Cyclic GMP-mediated macromolecular extravasation from angiogenic microvessels in vivo

Previously, we reported an abrupt reduction in chick chorioallantoic membrane (CAM) microvascular permeability to macromolecules between days 4.5 and 5.0 of the 21-day gestation. Further, exogenous activation of the cAMP pathway at day 4.5 served to restrict normal macromolecular extravasation. Here, we evaluated the influence of the cGMP pathway on macromolecular efflux at day 5.0. Zaprinast (10(-4) M), a selective inhibitor of the cGMP-specific phosphodiesterase (PDE V), acutely increased basal levels of FITC-dextran 40 extravasation. Further, the cGMP analogue, 8 br-cGMP (10(-4) and 10(-3) M) and the soluble guanylate cyclase activator, sodium nitroprusside (SNP, 10(-5) and 10(-4) M) increased tracer extravasation in a dose-dependent fashion. The cGMP-mediated increase was not associated with gap formation along the junctional clefts, however, vesiculo-vacuolar structures were characteristic of CAM endothelial ultrastructure. KT 5823 (10(-5) M), the highly selective protein kinase G (PKG) inhibitor, also served to increase basal tracer extravasation. The nonselective PDE inhibitor, IBMX (10(-4) M) had no effect alone, but reduced the permeability effects of both 8 br-cGMP and SNP. Rolipram (10(-4) M), a selective PDE IV inhibitor, on the other hand, potentiated the effect of 8 br-cGMP. These results serve to suggest that cAMP degradation, rather than PKG activation, is a principal component of the cGMP-mediated increase in CAM endothelial permeability in vivo.

Predominant role of endothelial nitric oxide synthase in vascular endothelial growth factor-induced angiogenesis and vascular permeability

Nitric oxide (NO) plays a critical role in vascular endothelial growth factor (VEGF)-induced angiogenesis and vascular hyperpermeability. However, the relative contribution of different NO synthase (NOS) isoforms to these processes is not known. Here, we evaluated the relative contributions of endothelial and inducible NOS (eNOS and iNOS, respectively) to angiogenesis and permeability of VEGF-induced angiogenic vessels. The contribution of eNOS was assessed by using an eNOS-deficient mouse, and iNOS contribution was assessed by using a selective inhibitor [l-N(6)-(1-iminoethyl) lysine, l-NIL] and an iNOS-deficient mouse. Angiogenesis was induced by VEGF in type I collagen gels placed in the mouse cranial window. Angiogenesis, vessel diameter, blood flow rate, and vascular permeability were proportional to NO levels measured with microelectrodes: Wild-type (WT) > or = WT with l-NIL or iNOS(-/-) > eNOS(-/-) > or = eNOS(-/-) with l-NIL. The role of NOS in VEGF-induced acute vascular permeability increase in quiescent vessels also was determined by using eNOS- and iNOS-deficient mice. VEGF superfusion significantly increased permeability in both WT and iNOS(-/-) mice but not in eNOS(-/-) mice. These findings suggest that eNOS plays a predominant role in VEGF-induced angiogenesis and vascular permeability. Thus, selective modulation of eNOS activity is a promising strategy for altering angiogenesis and vascular permeability in vivo.

Analysis of biological effects and signaling properties of Flt-1 (VEGFR-1) and KDR (VEGFR-2). A reassessment using novel receptor-specific vascular endothelial growth factor mutants

Endothelial cells express two related vascular endothelial growth factor (VEGF) receptor tyrosine kinases, KDR (kinase-insert domain containing receptor, or VEGFR-2) and Flt-1 (fms-like tyrosine kinase, or VEGFR-1). Although considerable experimental evidence links KDR activation to endothelial cell mitogenesis, there is still significant uncertainty concerning the role of individual VEGF receptors for other biological effects such as vascular permeability. VEGF mutants that bind to either KDR or Flt-1 with high selectivity were used to determine which of the two receptors serves to mediate different VEGF functions. In addition to mediating mitogenic signaling, selective KDR activation was sufficient for the activation of intracellular signaling pathways implicated in cell migration. KDR stimulation caused tyrosine phosphorylation of both phosphatidylinositol 3-kinase and phospholipase Cgamma in primary endothelial cells and stimulated cell migration. KDR-selective VEGF was also able to induce angiogenesis in the rat cornea to an extent indistinguishable from wild type VEGF. We also demonstrate that KDR, but not Flt-1, stimulation is responsible for the induction of vascular permeability by VEGF.

