模拟高原环境下高原肺水肿大鼠模型的建立

目的在人工实验舱模拟高原环境下,探讨建立高原肺水肿大鼠模型的条件。方法 Wistar大鼠,雌雄各半,随机分为5组:空白对照组、低氧24 h组、低氧48 h组、低氧72 h组、低氧7 d组,测定大鼠肺组织含水量,肺组织中TNF-α、IL-6含量及病理改变。结果与正常对照组相比,低氧24、48、72 h组大鼠肺组织含水量依次为(81.58±0.86)%、(82.13±0.57)%、(82.21±0.88)%,高于正常对照组(78.72±0.52)%,肺组织中IL-6依次为(329.30±133.58)、(323.92±127.42)、(506.29±197.19)pg/mL,TNF-α依次(221.08±20.26)、(208.05±20.33)、(244.63±51.53)pg/mL,高于正常对照组IL-6(187.26±69.49)pg/mL,TNF-α为(91.81±22.24)pg/mL。低氧7d组肺组织含水量(81.47±0.65)%、肺组织中IL-6(241.33±83.60)pg/mL、TNF-α(109.99±31.98)pg/mL,均显著低于低氧72h组,病理学结果显示72h组肺组织有炎性细胞浸润,肺泡壁有明显的充血和水肿。结论模拟海拔5000 m环境,建立大鼠肺水肿模型的较好的时间为72 h。     

Endothelin receptor blockade decreases lung water in young rats exposed to viral infection and hypoxia

Viral respiratory infections may increase the susceptibility of young animals to hypoxia-induced pulmonary edema. Because hypoxia stimulates endothelin production, we hypothesized that an increase in lung endothelin contributes to these alterations in lung water. Weanling rats were infected with Sendai virus, causing a mild respiratory infection. At day 7 after infection, animals were exposed to hypoxia (inspired O(2) fraction = 0.1) for 24 h. Exposure to virus plus hypoxia led to increases in lung water compared with control groups (P < 0.001). Lung endothelin levels were significantly higher in the virus plus hypoxia group than in control groups (P < 0.001). A second group of infected animals received bosentan, a nonselective endothelin receptor antagonist, during exposure to hypoxia. Bosentan-treated animals showed less lung water accumulation, less lung lavage fluid protein, and less perivascular fluid cuffing than untreated animals (P < 0.01). We conclude that the combination of a recent viral respiratory infection and exposure to moderate hypoxia led to increases in endothelin in the lungs of young rats and that endothelin receptor blockade ameliorates the hypoxia-induced increases in lung water found in these animals.     

Pulmonary vascular reactivity in Fischer rats

We previously reported that Fischer (F) rat lungs developed more extensive injury when challenged with oxidants than age-matched Sprague-Dawley (SD) rat lungs. We now describe a reduced pulmonary vascular response to alveolar hypoxia and angiotensin II (ANG II) in F compared with SD rats. The comparative studies were performed with isolated lungs perfused with salt solution or blood, catheter-implanted awake rats, and isolated main pulmonary arterial rings. Isolated lungs from F rats perfused with either blood or salt solution had reduced vasoconstriction in comparison with lungs from SD rats when exposed to alveolar hypoxia or challenged with ANG II. Instrumented awake F rats had a smaller mean increase in total pulmonary vascular resistance (PVR) than SD rats (35 vs. 94 mmHg.min.l-1, P less than 0.05) when challenged with 8% oxygen. The contractile response of isolated pulmonary artery but not thoracic aortic rings to KCl and ANG II was reduced in F compared with SD rats. In addition, F rats exposed to 4 wk of hypobaric hypoxia developed less pulmonary hypertension and right ventricular hypertrophy (when corrected for the hematocrit) than SD rats. We conclude that the oxidant stress-sensitive inbred F rat strain is characterized by a lung vascular bed that is relatively unresponsive to vasoconstricting stimuli. The mechanism underlying this genetic difference in lung vascular control remains to be defined.     

