Quick determination of amniotic-fluid lecithin concentration for prediction of neonatal respiratory distress

A Method of Assessing Amniotic Fluid Lecithin Concentrations and Predicting Foetal Lung Maturity, by Estimating Total Palmitic Acid Concentration Using G.L.C

A rapid G.L.C. method for estimating total palmitic acid in amniotic fluid is described and it is shown that the principal source of this substance is lecithin. Thus, the technique is a convenient means of assessing amniotic fluid lecithin concentrations and of predicting the maturity of the foetal lung.

A Simplified Method for the Estimation of Lecithin in Amniotic Fluid

A simplified method for the determination of lecithin in amniotic fluid by thin-layer chromatography is described. The results are similar to those found in previous reports and are suitable for the clinical prediction of foetal lung maturity. Factors which may influence the interpretation of the results are discussed.

SP-A-enriched surfactant for treatment of rat lung transplants with SP-A deficiency after storage and reperfusion

BACKGROUND

The function of pulmonary surfactant is affected by lung transplantation, contributing to impaired lung transplant function. A decreased amount of surfactant protein-A (SP-A) after reperfusion is believed to contribute to the impaired surfactant function. Surfactant treatment has been shown to improve lung transplant function, but the effect is variable. We investigated whether SP-A enrichment of surfactant improved the efficacy of surfactant treatment in lung transplantation.

METHODS

Left and right lungs of Lewis rats, inflated with 50% O2, were stored for 20 hr at 8 degrees C. Surfactant in bronchoalveolar lavage fluid from right lungs was investigated after storage (n=6). Left lungs were transplanted into syngeneic recipients and treated with SP-A-deficient surfactant (n=6) or SP-A-enriched surfactant (n=6) just before reperfusion. Air was instilled into untreated lung transplants (n=6). Sham operated (n=4) and normal (n=8) animals served as controls. Lung function was measured during 1 hr of reperfusion; surfactant components in bronchoalveolar lavage fluid were measured after reperfusion.

RESULTS

After storage the amount of SP-A decreased by 27%, whereas surfactant phospholipids changed minimally. After reperfusion a further decrease of SP-A was paralleled by profound changes in surfactant phospholipids. Lung transplant function, however, remained relatively good. After instillation of SP-A-enriched surfactant, PO2 values were reached that approximated sham control PO2 values, whereas after SP-A-deficient surfactant treatment, the PO2 values did not improve.

CONCLUSION

Enrichment of surfactant with SP-A for treatment of lung transplants improves the efficacy of surfactant treatment.

Effects of early surfactant treatment persisting for one week after lung transplantation in rats

We investigated whether pulmonary surfactant in rat lung transplants recovered during the first week post-transplantation, along with symptoms of the reimplantation response, and whether this recovery was affected by early surfactant treatment. The severity of pulmonary injury was varied by transplanting left lungs with 6-h and 20-h ischemia (n = 12 and 19, respectively). Half of the transplants were treated by instillation of surfactant before reperfusion. Lungs from sham operated, and normal rats (n = 4 and 5, respectively) served as controls. The pulmonary injury severely impaired lung transplant function; 10 of the worst affected animals died. After 1 wk, symptoms of reimplantation response and properties of pulmonary surfactant were assessed. If untreated, the reimplantation response had almost resolved in the 6-h but not in the 20-h ischemia group; pulmonary surfactant, however, continued to be deficient in both ischemia groups (low amounts of surfactant phospholipids and surfactant protein A [SP-A]). Surfactant treatment improved the recovery from injury in the 20-h ischemia group resulting in normal lung function and amounts of surfactant phospholipids. Amounts of SP-A were not improved by surfactant treatment. In conclusion, early surfactant treatment enhances recovery from transplantation injury and is persistently beneficial for pulmonary surfactant in lung transplants.

Ganglioside and phospholipid composition of forebrain, cerebellum, and brain stem from adult and newborn rats

The aim of this study was to elucidate whether sex or pregnancy state might affect the content and/or pattern of gangliosides from the forebrain, cerebellum and brain stem of rats. Adult male, mother (1-day after offspring) and nonpregnant rats of similar age were analyzed. Non-significant differences in ganglioside concentrations and patterns were found for the respective neural area of adult male and female rats except for a decrease in cerebellum and brain stem content from mothers and 12.0 months-old males, respectively. Thus, it seems that neither sex nor pregnancy hormones affect these parameters. By contrast, significant differences were found for pattern and ganglioside contents between adult (male and female) rats and newborns (1 day-old). Newborns showed a significant decrease in their forebrain (2.5-fold), cerebellum (2.0-fold) and brain stem (2.0-fold) ganglioside content when compared with adult (male and female) rats. Significant increases (p less than 0.001) were found in the phospholipid and cholesterol contents in the different brain areas in mothers versus their newborns. The phospholipid pattern also showed significant changes in all brain areas, with an increase (p less than 0.001) in phosphatidylethanolamine percentage in adult animals, among the main variations. An explanation for these facts is suggested.

