慢性亚致死性缺氧对未成熟脑结构和发育的影响

现代新生儿学的发展促使极低体质量早产儿的存活率显著提高,同时严重慢性肺部疾病患儿增多,特别是支气管肺发育不良(BPD).中重度BPD患儿多数有远期感觉、运动和认知缺陷.有些功能缺陷可能发展至学龄期或成年甚至持续终生.越来越多的临床数据表明BPD显著影响新生儿脑生长和发育,其病程中伴随的慢性亚致死性缺氧是引起极低体质量早产儿远期脑损伤和脑瘫等神经系统并发症的重要因素之一.动物研究发现慢性缺氧导致新生鼠脑皮层下和胼胝体白质损伤、进行性脑室扩大和胶质增生,突触发育前后失衡及神经递质传导障碍,从而可能显著影响感觉、运动及认知等脑功能发育.     

Neonatal hypoxia in the rat: effects on exocrine pancreatic development

BACKGROUND: Glucocorticoids profoundly affect pancreatic development during the suckling period. Increases in circulating glucocorticoids during exposure to hypoxia may alter the normal pattern of pancreatic enzyme development. METHODS: Rats were exposed to hypoxia from birth to 7 days (suckling) or from 28 to 35 days of age (weaned at day 21). RESULTS: Hypoxia in neonatal rats (0-7 days) led to decreased pancreatic weight, and trypsin, lipase, and amylase activity compared with normoxic controls. In contrast, rats exposed to hypoxia from 28 to 35 days of age had decreased lipase activity but no change in other pancreatic parameters. Two weeks after hypoxia (0-7 days) pups were returned to normoxia, and their body weights remained smaller than the age-matched, previously normoxic controls. Pancreatic enzyme activities were decreased in the group recovering from hypoxia compared with controls. Recovery of enzyme activities was observed 3 weeks after hypoxic rats were returned to normoxia. Normoxic pups were given dexamethasone to simulate the hyperglucocorticoid state in hypoxia at 7-day olds. Dexamethasone administration led to decreased body weight, but increased pancreatic weight and enzyme activity compared with normoxic, age-matched controls. CONCLUSIONS: Hypoxia in newborn rats delays the maturation of pancreatic exocrine enzymes. The mechanism is not related to increased serum glucocorticoids.     

Metallothionein in rat lung during postnatal development

Zn and Cu concentration, content, and distribution in lung were quantitated in neonatal and adult Lewis rats. Total lung Cu and Zn content rose dramatically during postnatal development, paralleling increases in lung and body weight. Cu concentration was 2-fold higher in adult lung than in neonatal lung whereas Zn concentration was unaffected by developmental age. A Cu-containing protein with an approximate molecular weight of 10,000 Da was identified immunologically as metallothionein (MT). At term, native MT concentration in the lung was 4-fold higher than in adult lungs. By day 4 postpartum, MT concentration was reduced by half and reached a level characteristic of the adult by 7 days postpartum. MT was localized in nuclear and cytoplasmic compartments of positive lung cells by immunofluorescent techniques; initially, nuclear MT staining was more intense than cytoplasmic staining.     

Chronic hypoxia impairs murine hippocampal development and depletes the postnatal progenitor pool by attenuating mammalian target of rapamycin signaling

Chronic hypoxia (CH) is a major risk factor for impaired cognitive function in various disease states, particularly in the context of cyanotic congenital heart disease. Although most brain development occurs prenatally, the dentate gyrus (DG) of the hippocampus harbors progenitor stem cells that contribute to its ongoing development postnatally. It is unclear how exposure to CH might affect postnatal hippocampal development, so we used a transgenic mouse that expresses enhanced green fluorescent protein (eGFP) within this progenitor population to determine the effect of CH on the DG. We find that exposure to 10% oxygen from postnatal d 3 to 28 results in a smaller DG with long-term impairment of hippocampal neurogenesis. Because the mammalian target of rapamycin (mTOR) pathway is a well-known regulator of cell proliferation and growth and is sensitive to hypoxia, we investigated its activation on exposure to CH and find it to be attenuated specifically in neural progenitor cells. Systemic inhibition of the mTOR pathway using rapamycin also caused impairment of hippocampal neurogenesis that mimics exposure to CH. Our findings demonstrate that CH results in long-term impairment of hippocampal neurogenesis and is mediated, in part, by attenuation of the mTOR pathway.     