Huperzine A Ameliorates Cognitive Deficits and Oxidative Stress in the Hippocampus of Rats Exposed to Acute Hypobaric Hypoxia

Acute exposure to high altitudes can cause neurological dysfunction due to decreased oxygen availability to the brain. In this study, the protective effects of Huperzine A on cognitive deficits along with oxidative and apoptotic damage, due to acute hypobaric hypoxia, were investigated in male Sprague–Dawley rats. Rats were exposed to simulated hypobaric hypoxia at 6,000 m in a specially fabricated animal decompression chamber while receiving daily Huperzine A orally at the dose of 0.05 or 0.1 mg/kg body weight. After exposure to hypobaric hypoxia for 5 days, rats were trained in a Morris Water Maze for 5 consecutive days. Subsequent trials revealed Huperzine A supplementation at a dose of 0.1 mg/kg body weight restored spatial memory significantly, as evident from decreased escape latency and path length to reach the hidden platform, and the increase in number of times of crossing the former platform location and time spent in the former platform quadrant. In addition, after exposure to hypobaric hypoxia, animals were sacrificed and biomarkers of oxidative damage, such as reactive oxygen species, lipid peroxidation, lactate dehydrogenase activity, reduced glutathione, oxidized glutathione and superoxide dismutase were studied in the hippocampus. Expression levels of pro-apoptotic proteins (Bax, caspase-3) and anti-apoptotic protein (Bcl-2) of hippocampal tissues were evaluated by Western blotting. There was a significant increase in oxidative stress along with increased expression of apoptotic proteins in hypoxia exposed rats, which was significantly improved by oral Huperzine A at 0.1 mg/kg body weight. These results suggest that supplementation with Huperzine A improves cognitive deficits, reduces oxidative stress and inhibits the apoptotic cascade induced by acute hypobaric hypoxia.     

Blunted pulmonary pressor responses to hypoxia in blood perfused, ventilated lungs isolated from oxygen toxic rats: Possible role of prostaglandins

To determine the effects of high oxygen (O₂) tension on pulmonary vascular reactivity, we exposed rats either to 100% O₂ for 48 hrs or 40% O₂ for 3 to 5 weeks. Lungs from all rats were isolated, blood perfused and ventilated, and pressor responses to airway hypoxia and to infused angiotensin II were measured. We found that chronic subtoxic hyperoxia did not augment subsequent hypoxic vasoconstriction, and that 48 hrs of 100% O₂ markedly blunted hypoxic vasoconstriction. Meclofenamate restored hypoxic vasoconstriction to control levels in the lungs with blunted responses. Evidence for O₂ toxicity in the lungs exposed to 100% O₂ included interstitial swelling with alveolar exudates seen by light microscopy, and lung edema by water content calculations. We conclude that 1) chronic subtoxic hyperoxia does not influence subsequent hypoxic vasoconstriction, and 2) a dilator prostaglandin produced in the lung is a potent inhibitor of hypoxic vasoconstriction in O₂ toxic lungs.     

Hypoxia decreases proteins involved in epithelial electrolyte transport in A549 cells and rat lung

Fluid reabsorption from alveolar space is driven by active Na reabsorption via epithelial Na channels (ENaCs) and Na-K-ATPase. Both are inhibited by hypoxia. Here we tested whether hypoxia decreases Na transport by decreasing the number of copies of transporters in alveolar epithelial cells and in lungs of hypoxic rats. Membrane fractions were prepared from A549 cells exposed to hypoxia (3% O(2)) as well as from whole lung tissue and alveolar type II cells from rats exposed to hypoxia. Transport proteins were measured by Western blot analysis. In A549 cells, alpha(1)- and beta(1)-Na-K-ATPase, Na/K/2Cl cotransport, and ENaC proteins decreased during hypoxia. In whole lung tissue, alpha(1)-Na-K-ATPase and Na/K/2Cl cotransport decreased. alpha- and beta-ENaC mRNAs also decreased in hypoxic lungs. Similar results were seen in alveolar type II cells from hypoxic rats. These results indicate a slow decrease in the amount of Na-transporting proteins in alveolar epithelial cells during exposure to hypoxia that also occurs in vivo in lungs from hypoxic animals. The reduced number of transporters might account for the decreased transport activity and impaired edema clearance in hypoxic lungs.     

Isoproterenol improves ability of lung to clear edema in rats exposed to hyperoxia.

Exposure of adult rats to 100% O(2) results in lung injury and decreases active sodium transport and lung edema clearance. It has been reported that beta-adrenergic agonists increase lung edema clearance in normal rat lungs by upregulating alveolar epithelial Na(+)-K(+)-ATPase function. This study was designed to examine whether isoproterenol (Iso) affects lung edema clearance in rats exposed to 100% O(2) for 64 h. Active Na(+) transport and lung edema clearance decreased by approximately 44% in rats exposed to acute hyperoxia. Iso (10(-6) M) increased the ability of the lung to clear edema in room-air-breathing rats (from 0.50 +/- 0.02 to 0.99 +/- 0. 05 ml/h) and in rats exposed to 100% O(2) (from 0.28 +/- 0.03 to 0. 86 +/- 0.09 ml/h; P < 0.001). Disruption of intracellular microtubular transport of ion-transporting proteins by colchicine (0. 25 mg/100 g body wt) inhibited the stimulatory effects of Iso in hyperoxia-injured rat lungs, whereas the isomer beta-lumicolchicine, which does not affect microtubular transport, did not inhibit active Na(+) transport stimulated by Iso. Accordingly, Iso restored the lung's ability to clear edema after hyperoxic lung injury, probably by stimulation of the recruitment of ion-transporting proteins (Na(+)-K(+)-ATPase) from intracellular pools to the plasma membrane in rat alveolar epithelium.     