Hypercholesterolemia impairs myocardial perfusion and permeability: role of oxidative stress and endogenous scavenging activity

OBJECTIVES

We intended to study the effect of hypercholesterolemia (HC) on myocardial perfusion and permeability response to increased cardiac demand.

BACKGROUND

Hypercholesterolemia is associated with increased incidence of cardiac events and characterized by impaired coronary vascular function, possibly mediated partly through increased pro-oxidative conditions in plasma and tissue. However, it is yet unclear whether HC is also associated with impaired myocardial perfusion and vascular permeability responses in vivo.

METHODS

For 12 weeks pigs were fed a normal, HC or HC diet supplemented daily with antioxidants (HC + AO, 100 IU/kg vitamin E and 1 g vitamin C). Myocardial perfusion and vascular permeability were measured in vivo using electron beam computed tomography before and after cardiac challenge with intravenous adenosine. Plasma and tissue oxidative status was determined ex vivo.

RESULTS

Plasma cholesterol increased in all cholesterol-fed pigs but was associated with increased markers of oxidative stress only in HC pigs. Myocardial perfusion increased in response to adenosine in normal and HC + AO (+37 +/- 13% and +58 +/- 22%, respectively, p < 0.05 vs. baseline) but not in HC, whereas vascular permeability index increased only in HC pigs (+ 92 +/- 25%, p = 0.002). In HC animals, tissue endogenous oxygen radical scavengers and antioxidant vitamins were depleted and LDL oxidizability enhanced, but both were normalized in HC + AO pigs. Myocardial perfusion response was directly, and permeability inversely, associated with plasma and tissue vitamin concentrations.

CONCLUSIONS

This study demonstrates that experimental HC is associated with blunted myocardial perfusion and increased vascular permeability responses in vivo to increased cardiac demand, which may be partly mediated by a shift in oxidative status.

Effect of changing vascular volume on measurement of protein reflection coefficient in ischemic lungs

In ischemic organs, the protein reflection coefficient (sigma) can be estimated by measuring blood hematocrit (Hct) and protein after increasing static vascular pressure (P(v)). Our original equation for sigma (J Appl Physiol 73: 2616-2622, 1992) assumed a constant vascular volume during convective fluid flux (). In this study, we 1) quantified the rate of vascular volume change (dV/dt) still present in ischemic single ferret lungs after 20 min of P(v) = 30 Torr and 2) developed an equation for sigma that allowed a finite dV/dt. In 25 lungs, we estimated the dV/dt after 20 min at P(v) = 30 Torr by subtracting from the rate of lung weight gain (W(L)). The relationship between (0.15 +/- 0.02 ml/min) and W(L) (0.24 +/- 0.02 g/min) was significant (R = 0.66, P < 0.001), but the slope was <1 (0.41 +/- 0.10, P < 0.05). dV/dt (0.10 +/- 0.02 ml/min) was similar in magnitude to at 20 min. The modified equation for sigma revealed that a finite dV/dt caused the original sigma measurement to underestimate true sigma. A low sigma, high, high baseline Hct, and long filtration time enhanced the error. The error was small, however, and could be minimized by adjusting experimental parameters.

Thrombin-mediated permeability of human microvascular pulmonary endothelial cells is calcium dependent

BACKGROUND

In response to inflammation, endothelial cytoskeleton rearrangement, cell contraction, and intercellular gap formation contribute to a loss of capillary barrier integrity and resultant interstitial edema formation. The intracellular signals controlling these events are thought to be dependent on intracellular calcium concentration ([Ca2+]i). We hypothesized that, in human pulmonary microvascular endothelial cells, a thrombin-induced increase in permeability to albumin would be dependent on Ca2+i and subsequent actin cytoskeleton rearrangements.

METHODS

Human lung microvascular endothelial cells, grown on 0.4 micromol/L pore membranes, were activated with 10 nmol/L human thrombin in Hank's balanced salt solution/0.5% fetal bovine serum. Select cultures were pretreated (45 minutes) with 4 micromol Fura-2/AM to chelate Ca2+i. Permeability was assessed as diffusion of bovine serum albumin/biotin across the monolayer. Similarly treated cells were stained with rhodamine-phalloidin to demonstrate actin cytoskeletal morphology. Separately, cells loaded 2 micromol Fura-2/AM were assessed at OD340/380nm after thrombin exposure to detect free Ca2+i.

