Stimualtion of glycerolphosphate phosphatidyltransferase activity in fetal rabbit lung by cortisol administration

Hormonal influences during fetal lung development

Maturation of the fetal lung is accelerated by in utero treatment with corticosteroids and thyroid hormones. Other agents such as catecholamines, thyrotropin-releasing hormone, oestradiol, heroin and cyclic AMP also influence pulmonary phospholipid metabolism. Glucocorticoids cause precocious development of both lung morphology and the surfactant system in type II cells, resulting in more stable lungs with increased air space. The properties of glucocorticoid action are consistent with enzyme induction mediated by interaction of steroid with cytoplasmic glucocorticoid receptors. Receptors are present in lung of many species, including the human fetus, and in both pulmonary fibroblasts and type II cells. Corticosteroid therapy of women in premature labour is currently used to reduce the incidence of infant respiratory distress syndrome (RDS). Treatment of the mother with 12 mg betamethasone causes an approximately four-fold maximal increase in unbound glucocorticoid activity in fetal plasma which is calculated to cause 80% nuclear occupancy by receptor-steroid complex. It is likely that endogenous corticoids influence normal lung development; possible sources of cortisol include the fetal adrenal, maternal adrenal, and conversion of cortisone to cortisol by amniotic membranes and lung fibroblasts. Thyroid hormones have effects similar to corticosteroids, but appear to influence different biochemical steps. Synthetic analogues of triiodothyronine (T3) are available which readily cross the placenta, in contrast to T3 and thyroxine, and accelerate surfactant synthesis and release. Thyroid hormones probably act through nuclear receptors which are present in lung of both animals and the human. Thyroid treatment in utero also appears to accelerate lung maturation and prevent RDS in premature infants.

Effect of maternal dexamethasone treatment on the type II pneumocytes in hypoplastic lung by oligohydramnios: an ultrastructural study

A previous study documented the effects of maternal corticosteroid treatment on structural growth and functional development in fetal lungs associated with pathogenic conditions such as oligohydramnios using immunohistochemical and morphometric analyses. The purpose of the present study was to examine the effect of maternal dexamethasone treatment the expression of lamellar body in type II pneumocytes of the fetal rabbit lungs with hypoplasia induced by oligohydramnios using electron microscopy. Using an amniotic shunting rabbit model, pregnant rabbits were injected intravenously with either 0.1 ml of saline or 0.25 mg/kg/day of dexamethasone in 0.1 ml of saline 48 and 24 h before the delivery of fetuses, at day 30 of gestation. The number of lamellar bodies per type II pneumocyte was counted in each group using electron micrographs. The number of lamellar bodies per type II pneumocyte in the lungs of the shunted group that received saline was consistently and significantly less than that of the other three groups (5.49 +/- 2.07 vs. 7.34 +/- 2.27: shunted group that received dexamethasone, 7.58 +/- 2.08: non-shunted group that received saline, 7.79 +/- 1.90: non-shunted group that received dexamethasone; P < 0.01). These results suggest that maternal dexamethasone treatment accelerates the maturation of the surfactant system, especially the expression of lamellar bodies in type II pneumocytes, even in hypoplastic lungs induced by oligohydramnios.

Maternal dexamethasone treatment enhances the expression of surfactant apoprotein A in the hypoplastic lung of rabbit fetuses induced by oligohydramnios

