Assessment of fetal pulmonary maturity by phospholipid analysis of amniotic fluid lamellar bodies

Amniotic fluid embolism and leukotrienes--the role of amniotic fluid surfactant in leukotriene production

Surfactant rich lipid (lipid) was extracted from cell free 10,000 x g pellets of amniotic fluid. White blood cells (WBC) were isolated from human donors. 36 x 10(7) WBC and 5 g rabbit lung were incubated with pretreated lipid or dipalmitoyl lecithin (lecithin). Leukotrienes (LTs) were identified by high performance liquid chromatography (HPLC) and bioassay, and quantified by radioimmunoassay. Peaks of LTC4 and LTD4 on HPLC and guinea-pig ileum contraction could be identified in lipid and lecithin groups, but not in the control group. LTC4 production by lipid and lecithin groups was significantly higher than that by the control group. An involvement of amniotic fluid surfactant in leukotriene production is suggested.

Current perspectives in assessment of fetal pulmonary surfactant status with amniotic fluid

In recent years, improvements in analytical methodology and clinical management of maternal-fetal diseases have altered the understanding of data from amniotic fluid analysis. Delays in phospholipid production or lung function are not currently reported in maternal diabetes. Fetal lung function following glucocorticoid therapy or premature membrane rupture is uncoupled from amniotic fluid phospholipid concentrations, which do not have the usual significance in these circumstances. Phosphatidylglycerol (PG) is present prior to the usual time it is detected by thin layer chromatography (TLC) methods, which vary in sensitivity for PG. Consequently, the significance of its "absence" is highly varied. These observations are discussed in light of the earlier methods and data, along with new perceptions of the functions of the individual phospholipids and apoproteins, the regulatory mechanism of surfactant production, and the relationship of amniotic fluid components to neonatal lung function.

Fetal lung maturity tests on the 10,000 X g pellet

Centrifugation has a profound effect on tests of fetal lung maturity performed on amniotic fluid. We have investigated the effect of a 700 X g centrifugal force for 10 min and a 10,000 X g force for 20 min on a battery of tests. While 91% of the OD650 was removed by the 10,000 X g centrifugal force, the supernatant fraction retained 34% and 38% of the L/S ratio and enzymatic lecithin respectively, when compared to the sample before centrifugation. Phosphatidylglycerol, when present in an amniotic fluid, was always absent from the 10,000 X g supernatant but present in the pellet formed by this centrifugal force. The pellet after 10,000 X g was unsuitable for OD650 and L/S ratio determinations but contained 63% of the enzymatic lecithin. When the pellet tests were subjected to a clinical trial, respiratory immaturity did not occur when phosphatidylglycerol was present or when the 10,000 X g pellet may be a useful means of detecting amniotic fluid surfactant and thus determining fetal lung maturity.

Beta-adrenergic-induced surfactant synthesis, secretion, and reutilization in fetal rabbit lung and isolated differentiating type II alveolar cells

In vivo and in vitro approaches were used to examine the role of beta-adrenergic agonists in the regulation of surfactant synthesis and secretion in the lung. Rabbit fetuses of either 28 or 30 gestational days were treated with isoxsuprine. Fetuses from half of the does in each group were removed and allowed to breathe for 30 minutes. The others were left in utero. Intracellular and extracellular surfactant pools were isolated. Breathing increased secreted surfactant. On the twenty-eighth day without breathing, isoxsuprine treatment increased secretion of surfactant. The reverse effect was noted in the group that received the drug and also breathed. In contrast, on the thirtieth day, the drug inhibited surfactant release in those fetuses that did not breathe. In in vitro studies, undifferentiated type II alveolar cells were isolated and stimulated to differentiate. Subsequent exposure to isoxsuprine (5 or 10 mumol/L) stimulated both the synthesis and secretion of radiolabeled disaturated phosphatidylcholine. Concurrent incubation of those cells exposed to 10 mumol/L isoxsuprine with either unsaturated or disaturated phosphatidylcholine that was carbon 14 labeled showed a strong preference for incorporation of the latter phospholipid into total cellular phosphatidylcholine. These results suggest that beta-adrenergics may inhibit as well as stimulate secretion of surfactant by type II alveolar cells and that these cells may reincorporate secreted disaturated phospholipid.

