评估胎肺成熟方法的概述

目前早产仍是导致新生儿死亡的最大威胁,故评估胎肺成熟是产前检查的重要步骤。评估胎肺成熟的方法可分为生物化学和生物物理学两种方法。传统的生物化学方法,如卵磷脂/鞘磷脂和磷脂酰甘油测定的诊断价值较高,而新的生物物理学方法简单、快速,便于临床应用。上述实验方法的进一步研究和改进对临床产前胎肺成熟的诊断有较高价值。     

胎肺成熟度的判断

胎肺发育不成熟可致新生儿呼吸窘迫综合征,检测肺表面活性物质含量的多少是评价胎肺发育成熟度的有效方法.近30年来各种检测方法不断完善以提高其检测精确度,缩短检测时间.然而各种检测结果均存在特异性较低、阳性预测价值不高的缺点.该文总结了目前常用的肺表面活性物质的检测方法及其进展,各试验的灵敏性、特异性、阳性预测值、阴性预测值及其之间的比较,以协助临床正确判断胎肺发育程度.     

糖皮质激素促肺成熟作用的研究进展

大量研究证实围生期使用糖皮质激素可促进肺成熟,显著降低新生儿呼吸窘迫综合征的发病率和病死率.其作用机制主要是促进肺泡发育和肺表面活性物质系统的成熟.同时,围生期使用糖皮质激素对胎儿和新生儿造成的不良影响正受到越来越多的关注.产前重复使用糖皮质激素和生后早期静脉使用糖皮质激素的安全性仍不确定.糖皮质激素的给药途径、不同剂量糖皮质激素的作用效果和机制仍需深入研究.该文对近年来产前使用糖皮质激素和新生儿早期使用糖皮质激素促肺成熟作用的临床研究和动物实验研究进行综述.     

The effect of primary cytomegalovirus infection on fetal lung maturity indices

The aim of this study was to evaluate the impact of primary cytomegalovirus (CMV) infection on fetal pulmonary surfactant production as assessed by different tests for the diagnosis of fetal lung maturity (FLM) on amniotic fluid (AF). A cross-sectional cohort study. AF samples from 11 pregnant women with primary CMV infection were examined for FLM between the 26th and 37th week of gestation. Normal pregnancies (n = 11) were matched for gestational age at amniocentesis and at delivery, birth weight, Apgar score and gender sex. FLM was assessed by planimetric and stoichiometric lecithin to sphingomyelin ratio (L/S), phosphatidylglycerol (PG) presence and lamellar bodies count (LB). Maternal immunological parameters (T-cells, natural killer [NK] activity) were also considered. Mean planimetric L/S ratio (4.2+/-2.1 vs 2.3+/-0.7, P < 0.01) and LB count (42.6 x 10(3)+/-19.0 x 10(3) vs 16.8 x 10(3)+/-11.5 x 10(3), P < 0.004) were higher in controls when compared to CMV infected patients. Moreover, planimetric L/S ratio was higher in five CMV non-infected babies compared to six CMV-infected babies (3.1+/-1.3 vs 1.9+/-0.8, P < 0.05). When FLM was related to maternal immunological results, planimetric and stoichiometric L/S and LBs count were negatively correlated with CD8+ T-cells (r = -0.8, P < 0.05; r = -0.9, P < 0.05; r = -0.9, P < 0.01, respectively); LBs was also negatively correlated with CD14+ T-cells (r = -0.8, P < 0.03). In contrast, a positive correlation was found between stoichiometric L/S and NK activity (r = 0.9, P > 0.01). Maternal primary CMV infection impairs FLM indices as a possible result of reduced surfactant release and/or production. Significant correlations were found between immunity status of CMV-infected mothers and FLM tests.     

IL-6 is constitutively expressed during lung morphogenesis and enhances fetal lung explant branching

Previous studies have shown that chorioamnionitis, with increased IL-6, promotes fetal lung maturation and decreases the incidence of respiratory distress syndrome in premature neonates. However, the expression pattern and the effects of IL-6 on fetal lung growth mechanisms remain unknown. IL-6 expression was assessed by in situ hybridization and by real-time PCR between 14.5 and 21.5 d postconception. Normal and nitrofen-induced hypoplastic lung explants were cultured with increasing IL-6 doses or IL-6 neutralizing antibodies. Branching, cellular proliferation (Ki-67) and MAPK phosphorylation in fetal lung explants were analyzed. Pulmonary primitive epithelium expressed IL-6 constitutively throughout all gestational ages, displaying highest levels during earliest stages. In normal and hypoplastic lung explants, IL-6 neutralizing antibodies significantly reduced, whereas IL-6 supplementation induced a biphasic effect (lower doses increased, while the highest dose did not accomplish additional effect) on branching and cellular proliferation. IL-6 enhanced p38-MAPK phosphorylation without changing MEK1/2 and JNK pathways. The present study suggests a physiological role for IL-6 on pulmonary branching mechanisms most likely involving p38-MAPK intracellular signalling pathway.     

