High tidal volume ventilation induces lung injury after hepatic ischemia-reperfusion

Ischemia-reperfusion not only damages the affected organ but also leads to remote organ injuries. Hepatic inflow interruption usually occurs during hepatic surgery. To investigate the influence of liver ischemia-reperfusion on lung injury and to determine the contribution of tidal volume settings on liver ischemia-reperfusion-induced lung injury, we studied anesthetized and mechanically ventilated rats in which the hepatic inflow was transiently interrupted twice for 15 min. Two tidal volumes, 6 ml/kg as a low tidal volume (IR-LT) and 24 ml/kg as a high tidal volume (IR-HT), were assessed after liver ischemia-reperfusion, as well as after a sham operation, 6 ml/kg (NC-LT) and 24 ml/kg (NC-HT). Both the IR-HT and IR-LT groups had a gradual decline in the systemic blood pressure and a significant increase in plasma TNF-alpha concentrations. Of the four groups, only the IR-HT group developed lung injury, as assessed by an increase in the lung wet-to-dry weight ratio, the presence of significant histopathological changes, such as perivascular edema and intravascular leukocyte aggregation, and an increase in the bronchoalveolar lavage fluid TNF-alpha concentration. Furthermore, only in the IR-HT group was airway pressure increased significantly during the 6-h reperfusion period. These findings suggest that liver ischemia-reperfusion caused systemic inflammation and that lung injury is triggered when high tidal volume ventilation follows liver ischemia-reperfusion.     

The renal cortical lymphatic system in the rat, hamster, and rabbit

Rat, hamster, and rabbit renal cortical lymphatics were examined by light and electron microscopy. Rat and hamster kidneys possessed both intra- and interlobular lymphatics that were structurally similar at the light microscopic level. Ultrastructural examination of the hamster lymphatic endothelium, however, revealed an unusual arrangement of cytoplasmic extensions not seen in the other two species. The intralobular lymphatics were related primarily to tubules, afferent arterioles, and renal corpuscles and were consistent with lymph formation from both plasma filtrate and tubular reabsorbate. Interlobular lymphatics were seen in connective tissue associated with the interlobular blood vessels. Rabbit cortex contained only interlobular lymphatics. Cross-sectional area, maximum diameter, volume density, and profile density were determined by stereological measurements using a computer-based image analyzer. The morphological data from the rat were used, in combination with published values for lymph flow, to calculate the rate of lymph formation per unit area of endothelium in lymphatics of the renal cortex. Among kidneys fixed by retrograde perfusion, the cortical lymphatic system was most extensive in maximum diameter, volume density, and profile density. It was smallest in the rabbit and intermediate in the rat. Lower volume and profile density were found for rat kidneys fixed by the dripping technique. It was concluded that: tubular reabsorbate probably contributes to renal lymph in the rat and hamster, but not in the rabbit; significant differences exist in the extent of the renal lymphatic systems among the three species, with the hamster kidney having the richest network and the rabbit the poorest; the method of fixation influences the measured size and density of renal cortical lymphatics; and the estimated rate of lymph formation in the kidney of the rat is roughly comparable to that in the dog.     

High tidal volume ventilation induces NOS2 and impairs cAMP- dependent air space fluid clearance

Tidal volume reduction during mechanical ventilation reduces mortality in patients with acute lung injury and the acute respiratory distress syndrome. To determine the mechanisms underlying the protective effect of low tidal volume ventilation, we studied the time course and reversibility of ventilator-induced changes in permeability and distal air space edema fluid clearance in a rat model of ventilator-induced lung injury. Anesthetized rats were ventilated with a high tidal volume (30 ml/kg) or with a high tidal volume followed by ventilation with a low tidal volume of 6 ml/kg. Endothelial and epithelial protein permeability were significantly increased after high tidal volume ventilation but returned to baseline levels when tidal volume was reduced. The basal distal air space fluid clearance (AFC) rate decreased by 43% (P < 0.05) after 1 h of high tidal volume but returned to the preventilation rate 2 h after tidal volume was reduced. Not all of the effects of high tidal volume ventilation were reversible. The cAMP-dependent AFC rate after 1 h of 30 ml/kg ventilation was significantly reduced and was not restored when tidal volume was reduced. High tidal volume ventilation also increased lung inducible nitric oxide synthase (NOS2) expression and air space total nitrite at 3 h. Inhibition of NOS2 activity preserved cAMP-dependent AFC. Because air space edema fluid inactivates surfactant and reduces ventilated lung volume, the reduction of cAMP-dependent AFC by reactive nitrogen species may be an important mechanism of clinical ventilator-associated lung injury.     