Amniotic fluid phospholipids and foetal lung maturation

An analysis was made of samples of amniotic fluid from 82 pregnant women with normal pregnancies, ranging from 29 to 40 weeks of amenorrhoea. Lipid extraction was quantitative and individual phospholipids were isolated by two-dimensional chromatography. The lecithin/sphingomyelin ratio (L/S) increased significantly (t = 2.17; p less than 0.05) between 35 and 36 weeks of amenorrhoea (from 2.9 +/- 1.0 to 4.3 +/- 1.7). Phosphatidyl-glycerol (PG) was detected from 35 weeks of pregnancy, the time at which the incidence of amniotic samples with mature surfactant (L/S greater than or equal to 2.7 and presence of PG) was 9%; mature surfactant incidence increased to 55.5% at 36 weeks and 100% at 37 or more weeks. There was a good correlation between surfactant levels in amniotic fluid and new-born respiratory function.

Subcellular distribution of disaturated phosphatidylcholine in developing rabbit lung

To determine the subcellular distribution of disaturated phosphatidylcholine (DSPC) in lung tissue during perinatal development, fetal rabbits at 24, 26, 28 and 31 (term) days gestation and newborns were studied. Following alveolar lavage, fractions enriched in nuclei-cellular debris, mitochondria, microsomes, surfactant (lamellar bodies) and cytosol were prepared from the residual tissue homogenate, and their DSPC content was determined. The DSPC content of the unfractionated residual lung tissue homogenate progressively and significantly increased during fetal development, rising from 9.09 +/- 0.91 to 17.45 +/- 2.88 mg/g dry lung between 24 days gestation, and term. Between 24 and 26 days gestation the overall increase in tissue DSPC was due to a two-fold increase in the mitochondrial, microsomal and cytosolic pools. Lamellar bodies were first isolable at 26 days gestation. The DSPC content of this fraction increased six-fold (from 0.10 +/- 0.02 to 0.67 +/- 0.15 mg/g dry lung) between 26 and 28 days gestation and a further seven-fold (to 4.63 +/- 1.06 mg/g dry lung) by term, accounting for the overall increase in the tissue homogenate value during this time period. By the first postnatal day, microsomal and cytosolic DSPC increased another two-fold, but no significant change occurred in the other subcellular fractions. Alveolar lavage DSPC progressively increased over the time period studied. While there was no change in the lamellar body DSPC/total PC ratio during fetal development, each of the mitochondrial, microsomal and cytosolic ratios decreased between days 26 and 28 of gestation and then increased at term.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphatidylinositol and not phosphatidylglycerol is the important minor phospholipid in rhesus-monkey surfactant

Pulmonary surfactant was isolated from lung tissue and alveolar washes of lungs of adult rhesus monkeys (Macaca mulatta). The phospholipid composition was determined and compared to the composition of human surfactant fractions. Contrary to human surfactant, phosphatidylinositol is the major acidic phospholipid, whereas phosphatidylglycerol is only a minor component in rhesus-monkey surfactant. These differences are not caused by a difference in plasma myo-inositol concentrations between the two species.