Neonatal calves develop airflow limitation due to chronic hypobaric hypoxia

Neonates and infants presenting with pulmonary hypertension and chronic hypoxia often exhibit airway obstruction. To investigate this association, we utilized a system in which neonatal calves are exposed to chronic hypobaric hypoxia and develop severe pulmonary hypertension. For the present study, one of each pair of six age-matched pairs of neonatal calves was continuously exposed to hypobaric hypoxia at 4,500 m (CH); the other remained at 1,500 m. At 2 wk of age, mean pulmonary arterial pressure (MPAP), dynamic lung compliance (Cdyn), resistance (RL), and static respiratory system compliance (Crs) were measured at 4,500 m in both CH and control calves exposed acutely to hypoxia (C). These measurements were repeated after cumulative administrations of nebulized methacholine (MCh). Tissues were removed for histological examination and assessment of bronchial ring contractility to MCh and KCl. After 2 wk of hypobaric hypoxia, MPAP (C 35 +/- 1.7 vs. CH 120 +/- 7 mmHg, P less than 0.001) and RL (C 2.64 +/- 0.16 vs CH 4.99 +/- 0.47 cmH2O.l-1s, P less than 0.001) increased. Cdyn (C 0.100 +/- 0.01 vs. CH 0.082 +/- 0.007 l/cmH2O) and Crs (CH 0.46 +/- 0.003 vs. C 0.59 +/- 0.009 l/cmH2O) were not significantly different. Compared with airways of C calves, airways of CH animals did not exhibit in vivo or in vitro MCh hyperresponsiveness; however, in vitro contractility to KCl of airways from CH animals was significantly increased. Histologically, airways from the CH calves showed increases in airway fibrous tissue and smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Excitability changes of cortical neurons during the postnatal period in rats exposed to prenatal hypobaric hypoxia

Pregnant rats were exposed to intermittent hypobaric hypoxia (at a simulated altitude of 7000 m or 5000 m) and the excitability of cortical neurons of their pups was tested. Stimulation of the sensorimotor cortex of rats prenatally exposed to hypoxia shortened the duration of cortical afterdischarges in 12-day-old rats, but did not change the excitability in 25-day-old animals. Shortening of the first afterdischarge in 35-day-old rats but the prolongation of the first afterdischarge in adult rats (as compared to the duration of cortical afterdischarges in rats not exposed to prenatal hypoxia) were registered. The possible mechanisms of different excitability of cortical neurons in rats prenatally exposed to hypobaric hypoxia are discussed.     

Myocardial hypertrophy in rats exposed to simulated high altitude

Myocardial hypertrophy in Sprague-Dawley adult rats exposed to hypobaric hypoxia (0.40 atmosphere of air/18 h daily for 7 days) in a hypobaric chamber was investigated. Changes in the myocardial mass were evaluated on the basis of the dry heart weight and expressed as mg/100 g of total body weight (mean +/- SEM). Data are presented indicating that: chronic hypobaric hypoxia causes a significant degree of myocardial hypertrophy in rats; hypertrophic process involves both ventricles (the right more than the left); removal of the hypoxic stimulus leads to the disappearance of hypertrophy when evaluated as an increase in dry heart weight; hypoxia affects the synthesis of a significant amount of connective tissue in the left ventricle, which is not exposed to pressure load. The r?le of neurohumoral factors (i.e., adrenergic stimulation and catecholamines) in the development of the ventricular hypertrophy is suggested.     