Pulmonary injury in rats following continuous exposure to 60% O2 for 7 days

Morphological, biochemical, and physiological studies were done on rats exposed to 60% O2 for 7 days. This exposure did not induce O2 tolerance but instead caused a significant decrease in survival time of animals subsequently exposed to pure O2. The activity of lung superoxide dismutases and glucose-6-phosphate dehydrogenase were unchanged after exposure to 60% O2. A decrease in lung compliance was suggested by changes in the total lung capacity and in the pressure-volume curves of excised lungs. Ventilation of these animals with large tidal excursion resulted in pulmonary edema. Morphometric analyses revealed a significant decrease in alveolar air volume and an increase in the number of alveolar macrophages. The most significant lesions involved the pulmonary vascular bed. The volume and thickness of the capillary endothelium was decreased. There were focal areas of pericapillary fluid accumulations, and a number of the smaller vessels had perivascular edema. These findings suggest that significant pulmonary injury occurs in rats exposed to 60% O2 and that the primary site of injury is the pulmonary capillary endothelium.     

Intralobular Pulmonary Lymphatic Distribution in Normal Human Lung Using D2-40 Antipodoplanin Immunostaining

It has been assumed for a long time that except for limited areas close to respiratory bronchioles or their satellite arteries, there is no evidence of lymphatic vessels deep in the pulmonary lobule. An immunohistochemical study using the D2-40 monoclonal antibody was performed on normal pulmonary samples obtained from surgical specimens, with particular attention to the intralobular distribution of lymphatic vessels. This study demonstrated the presence of lymphatics not only in the connective tissue surrounding the respiratory bronchioles but also associated with intralobular arterioles and/or small veins even less than 50 μm in diameter. A few interlobular lymphatic vessels with a diameter ranging from 10 μm to 20 μm were also observed further away, in interalveolar walls. In conclusion, this study, using the D2-40 monoclonal antibody, demonstrated the presence of small lymphatic channels within the normal human pulmonary lobules, emerging from interalveolar interstitium, and around small blood vessels constituting the paraalveolar lymphatics. This thin intralobular lymphatic network may play a key pathophysiological role in a wide variety of alveolar and interstitial lung diseases and requires further investigation. (J Histochem Cytochem 57:643–648, 2009)     

Concentration of aerosolized 99mTc-albumin in the pulmonary lymph of anesthetized sheep

We examined the lymphatic concentration of 99mTc-albumin deposited in the air spaces of anesthetized sheep to determine whether changes in the concentration reflected changes in lung epithelial function. Five control sheep were ventilated with an aerosol of 99mTc-albumin for 6 min, and the lung lymphatic concentration of the tracer was monitored for the next 2 h. During the last 45 min the lymphatic concentration stabilized at a value that was 0.03 +/- 0.01% of the estimated value in the air spaces. Pulmonary vascular hypertension, induced in seven sheep by increasing the left atrial pressure 20 cmH2O for 4 h, increased the lung lymph flow from a base-line value of 3 +/- 2 to 21 +/- 14 ml/h. This caused the concentration of the 99mTc-albumin in the lymph to double to 0.07 +/- 0.03% of the air space concentration (P less than 0.01). Lung injury induced by infusing 0.08-0.10 ml/kg oleic acid intravenously in seven other sheep increased the lymphatic concentration of the 99mTc-albumin 10-fold to 0.31 +/- 0.09% of the air space concentration (P less than 0.01). The increased tracer concentration in the sheep with pulmonary vascular hypertension could be the result of the increased lymph flow causing a diversion of tracer into the lymphatics. However, a mathematical model showed that the 10-fold increase in the lymphatic concentration in the sheep with lung injury was primarily the result of an increase in both permeability and surface area of the epithelium that participated in the transfer of the 99mTc-albumin from the air spaces into the lung tissue drained by the lymphatics.(ABSTRACT TRUNCATED AT 250 WORDS)     

