Interaction of thrombin and platelets with the vascular endothelium

Thrombin is a potent stimulus for prostacyclin (PGI2) release from the vascular endothelium. Treatment of the endothelium with high concentrations of aspirin to block PGI2 formation was associated with increased platelet adherence in a system employing thrombin and 51Cr-labeled platelets. Addition of exogenous PGI2 to the aspirin-treated endothelium restored platelet adherence to the low baseline values. After an initial exposure of the endothelium to thrombin, the cultured endothelium was unable to respond to a second thrombin stimulus with release of PGI2. During this refractory period, the absence of PGI2 was associated with increased platelet adherence. Thus thrombin, an active coagulant and thrombogenic substance, has the capability to release PGI2, the most potent inhibitor of platelet aggregation known to exist in vivo.     

Presence of T-antigen on the vascular endothelium

Bacterial neuraminidase plays an important role in the pathogenesis of some haemolytic anaemias. It divides neuraminic acid from the red cell surface to expose a hidden antigen (Thomsen-Friedenreich antigen, T). A physiologically circulating antibody can then react with the uncovered T and cause a rapid haemolysis. This study demonstrates the presence of T on human vascular endothelium. Similar to red cells it is exposed by the action of bacterial neuraminidase. The subsequent reaction with the physiological antibody could be involved in the pathogenesis of vascular damage observed in severe cases of bacterial septicaemia.     

Functions and dysfunctions of the vascular endothelium

Endothelium represents a large paracrine gland with an enormous reactive surface. By means of its numerous vasodilation and vasospastic factors it manages the basal and working tonus of vessels and thus also the regional flow and the access of target tissues to hormones and metabolic substrates. It manages also the proliferation and migration of myocytes of the vascular wall and thus its adaptation to overload. The dysfunctional states of endothelium are observed in arterial hypertensions, diabetes, dyslipoproteinaemia, and they grow with age. They are the first stage of atherothrombogenic processes. They manifest themselves by a decreased vasodilation reserve of the vascular wall to strain, insulin and many other stimuli. On the contrary, quite frequently they paradoxically react to physical strain, acetylcholine, histamine, ATP etc. by vascular spasms which can determine vasospastic and microvascular angina pectoris including spasms and occlusions of e.g. coronary arteries in sites of insignificant stenoses with the origin of infarctions. The damaged endothelium, so to explain, conceives these stimuli in accordance with the encoded programme as a stimulus to the protection from haemorrhage during stress (fight or flight) and develops "suicidal" defensive reaction against them which we are nowadays able to modulate by administration of ACE-inhibitors, beta-blockers, hypolipidaemic drugs, inhibitors of cyclooxygenase-1 (30-100 mg of aspirin), Ca-antagonists and antioxidants including numerous non-pharmacological procedures. We can retard or halt the process of atherothrombogenesis and avoid or lower thus the number of sudden vascular ventricular as well as brain episodes, including the congestive heart failures, limb amputations and ischaemic damage of the brain. (Fig. 4, Ref. 70.)     

The vascular endothelium: physiopathology and participation in thrombogenesis

Even though homeothermic animals regulate the body temperature, fluctuations up to 2-3 degrees C may occur during physiological conditions. In many species, including the rat, a similar variation can be measured in the brain temperature. Such changes are expressed throughout the brain with a preserved gradient between the warmer basal and cooler dorsal parts. In spite of these recordable physiological changes, spatial learning is quite robust, in that it occurs at brain temperatures between 30 and 39 degrees C. Even drastic cooling (to below 15 degrees C) fails to affect consolidation or storage of information when the animal is tested after rewarming. The physiological temperature fluctuations have significant consequences for electrophysiological responses in the brain. Various bioelectrical signals are more sensitive during warming, axonal conduction is speeded up, and stimulus-elicited transmitter release becomes faster and more synchronized. Action potentials have shorter rise and decay times in warm conditions, and the amplitude becomes slightly smaller. Population responses are differently affected by these changes. Dentate field potentials in response to stimulation of perforant-path fibers appear with shorter latency in warm conditions, and the rate of rise in the field EPSP is increased. Paradoxically, the amplitude of the population spike is reduced. This is due to a combination of reduced amplitude of individual action potentials and reduced efficiency of the summation of groups of action potentials. Due to the large effects of temperature on hippocampal field potentials, it is mandatory that brain temperature changes are monitored and/or controlled whenever such responses are recorded in freely moving and anesthetized animals.     

