Suppression by isoproterenol of endothelial cell morphology and barrier function changes induced by platelet-activating factor

Thrombin-Induced Force Development in Vascular Endothelial Cells: Contribution to Alteration of Permeability Mediated by Calcium-Dependent and -Independent Pathways

Endothelial cell (EC) barrier dysfunction is associated with many types of vascular diseases. Investigators have hypothesized that altered EC contraction in conjunction with morphological changes may lead to EC dysfunction. However, the nature of EC contraction and its regulatory mechanisms are not fully understood. In this study we measured thrombin-induced force in bovine arterial EC force using EC fibers that were grown in a collagen matrix. Contraction, which occurred in time- and dose-dependent fashion, was elicited by thrombin. The thrombin-enhanced EC layer permeability was correlated with EC fiber contraction. These results suggest that EC contractile response is involved in alteration of EC barrier function. During the initial period of thrombin stimulation, cadherin complexes were disrupted and cell-to-cell connections were reduced. This was dependent on the transient increase in intracellular calcium concentration and myosin phosphorylation. Rho kinase activation led to rearrangement of actin stress fibers (ASF). Paracellular holes were created in the EC layer in parallel to EC morphological change. Our findings suggest that EC layer permeability is regulated by two distinguishable steps. In the initial period, the cell-to-cell connection was reduced in a calcium-dependent fashion. Subsequently, Rho kinase and ASF-mediated force development increased EC layer permeability via morphological change of EC.

The indirect effect of Tityus discrepans on rabbit pulmonary vasculature

Serum (IS) was obtained 0.5, 2, 4 or 6 h after inoculating s.c. six rabbits (approximately 2 kg) in each time period with 1 mg/kg of Tityus discrepans (Td) venom; the control was serum obtained from four rabbits 4 h after injecting them 1 ml s.c. of 0.9% NaCl. IS produced a transient (<25 min) rise in pulmonary artery pressure of isolated and perfused rabbit lungs, other lung parameters were not altered. We found that both scorpion venom and IS produced a approximately 50% transient increase of transendothelial electric resistance in cultured tissue human umbilical cord vein. Neither venom nor IS changed the transepithelial electrical resistance of tissue cultured human airway epithelia. The experiments suggest that humoral factors contained in the inoculated serum modify vascular endothelium in a much more effective manner than the venom by itself. These experiments also make it unlikely that vascular endothelium is the source of the humoral factors contained in inflammatory serum.

Migration of human hematopoietic progenitor cells across bone marrow endothelium is regulated by vascular endothelial cadherin

The success of stem cell transplantation depends on the ability of i.v. infused stem cells to engraft the bone marrow, a process referred to as homing. Efficient homing requires migration of CD34(+) cells across the bone marrow endothelium, most likely through the intercellular junctions. In this study, we show that loss of vascular endothelial (VE)-cadherin-mediated endothelial cell-cell adhesion increases the permeability of monolayers of human bone marrow endothelial cells (HBMECs) and stimulates the transendothelial migration of CD34(+) cells in response to stromal cell-derived factor-1alpha. Stromal cell-derived factor-1alpha-induced migration was dependent on VCAM-1 and ICAM-1, even in the absence of VE-cadherin function. Cross-linking of ICAM-1 to mimic the leukocyte-endothelium interaction induced actin stress fiber formation but did not induce loss of endothelial integrity, whereas cross-linking of VCAM-1 increased the HBMEC permeability and induced gaps in the monolayer. In addition, VCAM-1-mediated gap formation in HBMEC was accompanied by and dependent on the production of reactive oxygen species. These data suggest that modulation of VE-cadherin function directly affects the efficiency of transendothelial migration of CD34(+) cells and that activation of ICAM-1 and, in particular, VCAM-1 plays an important role in this process through reorganization of the endothelial actin cytoskeleton and by modulating the integrity of the bone marrow endothelium through the production of reactive oxygen species.

