and tumor necrosis factor α levels following PD-4-I treatment, which appeared not to correlate with barrier-stabilizing effects of rolipram.

CONCLUSIONS

These data provide further evidence that systemic application of PD-4-I could be suitable for therapeutic microvascular barrier stabilization and improvement of microcirculatory flow in sepsis.

Myosin light chain kinase signaling in endothelial barrier dysfunction

Microvascular barrier dysfunction is a serious problem that occurs in many inflammatory conditions, including sepsis, trauma, ischemia-reperfusion injury, cardiovascular disease, and diabetes. Barrier dysfunction permits extravasation of serum components into the surrounding tissue, leading to edema formation and organ failure. The basis for microvascular barrier dysfunction is hyperpermeability at endothelial cell-cell junctions. Endothelial hyperpermeability is increased by actomyosin contractile activity in response to phosphorylation of myosin light chain by myosin light chain kinase (MLCK). MLCK-dependent endothelial hyperpermeability occurs in response to inflammatory mediators (e.g., activated neutrophils, thrombin, histamine, tumor necrosis factor alpha, etc.), through multiple cell signaling pathways and signaling molecules (e.g., Ca(++) , protein kinase C, Src kinase, nitric oxide synthase, etc.). Other signaling molecules protect against MLCK-dependent hyperpermeability (e.g., sphingosine-1-phosphate or cAMP). In addition, individual MLCK isoforms play specific roles in endothelial barrier dysfunction, suggesting that isoform-specific inhibitors could be useful for treating inflammatory disorders and preventing multiple organ failure. Because endothelial barrier dysfunction depends upon signaling through MLCK in many instances, MLCK-dependent signaling comprises multiple potential therapeutic targets for preventing edema formation and multiple organ failure. The following review is a discussion of MLCK-dependent mechanisms and cell signaling events that mediate endothelial hyperpermeability.

Phosphodiesterase-4 inhibition as a therapeutic approach to treat capillary leakage in systemic inflammation

In sepsis and systemic inflammation, increased microvascular permeability and consecutive breakdown of microcirculatory flow significantly contribute to organ failure and death. Evidence points to a critical role of cAMP levels in endothelial cells to maintain capillary endothelial barrier properties in acute inflammation. However, approaches to verify this observation in systemic models are rare. Therefore we tested here whether systemic application of the phosphodiesterase-4-inhibitors (PD-4-Is) rolipram or roflumilast to increase endothelial cAMP was effective to attenuate capillary leakage and breakdown of microcirculatory flow in severe lipopolysaccharide (LPS)-induced systemic inflammation in rats. Measurements of cAMP in mesenteric microvessels demonstrated significant LPS-induced loss of cAMP levels which was blocked by application of rolipram. Increased endothelial cAMP by application of either PD-4-I rolipram or roflumilast led to stabilization of endothelial barrier properties as revealed by measurements of extravasated FITC-albumin in postcapillary mesenteric venules. Accordingly, microcirculatory flow in mesenteric venules was significantly increased following PD-4-I treatment and blood gas analyses indicated improved metabolism. Furthermore application of PD-4-I after manifestation of LPS-induced systemic inflammation and capillary leakage therapeutically stabilized endothelial barrier properties as revealed by significantly reduced volume resuscitation for haemodynamic stabilization. Accordingly microcirculation was significantly improved following treatment with PD-4-Is. Our results demonstrate that inflammation-derived loss of endothelial cAMP contributes to capillary leakage which was blocked by systemic PD-4-I treatment. Therefore these data suggest a highly clinically relevant and applicable approach to stabilize capillary leakage in sepsis and systemic inflammation.

Rapamycin inhibits VEGF-induced microvascular hyperpermeability in vivo

OBJECTIVE

To test the hypothesis that rapamycin inhibits induced microvascular hyperpermeability directly in vivo.

METHODS

Male golden Syrian hamsters (80-120 g) were treated with either rapamycin (at 0.1, 0.5, 2, and 10 mg/kg i.p.) or vehicle at 24 hours and at 1 hour prior to preparation of the cheek pouch. Caveolin-1 scaffolding (1 mg/kg; positive inhibitory control) was injected i.p. 24 hours prior to the experiment. 10(-8) M vascular endothelial growth factor (VEGF) or 10(-7) M platelet-activating factor (PAF) were topically applied to the cheek pouch. Microvascular permeability and arteriolar diameter were assessed using integrated optical intensity (IOI) and vascular wall imaging, respectively.

RESULTS

Rapamycin at 0.1 and 0.5 mg/kg significantly reduced VEGF-stimulated mean IOI from 63.0 +/- 4.2 to 9.7 +/- 5.0 (85% reduction, P < 0.001) and 3.6 +/- 2.7 (95% reduction, P < 0.001), respectively. Rapamycin at 2 mg/kg also lowered VEGF-stimulated hyperpermeability (40% reduction, P < 0.05). However, 10 mg/kg rapamycin increased VEGF-induced microvascular hyperpermeability. Rapamycin at 0.5 mg/kg attenuated VEGF-induced vasodilation and PAF-induced hyperpermeability, but did not inhibit PAF-induced vasoconstriction.

CONCLUSIONS

At therapeutically relevant concentrations, rapamycin inhibits VEGF- and PAF-induced microvascular permeability. This inhibition is (i) a direct effect on the endothelial barrier, and (ii) independent of arteriolar vasodilation. Rapamycin at 10 mg/kg stimulates effectors that increase microvascular permeability.

Myosin light chain kinase in microvascular endothelial barrier function

Microvascular barrier dysfunction is implicated in the initiation and progression of inflammation, posttraumatic complications, sepsis, ischaemia-reperfusion injury, atherosclerosis, and diabetes. Under physiological conditions, a precise equilibrium between endothelial cell-cell adhesion and actin-myosin-based centripetal tension tightly controls the semi-permeability of microvascular barriers. Myosin light chain kinase (MLCK) plays an important role in maintaining the equilibrium by phosphorylating myosin light chain (MLC), thereby inducing actomyosin contractility and weakening endothelial cell-cell adhesion. MLCK is activated by numerous physiological factors and inflammatory or angiogenic mediators, causing vascular hyperpermeability. In this review, we discuss experimental evidence supporting the crucial role of MLCK in the hyperpermeability response to key cell signalling events during inflammation. At the cellular level, in vitro studies of cultured endothelial monolayers treated with MLCK inhibitors or transfected with specific inhibiting peptides have demonstrated that induction of endothelial MLCK activity is necessary for hyperpermeability. Ex vivo studies of live microvessels, enabled by development of the isolated, perfused venule method, support the importance of MLCK in endothelial permeability regulation in an environment that more closely resembles in vivo tissues. Finally, the role of MLCK in vascular hyperpermeability has been confirmed with in vivo studies of animal disease models and the use of transgenic MLCK210 knockout mice. These approaches provide a more complete view of the role of MLCK in vascular barrier dysfunction.