RESULTS

Intracellular Ca2+ levels increased 15-fold (2 seconds) and fell to baseline (10 minutes) after thrombin. Permeability increased 10-fold (30 minutes), and a shift from cortical to actin stress fiber morphology was observed. Chelation of Ca2+i diminished permeability to baseline and reduced the percentage of cells exhibiting stress fiber formation.

CONCLUSION

Thrombin stimulates pulmonary capillary leak by affecting the barrier function of activated pulmonary endothelial cells. These data demonstrate a thrombin-stimulated increase in monolayer permeability, and cytoskeletal F-actin stress fibers were, in part, regulated by endothelial Ca2+i. This early, transient rise in Ca2+i likely activates downstream pathways that more directly affect the intracellular endothelial structural changes that control vascular integrity.

Modulation of alveolar-capillary sodium handling as a mechanism of protection of gas transfer by enalapril, and not by losartan, in chronic heart failure

OBJECTIVES

We sought to compare the protective efficacy of enalapril and losartan on lung diffusion in chronic heart failure (CHF).

BACKGROUND

In CHF, hydrostatic overload causes disruption of the alveolar-capillary membrane and depression of carbon monoxide diffusion (DCO); enalapril improves DCO through mechanisms still undefined; and saline infusion in the pulmonary circulation worsens DCO, putatively because of an upregulated sodium transport to the alveolar interstitium. We investigated whether enalapril modulates sodium handling and whether losartan shares the same properties.

METHODS

In 29 patients with CHF, DCO, its membrane diffusion subcomponent (DM) and right atrial and pulmonary wedge pressures were monitored during saline infusion, in the control condition, during enalapril therapy (20 mg/day) for two weeks and after crossover to losartan (50 mg/day) for two weeks (first 20 patients), or after the combination of enalapril with aspirin (325 mg/day) for one week (last 9 patients).

RESULTS

Saline, 150 ml, lowered DCO (-7.9%; p < 0.01) and DM (-9.9%; p < 0.01) without hydrostatic variations. Responses to 750 ml of saline were qualitatively similar. After treatment with enalapril, baseline DCO (p < 0.01) and DM (p < 0.01) were augmented; after sodium loading, the percent reductions of DCO (p < 0.01) and DM (p < 0.01) were comparable to those before it, resulting in higher absolute values. This suggests that the greater the gas conductance improvement with enalapril, the lower the impedance with saline. Losartan was ineffective on gas transfer at rest and under salt challenge. Aspirin counteracted the benefits of enalapril.

CONCLUSIONS

In CHF, enalapril protects lung diffusion, possibly through a prostaglandin-mediated modulation of sodium overfiltration to the alveolar interstitium; losartan does not share this ability.

Requirement for Ca2+ signaling in the mechanism of thrombin-induced increase in endothelial permeability

We compared the thrombin-activated responses in human umbilical vein endothelial cells (HUVECs) and a HUVEC-derived cell line, ECV304. Thrombin induced a 40-50% decrease in transendothelial monolayer electrical resistance and a twofold increase in 125I-albumin permeability in HUVECs, whereas it failed to alter the endothelial barrier function in ECV304 cells. Thrombin produced a brisk intracellular Ca2+ concentration transient and phosphorylation of 20-kDa myosin light chain in HUVECs but not in ECV304 cells. Thrombin-induced phosphoinositide hydrolysis was comparable in ECV304 cells and HUVECs, indicating the activation of thrombin receptors in both cell types. La3+ reduced both the thrombin-induced decrease in endothelial monolayer electrical resistance and the increase in 125I-albumin permeability in HUVECs. Because the absence of Ca2+ signaling could explain the impairment in the permeability response in ECV304 cells, we studied the effect of increasing intracellular Ca2+ concentration in ECV304 cells with thapsigargin. Exposure of ECV304 cells to thapsigargin caused decreased endothelial monolayer electrical resistance and increased 125I-albumin permeability. These results indicate that Ca2+ influx and activation of Ca2+-dependent signaling pathways are important determinants of the thrombin-induced increase in endothelial permeability.