Vascular-endothelial-cadherin modulates endothelial monolayer permeability

Vascular endothelial (VE)-cadherin is the endothelium-specific member of the cadherin family of homotypic cell adhesion molecules. VE-cadherin, but not the cell adhesion molecule platelet/endothelial cell adhesion molecule (PECAM-1), markedly colocalizes with actin stress fibers at cell-cell junctions between human umbilical vein endothelial cells. Inhibition of VE-cadherin-mediated, but not PECAM-1-mediated, adhesion induced reorganization of the actin cytoskeleton, loss of junctional VE-cadherin staining and loss of cell-cell adhesion. In functional assays, inhibition of VE-cadherin caused increased monolayer permeability and enhanced neutrophil transendothelial migration. In a complementary set of experiments, modulation of the actin cytoskeleton was found to strongly affect VE-cadherin distribution. Brief stimulation of the beta2-adrenergic receptor with isoproterenol induced a loss of actin stress fibers resulting in a linear, rather than ‘jagged’, VE-cadherin distribution. The concomitant, isoproterenol-induced, reduction in monolayer permeability was alleviated by a VE-cadherin-blocking antibody. Finally, cytoskeletal reorganization resulting from the inactivation of p21Rho caused a diffuse localization of VE-cadherin, which was accompanied by reduced cell-cell adhesion. Together, these data show that monolayer permeability and neutrophil transendothelial migration are modulated by VE-cadherin-mediated cell-cell adhesion, which is in turn controlled by the dynamics of the actin cytoskeleton.

Effect of Fenoterol on PAF-induced lung edema in isolated and perfused rabbit lungs

We have studied the effects of fenoterol on PAF-induced response in pulmonary circulation. We used 28 isolated and perfused rabbit lungs preparations: eight control preparations (CP), four vehicles preparations (VP), eight PAF preparations (PP) with two doses of PAF, one called low dose (LD = 0.5 microg/kg of weight) and the other high dose (HD = 1 microg/kg of weight) and eight Fenoterol preparations (FP) which we administered 0.05 mg of Fenoterol for 15 min, followed by a LD and HD of PAF. FP prevented elevation of pulmonary artery pressure (Ppa) as compared to PP, at LD of PAF: 12.615 (CI 95%: 8.57-20.885) versus 83.705 (CI 95%: 50.55-114.3) cm of water; and at HD of PAF: 19.38 (CI 95%: 11.235-28.94) versus 205.1 (CI 95%: 141.3-271) cm of water respectively. FP prevented the increase in fluid filtration rate (FFR) observed in PP at both doses of PAF LD: 0.765 (CI 95%: 0.07-3.385) versus 0.01 (CI 95%: -0.05-0.005) g/min; HD: 5.515 (CI 95%: 2.425-8.865) versus 0.03 (CI 95%: 0-0.33) g/min. Our results suggest that PAF has a vasoconstrictor effect that produces lung edema and this effect is inhibited by fenoterol.

Vascular barrier-enhancing effect of an endogenous beta-adrenergic agonist

Exogenous catecholamines have been proved to be active in the reduction of vascular permeability induced by various inflammatory mediators via beta-adrenoceptor activation, but it is not known whether an endogenous beta-adrenergic agonist has any effect. We studied it in skin and lung vessels. The results revealed that an intravenous bolus of isoproterenol (10 micrograms/kg) attenuated platelet-activating factor- and histamine-induced Evans blue dye extravasation in rat dorsal skin, while intraperitoneal administration of beta-adrenoceptor blocker propranolol (0.1 mg/kg) significantly increased the dye extravasation. Blockade of beta-adrenoceptor by propranolol for 12 h noticeably increased wet/dry lung weight ratio, lung water content, bronchoalveolar lavage (BAL) protein concentration, leukocyte count, and lipoperoxide degradation product malondialdehyde (MDA) content. In isolated perfused lung in vitro, propranolol (2.5 micrograms/ml) had no obvious effects on lung weight gain, fluid filtration coefficient, and pulmonary vascular pressure during the 20-min perfusion compared with control. The results suggested that endogenous beta-adrenergic agonist is an important factor in the maintenance of vascular integrity and the quiescent state of leukocytes, indicating the antiinflammatory role of catecholamines in physiological states and critical illnesses.