Temperature affects lung fluid and recoil during high tidal ventilation at low resting volume

Effects of tidal volume (VT), end-expiratory pressure (EEP), and environmental temperature (Tenv) on elastic recoil force (Pel) and edema formation were examined in open-chest anesthetized rabbits. Sixty-two rabbits in four groups were ventilated for 3 h with VT of either 10 or 25 ml/kg body wt, EEP of 0 or 2 cmH2O, and Tenv of 18 or 35 degrees C. After ventilation, Pel at 80% of total lung capacity (P80) was significantly increased when ventilation was performed with the combination of large VT, 0 EEP, and low Tenv. This change was prevented by altering any one of the three conditions, e.g., small VT, positive EEP, or high Tenv. Similarly, elevation of minimum surface tension and reduction of surface activity index of lavages from excised lungs after ventilation were observed only when increased P80 was noted. Additionally, the increase of P80 was well correlated with increment of wet weight-to-dry weight ratio and degree of perivascular cuffing and alveolar edema formation of excised lungs. These results indicate that elevation of Pel after high tidal ventilation in open-chest animals in vivo was influenced by level of EEP and Tenv and that the degree of edema formation was closely related to the increase of Pel. The increased Pel is presumably primary and causes fluid accumulation.     

Lymphatic ontogeny and effect of hypoplasia in developing lung

The pulmonary lymphatic vasculature plays a vital role in maintaining fluid homeostasis required for efficient gas exchange at capillary alveolar barriers and contributes to lung fluid clearance at birth. To further understanding of pulmonary lymphatic function at birth, lineage-tracing analysis of mouse lung was used. Lineage analysis confirmed that lymphatic endothelial cells (LEC) bud from extrapulmonary lymphatics and demonstrated that LEC migrate into developing lung along precise pathways. LEC cluster first in the primary bronchovascular region then along the secondary broncho-arterial regions and along veins. Small lymphatic vessels in distal lung develop from LEC that have migrated into lung mesenchyme from the extrapulmonary lymphatics. Finally, proximal and distal lymphatics remodel to form vessels with lumens in stereotypical locations. Loss of function analysis with lung-specific expression of a secreted form of the extracellular domain of vascular endothelial growth factor receptor-3 (dnR3) caused significant embryonic pulmonary lymphatic hypoplasia with fourfold reduction in distal LEC. Lung-specific expression of dnR3 did not affect blood vascular development, overall lung organogenesis or lymphatic development in other organs. Neonatal mice with pulmonary lymphatic hypoplasia developed respiratory distress with significantly increased mortality. During the transition to air breathing, lymphatic hypoplasia adversely affected fetal lung fluid clearance as determined by wet/dry weight analysis and morphometric analysis of bronchovascular cuffing and mesenchymal thickening. Surfactant synthesis was unaffected. Together, these data demonstrate that lung lymphatics develop autonomously and that pulmonary lymphatic hypoplasia is detrimental to survival of the neonate due to impaired lung fluid clearance.     

Regional differences in interstitial fluid albumin concentration in edematous lamb lungs.