Scanning electron microscopy of pulmonary vascular endothelium in rats with hypoxia-induced hypertension

Scanning electron microscopy was used to study the endothelial surface of the pulmonary trunk, artery, and vein in normobaric control rats as well as in rats exposed to hypobaric hypoxia for 7 and 21 days. The individual endothelial cells of the normobaric pulmonary trunk and hilar artery were flat and slightly elongated with elevated nuclear regions, and those of the intermediate-sized artery were more elongated and had more microvilli than the large arteries studied. Their endothelial cell boundaries were outlined by beaded cytoplasmic projections. The surfaces of the normobaric hilar and intermediate-sized veins were smooth and demonstrated numerous longitudinal streaks. These venous endothelial cells were elongated and their cell boundaries were outlined by low discontinuous marginal folds. Exposure to hypobaric hypoxia caused the following changes on the arterial surface: elevation of the endothelial cells; formation of microvilli-rich cell clusters; formation of hollow defects; and the attachment of leukocytes. Hypobaric hypoxia also caused the disappearance of the longitudinal streaks and the occurrence of microvilli-rich cells in the hilar veins. The endothelial surface modifications in the hypobaric rats could be related to thickening of the endothelium, intimal edema, increased intimal connective tissue, luminal invasion of leukocytes, and increased endothelial cell proliferation, known to occur in systemic arteries of hypertensive animals.     

Effect of short-term or intermittent hypobaric hypoxia on plasma lipids in young rats

Changes in the level of plasma lipids (cholesterol, fatty acids and lipoproteins) were followed in young rats exposed once or repeatedly to hypobaric hypoxia. A single exposure to hypoxia increased the level of LDL lipoproteins but did not influence the concentration of cholesterol and fatty acids in 18-day-old rats. Repeated exposure to hypobaric hypoxia caused a statistically significant increase in the concentration of cholesterol, fatty acids, chylomicra, low density beta-lipoproteins (LDL) and very-low-density beta-lipoproteins (VLDL) in 18-day-old rats, while the level of high-density alpha-lipoproteins (HDL) decreased. In animals that had been repeatedly exposed to hypoxia in their youth, a significant decrease of the LDL lipoprotein fraction was observed at the age of 108 days.     

Hypoxia enhances unilateral lung injury by increasing blood flow to the injured lung

We hypothesized that in unilateral lung injury, bilateral hypoxic ventilation would induce vasoconstriction in the normal lung, redirect blood flow to the injured lung, and cause enhanced edema formation. Unilateral left lung injury was induced by intrabronchial instillation of 1.5 ml/kg of 0.1 N HCl. After HCl injury, blood flow to the injured left lung decreased progressively from 0.70 +/- 0.04 to 0.37 +/- 0.05 l/min and percent of flow to the injured left lung (QL/QT) decreased from 37.7 +/- 2.2 to 23.6 +/- 2.2% at 240 min. Exposure to hypoxia (12% O2) for three 10-min episodes did not affect QL/QT in normal animals, but after unilateral HCl injury, it caused blood flow to the injured left lung to increase significantly. A concomitant decrease in blood flow occurred to the noninjured right lung, resulting in a significant increase in QL/QT. The enhanced blood flow to the injured lung was associated with a significant increase in the wet-to-dry lung weight ratio in the dependent regions of the injured lung. These findings demonstrate that in unilateral HCl-induced lung injury, transient hypoxia can enhance blood flow to the areas of injury and increase lung edema formation.     

Effect of prenatal hypobaric hypoxia on activity of the rat brain phosphoinositide system

Activity of the phosphoinositide system of intracellular signalization was studied in offspring of rats exposed to severe hypobaric hypoxia at the 14–16th (group 1) or the 18–20th day (group 2) of prenatal hypoxia. At the age of 15 days, in animals of both experimental groups the basal level of triphosphoinositides in the brain cortex was shown to be elevated as compared with control. In the group 1, this parameter also remains elevated in adult animals. Application of glutamate produces a more pronounced increase of the inositephosphates in brain slices of the 15-day old rats of the group 1 than in slices of animals of the control group. In the 15-day old rats of the group 2, as compared with control, the phosphoinositide response to glutamate application was reduced. No changes in the inositephosphate levels were revealed after application of glutamate upon slices of adult (the 90-day old) control animals and of adult rats of the group 2. In slices of adult rats of the group 1, on the contrary, the glutamate application produced an increase of the inositephosphate content. The obtained data indicate essential changes of the phosphoinositide metabolism in the brain of rats exposed to action of hypoxia at the period of prenatal development. The character and the severity of these changes depend on the period of development when action of hypoxia occurs.     