Changes in permeability of strial vessels following vibration given to auditory ossicle by drill

We produced drill-induced damage of the auditory ossicles of guinea pigs to study changes over time in the permeability of the blood vessels of the stria vascularis to horseradish peroxidase (HRP). In group A, the stimulus was applied for 10 seconds after intravenous injection of HRP. In group B, it was applied for 30 seconds, and in group C, for 60 seconds. The cochlea was fixed with 2% glutaraldehyde perfused through the round window, and the guinea pigs were then decapitated. The stria vascularis of the basal and third turns was examined. The leakage of HRP from the blood vessels of the stria vascularis significantly increased in relation to the duration of the stimulus in both the basal and third turns. The damage to intermediate cells also tended to be in relation to the duration of the stimulus. Extravascular permeation of HRP took place through the tubules in the endothelial cytoplasm. The vibratory stimulation presumably opened channels that are not normally open.

[Experimental study for lung fluid transport by epithelial cells and aquaporins]

OBJECTIVE

To explore the effects of aquaporins (AQP) 1, 4 on water transport between airspace and pulmonary capillary and high pressure pulmonary edema. The other purpose was to study the active alveolar fluid transport as well as alveolar fluid clearance (AFC) in different pH of airspace.

METHODS

The effects of AQP1, 4 on water transport between airspace and pulmonary capillary and high pressure pulmonary edema were studied by surface fluorescence methods and gravimetric method respectively, AFC and AFC in airspace with different pH were measured by isotope method.

RESULTS

AQP1 knockout inhibited water transport through pulmonary capillary and also reduced high pressure pulmonary edema. Salbutamol increased AFC, but it was reduced when propranolol was used together. AFC was improved by terbutaline, isoproterenol, salmeterol when pH > 2.5 in airspace, but the effect was reduced after pH < 2.5 in airspace. Sodium channel inhibitor, Benzamil, could also inhibit AFC.

CONCLUSIONS

AQP1 knockout significantly reduced water transport through alveolar capillary, and also reduced high pulmonary edema slightly. beta adrenergic stimulant improved AFC in mechanically ventilated rats. Intact airspace is very important for the function of AFC, however, the effect of AFC was impaired after lung injury induced by pH < 2.5 in airspace.

Intraluminal acid and gastric mucosal integrity: the importance of blood-borne bicarbonate

The acid-secreting gastric mucosa resists intraluminal acid better than the nonsecreting. Here we investigated pH at the epithelial cell surface, mucosal permeability, and blood flow during intraluminal administration of acid (100 mM) in acid-stimulated and nonstimulated gastric corpus mucosae. Surface pH (H(+)-selective microelectrodes), permeability (clearance of (51)Cr-EDTA), and mucosal blood flow (laser-Doppler flowmetry) were studied in Inactin-anesthetized rats. Acid secretion was stimulated with pentagastrin (40 microg. kg(-1). h(-1)) or impromidine (500 microg. kg(-1). h(-1)), or HCO(3)(-) (5 mmol. kg(-1). h(-1)) given intravenously. Surface pH was only slightly reduced by intraluminal acid in acid secretion-stimulated or HCO(3)(-)-treated rats but was substantially lowered in nonstimulated rats. Clearance increased threefold and blood flow increased by approximately 75% in nonstimulated rats. During stimulated acid secretion or intravenous infusion of HCO(3)(-), clearance was unchanged and blood flow increased by only approximately 30% during intraluminal acid. Increased epithelial transport of HCO(3)(-) buffering the mucus gel is most probably the explanation for the acid-secreting mucosa being less vulnerable to intraluminal acid than the nonsecreting.

Haptoglobins as markers of blood-CSF barrier dysfunction: the findings in normal CSF

Cerebrospinal fluid from 39 healthy individuals showed evidence for increasing blood-CSF barrier permeability with age, and confirmed that haptoglobins are more sensitive but less predictive markers of barrier permeability than total protein. Haptoglobin (Hp) species were identified by polyacrylamide gel electrophoresis followed by immunoblotting. Hp 1-1 (35 A, 85 kDa) was detected in all (9/9) subjects who exhibited this phenotype. Hp 2-1 (42 A, 120 kDa) was detected in 53% (8/15) of subjects in whom Hp 2-1 was the phenotype. Hp 2-2 (54 A, 160 kDa) was detected in only 20% (3/15) of subjects who exhibited this phenotype. The likelihood of detecting any haptoglobin species corresponded to the molecular size and the consequent resistance offered by the barrier. Among younger subjects aged < or =45 years, a significant difference in incidence occurred between the two smaller species Hp 1-1 and Hp 2-1. However, among those aged >45, the significant difference in incidence was between the two larger species Hp 2-1 and Hp 2-2. The incidence of detection among those with Hp 2-1 phenotypes was higher in the older age group. The increased likelihood of detecting haptoglobins with age is in keeping with the notion that barrier function is compromised by age, and also indicates that Hp 2-1 and Hp 2-2 are sensitive markers of barrier function. The appreciable incidence of haptoglobins in normal CSF, even of the larger species, suggests reservation in assuming that their presence signifies barrier damage.