Previously the authors reported that oligohydramnios induced lung hypoplasia in rabbit fetuses and showed that sustained oligohydramnios, which was induced by amniotic shunting from gestational sacs into the maternal peritoneal cavity between 23 and 30 days' gestation, significantly retards not only lung structural growth but also the functional development of alveolar type II cells in surfactant apoprotein A (SP-A) expression. In the present study, the authors examined, both immunohistochemically and morphometrically, whether the maternal administration of dexamethasone restored SP-A synthesis in fetal hypoplastic lungs. The fetal rabbits were treated through maternal administration of dexamethasone (0.25 mg/kg/d) or saline 48 and 24 hours before delivery, at 30 days' gestation. The ratio of lung weight to body weight was significantly greater for the dexamethasone-treated fetuses compared with the saline-treated fetuses in both the shunted and the nonshunted groups (P < .05). Compared with the lungs of the saline-treated fetuses, those of the dexamethasone-treated fetuses had a statistically significant increase in SP-A expression, namely the number of SP-A-positive type II cells per unit area (P < .001), the ratio of SP-A-positive cells to the total number of cells (P < .01), and the percentage of SP-A-positive area per unit area (P < .05) in the shunted group. An increase in the ratio of SP-A-positive area to lung interstitial was found for the shunted group. However, similar findings were not observed in the nonshunted group. The results suggest that maternal dexamethasone treatment accelerates the functional development of alveolar type II cells in SP-A expression, even in hypoplastic lungs induced by oligohydramnios.

Effects of glucocorticoid and thyroid hormones on regulatory enzymes of fatty acid synthesis and glycogen metabolism in developing fetal rat lung

Although glucocorticoid and thyroid hormones are known to act synergistically to stimulate surfactant production, they have opposite effects on other parameters of fetal lung maturation. We recently reported that the developmental increases in de novo fatty acid synthesis and glycogen accumulation in fetal rat lung were accelerated by dexamethasone but prevented by triiodothyronine and that the dexamethasone-induced increases were diminished when the two hormones were administered together. We have now examined the effects of maternal administration of these hormones on activities of enzymes of lung fatty acid synthesis and glycogen metabolism in the rat. There was a developmental increase in fatty-acid synthase activity between 19 and 21 days gestation. This activity was increased by dexamethasone but decreased by triiodothyronine. When the two hormones were administered together the stimulatory effect of dexamethasone was decreased from 56% to 29%. The stimulatory effect on fatty-acid synthase was also observed in fetal lung explants cultured in the presence of dexamethasone. This shows that the effect of the hormone was directly on the fetal lung. Dexamethasone had no effect on liver fatty-acid synthase. There was a developmental decrease in acetyl-CoA carboxylase activity but it was not affected by the hormones. These data show that the developmental and hormone-induced changes in fetal lung de novo fatty acid synthesis are mediated by fatty-acid synthase. Although there were developmental changes in fetal lung 6-phosphofructokinase, glycogen synthase and glycogen phosphorylase activities, these enzymes were not affected by the hormones.

Comparison of the enzyme activities of phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol synthesis in freshly isolated type II pneumocytes and whole lung from the adult rat

We compared the activities of enzymes of phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol synthesis in whole lung tissue and freshly isolated type II pneumocytes from adult rats. The activities of 1-acylglycerophosphocholine acyltransferase and CDPdiacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase were 2.9- and 4.4-fold higher, respectively, in type II cell sonicates than in whole lung homogenates. There was little difference between the type II cells and whole lung in the activities of choline kinase, choline-phosphate cytidyltransferase, cholinephosphotransferase, phosphatidate phosphatase, phosphatidate cytidylytransferase or CDPdiacylglycerol-inositol 3-phosphatidyltransferase. Since the type II cell is the source of pulmonary surfactant, and disaturated phosphatidylcholine and phosphatidylglycerol are major components of surfactant, it is of interest that this cell is enriched in the activities of enzymes exclusively involved in the synthesis of these lipids. In view of possible proteolytic damage during isolation we compared freshly isolated type II cells with those cultured for 1 day. The rates of incorporation of [methyl-3H]choline and [2-3H]glycerol into phospholipids, L-[U-14C]phenylalanine into protein and [methyl-3H]thymidine into DNA were the same in the freshly isolated and cultured cells. The composition of the phospholipids synthesized from [2-3H]glycerol and sodium [1-14C]acetate were also the same. The freshly isolated cells were at least 90% pure and did not release significant amounts of lactate dehydrogenase. Since use of freshly isolated cells avoids cell loss during culture they provide an attractive alternative, particularly in studies requiring large amounts of material.