Attenuation of postnatal hypoxia in the premature newborn rat by maternal treatment with dexamethasone: its relationship with lung phospholipid content

The effect of maternal treatment with dexamethasone on blood PO2, PCO2, pH and lactate concentrations and on lung phospholipid content in premature newborn rats during the early neonatal period was studied. The postnatal hypoxia shown by premature newborn rats was prevented by this treatment. Postnatal hypercapnia was longer in premature newborns showed significantly lower lung phospholipid concentrations than term-delivered newborn animals. Maternal treatment with dexamethasone increased lung phospholipid concentrations which reached values close to those found in term newborns. Our results suggest that maternal treatment with dexamethasone prevents postnatal hypoxia in the premature newborn rat by increasing the lung phospholipid content, which results in an enhancement of oxygen transfer through the alveolar membranes and the attenuation of hyperlactiacidemia.     

Effects of hypoxia on norepinephrine uptake by developing rabbit lung

Pulmonary extraction of radiolabeled norepinephrine (NE) was evaluated in newborn rabbits aged 1 to 3 days. Twenty pups were raised from birth in an hypoxic environment (FiO2 = 0.16-0.17) and 10 were raised in room air for study as controls. NE extraction was measured using an isolated, perfused lung technique. In hypoxic animals, average percent removal of NE was significantly reduced (p less than 0.05) as compared to controls while pulmonary pressures were increased (p less than 0.05) compared to controls. The data suggest that hypoxia reduces the ability of the lung to clear norepinephrine. This may be a factor in systemic and pulmonary vasomotor responses to hypoxia.     

Antenatal endotoxin and glucocorticoid effects on lung morphometry in preterm lambs

In utero inflammation may accelerate fetal lung maturation but may also play a role in the pathogenesis of chronic lung disease. We examined the impact of endotoxin, a potent proinflammatory stimulus, on structural and functional maturation of preterm sheep lungs. Date bred ewes received 20 mg Escherichia coli endotoxin or saline by ultrasound guided intra-amniotic injection at 119 d gestation. A comparison group of animals received 0.5 mg/kg betamethasone, a known maturational agent, at 118 d gestation. Lambs were delivered by cesarean section at 125 d (term = 150 d) and ventilated for 40 min. Lung function data are reported elsewhere. Total and differential white cell counts were performed on amniotic fluid and fetal lung fluid samples. Morphometric analyses were performed on inflation fixed right upper lobes. Total cell count increased slightly but not significantly in both amniotic fluid and fetal lung fluid. Both endotoxin and betamethasone had similar effects on alveolarization: average alveolar volume increased by approximately 20% and total alveolar number decreased by almost 30%. Both treatments led to thinning of alveolar walls, although this was statistically significant in the betamethasone-treated group only. Although antenatal endotoxin leads to striking improvements in postnatal lung function, this may be at the expense of normal alveolar development.     

Chronic lung disease: oxygen dogma revisited

Since the discovery of retrolental fibroplasia, and the role of oxygen in its development, oxygen has been considered a double-edged sword in neonatal medicine, the utmost care being exercised in order not to give too much oxygen (1). However, the important observation that hypoxaemia might induce pulmonary vasoconstriction (2) and airway constriction (3) in infants at risk for bronchopulmonary dysplasia has resulted in only a minor upward adjustment of oxygen supplementation in many neonatal units. Since oxygen toxicity has long been linked not only to retinopathy of prematurity but also to bronchopulmonary dysplasia (4), it is relevant to ask whether an increased FiO₂ might have any detrimental effects on babies.     

Chronic glucose infusion inhibits development of beta-receptor binding in fetal lamb lung

We used chronic fetal glucose infusion to test the hypothesis that chronic fetal hyperglycemia and hyperinsulinemia inhibit the development of beta-receptor binding capacity (Bmax) in fetal lamb lung. Glucose was infused (14 +/- 4 mg/kg/h, mean +/- SD) into eight twin and four singleton fetuses from 112 days gestation until death between 118-145 days gestation. The other eight twins and eleven additional singleton fetuses served as controls. Serum glucose levels were elevated 2-fold and serum insulin levels were elevated 3-fold in the glucose-infused fetuses. In the control fetuses beta-receptor Bmax increased 2.5-fold between 130 days gestation and term. However, this increase was attenuated to 1.5-fold in the glucose infused fetuses, p less than 0.01. The 50% inhibition of Bmax was similar in both male and female fetuses, except that the Bmax fell to 30% lower levels in males, p less than 0.01. Chronic glucose infusion also resulted in an 80% reduction in lung lavage saturated phosphatidylcholine content, and an 85% reduction in tracheal fluid saturated phosphatidylcholine content, p less than 0.001. Lung lavage and tracheal fluid saturated phosphatidylcholine content correlated significantly with beta receptor Bmax (r = 0.9, r = 0.85). We conclude that chronic glucose infusion inhibits the development of beta-receptor binding in fetal lamb lung, and that this effect is greater in males than females. Such a mechanism could be a factor in the predisposition of infants of diabetic mothers to develop respiratory distress and could contribute to a male disadvantage in respiratory morbidity.     