Toxicological effects of aerial application of monocrotophos

Aerial application of the insecticide Nuvacron 40% (monocrotophos) had no significant effect on the cholinesterase level of plasma and erythrocytes of cattle, chicken, buffaloes, and human volunteers exposed to the spray. Contamination of canal water with the pesticide was completely eliminated within 24 hr, whereas that in the soil was reduced by 80% in 72 hr. The degradation of insecticide residue in grass was about 90% in seven days and in cotton leaves about 85% for the same period.     

The effects of temperature and strain rate on the strength of beryllium sheet

The stress-strain behavior and the deformation dynamics of compression rolled and hot upset beryllium sheet prepared from SR powder were investigated in tension over the range 25° to 355°C. The true stress-true strain curves were approximated by the relationσ =σ(0) +hε ^1/2. Both σ(0) andh decreased with temperature. σ(0) was higher at all temperatures for the compression rolled sheet, whereash was the same for the two materials. The difference in σ(0) was in the athermal component of the stress. The effects of temperature and strain rate on the flow-stress of the polycrystalline sheet agreed with those for prism slip in single crystals. Thermal activation analysis of the deformation dynamics yielded values of 123 to 158 b³ for the activation volume, 1.5×10⁷ sec^?1 for the preexponential factor and 1.8 ev (0.18 μb³) for the activation energy,Ho.     

Hypertension, the endothelium and the pathogenesis of chronic vascular disease

The endothelium lines all vessels of the body and is the most important structure for communication between the flowing blood and the vessel wall. Healthy endothelium has antiadhesive and antithrombotic properties and is crucial for maintaining blood flow. It serves as a permeability barrier and prevents noxious agents from entering the vessel wall. Endothelial cells have secretory functions and secrete vasorelaxant substances. Therefore, functioning endothelium sustains the homoeostasis of the vessel wall. Endothelial functions are impaired by risk factors for cardiovascular disease such as hypertension, hyperlipidemia and hyperglycemia. Hypertension leads to decreased generation of nitric oxide in endothelial cells, thereby diminishing their vasorelaxant properties. Hypertension also contributes to an increase in endothelial cell permeability leading to intimal edema. Thirdly, hypertension increases the expression of adhesion molecules and increases the adherence of leukocytes to the vessel wall. Hence, hypertension directly contributes to the pathological alterations of the endothelium and it seems that these effects initiate and accelerate the pathogenesis of chronic vascular disease.     

Alteration of vascular endothelium and endothelium smooth muscle interaction after carbogen gas perfusion of isolated rat and guinea pig heart

The aim of the study was to alter the vascular endothelium of the mammalian myocardium with respect to coronary flow regulation and vascular permeability. For this purpose, carbogen gas perfusion (GP) of Langendorff-type isolated rat and guinea pig heart was chosen. Perfusion of the hearts with carbogen gas was possible, as well as replacement of the GP by fluid perfusion. The energetic and mechanical state, the creatine kinase release, and the electron microscopic examination of the rat heart indicated only a moderate to minimal alteration of the cardiomyocytes after GP. As a result of GP a massive alteration of the vascular endothelium could be demonstrated in the rat heart, based on the release of the cytosolic endothelial marker enzyme, purine nucleoside phosphorylase, the partly altered vascular permeability and the morphologically detected endothelial damage to arterioles, capillaries and venules. Moreover, the reduced coronary flow response to short periods of anoxia (rat, guinea pig) and the inverted flow response to serotonin administration with maintained response to sodium nitroprusside (rat) in the post-gas perfusion period reflected an alteration of endothelial smooth muscular interaction in the rat and guinea pig heart. Furthermore, the distensibility of the coronary vasculature was increased in the rat and guinea pig heart in the post-gas perfusion period, where a relative autoregulatory behavior was maintained (rat) or partly maintained (guinea pig) in passively predilated vessels. In conclusion, carbogen gas perfusion of isolated hearts allows to induce preferred alteration of endothelium and endothelium-smooth muscle interaction.     