Glucocorticoids and beta-adrenergic-receptor agonists: their combined effect on fetal rabbit lung surfactant

In a previous study on pregnant rabbits (Am J Obstet Gynecol 1983; 147:437) we found that a prolonged infusion of the beta 2-adrenergic-receptor agonist terbutaline would first cause a release of fetal pulmonary surfactant, so that more was available in the airways. However, the airway fluid then contained less surfactant, indicating a depletion of stores. Since terbutaline is often used in high doses as a tocolytic agent, surfactant depletion could be a serious side effect. With further studies on rabbits, we wanted to test the hypothesis that with an accelerated surfactant synthesis, achieved with glucocorticoids, the increased release, evoked with the terbutaline, would never cause a depletion of the surfactant stores. Our results supported this hypothesis. Betamethasone, administered to the pregnant doe on the twenty-sixth and twenty-seventh days of gestation, 0.1 mg/kg, increased compliance of the fetal lungs, and more phospholipid phosphorus could be lavaged from the airways. These effects were further increased when, following steroid administration, the doe was infused with terbutaline. Depletion of the surfactant stores was never seen when betamethasone was given prior to the beta-adrenergic-receptor agonist.

Delayed pulmonary phosphatidylglycerol synthesis and reversal by prenatal dexamethasone in fetal rats of streptozotocin-diabetic mothers

Lung slices from fetal rats of streptozotocin-diabetic mothers incorporated [3H]glycerol and [3H]choline into phosphatidylglycerol and disaturated phosphatidylcholine, respectively. When compared to age-matched fetuses from nondiabetic mothers, lung phosphatidylglycerol synthesis of 21-day fetuses of diabetic mothers was significantly diminished, although [3H]glycerol incorporation into other phospholipids was not impaired. Synthesis of disaturated phosphatidylcholine was not diminished in lungs of 20-, 21-, or 22-day fetuses of diabetic mothers. Prenatal dexamethasone partially reversed the diminished phosphatidylglycerol synthesis at 21 days of gestation; the degree of stimulation was the same as that seen in 21-day fetuses of normal mothers but the maximal rate of [3H]glycerol incorporation was about 60% of that in 21-day fetuses of normal mothers. Fetal lung disaturated phosphatidylcholine synthesis was not stimulated by dexamethasone in diabetic pregnancies, in contrast to that seen in nondiabetic pregnancies. These data suggest that maternal diabetes interferes with the ability of fetal lungs to synthesize phosphatidylglycerol, a finding consistent with the delayed appearance of phosphatidylglycerol in the amniotic fluid of human diabetic pregnancies. In addition, maternal diabetes impairs the responsiveness of disaturated phosphatidylcholine synthesis to dexamethasone. Since phosphatidylglycerol synthesis is enhanced by prenatal dexamethasone, this therapy may still be effective for reducing the adverse impact of maternal diabetes on fetal lung development.

Glucocorticoids and hypothyroidism modulate development of fetal lung insulin receptors

We investigated the development of insulin receptors in membranes of fetal rabbit lung during normal ontogeny and the effect of glucocorticoids and hypothyroidism. Specific binding of 125I-insulin to fetal lung membranes increased progressively to a peak at 29 days gestation, declining by 30 days. Scatchard plots were curvilinear and revealed a progressive increase in receptor numbers (X 10(10)/mg protein) from 129 +/- 7 (mean +/- SE) at 22-24 days to 575 +/- 16 at 29 days, declining to 467 +/- 12 at 30 days, term being approximately 31 days. Affinities did not change throughout gestation and were similar to those of adult lung; receptor numbers in adults were significantly lower than in fetuses at 26-30 days. Epinephrine and PGE1 could evoke a doubling of cAMP production in adult and fetal lung membranes until 29 days. Concomitantly with the fall in fetal insulin receptor number at 30 days, cAMP production in response to epinephrine or PGE1 increased fivefold. Induction of fetal hypothyroidism decreased insulin receptor numbers in the lung of the 28-day fetus by 70% from control (P less than 0.001) without a change in receptor affinity. In contrast, betamethasone administration increased fetal lung insulin receptor numbers by 250% (P less than 0.001) but did not alter their affinity; maternal lung insulin receptors were not altered. Thus, normal ontogeny of the fetal lung insulin receptor is characterized by a progressive increase in number followed by decline immediately before parturition associated with a sharp increase of cAMP responsiveness of the membranes. Hypothyroidism and glucocorticoid exposure can modulate the normal development of the fetal lung insulin receptor.