Vascular leak in a rat model of preeclampsia

BACKGROUND/AIMS

Preeclampsia is a hypertensive disorder which develops de novo in women during pregnancy. The urinary excretion of the cardiotonic steroid, marinobufagenin (MBG), is increased prior to the development of hypertension. Preeclamptic patients are volume expanded but much of the excess salt and water appears to be located primarily in the interstitial space. Therefore, 'capillary leak' syndrome has been postulated in this disorder.

METHODS

We evaluated the vascular leakage in normal rats following MBG injection and in a rat model of human preeclampsia. We measured the changes in light intensity comparing that in the intravascular to the extravascular space by assessing 'leak' of fluorescein-labeled albumin (FITC-albumin) from mesenteric postcapillary venules.

RESULTS

FITC-albumin extravasation continued to increase in a time-dependent fashion after MBG infusion and was significant (p < 0.05) at 60 min of observation when compared to sham rats. We also observed a significant difference in 'vascular leakage' in preeclamptic rats compared to control non-pregnant and normal pregnant groups starting at 20 min after the FITC-albumin infusion.

CONCLUSION

We propose that MBG is involved in the production of a 'vascular leak' in our rat model of preeclampsia.

Hydroxyethyl Starch: The Effect of Molecular Weight and Degree of Substitution on Intravascular Retention In Vivo

BACKGROUND

Hydroxyethyl starch (HES) solution is characterized by its mean molecular weight (MW), concentration, and degree of substitution (DS). This character varies worldwide.

METHODS

After binding fluorescein-isothiocyanate (FITC-HES), we evaluated the retention rate of three types of 6% HES in the A2 and V2 blood vessels of rat cremaster muscles using intravital microscopy in a mild hemorrhage model (10% of total blood volume). After blood withdrawal, we infused three types of FITC-HES: HES-A (MW 150-200 kDa, DS 0.6-0.68), HES-B (MW 175-225 kDa, DS 0.45-0.55), or HES-C (MW 550-850 kDa, DS 0.7-0.8) before determining the FITC-HES retention rate in the intravital microscope.

RESULTS

For V2, the FITC-HES retention rates 120 min after the start of the infusion were 27% +/- 7.2% of baseline values (HES-A), 65% +/- 9.1% (HES-B), and 86% +/- 9.6% (HES-C); for A2 they were 27% +/- 6.6%, 73% +/- 10.2%, and 89% +/- 8.7%, respectively. HES-B and HES-C were retained in the vessels longer than HES-A (P = 0.028 for V2, P = 0.038 for A2 between HES-B and HES-A; P = 0.022 for V2, P = 0.037 for A2 between HES-C and HES-A). There was no difference in the rate of disappearance from the vessels between HES-B and HES-C.

CONCLUSIONS

HES-B and HES-C are equally retained in the blood vessels. Middle-sized HES-B with low DS and middle substitution pattern stayed in the blood vessels as long as the large-sized HES. HES solutions of varying characters should be examined to optimize HES infusion.

Apoptotic signaling induces hyperpermeability following hemorrhagic shock

Hemorrhagic shock (HS) disrupts the endothelial cell barrier, resulting in microvascular hyperpermeability. Recent studies have also demonstrated that activation of the apoptotic signaling cascade is involved in endothelial dysfunction, which may result in hyperpermeability. Here we report involvement of the mitochondrial "intrinsic" pathway in microvascular hyperpermeability following HS in rats. HS resulted in the activation of the mitochondrial intrinsic pathway, as is evident from an increase in the proapoptotic Bcl-2 family member BAK, release of mitochondrial cytochrome c into the cytoplasm, and activation of caspase-3. This, along with the in vivo transfection of the proapoptotic peptide BAK (BH3), resulted in hyperpermeability (as visualized by intravital microscopy), release of mitochondrial cytochrome c into the cytoplasm, and activation of caspase-3. Conversely, transfection of the BAK (BH3) mutant had no effect on hyperpermeability. Together, these results demonstrate involvement of the mitochondrial intrinsic apoptotic pathway in HS-induced hyperpermeability and that the attenuation of this pathway may provide an alternative strategy in preserving vascular barrier integrity.

Morphine Sulfate Attenuates Hemorrhagic Shock- Induced Hyperpermeability

Morphine sulfate is often administered for patients requiring surgical intervention for the control of hemorrhage. Recent data implicate morphine as an immune modulator that affects white blood cells and increases infection rates. In addition, morphine releases histamine, an inflammatory mediator that increases microvascular permeability. Both of these actions of morphine could aggravate the inflammatory progress after hemorrhagic shock. In this study, we evaluated the role of morphine sulfate on microvascular permeability and its effects on leukocyte adherence after hemorrhagic shock. After a control period, blood was withdrawn to reduce the mean arterial blood pressure to 40 mm Hg for 1 h in urethane-anesthetized Sprague-Dawley rats. Mesenteric postcapillary venules in a transilluminated segment of small intestine were examined to quantify changes in permeability and leukocyte adherence. The rats received an IV injection of fluorescein isothiocyanate-bovine albumin during the control period. The fluorescent light intensity emitted from the fluorescein isothiocyanate-bovine albumin was recorded with digital microscopy within the lumen of the microvasculature and compared with the intensity of light in the extraluminal space over time. These images were downloaded to a computerized image analysis program that quantitates changes in light intensity. This change in light intensity represents albumin extravasation. In addition, bright-field images were recorded on compact disk for playback to determine leukocyte adherence. Leukocytes stationary for more than 30 s or longer in a 100-micron segment of venule was considered adherent. Our results demonstrated a marked increase in fluorescein isothiocyanate-bovine albumin leakage into the extravascular space after hemorrhagic shock. Hemorrhagic shock was also associated with an increase in leukocytes adhering to the postcapillary venular endothelium. Morphine sulfate 10 microg/kg given before the shock period, attenuated both the hyperpermeability (P < 0.05) and the increase in leukocyte adherence (P < 0.05) after hemorrhagic shock. These results suggest that instead of aggravating the inflammatory response after hemorrhagic shock, morphine may provide protection to the microvasculature.