Chronic foreign body aspiration diagnosed by lung scan.

The case of a two-year-old child with foreign body aspiration is presented. It was complicated by a delay in diagnosis and treatment. Lung scan was helpful in eventually establishing the diagnosis. Key points in the management of patients with foreign body aspiration are reviewed and pathophysiologic mechanisms are discussed.     

Evaluation of genes identified by microarray analysis in favorable neuroblastoma

Purpose  

The biological heterogeneity of neuroblastoma results in a varied outcome ranging from spontaneous regression to fatal tumor progression. Microarray expression profiling and genetic polymorphism arrays may help identify key genes that differ in aggressive neuroblastomas from those observed in tumors associated with a favorable outcome.     

血管生成素-1在高氧诱导新生鼠支气管肺发育不良的表达及与肺发育的关系

目的探讨血管生成素(Ang-1)在高氧诱导支气管肺发育不良(BDP)新生大鼠中的表达。方法 48只生后2~3日龄的新生大鼠随机分为高氧组和对照组,每组24只,分别置于高氧(氧浓度≥95%)和空气中持续喂养;于高氧暴露第1、3、7天,光镜下观察大鼠肺组织形态结构变化,并采用实时荧光定量PCR和Western blotting方法分别检测大鼠肺组织中Ang-1 mRNA和蛋白表达水平。结果随着高氧暴露时间延长,光镜下高氧组逐渐表现出肺组织发育不良、肺泡结构简单化、肺泡数目减少和肺微血管发育受阻等病理改变。高氧暴露第7天,高氧组的Ang-1 mRNA和蛋白相对表达为0.33±0.18和0.20±0.07,低于对照组的0.83±0.46和0.57±0.44,差异有统计学意义(P均0.05)。结论 Ang-1是肺血管发育过程中的重要调节因子,参与了BPD病理发生。     

Developmental changes in cyclo-oxygenase mRNA induction by hypoxia in rat kidney

BACKGROUND: Prostaglandins, synthesized by cyclo-oxygenase (COX), regulate renal hemodynamics and also epithelial water and solute transport. Developmental changes occur in COX-2 mRNA expression and its response to lipopolysaccharide stimulation in rats. We examined age-related changes in COX mRNA expression induced by hypoxia in the renal cortex and medulla of developing rats. METHODS: Total RNA was extracted from 1- and 4-week-old male Wistar rats exposed to one or 4 h of hypoxia (8% O2). Cyclo-oxygenase mRNA was quantitatively analyzed using a real-time polymerase chain reaction with dual-labeled fluorogenic probes. RESULTS: Expression of COX-1 mRNA did not change in response to hypoxia in the cortex or medulla in either infantile or adult rats. In infantile rats, COX-2 mRNA expression was not induced by one or 4 h of hypoxia. In adults, 1- and 4-h exposures to hypoxia induced COX-2 mRNA in the renal cortex, and 1-h of exposure induced COX-2 mRNA in the medulla. CONCLUSIONS: Response of expression of COX-2 mRNA in rats exposed to acute hypoxia show age-related variability treated by acute hypoxia. Cyclo-oxygenase-2 might not play a major role in the hypoxic infantile rat kidney.     

What makes a good pediatric transplant lung: Insights from in vivo lung morphometry with hyperpolarized 3He magnetic resonance imaging

Obtaining information on transplanted lung microstructure is an important part of the current care for monitoring transplant recipients. However, until now this information was only available from invasive lung biopsy. The objective of this study was to evaluate the use of an innovative non‐invasive technique, in vivo lung morphometry with hyperpolarized ³He MRI—to characterize lung microstructure in the pediatric lung transplant population. This technique yields quantitative measurements of acinar airways’ (alveolar ducts and sacs) parameters, such as acinar airway radii and alveolar depth. Six pediatric lung transplant recipients with cystic fibrosis underwent in vivo lung morphometry MRI, pulmonary function testing, and quantitative CT. We found a strong correlation between lung lifespan and alveolar depth—patients with more shallow alveoli were likely to have a negative outcome sooner than those with larger alveolar depth. Combining morphometric results with CT, we also determined mean alveolar wall thickness and found substantial increases in this parameter in some patients that negatively correlated with DLCO. In vivo lung morphometry uniquely provides previously unavailable information on lung microstructure that may be predictive of a negative outcome and has a potential to aid in lung selection for transplantation.     