We have determined regional lung interstitial fluid albumin concentration in lambs with hydrostatic pulmonary edema and correlated it with lung lymph and plasma albumin concentrations. In anesthetized lambs, we raised left atrial pressure to 25-30 cmH2O by obstructing the aorta and volume overloading the lambs with infusions of Ringer lactate solution (group I, n = 10) or sheep's blood (group II, n = 9). We measured lung lymph flow and concentrations of total protein and albumin in plasma and lymph. With micropipettes we also collected interstitial fluid from interlobular septal pools and peribronchial, periarterial, and perivenous liquid cuffs near the hilum for measurement of albumin concentration by the gel immunoelectrophoresis method. In both groups, lung lymph flow increased with left atrial hypertension, and the ratio of lymph to plasma protein concentration fell. For group I, plasma and lymph albumin concentrations during the phase of hydrostatic edema were 1.97 +/- 0.49 and 1.15 +/- 0.36, respectively; for group II, they were 3.77 +/- 0.42 and 2.43 +/- 0.39 g/dl, respectively. Lung wet-to-dry weight ratio averaged 6.0 in both groups. Albumin concentration was always lower in interstitial fluid than in plasma. In both groups, albumin concentration was similar in periarterial and peribronchial fluid cuffs (group I 1.19 +/- 0.6 and 1.36 +/- 0.79 g/dl, respectively; group II 2.87 +/- 1.05 and 2.33 +/- 0.58 g/dl, respectively) but was always greater than that in perivenous and interlobular septal pools (group I 0.61 +/- 0.21 and 0.67 +/- 0.23 g/dl, respectively; group II 1.76 +/- 0.49 and 1.55 +/- 0.52 g/dl, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution of lymphatic vessels in mouse thymus: immunofluorescence analysis

Thymic blood and lymphatic vessels in humans and laboratory animals have been investigated in morphological studies. However, occasionally a clear distinction between blood vessels and lymphatic vessels cannot be made from morphological characteristics of the vasculature. To visualize thymic lymphatics in normal adult BALB/c mice, we used antibodies against specific markers of lymphatic endothelial cells. Expression of vascular endothelial growth factor receptor–3 (VEGFR–3) was detected throughout the thymus, i.e., the capsule, cortex, and medulla. Most thymic lymphatics were present in capillaries of ~20 μm in caliber. The plexuses of lymphatic capillaries were occasionally detectable. Lymphatic vessels were frequently adjacent to CD31–positive blood vessels, and some lymphatic vessels were seen in the immediate vicinity of or within the perivascular spaces around postcapillary venules. The identity of VEGFR–3–positive vessels as lymphatics was further confirmed by staining with additional markers: LYVE–1, Prox–1, neuropilin–2, and secondary lymphoid tissue chemokine (SLC). The distributions of LYVE–1 were similar to those of VEGFR–3. Most lymphatic vessels were also identified by Prox–1. Neuropilin–2 was restricted to lymphatic vessels in the thymus. The most abundant expression of SLC in the thymus was in medullar epithelial cells; SLC was also expressed in lymphatic vessels and blood vessels. Thus, lymphatic endothelium in mouse thymus was characterized by positive staining with antibodies to VEGFR–3, LYVE–1, Prox–1, neuropilin–2, or SLC, but not with an antibody to CD31. Our results suggest the presence of lymphatic capillary networks throughout the thymus.     

Activation of c-Src tyrosine kinase mediated the degradation of occludin in ventilator-induced lung injury

Background

Ventilator-induced lung injury (VILI) is characterized by increased alveolar permeability, pulmonary edema. The tyrosine kinase, c-Src, is involved in VILI but its role has not been fully elucidated. This study examined the relationship between c-Src activation and occludin levels in VILI both in vitro and in vivo.

Methods

For the in vivo study, Wistar rats were randomly divided into five groups: control (group C); normal tidal volume (group M); normal tidal volume + c-Src inhibitor (PP2) (group M + P); high tidal volume (group H); and high tidal volume + c-Src inhibitor (PP2) (group H + P). Rats in all groups but group C underwent mechanical ventilation for 4 h. For the in vitro study, MLE-12 cells pretreated with PP2 and siRNA underwent cyclic stretching at 8% or 20% for 0, 1, 2 and 4 h. The expressions of occludin, c-Src, and p-c-Src were analyzed by western blotting, hematoxylin and eosin (HE) staining, and immunofluorescence.

Results

For the in vivo study, rats in group H showed decreased occludin expression and activated c-Src compared with group C. HE staining and lung injury score showed more severe lung injury and alveolar edema in group H compared with group M and group C. Group H + P had less pulmonary edema induced by the high tidal volume ventilation. For the in vitro study, occludin expression decreased and c-Src activation increased as indicated by the phosphorylation of c-Src over time. Consistently, PP2 could restore occludin levels.

Conclusions

Mechanical ventilation can activate c-Src by phosphorylation and increase the degradation of occludin. c-Src inhibitor can ameliorate barrier function and lung injury by up-regulating occludin.     