Etiology of acute pulmonary edema during liver transplantation : a series of cases with analysis of the edema fluid

STUDY OBJECTIVES

To describe the clinical features of a group of patients who acutely developed pulmonary edema during orthotopic liver transplantation and to determine the nature (transudate vs exudate) of the edema.

DESIGN

Retrospective review of clinical records and radiographic studies.

SETTING

Operating room and ICU of a tertiary-care medical center hospital.

PATIENTS

End-stage liver disease patients undergoing orthotopic liver transplantation under general anesthesia.

INTERVENTIONS AND MEASUREMENTS

Pulmonary edema fluid obtained from seven patients within 15 min of first appearance was analyzed for protein content and compared with the protein content of a simultaneously obtained plasma sample. Hemodynamic data, fluid administration totals, and length of postoperative intubation and ICU stay were also collected.

RESULTS

Eight patients were identified. Six of the seven patients whose edema fluid was analyzed had edema fluid/plasma protein ratios > or =0.75, characteristic of increased permeability pulmonary edema (the one other patient had a ratio of 0.73). Hemodynamic monitoring at the time of onset of the edema effectively ruled out a cardiogenic etiology. One patient died intraoperatively; at autopsy, the cause of death was determined to be pulmonary fat embolization. In the other seven patients, production of edema fluid resolved within 6 h of admission to the ICU. The duration of ventilatory support ranged from 23 to 96 h, with a mean of 49 h.

CONCLUSIONS

The most likely cause of the reaction is transfusion-related acute lung injury (TRALI). An incidence of TRALI that is higher than previously reported in this population indicates that other elements, such as reperfusion of the newly implanted liver, may be contributing factors.

Interstitial fluid pressure surrounding rat mesenteric venules during changes in fluid filtration

The interstitial fluid pressure (P(isf)) has been measured in the exposed superfused mesenteries of anaesthetised rats using the micropipette servo-null technique. When mesenteries were superfused with Ringer-Locke solutions, P(isf) was close to atmospheric pressure with mean +/- S.E.M. values of -0.46 +/- 0.14 cmH(2)O (n = 22). Superfusing with paraffin oil did not alter P(isf) significantly, but P(isf) could be lowered considerably by removing fluid from the upper surface of the mesentery. Measurements of P(isf) were also made in the tissues immediately outside mesenteric venules as the pressure inside these vessels and the filtration of fluid through their walls was varied. No significant changes in perivascular P(isf) could be detected even though the intravascular pressure varied from 20 to 70 cmH(2)O. Addition of histamine or the mast cell degranulating agent compound 48/80 to the superfusate had no significant effect on P(isf). The findings are relevant to experiments on the permeability of single perfused mesenteric microvessels. They strengthen the assumption, which is made in these studies, that P(isf) is close to atmospheric pressure and does not change significantly with changes in the filtration and reabsorption of fluid through the vessel walls. Experimental Physiology (2001) 86.1, 33-38.

Capillary filtration is reduced in lungs adapted to chronic heart failure: morphological and haemodynamic correlates

OBJECTIVE

To determine pulmonary capillary filtration in experimental chronic heart failure and to investigate some morphological and haemodynamic mechanisms that could account for reduced filtration in lungs adapted to chronic heart failure.

METHODS

We studied pulmonary capillary filtration, vascular resistances and morphology in lungs from guinea-pigs adapted to chronic heart failure. Heart failure was induced by banding of the ascending aorta (n=66) or sham control operation (n=78) in guinea-pigs which were studied at 150+/-8 days post-operation.