Fever-range hyperthermia enhances L-selectin-dependent adhesion of lymphocytes to vascular endothelium

The L-selectin leukocyte adhesion molecule plays an important role in controlling leukocyte extravasation in peripheral lymph nodes and at sites of tissue injury or infection. Although febrile responses during infection and inflammation are associated with enhanced immune activity, the contribution of fever-range temperatures to controlling lymphocyte recruitment to tissues has not been previously examined. In this report we provide evidence that direct exposure of lymphocytes to fever-range temperatures (38-41 degrees C) in vitro for 9 to 24 h resulted in a >100% increase in L-selectin-dependent adhesion of these cells to lymph node high endothelial venules (HEV). Moreover, culture of lymphocytes under hyperthermia conditions markedly enhanced the ability of these cells to traffic in an L-selectin-dependent manner to peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches. In contrast, febrile temperatures did not increase LFA-1 function as assessed by measuring lymphocyte adhesion to ICAM-1-3T3 transfectants. Fever-range hyperthermia further did not increase L-selectin surface density on lymphocytes or L-selectin-dependent recognition of soluble carbohydrate substrates; however, a marked increase in ultrastructural immunogold-labeling of L-selectin was observed in response to thermal stimuli. These results suggest that elevated temperatures enhance L-selectin adhesion and/or avidity through the regulation of L-selectin conformation or organization in the plasma membrane. Finally, the observed thermal effects on L-selectin adhesion were attributed to soluble factors in the conditioned medium of heat-treated cells. Taken together, these data provide new insight into the potential physiologic role of the febrile response in enhancing lymphocyte recruitment to tissues through the regulation of L-selectin adhesion.     

Vascular permeability factor/vascular endothelial growth factor-mediated signaling in mouse mesentery vascular endothelium

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) is a multifunctional cytokine and growth factor that has important roles in both pathological and physiological angiogenesis. VPF/VEGF induces vascular hyperpermeability, cell division, and other activities by interacting with two specific receptor tyrosine kinases, KDR/Flk-1 and Flt-1, that are selectively expressed on vascular endothelium. The signaling cascade that follows VPF/VEGF interaction with cultured endothelium is only partially understood but is known to result in increased intracellular calcium, activation of protein kinase C, and tyrosine phosphorylations of both receptors, phospholipase C-gamma (PLC-gamma) and phosphatidylinositol 3'-kinase. For many reasons, signaling events elicited in cultured endothelium may not mimic mediator effects on intact normal or tumor-induced microvessels in vivo. Therefore, we developed a system that would allow measurement of VPF/VEGF-induced signaling on intact microvessels. We used mouse mesentery, a tissue whose numerous microvessels are highly responsive to VPF/VEGF and that we found to express Flk-1 and Flt-1 selectively. At intervals after injecting VPF/VEGF i.p., mesenteries were harvested, extracted, and immunoprecipitated. Immunoblots confirmed that VPF/VEGF induced tyrosine phosphorylation of several proteins in mesenteric microvessels as in cultured endothelium: Flk-1; PLC-gamma; and mitogen-activated protein kinase. Similar phosphorylations were observed when mesentery was exposed to VPF/VEGF in vitro, or when mesenteries were harvested from mice bearing the mouse ovarian tumor ascites tumor, which itself secretes abundant VPF/VEGF. Other experiments further elucidated the VPF/VEGF signaling pathway, demonstrating phosphorylation of both PYK2 and focal adhesion kinase, activation of c-jun-NH2-kinase with phosphorylation of c-Jun, and an association between Flk-1 and PLC-gamma. In addition, we demonstrated translocation of mitogen-activated protein kinase to the cell nucleus in cultured endothelium. Taken together, these experiments describe a new model system with the potential for investigating signaling events in response to diverse mediators on intact microvessels in vivo and have further elucidated the VPF/VEGF signaling cascade.     