Amniotic fluid proteins in relation to fetal maturity

Amniotic fluid total proteins and its fractions were estimated in 45 samples at different gestations. An increase in protein concentration was observed from 14 to 28 weeks of gestation followed by a fall. The fall of values beyond 28 weeks was statistically significant with a narrow scatter around the mean. Beyond 14 weeks of gestation protein value of 0.26 gm/dl or less probably indicates a mature fetus with gestation of 37 weeks or more. Study of protein fractions (polyacrylamide gel electrophoresis method) was not helpful in the assessment of fetal maturity.     

Measurement of reverse triodothyronine in material serum and amniotic fluid and its correlation with fetal lung maturity

Amniotic Fluid reverse T₃ (AFrT₃) was measured and it was correlated with serum (maternal) rT₃ levels as well as with L/S ratio. No significant correlation was found between maternal serum rT₃ and L/S ratio. Similarly no correlation was found between AFrT₃ and maternal rT₃. It is concluded that AFrT₃ level is not a good marker for antenatal detection of fetal hypothyroidism.     

Maternal serum alkaline phosphatase and fetal maturity

Total as well as heat stable alkaline phosphatase activity was determined in sera of 70 normal pregnant mothers. Rise in activity was observed with advancement of gestation and was due to increased concentration of heat stable fraction. Statistically significant differences in levels between various gestational age groups suggest the assay of this enzyme for assessment of fetal maturity. Total alkaline phosphatase activity of 15 K.A. units/dl or more, with more than 50% of it being heat stable fraction, indicated a mature fetus (37 weeks or more gestation).     

Transforming growth factor-alpha gene expression in late-gestation fetal rat lung.

Transforming growth factor-alpha (TGF-alpha) is a structural homologue of epidermal growth factor and competes for binding on a common transmembrane protein receptor/kinase. Although TGF-alpha appears to be more important than epidermal growth factor in embryogenesis and mammalian organogenesis, there is little information regarding its expression in developing lung. Accordingly, we measured levels of immunoreactive TGF-alpha and its gene expression in late-term fetal rat lung during the transition from the canalicular (19-20 d) to the saccular (21 d) stage. We report that at 19 d gestation intrapulmonary levels of TGF-alpha were 1.4 +/- 0.3 pmol/mg protein as determined by RIA, but had decreased by 50% at 21 d. To determine if the TGF-alpha gene is expressed in lung, RNA isolated from fetal rat lung was reverse transcribed, and a 302-bp fragment corresponding to a portion of the TGF-alpha gene was amplified by polymerase chain reaction. Southern blot hybridization with a 32P-labeled 2.3-kb EcoRI fragment of rat TGF-alpha cDNA clone showed a pattern of declining expression during late gestation. Therefore, fetal rat lung expresses TGF-alpha, as is evidenced by the synthesis of both the message and the protein. Because levels of protein were highest in the period of canalicular lung development when the respiratory acinus is formed and vascularized, a potential role for this intrapulmonary growth factor in pulmonary remodeling is suggested.     

Ontogeny of surfactant proteins A and B in human amniotic fluid as indices of fetal lung maturity.

Surfactant proteins A and B (SP-A and SP-B) were measured in human amniotic fluid by ELISA and correlated with lecithin to sphingomyelin ratio (L/S), phosphatidylglycerol (PG), and perinatal outcome. Amniotic fluid SP-A, SP-B, and L/S increased with advancing gestation. SP-A was detected at 19 wk gestation and increased dramatically in the 3rd trimester of pregnancy. SP-B was first detectable at 31 wk gestation and increased significantly to term. SP-A was a more specific predictor of nonrespiratory distress syndrome (RDS) than L/S or SP-B; however, the sensitivity of SP-A in predicting RDS was less than L/S less than 2.0 (26.3 versus 82.3%, respectively). In 209 pregnancies assessed within 48 h of delivery, the sensitivity of SP-B in predicting RDS (nondetectable SP-B) was comparable to the L/S, however, SP-B = 0 was frequently observed in mature infants, limiting its specificity for prediction of RDS. The greatest sensitivity and specificity were achieved with the measurement of L/S less than 2.0 and negative PG, which correctly predicted 100% of the infants with RDS and 94% of those who did not develop the disorder. Measurement of SP-A or SP-B did not improve the prediction of RDS. SP-A, SP-B, and L/S were not affected by infant sex, Apgar score, rupture of membranes, size for gestational age, maternal diabetes, hypertension, or exposure to medications. SP-A, SP-B, and L/S were significantly elevated in amniotic fluid from black mothers. SP-A was significantly elevated in amniotic fluid from mothers who smoked during pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of maternal vitamin-A administration on fetal lung vitamin-A stores in the perinatal rat