RESULTS

Reduced cardiac output, increased systemic vascular resistance and LV end diastolic pressure and increased LV and RV weight:body weight ratio (all P<0.05) indicated chronic heart failure at 5 months following aortic banding in guinea-pigs. Lung weight was increased (61%, P<0.05) in heart failure compared with controls, but lung water content was reduced (5.5%, P<0.05), a reversal of the pattern seen acutely. Studies in isolated perfused lungs demonstrated a reduced capillary filtration coefficient (0. 018+/-0.003 vs. 0.003+/-0.002 ml min(-1)mmHg(-1)g(-1), P<0.001), increased arterial (61%) and venous resistance (50%) in heart failure lungs, P<0.05. Wall thickness:lumen ratio was increased in small (<250 microm) pulmonary arterioles (0.15+/-0.02 vs. 0.08+/-0. 01) and venules (0.06+/-0.005 vs. 0.04+/-0.002) in heart failure, P<0.01. Alveolar septal volume fractions (35.2+/-5.1 vs. 23.1+/-2.7) and septal:air-space volume ratios (60.5+/-13.6 vs. 31.9+/-5.3) were also increased in heart failure, P<0.05.

CONCLUSIONS

Pulmonary adaptation to chronic heart failure is associated with vascular and alveolar remodelling that contributes to increased vascular resistance and reduced capillary filtration. These changes are likely to be important in mediating resistance to pulmonary oedema in chronic heart failure.

Regional transcapillary albumin exchange in rodent endotoxaemia: effects of fluid resuscitation and inhibition of nitric oxide synthase

Sepsis is characterized by increased microvascular permeability and regional variations in capillary perfusion, which may be modulated by nitric oxide (NO) and reversed by fluid resuscitation (FR). The effects of saline FR and NO synthase blockade [by N(G)-nitro-L-arginine methyl ester (L-NAME)] on microvascular albumin transport and perfused capillary density were assessed in anaesthetized Wistar rats with acute normodynamic endotoxaemia. Separate dual-isotope techniques were employed to measure the permeability index (PI(A)) and the permeabilityxsurface area product index (PI(B)), which provide different and complementary information regarding blood-tissue albumin exchange. PI(A) represents the tissue/blood distribution volume ratio of albumin. PI(B) is a composite measure of endothelial permeability and the vascular surface area available for albumin exchange, and therefore takes into account the effect of altered blood volume. Capillary density was quantified by fluorescence microscopy following circulation of Evans Blue-labelled albumin. Compared with controls, PI(A) was reduced significantly in lipopolysaccharide (LPS)-treated animals in skeletal muscle and skin, probably due to blood volume redistribution rather than to changes in permeability. PI(B) was increased significantly in LPS-treated animals in the kidney, mesentery, skeletal muscle, skin and lung, and in the small bowel following FR. FR also improved the LPS-induced metabolic base deficit, but did not alter capillary density. L-NAME significantly attenuated the LPS-induced rise in PI(B) in the lung. In conclusion, acute endotoxaemia induces tissue-dependent variations in microvascular albumin exchange. FR improves acid-base disturbance in endotoxaemia, through mechanisms other than microvascular recruitment. NO appears to increase microvascular permeability in endotoxaemia, an effect that may be attenuated by L-NAME, particularly in the lung.

Mediator involvement in antigen-induced bronchospasm and microvascular leakage in the airways of ovalbumin sensitized Brown Norway rats

1. To determine which mediators are involved in antigen-induced bronchospasm and microvascular leakage in the airways of ovalbumin sensitised Brown Norway rats we investigated the effect of a histamine H(1) receptor antagonist, mepyramine, a 5-HT receptor antagonist, methysergide, and a cys-leukotriene-1 receptor antagonist, montelukast. 2. Ovalbumin at 1 mg kg(-1) i.v. caused a significant increase in microvascular leakage in the airways and at 3 mg kg(-1) i.v. caused a significant increase in airways resistance. 3. Histamine (1 mg kg(-1) i.v.), 5-HT (0.1 mg kg(-1) i.v.) and leukotriene D(4) (LTD(4), 50 microg kg(-1) i.v.) caused a significant increase in microvascular leakage in the airways. 4. Mepyramine (1 mg kg(-1) i.v.), methysergide (0.1 mg kg(-1) i.v.), or montelukast (30 mg kg(-1) i.v.) inhibited histamine, 5-HT or LTD(4) -induced microvascular leakage respectively. 5. Methysergide (0.1 mg kg(-1) i.v.) reduced ovalbumin-induced microvascular leakage in the trachea and at 0.3 mg kg(-1) i.v. inhibited bronchospasm (38 and 58%, respectively). Montelukast (30 mg kg(-1) p.o.) reduced ovalbumin-induced microvascular leakage in airway tissue to basal levels (78%) and inhibited ovalbumin-induced bronchospasm (50%). Mepyramine (3 mg kg(-1) i.v.) had no effect on ovalbumin-induced leakage or bronchospasm. 6. A combination of all three compounds (mepyramine, methysergide and montelukast) reduced ovalbumin-induced microvascular leakage in airway tissue to basal levels (70 - 78%) and almost completely inhibited bronchospasm (92%). 7. Antigen-induced bronchospasm appears to equally involve the activation of 5-HT and cys-leukotriene-1 receptors whereas ovalbumin-induced microvascular leakage appears to be predominantly mediated by cys-leukotriene-1 receptors.