Endothelial nitric oxide synthase regulates microvascular hyperpermeability in vivo

Nitric oxide (NO) is an important regulator of blood flow, but its role in permeability is still challenged. We tested in vivo the hypotheses that: (a) endothelial nitric oxide synthase (eNOS) is not essential for regulation of baseline permeability; (b) eNOS is essential for hyperpermeability responses in inflammation; and (c) molecular inhibition of eNOS with caveolin-1 scaffolding domain (AP-Cav) reduces eNOS-regulated hyperpermeability. We used eNOS-deficient (eNOS-/-) mice and their wild-type control as experimental animals, platelet-activating factor (PAF) at 10(-7) m as the test pro-inflammatory agent, and integrated optical intensity (IOI) as an index of microvascular permeability. PAF increased permeability in wild-type cremaster muscle from a baseline of 2.4 +/- 2.2 to a peak net value of 84.4 +/- 2.7 units, while the corresponding values in cremaster muscle of eNOS-/- mice were 1.0 +/- 0.3 and 15.6 +/- 7.7 units (P < 0.05). Similarly, PAF increased IOI in the mesentery of wild-type mice but much less in the mesentery of eNOS-/- mice. PAF increased IOI to comparable values in the mesenteries of wild-type mice and those lacking the gene for inducible NOS (iNOS). Administration of AP-Cav blocked the microvascular hyperpermeability responses to 10(-7) m PAF. We conclude that: (1) baseline permeability does not depend on eNOS; (2) eNOS and NO are integral elements of the signalling pathway for the hyperpermeability response to PAF; (3) iNOS does not affect either baseline permeability or hyperpermeability responses to PAF; and (4) caveolin-1 inhibits eNOS regulation of microvascular permeability in vivo. Our results establish eNOS as an important regulator of microvascular permeability in inflammation.

Mitogen-activated protein kinases regulate platelet-activating factor-induced hyperpermeability

OBJECTIVE

The authors tested the hypothesis that p42/44- (ERK-1/2) and/or p38-mitogen-activated protein kinases (MAPK) are in vivo regulatory elements in the platelet-activating factor (PAF) activated signaling cascade that stimulates microvascular hyperpermeability.

METHODS

FITC-dextran 70 was used as the macromolecular tracer for microvascular permeability in the mouse mesenteric fat tissue. Interstitial integrated optical intensity (IOI) was used as an index of permeability.

RESULTS

An application of 10(-7) M PAF increased IOI from 23.1 +/- 3.6 to 70.8 +/- 7.4 (mean +/- SEM). Inhibition of ERK-1/2 with 3 microM and 30 microM AG126 reduced IOI to 32.3 +/- 2.5. Similarly, inhibition of p38-MAPK with 6 nM, 60 nM and 600 nM SB203580 lowered IOI to 29.1 +/- 2.4.

CONCLUSIONS

The results demonstrate that ERK-1/2 and p38MAPK participate in the signaling cascade that regulates PAF-induced microvascular hyperpermeability in vivo.

Effective permeability of hydrophilic substances through walls of lymph vessels: roles of endothelial barrier

The wall effective permeability of hydrophilic substances labeled with fluorescent dyes was evaluated in an isolated cannulated rat single lymph vessel through a videomicroscope system. Sodium fluorescein (NaFl; 332 mol wt) and FITC-dextrans (4,400, 12,000, and 71,200 mol wt) were administered into the intraluminal space of the lymph vessels and then excited by a Xenon lamp. Changes in the fluorescence intensity of the dyes were continuously measured by a silicon-intensified target camera through appropriate filters. The net flux of each dye in the wall of the lymph vessels was calculated by the relationship between the fluorescence intensity and the concentration of the dyes. NaFl and FITC-dextran 4,400 in the intraluminal space of isolated rat lymph vessels significantly penetrated the wall of the lymph vessels. FITC-dextran 12,000 in the intraluminal space of isolated rat lymph vessels slightly passed through the lymphatic wall, whereas FITC-dextran 71,200 did not penetrate the wall. Intraluminal pressures ranging from 4 to 8 cmH2O did not significantly affect the net flux of dyes used in the present study. After administration of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate into the lymph vessels, the net flux of FITC-dextran 4,400 and 12,000 but not 71,200 was augmented significantly. These results suggest that small molecular hydrophilic substances (≤4,400) are permeable from the intraluminal to extraluminal space of isolated lymph vessels and that the endothelial cell surface structure may play a barrier role in the effective permeability of large molecular hydrophilic substances (4,400 to 12,000) through the wall of the lymph vessels.

Hypothermia reduces microvascular permeability and reactive oxygen species expression after hemorrhagic shock

BACKGROUND

Hypothermia is a frequent manifestation after trauma-induced hemorrhagic shock. Clinical studies have suggested that hypothermia is an independent risk variable predisposing patients to an increase in morbidity. Thus, most of the current goal-directed resuscitation protocols are aimed at the establishment of euthermia. However, recent data suggest that hypothermia may provide protection by attenuating the inflammatory response after hemorrhagic shock. The purpose of this study was twofold: to examine the effects of mild to moderate hypothermia on barrier function after hemorrhagic shock, and to determine the role of reactive oxygen species (ROS) in this process.

METHODS

After a control period, blood was withdrawn to reduce the mean arterial pressure to 40 mm Hg for 1 hour in urethane-anesthetized rats. Mesenteric postcapillary venules in a transilluminated segment of small intestine were examined to quantitate changes in permeability and ROS expression. Sprague-Dawley rats received an intravenous injection of fluorescein isothiocyanate (FITC)-albumin during the control period. The fluorescent light intensity emitted from the FITC-albumin was recorded with digital microscopy within the lumen of the microvasculature and compared with the intensity of light in the extravascular space. The images were downloaded to a computerized image analysis program that quantitates changes in light intensity. This change in light intensity represents albumin-FITC extravasation.

RESULTS

Our results demonstrated a marked increase in albumin leakage after hemorrhagic shock that was significantly attenuated with mild (34 degrees C) and moderate (30 degrees C) hypothermia. In addition, hypothermia attenuated ROS expression after hemorrhagic shock.

CONCLUSION

These data suggest that hypothermia may protect barrier integrity after hemorrhagic shock by inhibition of oxygen radical expression.