Chronic lung injury in preterm lambs: abnormalities of the pulmonary circulation and lung fluid balance

Chronic lung disease of early infancy, or bronchopulmonary dysplasia, is a frequent complication of prolonged mechanical ventilation after premature birth. Pulmonary hypertension and edema are common features of this condition, which is often attributed to long-term, repetitive overinflation of incompletely developed lungs. The overall objective of this work was to examine the effects on the pulmonary circulation and lung fluid balance of different ventilation strategies using large versus small inflation volumes in an animal model of bronchopulmonary dysplasia. We studied 16 newborn lambs that were delivered prematurely (124+/-3 d gestation, term = 147 d) by cesarean section and mechanically ventilated for 3 to 4 wk. Ten lambs were ventilated at 20 breaths/min, yielding a tidal volume of 15+/-5 mL/kg, and six lambs were ventilated at 60 breaths/min, yielding a tidal volume of 6+/-2 mL/kg. All lambs received surfactant at birth and had subsequent surgery for closure of the ductus arteriosus and catheter placement to allow serial measurements of pulmonary vascular resistance and lung lymph flow. Chronic lung injury, documented by serial chest radiographs and postmortem pathologic examination, developed in all lambs irrespective of the pattern of assisted ventilation. Pulmonary vascular resistance, which normally decreases during the month after birth at term, did not change significantly from the first to the last week of study. Lung lymph flow, an index of net transvascular fluid filtration, increased with time in lambs that were ventilated at 20 breaths/min, but not in lambs ventilated at 60 breaths/min. Lymph protein concentration decreased with time, indicative of increased fluid filtration pressure, without evidence of a change in lung vascular protein permeability. Postmortem studies showed interstitial lung edema, increased pulmonary arteriolar smooth muscle and elastin, decreased numbers of small pulmonary arteries and veins, and decreased capillary surface density in distal lung of chronically ventilated lambs compared with control lambs that were killed either 1 d (same postconceptional age) or 3 wk (same postnatal age) after birth at term. Thus, chronic lung injury from prolonged mechanical ventilation after premature birth inhibits the normal postnatal decrease in pulmonary vascular resistance and leads to lung edema from increased fluid filtration pressure. These abnormalities of the pulmonary circulation may contribute to the abnormal respiratory gas exchange that often exists in infants with bronchopulmonary dysplasia.     

Influence of epidermal growth factor on fetal rat lung development in vitro

Epidermal growth factor (EGF) has been shown to enhance cell multiplication or differentiation in a number of developing tissues. We have examined the effects of this growth factor on the biochemical development of explants of fetal rat lung, cultured in serum-free medium for 48 h. EGF enhanced the rate of choline incorporation into phosphatidylcholine and disaturated phosphatidylcholine in a dose dependent fashion. Half maximal stimulation occurred at a concentration of 1.0 nM, similar to the Kd for EGF binding to rat lung cell membranes. There was also significant stimulation of acetate incorporation into all phospholipids, particularly phosphatidylglycerol (539%), and increased distribution of radioactivity from acetate in this phospholipid fraction. Exposure to EGF stimulated PC synthesis in 18- and 19-day explants (term is 22 days) whereas maximal enhancement of DNA synthesis occurred after this time. This sequence differs from that observed during early embryonic development when EGF initially enhances cell multiplication. An additive interaction with regard to enhancement of PC synthesis was observed with EGF and thyroid hormone, but not EGF and dexamethasone. EGF had no effect on the activity of the enzymes of the choline incorporation pathway of phosphatidylcholine synthesis or on the activity of enzymes involved with acidic phospholipid synthesis. Fetal lung EGF content and EGF binding capacity were not increased by glucocorticoid treatment and similarly glucocorticoid binding capacity was not increased by EGF. These data indicate that EGF enhances fetal rat lung phospholipid synthesis in a dose-dependent manner and suggest that this is a direct effect on the lung tissue mediated by specific receptors.