Vitamin A (retinol) is essential for normal differentiation and integrity of developing respiratory epithelium and its deficiency has been linked to an increased susceptibility to lung injury. Because significant vitamin-A storage occurs in the fetal lung near term in the perinatal rat, prematurely born animals deprived of adequate stores in their lungs may be susceptible to the adverse effects of vitamin-A deficiency. It would be desirable if lung vitamin-A stores could be augmented with maternal administration, but the feasibility of this strategy has not been reported. We therefore conducted this study in rats to determine whether maternal administration of vitamin A could increase the lung stores of vitamin A in the offspring. Vitamin-A-sufficient pregnant rats were given a single dose of either vitamin A (50,000 IU retinyl palmitate) or 0.9% saline solution on gestational day 16 (term = 21 days) by the intragastric route. High-performance liquid chromatography was used to measure concentrations of vitamin A and its esters in fetal and neonatal lungs and livers at times ranging from gestational day 17 through 21, and from postnatal day 1 through 14. The concentrations of vitamin-A esters in the lungs of fetuses and newborn pups of the vitamin-A-treated animals were significantly (1.7- to 7.1-fold) higher than those of the control group. This increase in the lung vitamin-A ester concentrations was seen within 24 h of maternal administration and persisted throughout the 14-day postnatal period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dexamethasone increases superoxide dismutase activity in serum-free rat fetal lung organ cultures

Dexamethasone (Dex) injected intraperitoneally to dams on gestational days 19 through 21 significantly enhances the normal late gestational rise of rat pulmonary superoxide dismutase activity. To study if Dex could act directly on lung cells to increase the activity of superoxide dismutase, rat fetal lung organ cultures were established from 21- or 22-day-old pups and maintained in serum free Waymouth 752/1 medium in 95% O2 for 72 h with and without 10 nM Dex in the medium. The cultures increased spontaneously in total superoxide dismutase activity from 17.5 +/- 3.1 to 33.5 +/- 6.2 U/mg DNA during this interval (+90%). The presence of 10 nM Dex caused an increase in enzyme activity to 40.1 +/- 9.3 U/mg DNA (+130%) demonstrating this hormone can act directly on the lung independent of the systemic metabolic consequences of corticosteroid administration. Dex decreased the rate of Cu,Zn superoxide dismutase synthesis (13.5 +/- 3.4 nmol Phe incorporated/mg DNA/h control vs 7.2 +/- 1.6, Dex) and seemed to also decrease the rate of enzyme degradation.     

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.     

The role of pulmonary corticosteroid 11-reductase activity in lung maturation in the fetal rat

Injection of 11-ketoprogesterone into fetal rats at day 17 of gestation reduced the pulmonary C-11 activation index (an indicator of net gain or loss of glucocorticoid activity) as measured at day 21 (P less than 0.001) and resulted in elevated levels of the inactive hormone 11-dehydrocorticosterone (P less than 0.001), but unchanged corticosterone levels. Adrenal weight was significantly increased (P less than 0.001). 11-Ketoprogesterone-injected fetuses had considerably larger lungs (P less than 0.001) with reduced saturated phosphatidylcholine content (P less than 0.001).     

Leptin deficiency causes pycnotic change in fetal cingulate cortical cells

Leptin is an obese gene product, and leptin-deficient ob/ob mice develop hyperphagia and reduced locomotor activity. Leptin is thought to be related to brain development, because leptin receptors are widely expressed in the brain, and because brain weight as well as brain protein and DNA contents were reduced in adult ob/ob mice. In this study, we investigated the effect of leptin on the fetal cingulate cortex, since the leptin receptor is expressed in the neurons of the cingulate cortex, which is involved in emotion as well as in sensory, motor, and cognitive processes. The ob/ob fetuses had more pycnotic cells than wild-type fetuses in the cingulate cortex at embryonic day (E) 18. Many pycnotic cells were observed in the intermediate zone of the cingulate cortex. Most cells observed in this area were neuronal lineage cells, while few undifferentiated cells and oligodendrocyte precursor cells were found. At E18 there was no significant difference in the rostrocaudal length of the corpus callosum, which contains the neuronal projection from the cingulate cortex, between ob/ob and wild-type fetuses. We also showed that the length of the cerebrum was greater and the width of the cerebrum and cerebellum were lesser in ob/ob fetuses than in wild-type at E16. These results suggest an increased cell death in neuronal lineage cells in the intermediate zone of the cingulate cortex in leptin-deficient ob/ob mice. Leptin deficiency may also alter the gross morphology of the brain in development, but not the formation of the corpus callosum.