Phosphatidylcholine synthesis and glycogen depletion in fetal mouse lung: developmental changes and the effects of dexamethasone

We measured the rate of choline incorporation into phosphatidylcholine in lung slices; the glucogen content of the lung; and the activities of pulmonary cholinephosphate cytidylyltransferase, cholinephosphotransferase and phosphatidate phosphatase in the mouse during late fetal and early postnatal development. We also examined the effect of maternal dexamethasone administration on these parameters of fetal lung maturation. There was a development increase in the rate of choline incorporation between 17 days gestation (term is 19 days) and the immediate newborn period. There was also a developmental decrease in the glycogen content of the lung but this did not occur until 18 days. There was a developmental increase in the activities of cholinephosphate cytidylytransferase and phosphatidate phosphatase but little change in the activity of cholinephosphotransferase. Dexamethasone doubled the rate of choline incorporation into phosphatidylcholine at 17 and 18 days gestation. It decreased the glycogen content of the fetal lung by 74% at 18 and 19 days, but had no effect at 16 and 17 days. Dexamethasone increased the activity of pulmonary cholinephosphate cytidylyltransferase by 37% and that of cholinephosphotransferase by 27% at 17 days. It increased the activity of phosphatidate phosphatase by 25% at 16 days and by 32% at 19 days. These data show that the normal development profile of these parameters of fetal lung maturation in the mouse, as well as the effects of glucocorticoids thereon, are generally similar to those in the rabbit and rat. However, stimulation of cholinephosphotransferase by glucocorticoids has not been generally observed in other species. Furthermore, since the changes in the rate of choline incorporation precede those in glycogen depletion, the data suggest that the relationship between phospholipid synthesis and glycogen degradation is not simply that of precursor to product.

Phospholipids of the lung in normal, toxic, and diseased states

The highly pulmonary concentration of 1,2-dipalmitoyl-sn-glycerol-3-phosphorylcholine (dipalmitoyllecithin) and its implication as an important component of lung surfactant have promoted investigation of phospholipid metabolism in the lung. This review will set the contents including recent informations for better understanding of phospholipid metabolism of the lung in normal state (physiological significances of lung phospholipids, characteristics of phospholipids in lung tissue and alveolar washing, biosynthetic pathways of dipalmitoyllecithin, etc.) as well as in toxic states (pulmonary oxygen toxicity, etc.) and in diseased states (idiopathic respiratory distress syndrome, pulmonary alveolar proteinosis, etc.) Since our main concern has been to clarify the most important route for supplying dipalmitoyllecithin, this review will be focused upon the various biosynthetic pathways leading to the formation of different molecular species of lecithin and their potential significance in the normal, toxic, and diseased lungs.

Effect of dexamethasone upon surfactant phosphatidylcholine and phosphatidylglycerol synthesis in organotypic cultures of type II cells

Organotypic cultures of pulmonary type II epithelial cells were treated with dexamethasone at concentrations between 10(-10) and 10(-5) M for 48 h followed by a 3 h incubation in 5.6 mM [U-14C]glucose. A surfactant and a residual fraction was isolated from the cultures by discontinuous sucrose gradient centrifugation. Phosphatidylcholine and phosphatidylglycerol were purified from each fraction and analyzed for total content. The specific activity of each phospholipid was measured as an index of the rate of synthesis. Dexamethasone treatment produced a dose-dependent increase in synthesis and content of surfactant phosphatidylcholine, with a maximum response occurring at 10(-6) M dexamethasone. At concentrations of 10(-5) M, dexamethasone ceased to produce a significant stimulation. Dexamethasone produced an increase in surfactant phosphatidylglycerol synthesis only at a concentration of 10(-8) M and higher. There was not a significant effect upon the content or rate of synthesis of phosphatidylcholine or phosphatidylglycerol in the residual fraction at any of the dexamethasone concentrations tested.