Surfactant replacement therapy in surfactant-deficient rabbits: early effects on lung function and biochemical aspects

Lung-surfactant-deficient rabbits (n = 6) requiring artificial ventilation were subjected to a weaning-off regimen following surfactant replacement therapy. Surfactant-deficient rabbits (n = 6) that did not receive surfactant but underwent the same procedure served as controls. All surfactant-treated rabbits survived (i.e., reestablished spontaneous air breathing) whereas all the control animals died. In the surfactant-treated animals lung function improved in such a way that during the weaning period PaCO2 did not increase and the level of PaO2 remained significantly higher than in the control animals. The static lung compliance and the stability and expansion indices in vitro were significantly higher in the surfactant-treated rabbits. The lamellar body fraction of the lungs of surfactant-treated animals contained a significantly higher amount of surfactant phospholipids than those of the control animals. It is concluded that the animal model used in this study is an excellent tool for testing early effects of different surfactant preparations.

Isolation, characterization and phospholipid composition of lamellar bodies and subcellular fractions from dog lung

1. Lamellar body fractions from dog lung can be separated by a procedure based on differential centrifugation before ultracentrifugation onto a discontinuous sucrose gradient. This fraction yields about 1% of total protein from the homogenate. 2. The different fractions obtained in the isolation were assayed for the measurement of four subcellular marker enzymes: beta-N-acetylglucosaminidase, acid phosphatase, 5'-nucleotidase and succinate dehydrogenase. 3. Lamellar bodies were not contaminated by mitochondria (0.7 succinate dehydrogenase relative specific activity), whereas high specific hydrolase activities were found (beta-N-acetylglucosaminidase and 5'-nucleotidase were enriched 1.8- and 2.8-fold, respectively). 4. The chemical criterion was established by measuring the specific components of lamellar bodies. The lamellar bodies have the highest phospholipid/protein ratio (0.35); cholesterol/protein ratio (0.15) and the highest phosphatidylglycerol percentages (7.9%). 5. The phospholipid composition of lamellar bodies is distributed among phosphatidylcholine (64.5%), phosphatidylethanolamine (11%), phosphatidylglycerol (7.9%), sphingomyelin (4%), phosphatidylserine and phosphatidylinositol (3%), respectively. The remainder were considered as trace amounts (less than 1%).

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.

Inositol affects the intracellular turnover of pulmonary surfactant phospholipids in the rat

Rats, given a diet supplemented with 20% inositol, had threefold increased plasma inositol concentrations. The pool size of their alveolar surfactant fraction and their lamellar body fraction were the same as in the control rats and differences in phospholipid composition of the surfactant fractions were mainly restricted to changes in the percentages phosphatidylinositol (PI) and phosphatidylglycerol (PG). The change in phospholipid composition did not affect the pressure-volume relationship of the lungs. The labeling of phosphatidylcholine (PC), saturated phosphatidylcholine (SPC) or PI in the alveolar lavage fraction was the same for both groups, whereas labeling of alveolar PG was delayed in the inositol-fed rats. The specific activity-time relationships of the lamellar body phospholipids differed significantly between the control and inositol-fed rats and the differences in disappearance rate of the label from these fractions suggest that approximately 25-30% of the lamellar body material in inositol-fed rats is directed to a third, intracellular pool. We conclude that an increase in PI and a concomitant decrease in PG content of surfactant do not affect the clearance of alveolar surfactant, but enlarge the turnover of the lamellar body fraction because of intracellular degradation.

A semi-automated and standardized method of determining the lamellar body content of amniotic fluid

We have simplified and standardized the method of determining the lamellar bodies (LB) in amniotic fluid as a measure of fetal lung maturity. For this purpose we have first diluted the amniotic fluid and then concentrated its LB by low-speed centrifugation at the interface of a 10% Nycodenz solution. As a standard we use liposomes which consist of phospholipids enclosing a Nycodenz solution with a density similar to that of the LB. The phosphorus content of the LB and liposome standard is then determined by an automated fluorimetric method. There is an excellent correlation between the newly described procedure and the lecithin/sphingomyelin ratio. One technician can easily analyse 40 samples in a working day.