Melatonin protects the heart, lungs and kidneys from oxidative stress under intermittent hypobaric hypoxia in rats

Melatonin (N-acetyl-5-methoxytryptamine) is the main secretory product of the pineal gland in all mammals including humans, but it is also produced in other organs. It has been previously demonstrated to be a powerful organ-protective substance under oxidative stress conditions. The aim of this study was to evaluate the protective effect of melatonin in several organs such as heart, lung, kidney, and of the reproductive system, such as testis and epididymis in animals exposed to intermittent hypobaric hypoxia and therefore exposed to oxidative stress and analyzed by lipid peroxidation. Ten-week-old male Wistar rats were divided into 6 groups for 96 hours during 32 days under: 1) Normobaric conditions, 2) plus physiologic solution, 3) plus melatonin, 4) intermittent hypobaric hypoxia, 5 plus physiologic solution and 6) plus melatonin. The animals were injected with melatonin (10 mg/kg body weight) at an interval of 96 hours during 32 days. Results indicated that melatonin decreased lipid peroxidation in heart, kidneys and lung under intermittent hypobaric hypoxia conditions. However, it did not exhibit any protective effect in liver, testis, epididymis and sperm count.     

Transient hypobaric hypoxia improves spatial orientation in young rats

To achieve a better understanding of learning and declarative memory under mild transient stress, we investigated the effect of brief hypobaric hypoxia on spatial orientation in rats. Young male Wistar rats aged 30 days were exposed for 60 min to hypobaric hypoxia, simulating an altitude of 7,000 m (23,000 ft) either shortly prior to attempting or after mastering an allothetic navigation task in the Morris water maze with a submerged platform. The post-hypoxic group performed significantly better in the navigation task than the control animals (the mean difference in escape latencies was 11 seconds; P=0.0033, two-way ANOVA with repeated measures, group x session). The experimental group also achieved a remarkably higher search efficiency (calculated as a percentage of successful trials per session), especially during the first four days following hypoxic stress (P=0.0018). During the subsequent training, the post-hypoxic group performed better than the control animals, whilst the efficiency levels of both groups progressively converged. Spatial memory retention and recall of well-trained rats were not affected by the transient hypobaric hypoxia. These results indicate that brief hypobaric hypoxia enhances rats' spatial orientation. Our findings are consistent with several studies, which also suggested that mild transient stress improves learning.     

Endothelin-mediated increases in lung VEGF content promote vascular leak in young rats exposed to viral infection and hypoxia

Viral respiratory infections increase the susceptibility of young animals to hypoxia-induced pulmonary edema formation. Previous work has shown that increased lung levels of endothelin (ET) contribute to this effect, though the mechanisms by which ET promotes vascular leak remain uncertain. Both in vitro and in vivo evidence suggests that ET can upregulate the production of VEGF, which is known to increase vascular permeability. We hypothesized that increases in lung ET promote increases in lung VEGF, which in turn increases vascular leak in the lung. Weanling rats were exposed to moderate hypoxia for 24 h while recovering from a mild viral respiratory infection, to hypoxia alone, or to viral infection alone. Lung VEGF mRNA and protein content were measured by RT-PCR and Western blotting, respectively. Animals exposed to hypoxia + virus demonstrated significant increases in lung VEGF mRNA and protein content. Immunohistochemical studies showed increased VEGF expression in alveolar septa and small pulmonary vessels in those animals. ET receptor blockade with bosentan prevented this increase in lung VEGF content, suggesting that ET promotes VEGF accumulation in the lung in this setting. Animals exposed to hypoxia + virus also demonstrated substantial increases in lung albumin extravasation, and those increases were blocked by both ET receptor blockade and VEGF antagonism. These findings suggest that ET-driven increases in lung VEGF content can contribute to the formation of pulmonary edema.     

Viral respiratory infection increases susceptibility of young rats to hypoxia-induced pulmonary edema

Recentclinical observations of a high incidence of preexisting respiratoryinfections in pediatric cases of high-altitude pulmonary edema promptedus to ask whether such infections would increase the susceptibility tohypoxia-induced pulmonary edema in young rats. We infected weanlingrats with Sendai virus, thus causing a mild respiratory infection.Within 7 days of infection, Sendai virus was essentially undetectableby using viral culture and immunohistochemical techniques. Animals atday 7 of Sendai virus infection werethen exposed to normobaric hypoxia (fraction of inspiredO₂ = 0.1) for 24 h and examinedfor increases in gravimetric lung water and in vascular permeability,as well as for histological evidence of increased lung water.Bronchoalveolar lavage was performed on a separate series of animals.Compared with control groups, infected hypoxic animals showedsignificant increases in perivascular cuffing, gravimetric lung water,and lung protein leak. In addition, infected hypoxic animals hadincreases in lavage fluid cell counts and protein content compared withcontrols. We conclude that young rats, exposed to moderate hypoxiawhile recovering from a mild viral respiratory infection, maydemonstrate evidence of early pulmonary edema formation, a finding ofpotential relevance to human high-altitude pulmonary edema.