Vascular endothelial growth factor stimulates differential signaling pathways in in vivo microcirculation

Vascular endothelial growth factor (VEGF) induces mild vasodilation and strong increases in microvascular permeability. Using intravital microscopy and digital integrated optical intensity image analysis, we tested, in the hamster cheek pouch microcirculation, the hypothesis that differential signaling pathways in arterioles and venules represent an in vivo regulatory mechanism in the control of vascular diameter and permeability. The experimental design involved blocking specific signaling molecules and simultaneously assessing VEGF-induced changes in arteriolar diameter and microvascular transport of FITC-Dextran 150. Inhibition of Akt [indirectly via phosphatidylinositol 3-kinase with LY-294002 or wortmannin] or PKC (with bisindolylmaleimide) reduced VEGF-induced hyperpermeability. However, phosphatidylinositol 3-kinase/Akt inhibition enhanced the early phase and attenuated the late phase of VEGF-induced vasodilation, whereas blocking PKC had no effect. Inhibition of extracellular signal-regulated kinase (ERK)-1/2 (with PD-98059 or AG-126) also reduced VEGF-induced hyperpermeability but did not block VEGF-induced vasodilation. Blockade of endothelial nitric oxide synthase (with N(omega)-monomethyl-l-arginine) inhibited VEGF-induced changes in both permeability and diameter. Furthermore, immunofluorescence studies with human umbilical vein endothelial cells revealed that bisindolylmaleimide, PD-98059, and l-NMMA attenuate VEGF-induced reorganization of vascular endothelial cadherin. Our data demonstrate that 1) endothelial nitric oxide synthase is a common convergence pathway for VEGF-induced changes in arteriolar diameter and microvascular permeability; 2) PKC and ERK-1/2 do not play a major role in VEGF-induced vasodilation in the hamster cheek pouch microcirculation; and 3) Akt, PKC, and ERK-1/2 are elements of the signaling cascade that regulates VEGF-stimulated microvascular hyperpermeability. Our data provide evidence for differential signaling as a regulatory step in VEGF-stimulated microvascular dynamics.

An intravital microscopy study of radiation-induced changes in permeability and leukocyte–endothelial cell interactions in the microvessels of the rat pia mater and cremaster muscle

Using intravital microscopy and a closed window method, we measured irradiation-induced changes in the vascular permeability and cell interactions in microcirculation networks of the rat pia mater; the same effects were monitored in the cremaster muscle as a control. The closed cranial window has many advantages, including long-term direct visualization of microcirculation. The method allows for repeated testing of the same vessel or network, thereby reducing variability. The method also allows for measurement of permeability changes and the accompanying leukocyte-endothelial cell interactions in the same network or vessel, which permits correlative studies of these phenomena. However, this method is not without challenges. The optical conditions are difficult, because the brain is three-dimensional and its parenchyma is more complex than the thinner, flatter peripheral tissues. To overcome this limitation, we performed a dynamic background subtraction. The background is dynamically related to vessel intensity, and changes in intensity were determined by eliminating the effects of neighboring and underlying vessels. We applied this method to studying the effects of ionizing radiation on the blood-brain barrier (BBB) permeability and cell interactions and the modulation of these effects by anti-ICAM-1 antibodies. Our results demonstrate that this method is sensitive to changes in these properties of the BBB.

Microvascular permeability of rat cerebral pia mater by using image computer analysis

Microcirculation viviperception and fluorescent tracer techniques were used and digital image analysis applied for quantitative measurement of fluorescein sodium (FiNa) permeability in microvessels of the cerebral pia mater. The diffusion permeation equations of FiNa within the blood vessels and through the vessel walls into the perivascular tissue of normal rats and ischemic rats were established with two vessels as study object, thus the permeation speed equations under different ischemic conditions were deduced. Based on analysis of the results, we deduced the relation between the permeability and the intersection angle of two vessels.

RESULT

logarithm model showed a good fit of the experiment data. The permeation equation showed logarithmic distribution and then tended towards stability. FiNa could pass through microvessel walls with the highest speed in the one-hour ischemic rat group, and the permeation speed of FiNa in rats receiving reperfusion after twelve hours of ischemia was much faster than that in normal rats.

CONCLUSION

the method can be useful for quantitative analysis of cerebral pia mater microvascular permeability

Microcirculatory alterations in a Mongolian gerbil sinus-vein thrombosis model

BACKGROUND AND PURPOSE

The pathophysiology of sinus vein thrombosis (SVT) is still controversial in patients and experimental animals, the microcirculatory alterations in particular. This study was designed to develop a new sinus vein thrombosis model and to further elucidate pathophysiological events such as the relationship between local and regional cerebral blood flow and haemoglobin oxygen saturation (HbSO2), changes of the microvasculature, leukocyte behaviour and brain tissue damage.

METHODS

In a first experimental series, animals were divided into two groups which resulted from different procedures of inducing SVT. In the SSS middle occlusion group (SMO group), SVT was induced by the ligation of the superior sagittal sinus right in the middle between the bregma and the confluence sinum. In the SSS posterior occlusion group (SPO group) the ligation was performed close to the confluence sinum. Regional cerebral blood flow (rCBF) was assessed at 36 identical locations by laser Doppler flowmetry together with regional haemoglobin oxygen saturation (HbSO2). In a second series of experiments SVT was induced by ligation of the SSS close to the confluence sinum (SVT group) to study effects on the cortical microcirculation. A sham operation was performed in six animals (sham group). In both groups, an intravital microscopic double tracing technique was utilised for evaluating microvessel structures and leukocyte behaviour. The images were recorded on videotape for evaluating alterations of microvessel (venules, arterioles and capillaries) diameters and numbers of leukocyte rollers and stickers by a digital video analyser. Animals were sacrificed for histological evaluation after 5 days.

RESULTS

The posterior sinus ligation caused a significant decrease of rCBF and HbSO2 and brain tissue damage which was not seen in the SMO group. Alteration of rCBF and HbSO2 were positively correlated with infarct size in the SPO group only, where venous infarction was easily reproduced. Therefore, it is suggested that this model is suitable for studying SVT in Mongolian gerbils. Intravital microscopy of the cortical microcirculation revealed no significant changes of vessels diameter in the sham group, whereas a significant dilation of veins and capillaries was seen in the SVT group. Numbers of leukocyte rollers and stickers were positively correlated with infarct size.

CONCLUSION

Microcirculatory alterations and brain tissue damage from SVT in the Mongolian gerbil depend on the SSS occlusion site. The newly established mongolian gerbil sinus-vein thrombosis model has advantages compared to previously reported sinus-vein thrombosis models such as easy handling, easy technique, highly reproducibility, and good observation of microcirculatory event. The model allows for studies of cerebral low-flow conditions such as expected to occur in an ischaemic penumbra zone.

Determination of macromolecular exchange and PO2 in the microcirculation: a simple system for in vivo fluorescence and phosphorescence videomicroscopy

We have developed a system with two epi-illumination sources, a DC-regulated lamp for transillumination and mechanical switches for rapid shift of illumination and detection of defined areas (250-750 microm(2)) by fluorescence and phosphorescence videomicroscopy. The system permits investigation of standard microvascular parameters, vascular permeability as well as intra- and extravascular PO2 by phosphorescence quenching of Pd-meso-tetra (4-carboxyphenyl) porphine (PORPH). A Pechan prism was used to position a defined region over the photomultiplier and TV camera. In order to validate the system for in vivo use, in vitro tests were performed with probes at concentrations that can be found in microvascular studies. Extensive in vitro evaluations were performed by filling glass capillaries with solutions of various concentrations of FITC-dextran (diluted in blood and in saline) mixed with different amounts of PORPH. Fluorescence intensity and phosphorescence decay were determined for each mixture. FITC-dextran solutions without PORPH and PORPH solutions without FITC-dextran were used as references. Phosphorescence decay curves were relatively unaffected by the presence of FITC-dextran at all concentrations tested (0.1 microg/ml to 5 mg/ml). Likewise, fluorescence determinations were performed in the presence of PORPH (0.05 to 0.5 mg/ml). The system was successfully used to study macromolecular extravasation and PO2 in the rat mesentery circulation under controlled conditions and during ischemia-reperfusion.