呼吸机相关肺损伤模型建构的最佳潮气量

目的:应用大潮气量机械通气探讨制作兔的呼吸机相关肺损伤模型的最佳潮气量。方法:根据黄金分割法原理,采用三种不同潮气量68mL/kg、60mL/kg和45mL/kg各持续通气1分钟造成兔的急性肺损伤,取0h,12h,24h,48h四个时间点进行观察,观察兔存活情况,计算各时间点肺湿/干重比观察肺水肿严重程度及变化,组织病理学切片观察各时间点肺组织形态学改变。结果:1、潮气量68mL/kg组、60mL/kg组和45mL/kg组兔48h存活率分别为58.33%(7/12)、91.67%(11/12)和100%(12/12);与正常对照组相比,三组肺湿/干重比在0小时无明显变化,12小时明显增高,在24小时时达峰值,48小时后降低。3、镜下观察机械通气后不同时间肺组织均有不同程度形态学改变,68mL/kg组肺组织形态学改变非常明显,60mL/kg组肺组织形态学改变明显,45mL/kg组肺组织形态学改变不明显。结论:大潮气量通气成功建立兔的呼吸机相关肺损伤实验动物模型,潮气量指标为60mL/kg。     

Morphometry Analysis of Lymphatics in Pulmonary Adenocarcinomas With a Lepidic Growth Pattern

Lymph vessels play an important role in tumor progression. Pulmonary adenocarcinomas, accounting for half of non-small-cell lung carcinomas, compose a spectrum of histological types, exclusively or without a lepidic growth pattern (LGP) along preserved interalveolar septa. In that context, this study was designed to investigate the lymphatic vascular pattern associated with LGP and the concomitant invasive component of pulmonary adenocarcinomas. Using the D2-40 monoclonal antibody as a marker of lymphatic endothelial cells, the lymphatic vessel density (LVD) and vessel-area fraction (LVAF) were morphometrically analyzed in four adenocarcinomas in situ (AIS) and the LGP of eight invasive adenocarcinomas (LPIA), and compared with their invasive pattern (IPIA). LVD in AIS (2.1 ± 0.7 mm⁻²) and LPIA (2.4 ± 1 mm⁻²) were significantly lower than that in IPIA (14.9 ± 13.6 mm⁻²) (p=0.001). Moreover, the lymphatic vascular pattern in LGP was similar to that of normal lung, with isolated small lymphatic vessels within the interalveolar septa. Our results showing the scarcity of lymphatics in LGP suggest an absence of septal lymphangiogenesis associated with the LGP pattern in lung adenocarcinomas, which could explain, at least partially, the better prognosis observed in tumors with exclusive or predominant lepidic spread compared with other subtypes.     

大潮气量致急性肺损伤犬呼吸机相关性肺损伤模型的构建

目的建立大潮气量致急性肺损伤（ALI）犬呼吸机相关性肺损伤（VILI）模型。方法健康雄性杂种犬12只用油酸静脉注射法制备犬ALI模型,造模成功后进行支持通气15min过渡,然后随机分为VILI组及对照组行机械通气6 h,每组6只。VILI组潮气量（Vt）=20 mL/kg,对照组Vt=6 mL/kg,两组呼气末正压（PEEP）均为10 cmH2O。动态观察各组血气交换指标变化。通气6 h后取支气管肺泡灌洗液（BALF）作白蛋白浓度检查,取肺组织作病理切片肺损伤评分。结果各组在油酸静脉注射后（2.50±0.80）h达到ALI标准。VILI组在犬机械通气6 h后PaO2、SaO2及氧合指数（OI）较对照组略下降（P〈0.05）,而PaCO2波动不大,且心率、血压波动也较对照组小（P〈0.05）。VILI组BALF中蛋白浓度和肺组织损伤评分均较对照组显著升高（分别P〈0.05,P〈0.01）。结论本实验成功建立了大潮气量致ALI犬VILI模型。     

Contractile activity of lymphatic vessels is altered in the TNBS model of guinea pig ileitis