Hormonal induction of pulmonary maturation in the rabbit fetus: effects of maternal treatment with estradiol-17 beta on th endogenous levels of cholinephosphate, CDP-choline and phosphatidylcholine

1. Administration of estradiol-17 beta to pregnant rabbits at 25 days gestation (term, 31 days) resulted n a significant increase in the incorporation of [14C]-choline, but not [14C]ethanolamine, into the lipids of fetal lung slices. The incorporation of [35S]methionine was not affected. 2. Enzymatic assays conducted in vitro revealed no significant effect on either the activities of several enzyme markers for subcellular organelles, the activities of the enzymes responsible for the production of phosphatidylglycerol and phosphatidylinositol, membrane-bound or aqueously dispersed phosphatidate-dependent phosphatidic acid phosphohydrolase activities or the activities of the auxiliary enzymes responsible for the synthesis of dipalmitoylphosphatidylcholine. 3. The activity of the enzymes involved in the choline pathway for the de novo biosynthesis of phosphatidylcholine were not significantly altered except for a 66% increase in the CTP:cholinephosphate cytidylyltransferase activity assayed in the cytosol. The addition of phosphatidylglycerol stimulated cholinephosphate cytidylyltransferase activity approx. 3-fold. However, in the presence of this lipid, the activities in cytosol from control and treated fetuses were similar, indicating that the increased activity noted in the absence of phosphatidylglycerol was due to an activation of existing cytidylyltransferase activity rather than an increase in total enzyme units. 4. Estrogen treatment of the does was also associated with a marked decrease in the levels of cholinephosphate in fetal lung and significant increases in the levels of CDPcholine and phosphatidylcholine. These alterations in pool size are consistent with an increase in the activity of cholinephosphate cytidyltransferase in vivo. The results suggest that cholinephosphate cytidylyltransferase may catalyse an important rate-determining reaction in the synthesis of phosphatidylcholine in fetal lung. The data also support the view that the reaction catalysed by CDPcholine:diacylglycerol cholinephosphotransferase also has a regulatory role during development.

Lung development and the pulmonary surfactant system: hormonal ifluences

The effect of hormones on developmental events is not a new area of scientific investigation. However, in the last decade, the developing lung has been the focus of an increasing amount of basic and applied research. Inadequate development of the newborn's respiratory system precludes extra-uterine existence; indeed, such respiratory inadequacy has been a leading cause of death in premature infants. Tremendous strides have been made in understanding the basic cell biology of the developing lung. Much has been learned about the source, composition, and function of pulmonary surfactant, a surface-active material produced by the lung and essential to alveolar stability. Deficient stores of this material is a major etiologic factor in the respiratory distress syndrome of the newborn (RDS). This fact, coupled with observations that certain hormones can accelerate lung development and the consequent availability of adequate stores of pulmonary surfactant, has led to a large body of literaturae dealing with the effects of hormones (and other agents) on lung development. It is the purpose of this literature review (1) to discuss the various kinds of investigations which have linked surfactant synthesis to the type II pulmonary epithelial cell; and (2) to review the current status of research dealing with the effects of glucocorticoids and thyroid hormones on lung maturation.