非绿柱石铍矿生产工业氧化铍的工艺研究与实践

叙述了非绿柱石铍矿生产工业氧化铍的工艺,特别是高氟铍矿生产工业氧化铍的方法,介绍了水口山工业氧化铍的生产状况。     

Outer surface lipoproteins of Borrelia burgdorferi activate vascular endothelium in vitro

Previously, we reported that activation of vascular endothelium by the Lyme disease pathogen Borrelia burgdorferi results in enhanced expression of endothelial cell adhesion molecules and promotion of the transendothelial migration of neutrophils in vitro. To investigate the role of spirochetal lipoproteins in this process, we assessed the ability of a synthetic lipohexapeptide corresponding to the N terminus of B. burgdorferi outer surface protein A (OspA) to activate human umbilical vein endothelial cells (HUVEC). Using a whole-cell enzyme-linked immunosorbent assay, we demonstrated that OspA lipopeptide activated endothelium in a dose-dependent fashion, as measured by upregulation of E-selectin. Near-maximal stimulation was achieved with 100 micromolar lipopeptide. In addition, the lipopeptide increased expression of vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1). Similar results were obtained with 25 nM native OspA or lipidated recombinant OspA or OspB. Incubation of HUVEC with nonlipidated OspA peptide, nonlipidated recombinant OspA or OspB, or tripalmitoyl-S-glyceryl-cysteine had little or no effect on expression of these adhesion molecules. A mutant strain of B. burgdorferi that lacked OspA and OspB upregulated expression of E-selectin to the same degree as its wild-type counterpart, indicating that other spirochetal components also possess the ability to activate endothelium. Conditioned medium from HUVEC incubated with OspA lipopeptide or lipidated recombinant OspA induced chemotaxis of neutrophils in Boyden chamber assays, whereas the OspA preparations alone were devoid of chemotactic activity. When HUVEC grown on connective tissue substrates were treated with OspA lipopeptide, subsequently added neutrophils migrated across the endothelial monolayers. These results implicate the outer surface lipoproteins of B. burgdorferi as potential effector molecules in the promotion of a host inflammatory response.     

Role of gender and vascular endothelium in rat aorta response to 17 beta-estradiol

Estrogen supplementation in postmenopausal women offers significant cardiovascular protection. The mechanism for this benefit is unclear but may be due to an interaction of estrogen with the blood vessel wall (vascular smooth muscle and endothelium). We examined the response of weight-matched female and male endothelium-intact and -denuded aortae to 17 beta-estradiol, its interaction with noradrenaline, and the effect of N-nitro-L-arginine. Estradiol produced relaxation responses that were significantly greater in female endothelium-intact preparations. This response was sensitive to N-nitro-L-arginine, while the response to 17 beta-estradiol in male endothelum-intact and both female and male endothelum-denuded preparations was resistant. Estradiol also inhibited contractions to noradrenaline, which was more pronounced in the female endothelium-intact aortic rings. These data imply that estradiol interacts preferentially with the female vascular endothelium, but there exists an endothelium-independent process that can also be activated in the male aorta. Further studies are warranted to elucidate these differential mechanisms.     

Signaltransduction in vascular endothelium: the role of intracellular calcium and ion channels