The ability of the lymphatic system to actively remove fluid from the interstitium is critical to the resolution of edema. The response of the lymphatics to inflammatory situations is poorly studied, so we examined mesenteric lymphatic contractile activity in the 2,4,6-trinitrobenzenesulfonic acid (TNBS) model of guinea pig ileitis, a well-accepted animal model of intestinal inflammation, by videomicroscopy in vivo and in vitro 1, 3, and 6 days after induction of ileitis. Lymphatic function (diameter, constriction frequency, amplitude of constrictions, and calculated stroke volume and lymph flow rate) of isolated vessels from TNBS-treated guinea pigs were impaired compared with sham-treated controls. The dysfunction was well correlated with the degree of inflammation, with differences reaching significance (P < 0.05) at the highest inflammation-induced damage observed at day 3. In vivo, significantly fewer lymphatics exhibited spontaneous constrictions in TNBS-treated than sham-treated animals. Cyclooxygenase (COX) metabolites were suggested to be involved in this lymphatic dysfunction, since application of nonselective COX inhibitor (10 microM indomethacin) or a combination of COX-1 and COX-2 inhibitors (1 microM SC-560 and 10 microM celecoxib) markedly increased constriction frequency or induced them in lymphatics from TNBS-treated animals in vivo and in vitro. The present results demonstrate that lymphatic contractile function is altered in TNBS-induced ileitis and suggest a role for prostanoids in the lymphatic dysfunction.     

Effect of interstitial edema on lung lymph flow in goats in the absence of filtration.

We tested the effect of interstitial edema on lung lymph flow when no filtration occurred. In 16 anesthetized open-thorax ventilated supine goats, we set pulmonary arterial and left atrial pressures to nearly zero and measured lymph flow for 3 h from six lungs without edema and ten with edema. Lymph flow decreased exponentially in all experiments as soon as filtration ceased. In the normal lungs the mean half time of the lymph flow decrease was 12.7 +/- 4.8 (SD) min, which was significantly shorter (P less than 0.05) than the 29.1 +/- 14.8 min half time in the edematous lungs. When ventilation was stopped, lymph flow in the edematous lungs decreased as rapidly as in the normal lungs. The total quantity of lymph after filtration ceased was 2.7 +/- 0.8 ml in normal lungs and 9.5 +/- 6.3 ml in edematous lungs, even though extravascular lung water was doubled in the latter (8.4 +/- 2.4 vs. 3.3 +/- 0.4 g/g dry lung, P less than 0.01). Thus the maximum possible clearance of the interstitial edema liquid by the lymphatics was 6.3 +/- 4.8%. When we restarted pulmonary blood flow after 1-2 h in four additional goats, lymph flow recovered within 30 min to the baseline level. These findings support the hypothesis that lung lymph flow originates mainly from alveolar wall perimicrovascular interstitial liquid and that the contribution of the lung lymphatic system to the clearance of interstitial edema (bronchovascular cuffs, interlobular septa) is small.     

Alveolar macrophages contribute to alveolar barrier dysfunction in ventilator-induced lung injury

In patients requiring mechanical ventilation for acute lung injury or acute respiratory distress syndrome (ARDS), tidal volume reduction decreases mortality, but the mechanisms of the protective effect have not been fully explored. To test the hypothesis that alveolar macrophage activation is an early and critical event in the initiation of ventilator-induced lung injury (VILI), rats were ventilated with high tidal volume (HV(T)) for 10 min to 4 h. Alveolar macrophage counts in bronchoalveolar lavage (BAL) fluid decreased 45% by 20 min of HV(T) (P < 0.05) consistent with activation-associated adhesion. Depletion of alveolar macrophages in vivo with liposomal clodronate significantly decreased permeability and pulmonary edema following 4 h of HV(T) (P < 0.05). BAL fluid from rats exposed to 20 min of HV(T) increased nitric oxide synthase activity nearly threefold in na?ve primary alveolar macrophages (P < 0.05) indicating that soluble factors present in the air spaces contribute to macrophage activation in VILI. Media from cocultures of alveolar epithelial cell monolayers and alveolar macrophages exposed to 30 min of stretch in vitro also significantly increased nitrite production in na?ve macrophages (P < 0.05), but media from stretched alveolar epithelial cells or primary alveolar macrophages alone did not, suggesting alveolar epithelial cell-macrophage interaction was required for the subsequent macrophage activation observed. These data demonstrate that injurious mechanical ventilation rapidly activates alveolar macrophages and that alveolar macrophages play an important role in the initial pathogenesis of VILI.     