Chemical and enzymatic synthesis of fructose analogues as probes for import studies by the hexose transporter in parasites

Various D-fructose analogues modified at C-1 or C-6 positions were synthesized from D-glucose by taking advantage of the Amadori rearrangement or using the aldol condensation between dihydroxyacetone phosphate and appropriate aldehyde catalyzed by fructose 1,6-diphosphate aldolase from rabbit muscle. The affinities of the analogues for the glucose transporter expressed in the mammalian form of Trypanosoma brucei were determined by inhibition of radiolabelled 2-deoxy-D-glucose (2-DOG) transport using zero-trans kinetic analysis. Interestingly, the analogues bearing an aromatic group (i.e. a fluorescence marker) at C-1 or C-6 positions present comparable apparent affinities to D-fructose for the transporter. This result could find applications for hexose transport studies and also provides criteria for the design of glucose import inhibitors.

Platelet-activating factor modulates microvascular dynamics through phospholipase C in the hamster cheek pouch

We studied the interactions between platelet-activating factor (PAF) and phospholipase C (PLC) in the modulation of microvascular responses in the hamster cheek pouch using intravital microscopy and computer-assisted image analysis. Changes in arteriolar diameter and in integrated optical intensity (IOI, an index of vascular permeability) were measured. Fluorescein-isothiocyanate-labeled dextran 150 (FITC-Dx 150) served as a tracer for macromolecular transport. 2-Nitro-4-carboxyphenyl N,N-diphenylcarbamate (NCDC) and 1-(6-((17beta-3-methoxyestra-1,3, 5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5,-dione (U-73122), two PLC inhibitors, were applied topically in separate experiments. PAF at 10(-7) M elevated IOI from baseline to a mean +/- SEM value of 70. 7 +/- 8.9 units. Pretreatment with 10(-4) and 10(-5) M NCDC and with U-73122 at 10(-5) and 10(-6) M attenuated the maximal increment in mean IOI (+/-SEM) induced by PAF at 10(-7) M to mean +/- SEM values of 30.6 +/- 6.5, 39.3 +/- 6.0, 12.1 +/- 4.8, and 41.5 +/- 6.0, respectively. The simultaneous vasoconstrictor action of 10(-7) M PAF was expressed as the experimental-to-baseline ratio, with the baseline diameter adjusted to a value of 1. PAF constricted the arterioles to a mean +/- SEM ratio of 0.30 +/- 0.07. Pretreatment with the PLC inhibitors NCDC at 10(-4) and 10(-5) M NCDC and with U-73122 at 10(-5) and 10(-6) M attenuated 10(-7) M PAF-induced vasoconstriction to mean +/- SEM diameter ratios of 0.55 +/- 0.05, 0. 48 +/- 0.06, 0.55 +/- 0.08, and 0.58 +/- 0.06, respectively. Our results demonstrate that PLC is an element of the biochemical pathway involved in PAF modulation of microvascular permeability and in PAF modulation of arteriolar diameter.

Nitric oxide decreases microvascular permeability in bradykinin stimulated and nonstimulated conditions

This study examined the occurrence of endothelial nitric oxide (NO)-synthase (NOS-III) in terminal mesenteric vessels and the involvement of NO in microvascular permeability. Possible effects were studied in bradykinin (BK)-induced and basal conditions. NOS expression was investigated by using NOS-III immunohistochemistry and nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry on the light- and electron-microscopic levels. Permeability was examined in dissected mesenteries of male rats weighing 250-300 g. Tissue treatment was performed with BK (100 nM), sodium nitroprusside (SNP, 1 and 10 microM), L-nitroarginine (L-NA, 300 microM), BK and L-NA, BK and SNP, L-NA and SNP, as well as with BK, SNP (10 microM), and the guanylylcyclase inhibitor ODQ (10 microM), and BK and ODQ alone. Pharmacologically induced permeability changes were studied with fluorescein isothiocyanate (FITC)-dextran 70 kDa as a tracer for macromolecular transport. Video images were analyzed with computer determination of integrated optical density (IOI). Results were statistically verified by analysis of variance and t test. Microvascular permeability was increased by 168% after BK treatment and was enhanced by NO-synthesis inhibition with L-NA by 607%. However, the NO donor SNP led to a reduced tracer extravasation to 105 and 58%, respectively, an effect blocked by ODQ. Under basal conditions without prior BK induction, L-NA also causes an increase of IOI by 25%, whereas coapplication with SNP resulted in only a 10% increase of permeability. These results point out that NO has a modulatory role for microvascular permeability by supporting the barrier function of the endothelial lining in stimulated and nonstimulated conditions.

Respective role of lipoxygenase and nitric oxide-synthase pathways in plasma histamine-induced macromolecular leakage in conscious hamsters

1. Intravital microscopy technique was used to determine the distribution of a fluorescent plasma marker (fluorescein-isothiocyanate-dextran, 150 kD; FD-150) into venular and interstitial compartments of dorsal skin fold preparations in conscious hamsters. 2. One mg kg(-1) histamine (i.v.) caused a biphasic decrease in venular fluorescence due to FD-150 extravasation in all organs (general extravasation). Immediately after injection, the venular fluorescence decreased and plateaued in 60 min. Ninety minutes after histamine injection, venular fluorescence further decreased until 180 min. Prior treatment with indomethacin (0.1 mg kg(-1), i.v.) did not modify the time-course of general extravasation but prevented histamine-induced venule dilatation. 3. Prior treatment with the 5-lipoxygenase activating protein (FLAP) inhibitor, 3-[1-(p-chlorobenzyl)-5-(isopropyl)-3-t-butylthioindol-2-yl]-2,2-d imethyl-propanoic acid sodium (MK-886)(10 microg kg(-1), i.v.), the leukotriene receptor antagonist, benzenemethanol a-pentyl-3-(2-quinolinylmethoxy) (REV-5901)(1 mg kg(-1), i.v.), or the glutathione-S-transferase inhibitor, ethacrynic acid (1 mg kg(-1), i.v.), delayed by 60 min the onset of general extravasation caused by 1 mg kg(-1) histamine. 4. Prior treatment with lipoxygenase pathway inhibitors and N(G)-nitro-L-arginine-methylester (L-NAME)(100 mg kg(-1), i.v.) abolished the general extravasation and venule dilatation induced by 1 mg kg(-1) histamine. 5. Injection of 1 microg kg(-1) (i.v.), of leukotriene-C4 (LTC4) or -D4 (LTD4) induced immediate and sustained general extravasation and reduction in venule diameter, these effects being blocked by REV-5901. 6. Histamine (1 mg kg(-1), i.v.) induced biphasic decline in mean arterial blood pressure (MAP). An initial phase (from 0 to 60 min) was followed by a late phase beginning 90 min after histamine injection. L-NAME (100 mg kg(-1), i.v.) and aminoguanidine (1 mg kg(-1), i.v.) prevented the late phase of histamine-induced hypotension. 7. Thus, plasma histamine can trigger both an immediate cysteinyl-leukotriene (Cys-LT)-dependent and a late nitric oxide (NO)-mediated inflammatory cascade. Although the cyclo-oxygenase (COX) pathway might account for histamine-induced venule dilatation, it would not influence histamine-induced extravasation.