The effects of dexamethasone therapy on permeability, blood flow and iNOS expression in experimental glioma

Most studies of dexamethasone (DXN) effects on experimental glioma have used doses 10-500 higher (on mg/kg basis) than those used for patients with brain tumour. The relevance of findings to patients with glioma are therefore uncertain. In order to evaluate the effects of clinical doses of DXN (0.22 mg kg(-1)day(-1)) on the pathophysiology of an experimental glioma we have treated rodents with established C6 gliomas for 3 days. The effects of therapy on local cerebral blood flow (LCBF), tumour blood flow (TBF), tumour capillary permeability (TCP), and inducible nit ric oxide synthase (iNOS) mRNA expression were evaluated. DXN caused a significant reduction in TCP (21 +/- 1.9 to 7.7 +/- 2.2 ml.gm(-1)min(-1)10(-3)) and iNOS mRNA production within and around tumour, but no significant change in either TBF or LCBF. The reduction in TCP was identical to that reported after higher doses of DXN and is probably mediated by glucocorticoid receptors. Further in vivo stud ies using either behavioural or neuropathological paradigms in rodents with established cerebral glioma should be treated with similar doses of DXN to optimise clinical relevance.

Nitric oxide mediates platelet activating factor-induced microvascular leakage in rat airways

Platelet activating factor (PAF), a highly potent chemical mediator in inflammation and allergic reactions, induces microvascular leakage in several tissues. In rat airways, PAF-induced microvascular leakage is probably mediated by an endothelial cell receptor in the microvessels. Nitric oxide (NO), first identified as endothelium-derived relaxing factor, has been suggested to be a mediator of airway microvascular leakage. However, the role of NO in PAF-induced microvascular leakage in the airways has not yet been established. The aim of this study was to investigate the role of NO in PAF-induced microvascular leakage in rat nasal mucosa and trachea. We injected PAF (1 microg/kg) intravenously, and the amount of PAF-induced microvascular leakage was measured with extravasation of Evans blue dye (30 mg/kg, injected intravenously 5 minutes before the injection of PAF) by means of spectrophotometry and fluorescence microscopy. Five Sprague-Dawley rats were pretreated with NG-nitro-L-arginine methyl ester (L-NAME; 10 mg/kg, intravenously injected 1 hour before the injection of PAF) to inhibit NO synthase, and control rats (n = 4) were pretreated with normal saline solution. The average amount of extravasated Evans blue dye was significantly lower in the L-NAME-pretreated rats than in the control rats (t-test, p < .01). Tissue sections of the L-NAME-pretreated rats clearly showed a decreased extravasation of Evans blue dye on fluorescence microscopy. In conclusion, pretreatment with L-NAME clearly inhibited PAF-induced microvascular leakage in the nasal mucosa and trachea of rats. This finding implies that PAF may activate the constitutive endothelial NO synthase in the microvessels, and that activated endogenous NO may mediate PAF-induced microvascular leakage in rat airways.

Vascular permeability in allergic conjunctivitis in mice lacking histamine H1 receptors

To clarify the role of histamine H1 receptors in allergic conjunctivitis, changes in vascular permeability of the conjunctiva were measured in histamine H1 receptor deficient mice. Wild-type mice showed a significant increase in vascular permeability of the conjunctiva induced by histamine. However, no such increase was found in histamine H1 receptor deficient mice. On the other hand, no differences were observed between wild-type and histamine H1 receptor deficient mice in response to serotonin. A significant increase in vascular permeability was observed in actively sensitized wild-type mice, whereas no increase was observed in histamine H1 receptor deficient mice. Similar findings were noted in passively sensitized animals. Histamine contents of the conjunctiva were significantly decreased by topical application of antigen in both wild-type and histamine H1 receptor deficient mice after active sensitization with antigen. These findings suggested that vascular permeability in the conjunctiva in allergic conjunctivitis is entirely regulated through histamine H1 receptor.