Benzamil, a blocker of epithelial Na(+) channel-induced upregulation of artery oxygen pressure level in acute lung injury rabbit ventilated with high frequency oscillation

The epithelial Na(+) transport via an epithelial Na(+) channel (ENaC) expressed in the lung epithelium would play a key role in recovery from lung edema at acute lung injury by removing the fluid in lung luminal space. The lung edema causes dysfunction of gas exchange, decreasing oxygen pressure level of artery [P(aO(2))]. To study if ENaC plays a key role in recovering P(aO(2)) from a decreased level to a normal one in acute lung injury, we applied benzamil (20microM, a specific blocker of ENaC) to the lung luminal space in acute lung injury treated with high frequency oscillation ventilation (HFOV) that is a lung-protective ventilation with a lower tidal volume and a smaller pressure swing than conventional mechanical ventilation (CMV). Benzamil facilitated the recovery of P(aO(2)) in acutely injured lung with HFOV but not CMV. The observation suggests that in acutely injured lung treated with HFOV an ENaC blocker, benzamil, can be applied as a therapeutic drug for acute lung injury combing with HFOV.     

Differential roles of p55 and p75 tumor necrosis factor receptors on stretch-induced pulmonary edema in mice

Ventilator-induced lung injury plays a crucial role in the outcome of patients with acute lung injury. Previous studies have shown a role for the cytokine tumor necrosis factor-alpha (TNF) in stretch-induced alveolar neutrophil recruitment, but the involvement of TNF in stretch-induced pulmonary edema is unclear. We investigated the effects of TNF through its individual p55 and p75 receptors on early pulmonary edema formation during high stretch ventilation, before neutrophil infiltration. Anesthetized wild-type or TNF receptor single/double knockout mice were ventilated with high tidal volume ( approximately 38 ml/kg) for 2 h or until they developed arterial hypotension. Pulmonary edema was assessed by physiological parameters including respiratory mechanics and blood gases, and by lavage fluid protein, lung wet:dry weight ratio, and lung permeability measurements using fluorescence-labeled albumin. High stretch ventilation in wild-type and TNF receptor double knockout animals induced similar pulmonary edema, and only 25-30% of mice completed the protocol. In contrast, the p55 receptor knockout mice were strongly protected from edema formation, with all animals completing the protocol. Myeloperoxidase assay indicated that this protective effect was not associated with decreased pulmonary neutrophil sequestration. The p75 receptor knockout mice, however, displayed increased susceptibility to edema formation, and no animals survived the full 2 h. These results demonstrate a novel role for TNF signaling (independent from its effects on neutrophil recruitment) specifically through the p55 receptor, in promoting high stretch-induced pulmonary edema, whereas p75 signaling may play an opposing role.     

Monokine-induced acute lung injury in rabbits

Interleukin-1 (IL-1) mediates components of the acute phase response, stimulates granulocyte metabolism, and induces endothelial cell surface changes. We studied in unanesthetized rabbits the effects of intravenous divided dose infusions of a murine monokine preparation containing IL-1 activity, on circulating granulocytes, their sequestration within the pulmonary microvasculature, pulmonary edema formation, and changes in pulmonary vascular permeability. Monokine administration induced significant (P less than 0.01) granulocytopenia as well as a significant (P less than 0.001) increase in mean alveolar septal wall granulocytes per high power field (HPF) compared with saline-injected controls. Infusions of the monokine preparation significantly (P less than 0.005) increased lung wet-to-dry weight ratios as well as significantly (P less than 0.025) increased pulmonary extravasation of radiolabeled albumin. Electron microscopic analysis of lung sections obtained from monokine-infused animals demonstrated endothelial injury, perivascular edema, and extravasation of an ultrastructural tracer. We conclude that a monokine preparation containing IL-1 activity can induce profound granulocytopenia, pulmonary leukostasis, and acute pulmonary vascular endothelial injury.