Effects of artificial ventilation on surfactant phospholipid metabolism in rabbits

Surfactant phospholipid metabolism and lung stability were studied in mechanically ventilated and in spontaneously breathing rabbits (control group). During ventilation the dynamic lung-thorax compliance decreased to 79% after 6 h. Static compliance and amount and composition of surfactant phospholipids remained unaltered. These data indicate inactivation of alveolar surfactant during ventilation, which is reversible by a single large inflation. Incorporation of injected radioactively labeled palmitate into saturated phosphatidylcholine (SPC) of the lamellar body fraction increased significantly in the ventilated group; maximal specific activity increased from 20 dpm/nmol SPC at 6 h in the control group to 30 dpm/nmol SPC at 2 h in the ventilated group. The clearance of radioactivity from the lamellar bodies into the alveolar lumen was greatly enhanced in the ventilated group. The results are explained by assuming that as a result of the inactivation of alveolar surfactant, endocytosed surfactant is degraded in the type II cells instead of being recycled and that the degradation products are subsequently reutilized in surfactant synthesis. This interpretation is supported by computer simulations.

High-frequency oscillation affects surfactant phospholipid metabolism in rabbits

Surfactant phospholipid metabolism was studied in anesthetized rabbits ventilated with high-frequency oscillation at a frequency of 5 Hz and a mean airway pressure of 5 cm H2O. Blood gases were normal although some atelectasis was evident after 1 h. The static compliance of the lungs and amount and composition of surfactant phospholipids of the lamellar body and alveolar lavage fraction were comparable to values found for spontaneously breathing rabbits. The data obtained for the incorporation of radioactively labeled palmitate into phospholipids are compatible with intracellular degradation of newly synthesized surfactant phospholipids. This hypothesis is supported by two observations. First, the rapid initial increase in specific activity of SPC and PC of the lamellar body fraction is not accompanied by a similar rapid increase in specific activity of SPC and PC of the lamellar body fraction is not accompanied by a similar rapid increase in specific activity of the alveolar lavage fraction. Second, a dissociation occurs between the metabolism of PC and SPC for the lamellar body fraction but not for the alveolar lavage fraction. The change in metabolism might be caused by the absence of large pressure swings during this pattern of ventilation.

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.

Methods of evaluating fetal lung maturity

Respiratory distress syndrome occurs in infants born with immature lungs. The immature fetal lung lacks an adequate supply of surfactant, a phospholipid-rich substance which is produced in the type II cells of the alveolar epithelium. In the fetus, surfactant is secreted into the potential air spaces of the lung and passes into the amniotic fluid as gestation proceeds. It is now clear that most methods currently in use for assessing fetal lung maturity depend on the detection of a sudden release of surfactant into the amniotic fluid as the lung reaches a critical stage of maturity. These methods, which include the lecithin/sphingomyelin ratio, the lung profile, total phospholipid or lecithin concentration, fluorescence depolarization, lamellar body phospholipid concentration, and the "shake" test, are reviewed in the light of recent understanding of the nature of surfactant. In assessing each method, we have examined possible sources of error in performing the test in the laboratory, factors which could theoretically limit its ability to reflect the state of fetal lung maturity and current information regarding its reliability, in terms of clinical performance. Guidelines for future research in this area are also suggested.

Premature changes in surface activity in lung fluid of fetal lambs

The present study was conducted to monitor changes in surface activity of lung and amniotic fluid of premature lambs. Lung fluid was continuously obtained from 10 tracheotomized fetal lambs (gestational age 98-112 days) until (premature) parturition. Amniotic fluid was sampled twice a week from 3 other lambs by catheterization, and during cesarean section at the end of the gestational period from another 3 lambs. Surface activity in lung fluid increased on the first postoperative day, the more so when this occurred at a later fetal age in the period of 98-112 days. These findings show that even before day 110 'stress' can result in a release of surface active material. A return to low surface activity (about 26 mN/m) was observed within 3 to 6 days. Thereafter, between days 110 and 120, surface activity increased steeply within the individual animals but with large variability between the fetuses. The steep and premature increased was followed by a further but slow increase during the mature period and Ymin values of approximately 2 mN/m were reached. Amniotic fluid surface activity changed slowly with gestational age, but did not reach Ymin values of less than 15 mN/m. Lung fluid total phospholipid phosphorus values were low (about 6 micro M) up to 125 days, when they increased rapidly (greater than 16 micro M). Lung fluid production increased from 4.9 ml/h at the beginning of the experiment to 12.1 ml/h after day 130 but decreased dramatically 1-3 days before (premature) parturition. Experiments on fetal lung maturation should be started before day 105 of gestation and we suggest that measurement of surface activity of fetal lung fluid may be useful in monitoring changes in the premature alveolar type II cells of lambs.

Influence of labour on the lecithin, lecithin/sphingomyelin (L/S) ratio and palmitic acid values in the amniotic fluid

The lecithin/sphingomyelin (L/S) ratio, lecithin concentrations and palmitic acid levels in amniotic fluid were studied during labour and compared with values found before labour. All were significantly higher in women in labour. The explanation and significance of this finding are briefly discussed.