Microvascular transport is associated with TNF plasma levels and protein synthesis in postischemic muscle

To better understand the mechanisms of ischemia-reperfusion (I/R) injury, we tested the hypothesis that protein synthesis is involved in the production of tumor necrosis factor (TNF) and in the microvascular transport changes in I/R. To evaluate the hypothesis, we inhibited protein synthesis with topically applied actinomycin D (AMD), measured I/R-induced changes in microvascular transport, and bioassayed the venous plasma levels of TNF. The rat cremaster muscle I/R model consisted of 4 h of ischemia followed by 2 h of reperfusion. Changes in transport were determined by integrated optical intensity (IOI) using FITC-Dextran 150 as tracer. Animals were separated into four groups: 1) control (C), 2) control treated with AMD (C + AMD), 3) I/R, and 4) I/R treated with AMD (I/R + AMD). The mean (+/-SE) maximal IOI in C and C + AMD were 3.0 +/- 1.0 and 3. 7 +/- 0.7 units, respectively. I/R elevated mean maximal IOI to 21.8 +/- 1.9 units (P < 0.05 vs. C, C + AMD, I/R + AMD). Treatment with AMD reduced the I/R-induced mean maximal IOI to 9.7 +/- 2.0 units (P < 0.05 vs. I/R). In I/R group, plasma TNF levels increased (relative to preischemia baseline) immediately after the release of the vascular occlusion to 250 pg/ml and reached a peak value of 342 pg/ml at 60 min of reperfusion. In the I/R + AMD group, AMD reduced TNF increase to 44 pg/ml. The C and C + AMD groups showed no differences in TNF values during the 6 h of observation. We conclude that protein synthesis and TNF generation are at least partially involved in I/R-induced changes in microvascular transport.

L-arginine and NG-nitro-L-arginine methyl ester cause macromolecule extravasation in the microcirculation of awake hamsters

We investigated the effects of L-arginine and NG-nitro-L-arginine methyl ester (L-NAME) on macromolecule extravasation in the microcirculation of awake hamsters by computer-assisted image analysis of the distribution of FITC (fluorescein isothiocyanate)-dextran fluorescence in dorsal fold skin preparations. This analysis made it possible to simultaneously study the time course of local (skin) and general (all irrigated organs) extravasation in 180-min experiments. Bolus injection of 30 or 150 mg/kg (i.v.) L-arginine induced immediate local and general macromolecule leakage and delayed venule dilation beginning 1 h later. Injection of 20 or 100 mg/kg (i.v.) L-NAME caused rapid venule constriction followed by local and general extravasation beginning 45-60 min later. These effects of L-arginine and L-NAME were not mimicked by their biologically inactive isomers, D-arginine and D-NAME. Simultaneous bolus injection of 20 mg/kg L-NAME and 150 mg/kg L-arginine caused no significant change in fluorescence distribution or venule diameter. L-arginine effects on macromolecule extravasation were mimicked by sodium nitroprusside (10 microg/kg, i.v.) and by 8-bromo-cGMP (1 mg/kg, i.v.). Sodium nitroprusside was ineffective on venule diameter. The effects of both L-arginine and sodium nitroprusside on FITC-dextran extravasation were prevented by simultaneous injection (10 microg/kg, i.v.) of the specific inhibitor of the soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). This dose of ODQ mimicked the effects of L-NAME on macromolecule extravasation and venule diameter. Taken together, these results suggest that activation or inhibition of basal NO synthesis might induce macromolecule leakage in the microcirculation of awake hamsters via temporally distinct cGMP-dependent mechanisms.

Histamine-induced biphasic macromolecular leakage in the microcirculation of the conscious hamster: evidence for a delayed nitric oxide-dependent leakage

1. Late effects (up to 3 h) of intravenously-injected histamine on FITC-dextran extravasation were investigated in the conscious hamster, by use of computer-assisted image analysis of fluorescence distribution in a microscopic window of dorsal skin fold preparations. This analysis allowed measurement of local (skin) and general (all organs) extravasations caused by a bolus injection of histamine (1 mg kg(-1), i.v.) 2. Histamine doses higher than 0.01 mg kg(-1) caused biphasic local and general extravasations. Initial phases developed fully within 15 min (for local) and 60 min (for general) and were followed by late phases beginning 90 min after histamine injection. Although the initial and late phases of histamine-induced extravasations had differential apparent reactivities to the autacoid, all the effects of histamine on the microcirculation (1 mg kg[-1]) were inhibited by pyrilamine (1 mg kg(-1), i.v.) but not by cimetidine (1 mg kg(-1), i.v.). 3. Pretreatment with N(G)-monomethyl-L-arginine (L-NMMA, 30 mg kg(-1), i.v.) or N(G)-nitro-L-arginine methyl ester (L-NAME, 100 mg kg(-1), i.v.) did not affect the initial phases but did prevent the late phases of local and general extravasations triggered by 1 mg kg(-1) histamine. The inhibitory effects of L-NAME were reversed by L-arginine (30 mg kg[-1]) but not by D-arginine (30 mg kg[-1]) according to the enantioselectivity of nitric oxide synthase (NOS). A late NO-mediated venular dilatation occurred in response to plasma histamine. 4. A low dose of aminoguanidine (1 mg kg(-1), i.v.), a selective inhibitor of the inducible isoform of NOS (iNOS), mimicked the inhibitory effects of L-NAME on the late phases of histamine-induced macromolecular extravasations and venular dilatation. 5. Pretreatment with dexamethasone (1 mg kg(-1), i.v.) prevented both the initial and late phases of histamine-induced extravasations. Fucoidan (1 or 25 mg kg(-1), i.v.) prevented the late phases without affecting initial phases, consistent with a role for leukocytes adhesion in the development of the late NO-mediated effects of histamine. 6. We conclude that intravenous injection of histamine triggers a biphasic inflammatory cascade via initial activation of H1 receptors which induces a late NO-mediated PMN-dependent extravasation process.