Lack of change in the composition of fetal lamb lung surfactant during gestation

Fetal surfactant from lamb lung fluids collected daily from day 114 to day 146 of gestation, was isolated by centrifugation (pellet material) and further purified by sucrose density gradient centrifugation. The concentration of the pellet material from lung fluid (crude surfactant) increased from day 125 till day 135 and fluctuated strongly from that period onwards, whereas lung fluid secretion increased linearly until a few days before parturition. The pellet phospholipid composition changed with gestational age, suggesting biochemical maturation of the surfactant-producing system. The purified surfactant fraction, of which approximately 85% was phosphatidylcholine, did not change however from day 122 onwards except for a small increase in the percentage of phosphatidylglycerol. Alveolar wash surfactant or the lamellar body material, isolated from fetal lungs at different gestational ages had the same composition as surfactant from lung fluids. Only the composition of lamellar bodies of '125 day' lungs differed slightly from that of the lung fluid surfactant. The similar characteristics of all purified surfactant fractions throughout gestation indicate that, in the fetal lamb, lung maturation is associated with an increase in surfactant production no significant changes in phospholipid composition.

Amniotic fluid phosphatidylglycerol and phosphatidylcholine phosphorus as predictors of fetal lung maturity

The contents of phosphatidylglycerol and phosphatidylcholine phosphorus in amniotic fluid (10,000 X g pellets) were studied as predictors of fetal lung maturity. The presence of phosphatidylglycerol predicted the absence of neonatal respiratory distress syndrome with 99% probability. When phosphatidylglycerol was absent, phosphatidylcholine phosphorus was a reliable predictor if measured 3 to 7 days before delivery. The probability that respiratory distress syndrome would not occur was 94% when phosphatidylcholine phosphorus was greater than 6. When measurement was performed within 2 days of delivery, the probability that respiratory distress syndrome would not occur fell to 69%. As measured in amniotic fluid, phosphatidylglycerol and phosphatidylcholine phosphorus are reliable antenatal predictors of fetal pulmonary maturity and, therefore, are useful in the management of a number of obstetric conditions.

An explanation of the low lecithin/sphingomyelin ratio of amniotic fluid in early pregnancy

We have attempted to determine why the lecithin/sphingomyelin (L/S) ratio of amniotic fluid is lower than 2 during an early stage of pregnancy. We found that, at 16 wk of gestation, long before the fetal lung secretes lecithin into the amniotic fluid, the L/S ratio was about 1. High-density lipoprotein isolated from the amniotic fluid also had such a low L/S ratio. The L/S ratios of the high-density lipoprotein from umbilical cord blood and maternal blood, however, were much higher, viz. 3.7 (+/- 0.25) and 6.4 (+/- 0.33), respectively. The increase coincided with a decrease in their fluorescence polarization. We suggest that the low L/S ratio of 16 wk amniotic fluid is caused by lipolysis of its lecithin, which is derived from fetal or maternal high-density lipoproteins.

Fetal pulmonary maturity as determined by particle electrophoresis

Particle electrophoresis has been used to investigate particles obtained from amniotic fluid. These particles are defined mainly as unilamellar and multilamellar liposomes by electron microscopy. A total of 172 samples of amniotic fluids from 132 pregnancies were included in this study. The electrophoretic results were compared to the total phospholipids and to neonatal outcomes in 42 cases. At least two kinds of particles from amniotic fluids with different electrophoretic mobilities (EPM) are evident. With a ratio of F greater than 1.0, the presence of electrophoretically faster particles was found to be associated with apparent fetal lung maturity. On the other hand when the ratio was F less than 1.0, this seems to indicate an immature fetal lung. Seventy-seven per cent of F values correspond to the total phospholipid content P regarding the prediction of fetal pulmonary maturity resp. immaturity. The correct prediction of fetal lung maturity was demonstrated in 42 patients delivered within 48 hours of amniotic fluid sampling. In 28 cases with a mature F value (greater than 1.0) the correct prediction of respiratory distress syndrome (RDS) was 100 per cent. Eight out of 14 patients with immature F values (less than 1.0) developed RDS. The F values were found to increase as pregnancy progressed. The electrophoretically differentiated amniotic fluid particles behave differently at low pH. Selection and electrophoretic measurement of particles were made in a subjective manner. This preliminary investigation suggests that the results correspond to those obtained by objective cell electrophoretic measurements.