Simvastatin improves disturbed endothelial barrier function

BACKGROUND

Recent clinical trials have established that inhibitors of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (statins) reduce the risk of acute coronary events. These effects of statins cannot be fully explained by their lipid-lowering potential. Improved endothelial function may contribute to the positive effects of statin treatment.

METHODS AND RESULTS

In the present study, we report that simvastatin reduces endothelial barrier dysfunction, which is associated with the development of atherosclerosis. Treatment of human umbilical vein endothelial cells for 24 hours with 5 micromol/L simvastatin reduced the thrombin-induced endothelial barrier dysfunction in vitro by 55+/-3%, as assessed by the passage of peroxidase through human umbilical vein endothelial cell monolayers. Similar effects were found on the thrombin-induced passage of (125)I-LDL through human aortic endothelial cell monolayers. This reduction in barrier dysfunction by simvastatin was both dose and time dependent and was accompanied by a reduction in the thrombin-induced formation of stress fibers and focal adhesions and membrane association of RhoA. Simvastatin treatment had no effect on intracellular cAMP levels. In Watanabe heritable hyperlipidemic rabbits, treatment for 1 month with 15 mg/kg simvastatin reduced vascular leakage in both the thoracic and abdominal part of the aorta, as evidenced by the Evans blue dye exclusion test. The decreased permeability was not accompanied by a reduction of oil red O-stainable atherosclerotic lesions.

CONCLUSIONS

These data show that simvastatin, in a relatively high concentration, improves disturbed endothelial barrier function both in vitro and in vivo. The data also support the beneficial effects of simvastatin in acute coronary events by mechanisms other than its lipid-lowering effect.

Lung function, permeability, and surfactant composition in oleic acid-induced acute lung injury in rats

Although acute lung injury (ALI) is associated with inflammation and surfactant dysfunction, the precise sequence of these changes remains poorly described. We used oleic acid to study the pathogenesis of ALI in spontaneously breathing anesthetized rats. We found that lung pathology can occur far more rapidly than previously appreciated. Lung neutrophils were increased approximately threefold within 5 min, and surfactant composition was dramatically altered within 15 min. Alveolar cholesterol increased by approximately 200%, and even though disaturated phospholipids increased by approximately 30% over 4 h, the disaturated phospholipid-to-total phospholipid ratio fell. Although the alveolocapillary barrier was profoundly disrupted after just 15 min, with marked elevations in lung fluid ((99m)Tc-labeled diethylenetriamine pentaacetic acid) and (125)I-labeled albumin flux, the lung rapidly began to regain its sieving properties. Despite the restoration in lung permeability, the animals remained hypoxic even though minute ventilation was increased approximately twofold and static compliance progressively deteriorated. This study highlights that ALI can set in motion a sequence of events continuing the respiratory failure irrespective of the alveolar surfactant pool size and the status of the alveolocapillary barrier.

Reversibility of increased microvessel permeability in response to VE-cadherin disassembly

We determined the role of vascular endothelial (VE)-cadherin complex in regulating the permeability of pulmonary microvessels. Studies were made in mouse lungs perfused with albumin-Krebs containing EDTA, a Ca(2+) chelator, added to study the VE-cadherin junctional disassembly. We then repleted the perfusate with Ca(2+) to restore VE-cadherin integrity. Confocal microscopy showed a disappearance of VE-cadherin immunostaining in a time- and dose-dependent manner after Ca(2+) chelation and reassembly of the VE-cadherin complex within 5 min after Ca(2+) repletion. We determined the (125)I-labeled albumin permeability-surface area product and capillary filtration coefficient (K(fc)) to quantify alterations in the pulmonary microvessel barrier. The addition of EDTA increased (125)I-albumin permeability-surface area product and K(fc) in a concentration-dependent manner within 5 min. The permeability response was reversed within 5 min after repletion of Ca(2+). An anti-VE-cadherin monoclonal antibody against epitopes responsible for homotypic adhesion augmented the increase in K(fc) induced by Ca(2+) chelation and prevented reversal of the response. We conclude that the disassembled VE-cadherins in endothelial cells are mobilized at the junctional plasmalemmal membrane such that VE-cadherins can rapidly form adhesive contact and restore microvessel permeability by reannealing the adherens junctions.