Inhibitory effects of fluorescein isothiocyanate photoactivation on lymphatic pump activity

The effects of photoactivation of fluorescein 5'-isothiocyanate (FITC)-dextran on lymphatic pump activity of rat mesenteric collecting vessel were studied in vivo. Rats were anesthetized with intraperitoneal alpha-chloralose and urethane, and the mesenteries were studied by using intravital videomicroscopic techniques. The diameter of the collecting lymph vessels were continuously monitored and lymphatic pump parameters (end diastolic diameter, end systolic diameter, stroke volume index, ejection fraction, contraction frequency, and pump flow index) were calculated. FITC-dextran (42 nmol/100 g body wt) without illumination caused no disturbance of lymphatic pump activity. Photoactivated FITC-dextran significantly increased end systolic diameter and decreased stroke volume index, ejection fraction, contraction frequency, and pump flow index. End diastolic diameter was not changed throughout the experiment. Superoxide dismutase (120 U/ml) and catalase (5000 U/ml) had no protective effect on photoactivated FITC-induced pump dysfunction, while histidine (singlet oxygen quencher, 10 mM) significantly prevented the disturbance of pump parameters. These results indicate that photoactivation of FITC induces negative chronotropic and negative inotropic effects in lymphatic pump activity through generation of singlet oxygen in the mesentery.

Novel neuropeptide Y receptor antagonists block vasoconstriction in the hamster cheek pouch microcirculation

We investigated the efficacy of novel neuropeptide Y (NPY) antagonists to inhibit the microcirculatory dynamics of NPY in the hamster cheek pouch microcirculation using intravital microscopy and computer-assisted image analysis. Changes in arteriolar diameter served as an index of vasomotor alterations. Fluorescein isothiocyanate-labeled Dextran 150 served as a tracer for measurements of macromolecular transport. GW 383 and GW 1229, two novel NPY receptor antagonists, were applied topically in separate experiments. Pretreatment with 10(-5), 10(-6) and 10(-7) M GW 383 and with 10(-6) and 10(-8) M GW 1229 attenuated the vasoconstriction induced by 10(-7) M NPY in a dose-dependent manner. Furthermore, pretreatment with 10(-7) and 10(-8) M GW 1229 significantly inhibited the 10(-9) M NPY-induced vasoconstriction. At these doses, the NPY antagonists did not alter microvascular permeability. Our results demonstrate that the novel NPY antagonists inhibit the vasoconstriction induced by NPY in the hamster check pouch microcirculation. We suggest that the inhibition is due to binding of antagonists to Y1-type NPY receptors.

Permselectivity of angiogenic microvessels following alteration of the endothelial fiber matrix by oligosaccharides

The endothelial glycocalyx, which is composed of integral and peripheral glycoconjugates, forms a fibrous matrix that confers macromolecular sieving properties on the microvascular wall. Changes in pore size within the matrix may regulate macromolecular access to the paracellular and/or vesicular transendothelial pathways. We tested the hypothesis that modifications of the endothelial glycocalyx might play a role in the ontogeny of endothelial permselectivity in proliferating microvessels of the chick chorioallantoic membrane (CAM). Accordingly, we evaluated the effects of Dolichos biflorus agglutinin (DBA) or Arachis hypogaea agglutinin (PNA) lectin binding, and N'N'diacetylchitobiose or hydroxyethyl starch polysaccharide (HES) incorporation on CAM endothelial restriction of FITC-dextrans 40 or 150 at Days 4.5 and 5.0 of development. Extravasation of FITC-dextrans was determined by recording their perivascular interstitial intensities. Following DBA, PNA, and N'N'diacetylchitobiose administration, interstitial accumulation of the tracers near first-order pre- and postcapillaries, and surrounding the capillaries, was similar to that of controls at both Days 4.5 and 5.0. At Day 4.5, pretreatment with HES significantly decreased extravasation of FITC-dextran 40. Thus, retention of HES molecules within the glycocalyx might tighten the matrix, and reduce access of dextran 40 to transendothelial pathways across the angiogenic microvessels.

Inhibition of nitric oxide synthase attenuates primed microvascular permeability in the in vivo microcirculation

PURPOSE

Changes in microvascular permeability play a critical role in the inflammatory sequence of tissue injury leading to leakage of proteins and subsequent edema. Primed responses induced by topical applications of platelet-activating factor (PAF) and histamine greatly increase microvascular permeability and mimic inflammation. We assessed the role of nitric oxide (NO) by use of 1-NG-monomethyl arginine (1-NMMA, a NO synthase inhibitor), on the primed microvascular permeability. We also explored the role of mast cells and a leukocyte adhesion complex by use of cromolyn sodium and 1B6 (a monoclonal antibody), respectively.

METHODS

Forty anesthetized hamsters were separated into five groups: group 1 (n = 5) received no intervention; group 2 (n = 5) received topical 10(-9) mol/L PAF and 10(-6) mol/L histamine at a 5-minute interval; group 3 (n = 5 at each dose) received PAF/histamine and 1-NMMA (at 10(-5) mol/L or 10(-6) mol/L); group 4 (n = 5 at each dose) received cromolyn sodium plus PAF/histamine; group 5 (n = 5) received 1B6 plus PAF/histamine. We examined the cheek pouch with intravital videomicroscopy under fluorescent epiillumination. We quantified microvascular permeability to fluorescein isothiocyanate-dextran 150 with computer-assisted images analysis on the basis of integrated optical intensity (IOI) measurements.

RESULTS

The mean (+/- SEM) IOI of the control group was 8.7 +/- 5.2, whereas the group primed with PAF and histamine was 62.4 +/- 10.8. The 1-NMMA (10(-5) mol/L and 10(-6) mol/L) abolished the changes in microvascular permeability (p < 0.05) yielding IOI values of 8.0 +/- 1.6 and 10.9 +/- 2.8, respectively. Cromolyn sodium and 1B6 did not significantly attenuate the primed response to PAF and histamine.

CONCLUSION

Inhibition of NO synthase attenuates primed macromolecular extravasation in vivo. Our results indicate that NO is involved in the primed reaction of PAF and histamine, causing increases in microvascular permeability. Our study suggests a role for NO in the microcirculatory changes observed in ischemia-reperfusion injury and shock.