The effect of parturition on amniotic fluid lecithin concentration

Amniotic fluid lecithin has been measured during the antenatal period and at comparable periods of gestation at the onset of spontaneous labour. Lecithin values were higher in labour, the difference being statistically significant in two of the three groups studied. Lecithin values were also measured serially during induced labour in 14 normal women at term. A significant fall was observed throughout labour. Creatinine levels were measured in the amniotic fluid in five of these patients and showed no significant change.

A comparative study between the values of lecithin, sphingomyelin, lysolecithin, the L/S index, and the Clements test in amniotic fluid

The relationship between the concentration of several phospholipids in amniotic fluid and the ocurrence of neonatal RDS was established some years ago. However the methods used for the determination of those substances are sophisticated and time consuming. They require specalized equipment and take at least 2 or 3 hours. CLEMENTS described a semiquantitative method which overcomes these disadvantages. The present study compared the concentration of lecithin, shingomyelin, lysolecithin and the L/S ratio against the results obtained when processing the same samples with the CLEMENTS Test. the results are expressed in mg/100 ml. for the different phospholipids and the test was evaluated as positive, intermediate or negative. a statistically significant correlation has been found between the values of lecithin, lysolecithin and L/S ratio and the results of the CLEMENTS Test, respectively. No correlation could be found with sphingomyelin (Figs. 1-4). It is concluded that the CLEMENTS Test can be a useful tool as a screening test available to any obstetrical centre.

A study of the lecithin/sphingomyelin ratio of amniotic fluid

1. There is a significant correlation between lecithin/sphingomyelin (L/S) ratios based on densitometry (L/S)D and L/S ratios based on phosphorus determinations ((L/S)P). 2. The fetal lung is mature when the (L/S)D, determined according to Verhoeven, A.G.J. and Merkus, H.M.W.M. (1974) Clin. Chim. Acta 53, 229--232, is 1.2. This value is equivalent to an (L/S)P of 1.8. 3. The acetone precipitation procedure, introduced by Gluck, L., Kulovich, M.V., Borer, R.C. and Keidel, W.N. (1974) Am. J. Obstet. Gynecol. 120, 142--155, is a necessary step for isolating surface-active lecithin. 4. Standardization of the (L/S)D test is feasible and should permit different laboratories to use the same transition point.

A comparison between the lecithin/sphingomyelin ratio of Gluck and other phospholipid values of amniotic fluid

We have found the lecithin/sphingomyelin ratio of Gluck (L/S ratio) to be very useful for predicting respiratory distress. It correlated reasonably well with three other phospholipid values: the total lecithin content, the acetone-insoluble lecithin content, and the total lecithin/total phospholipids ratio. When the L/S ratio of amniotic fluid was greater than 2.0 there was no respiratory distress, even if the other phospholipid values indicated that the fetal lungs were still immature.

Palmitic acid concentrations and lecithin/sphingomyelin ratios in amniotic fluid

Palmitic acid concentrations and L/S ratios have been estimated in amniotic fluid specimens with and without centrifugation and cold acetone precipitation. Although the number of cases was small, both of these measurements in uncentrifuged fluid seemed to reflect only indirectly on lung maturation in normal pregnancy while with centrifuged fluid the L/S value predicted RDS in one infant more reliably than palmitic acid concentration.

The origin of amnitoic fluid lecithin

Lecithin has been measured in amniotic fluid, pharyngeal aspirate, fetal and maternal plasma and fetal membranes from the same pregnancy. In the amniotic fluid from a term pregnancy 79 per cent of the lecithin is found in the reconstituted precipitate of centrifuged fluid. It is suggested that the lecithin of amniotic fluid may originate from sources other than fetal lung and that lecithin concentration is therefore a measure of overall fetal maturity.

Assessment of fetal lung maturity by estimation of amniotic fluid palmitic acid

The measurement of palmitic acid in amniotic fluid has been shown to be a rapid means of assessing the lecithin concentration. The level of palmitic acid increases quickly when the fetal lung matures at about 35 weeks' gestation, and the level in amniotic fluid obtained 24 hours or less before delivery clearly distinguishes which infants are likely to develop respiratory distress syndrome and which are mature.

Bubble stability test compared with lecithin assay in prediction of respiratory distress syndrome

A simple test for surfactant, utilizing bubble stability in ethanol, was performed in 106 samples of amniotic fluid obtained from 94 patients. Of these patients 80 delivered within 48 hours of the collection of the sample. The results were compared with the lecithin concentration in the same amniotic fluid samples and with the quality of respiration in the neonate. The test was "positive," indicating fetal pulmonary maturity, in 37 cases and none of these infants developed respiratory distress syndrome (R.D.S.). In only one of these cases, however, was gestation less than 37 weeks. The test was "intermediate" or "negative" in 43 cases but in 35 of these infants respiration at birth was perfectly normal.Performed by the method described by its originators, this simple test gives too many false negative results to be of value in routine clinical practice, although a positive result is helpful. The concept of the test is ingenious, however, and further developments may be expected.