Endothelial cells (ECs) provide an ideal surface for blood flow. They inhibit the initiation of blood-clotting, but can also under certain conditions activate this process. ECs influence thrombolysis as well as thrombogenesis. They are "antigen-presenting cells" and play a key role in angiogenesis. In addition, ECs control the permeability of the barrier between bloodvessels and interstitium. One of their most important functions is the regulation of the diameter of the blood vessels and their adaptation to the demanded hemodynamic needs. The production and release of diverse compounds, which interfere with different neighboured target cells, initiate this plethora of functions. Ca2+ signals in endothelial cells play the key role in the release of NO, prostacyclin (PGI2), platelet activating factor (PAF), von Willebrand factor (vWF), tissue plasminogen activator (tPA) and tissue factor pathway inhibitor (TFPI). Changes in the intracellular Ca2+ concentration ([Ca2+]i) are determined by release from intracellular stores and entry through the plasma membrane. The diversity of Ca2+ entry pathways and mechanisms of their control are described. At least two different types of Ca2+ entry channels exist: 1. typical highly Ca2+ selective ion channels which might be activated by depletion of intracellular Ca2+ stores (Ca2+ release-activated Ca2+ channels, CRAC), and 2. Non-selective Ca2+ permeable cation channels (NSC). The latter shares many features with an NSC induced by expression of the protein TRPC3. These channels are only weakly operated by store depletion and require a permissive Ca2+ and Ins(1,4,5)P3 concentration in the cytosol. CRAC channels are possible indirectly involved in Ca2+ entry during mechano-stimulation of ECs. After activation of these entry channels, influx of Ca2+ depends on the driving force. The following ion channels play a pivotal role in regulation of the driving force for Ca2+ entry: an inwardly rectifying K+ channel, identified as Kir2.1, a large-conductance, Ca2+ activated K+ channel (hslo) and at least two Cl- channels (a volume regulated Cl- channel, VRAC, and a Ca2+ activated Cl- channel, CaCC). It will be explained how these ion channels interact in the regulation of the long-lasting (plateau-type) increase in [Ca2+]i which mainly controls NO-synthesis and release. Furthermore, it will be demonstrated that Ca2+ oscillations depend on intracellular events rather than Ca2+ entry from the extracellular space.     

非绿柱石铍矿生产工业氧化铍的工艺研究与实践

叙述了非绿柱石铍矿生产工业氧化铍的工艺，特别是高氟铍矿生产工业氧化铍的方法，介绍了水口山工业氧化铍的生产状况。     

Alteration of endothelial cell monolayer integrity triggers resynthesis of vascular endothelium cadherin

Although cadherins appear to be necessary for proper cell-cell contacts, the physiological role of VE-cadherin (vascular endothelium cadherin) in adult tissue has not been clearly determined. To shed some light on this question, we have disturbed the adhesive function of VE-cadherin in human endothelial cell culture using a polyclonal anti-VE-cadherin antibody. This antibody disrupts confluent endothelial cell monolayers in vitro and transiently generates numerous gaps at cell-cell junctions. The formation of these gaps correlates with a reversible increase in the monolayer permeability. We present evidence that destruction of the homotypic interactions between the extracellular domains of VE-cadherin induces a rapid resynthesis of VE-cadherin, leading to restoration of endothelial cell-cell contacts. The expression of new molecules of VE-cadherin correlates with a modest but significant increase in VE-cadherin mRNA synthesis. Altogether, these results establish a critical role for VE-cadherin in the maintenance and restoration of endothelium integrity.     

Cardiac allograft vasculopathy: IgM antibody responses to donor-specific vascular endothelium

Stunning and slaughter trials were conducted to evaluate the influence of carcass orientation (inverted or supine), angle of feather extraction (parallel or perpendicular to the carcass surface), and slaughter method (exsanguination without or with spinal cord transection) on feather retention force (FRF) in commercial broilers sampled ante-, peri-, and post-mortem. The pectoral, sternal, and femoral feather tracts were sampled before and after stunning contralaterally, with a maximum indicating force gauge, from broilers suspended on a shackle (inverted) or laying on a table (supine). For all trials and sample periods FRF was consistently greater in the femoral area (547 to 679 g) than in the pectoral area (273 to 391 g), with the sternal feather tract requiring the least force at 246 to 343 g. Feathers extracted parallel to the carcass resulted in consistently greater FRF (9 to 29%) than feathers extracted at a perpendicular angle, at all sample periods. Broilers suspended on shackles ante- and peri-mortem had higher FRF values (5 to 30%) than those restrained in shackles in a supine position on a table. Other parameters resulted in minor and inconsistent alterations in FRF. Electrical stunning, when not followed by bleeding, resulted in small reductions in FRF (up to 7%). Bleeding after stunning without or with spinal cord transection resulted in variable peri-mortem FRF changes (+7 to -11% and +11 to -11%, respectively). Only in the pectoral feather tract was there a significant increase (5 to 6%) in FRF as broilers went from the ante- to peri-mortem state. At 2 and 6 min after stunning and initiation of exsanguination, post-mortem FRF was unaffected by carcass orientation for the pectoral and femoral tracts.