Fate of water-soluble polymers administered via different routes

The biological fate of synthetic water-soluble polymers administered to mice by injection at different sites is described. After intraperitoneal (ip), subcutaneous (sc), and intramuscular (im) injections of 125I-labeled poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) with various molecular weights, the time-course of polymer concentration in the blood was measured and analyzed pharmacokinetically. The location of PVA in the body was similar to that of PEG; that is, the elimination from the injection sites and the translocation from the injection sites into the blood circulation were similar for both polymers. The elimination rate of both polymers from the injection sites increased in the order ip > sc > im. After sc and im injections of polymers, the elimination rate decreased with an increase in the molecular weight, whereas the elimination rate of polymers injected showed no molecular weight dependence over the range studied, regardless of the type of polymers used. The time-course of polymer concentration in the blood depended largely on the injection route of the polymers, and the polymer elimination from the blood circulation was enhanced with the decreasing molecular weight of polymers injected. It was concluded that the molecular weight and the injection site are the important factors that affect the concentration profile of polymers in the blood circulation.

Computerised image analysis in conjunction with fluorescence microscopy for the study of blood-brain barrier permeability in vivo

The present paper describes a new method using computerised image analysis techniques for quantification of tracer extravasation over the blood-brain barrier as studied by intravital fluorescence microscopy. Cats were equipped with an open cranial window and continuously infused with fluorescein isothiocyanate-labelled dextran (FITC-dextran, mol. wt. 70,000) to maintain a steady plasma concentration. Several cortical fields were recorded in each experiment and the images stored on video tape for off-line analysis. This procedure, which largely eliminates the superficial pial vasculature and allows extraction of the extravasation areas, consists of the following steps: (1) averaging of images, (2) software shading correction based on the original images for compensation of optical non-uniformity, (3) correction of displacement artefacts, (4) intensity adjustment, (5) generation of subtraction images by subtracting the first image of a series from the subsequent ones, (6) median filtering and thresholding, (7) a length recognition algorithm, and (8) elimination of small areas. Compared to the previously described method, step (2) has been newly developed and steps (4) and (8) added to enhance sensitivity for detecting tracer extravasation. The degree of extravasation in a cortical field at a given time point [E(f) value] was calculated as the mean intensity of the remaining pixels. The E(f) is a quantitative value computed by a fully automatised procedure which takes into account the number, as well as the size and intensity, of extravasation areas in a given cortical field. The E(f) values obtained at different times in a series of experiments were averaged to give the E(I) value.(ABSTRACT TRUNCATED AT 250 WORDS)

Hapten-tagged plasma proteins as immunocytochemical probes for the study of vascular permeability

Bovine serum albumin and transferrin were covalently coupled with fluorescein isothiocyanate and digoxigenin, respectively, and intravenously co-injected in equal amounts in mouse. The derivation of the two proteins induces minor alterations of their physicochemical properties as well as of their physiological functions. The two tracers were revealed within vascular and extravascular compartments of diaphragm by quantitative postembedding immunocytochemistry, using antibodies against each of the haptens in conjunction with the protein AG-gold complexes. The influence of different fixatives and embedding protocols on the immunodetectability of the hapten-tagged proteins was assessed. Both resist reasonably well to osmication and embedding in Epon. None of the haptens reacted with the heterologous antibody. At 30 minutes after injection, the tracers were detected in blood plasma, interstitium, and endothelial plasmalemmal vesicles. The presence of both proteins within the interendothelial clefts was inconspicuous. The ratios between the labeling densities found over endothelium, interstitial space, and vascular lumen were similar for both tracers. This suggests that the endothelium of mouse diaphragm capillaries might exhibit comparable permeabilities towards serum albumin and transferrin which are similar in size and charge. The study shows that hapten-tagged polypeptides are close to the corresponding native macromolecules, and represent interesting tools for the morphological study of dynamic processes such as transcytosis.

Experimental determination of the linear correlation between in vivo TV fluorescence intensity and vascular and tissue FITC-DX concentrations

A novel in vivo calibration procedure was developed to determine the microvascular and tissue concentration of fluorescein isothiocyanate-labeled dextrans (FITC-Dx) in the hamster cheek pouch, using intravital fluorescence microscopy with manually controlled TV camera gain and threshold value. Two FITC-dextrans (70,000 and 150,000 MW) were used as tracers. Five minutes after the tracer was administered, selected venules (diameter 20-50 microns) were videotaped, and intravascular gray levels were obtained by digital image processing. Simultaneously, arterial blood samples were taken to measure vascular FITC-Dx concentrations with a spectrofluorometer. The gray levels and the concentrations were used to produce a calibration curve for the vascular FITC-Dx concentration. A similar calibration curve for the interstitial FITC-Dx concentration was obtained by first video recording interstitial space areas saturated with the tracer. After flushing out the tracer in the vessels, the hamster cheek pouch was then cut, weighted, and homogenized. The interstitial FITC-Dx concentration was finally measured with a spectrofluoromet. The gray levels and the concentrations were used to produce a calibration curve for the interstitial FITC-Dx concentration. The gray level was found to vary linearly with both the FITC-Dx vascular concentration (range 0.4-3.0 mg/ml) and the interstitial FITC-Dx concentration (0.12-1.50 mg/ml) in the hamster cheek pouch.

Mathematical modeling of mass transfer in microvascular wall and interstitial space

A one-dimensional, unsteady-state mathematical model was developed to describe the transfer of macromolecules across a microvascular wall and into the interstitial space. The proposed theoretical model accounts for both molecular diffusion and convective transfer through the microvascular wall as well as in the interstitial space. The resulting partial differential equations were simultaneously solved using the Laplace transform method. The inversion of the Laplace transformed equations was obtained by using contour integration in the complex region. The final solution is represented by two equations expressing the macromolecule concentration in the microvascular wall region and in the interstitial space, respectively, as functions of time, spatial coordinate, macromolecule concentration in the microvascular wall at the plasma-wall interface, wall thickness, wall-interstitial space equilibrium constant for the macromolecules, ratio of the cross-sectional area of the two regions, sieving coefficients, diffusivity coefficients, and average fluid velocity terms in the two regions. Plots of the macromolecule concentration in both regions as a function of time are presented and discussed for selected values of the parameters. An analytical expression for the total amount of mass which has accumulated in a portion of the interstitial space at any given time was also derived and used to determine the average fluid velocity term and the diffusivity coefficient for each of the two regions from published experimental data (A. Y. Bekker, A. B. Ritter, and W. N. Durán, 1989, Microvasc. Res. 34, 200-216). A numerical nonlinear regression method was used for this purpose. The values for the diffusivity coefficients found in this work for this particular data set compare favorably with the results previously obtained by other workers in similar systems. It is expected that our model will be used in the future to describe the dynamics of mass transfer across a microvascular wall and into the interstitial space, on the basis of the molecular diffusion and/or convective transport mechanisms, thus contributing to the solution of the controversy regarding the nature of the transfer mechanism controlling macromolecule transport in living systems.