Transplacental stimulation of lung development in the fetal rabbit by 3,5-dimethyl-3'-isopropyl-L-thyronine

The effect of thyroid hormone on maturation of fetal rabbit lung was studied with maternal treatment using 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT), a synthetic analogue of triiodothyronine. To investigate the in vivo kinetics and distribution of DIMIT, we prepared [3H]DIMIT and injected both pregnant rats (18-21 d gestation) and rabbits (25 d gestation). In the rat, maximal concentrations of radioactivity in maternal plasma, fetal plasma, and amniotic fluid occurred within 10 min, 1-2 h, and 4-6 h, respectively, after intramuscular injection. After 7 h the concentration of radioactivity in fetal plasma was 163 and 71% of the maternal level in rats and rabbits, respectively, indicating that DIMIT readily crosses the placenta. We treated pregnant rabbits for 1-2 d with DIMIT in doses of 0.5-3 mg/kg per d and examined the fetuses at 26 and 27 d gestation. Treatment did not affect fetal growth or viability. In fetal liver, DIMIT increased the activity of NADPH cytochromeac reductase by 64% and decreased the glycogen content by 73% compared to controls. The rate of choline incorporation by lung minces increased in dose-dependent manner to a maximum of +104% at 3 mg/kg DIMIT; this does stimulated by 38% the activity of lung phosphatidic acid phosphatase (PAPase), a corticosteroid-responsive enzyme, but there was no increase in tissue PAPase activity at most lower doses of DIMIT that enhanced choline incorporation. Treated lungs had 38% less glycogen tha controls, but there was no effect on tissue levels of DNA, protein, or phospholipid. DIMIT treatment increased the amount of total phospholipid (+163%). saturated phosphatidylcholine (+330%), and PAPase activity (+134%) in lung lavage fluid. The DIMIT effects on both choline incorporation by lung minces and phospholipid content of lavage fluid were substantially greater than what had occurred with an optimal dose of betamethasone. DIMIT also increased corticosteroid binding capacity in fetal plasma and produced a dose-dependent increase (maximal threefold) in total and free corticoids of both maternal and fetal plasma. It is estimated that elevated endogenous corticoids probably account for less than one-third of the increases in phospholipid synthesis and secretion observed at the higher doses of DIMIT. These data indicate that administration of DIMIT to pregnant rabbits accelertes maturation of the surfactant system in fetal lung. The magnitude of the effects on phospholipid synthesis and secretion, along with the minimal effect of PAPase activity in fetal lung tissue, suggest that thyroid hormones affect different biochemical processes from those influenced by glucocorticoids.

Phosphatidylcholine synthesis in the developing small intestine

1. Phosphatidylcholine synthesis in the foetal, newborn and adult small intestine of rats was studied by determination of cytidine diphosphocholine-1,2-diacylglycerocholine phosphotransferase (cholinephosphotransferase) and acyl-CoA-1-acyl-sn-glycerol-3-phosphocholine acyltransferase (lysophosphatidylcholine acyltransferase) activities and the incorporation of [1-14C]oleic acid into phosphatidylcholine. 2. Cholinephosphotransferase activity was low in foetal jejunum and ileum, increased 3-4 fold in the ileum by 6 days of age and by 12 days in the jejunum. Jejunal activity remained constant throughout weaning; ileal activity gradually decreased to values 25% of that of the jejunum. 3. Lysophosphatidylcholine acyltransferase activity was high in foetal jejunum and ileum, decreased 70% immediately after birth in the jejunum and increased to adult values by 12 days of age. Ileal activity decreased by 20% after birth, but decreased more rapidly at weaning to 30% of the activity in jejunum. 4. Initial rates and steady-state incorporation of [1-14C]oleic acid into phosphatidylcholine by jejunal rings of 10 day-old rats exceeded that observed in jejunal rings from adult rats by 2-4-fold. 5. In the postnatal jejunum, neither cholinephosphotransferase and lysophosphatidylcholine acyltransferase activities nor oleic acid incorporation were stimulated by cortisone administration in vivo.

Acceleration of pulmonary surfactant maturation in stresses pregnancies: a study of neonatal lung effluent

To determine the maturation of pulmonary surfactant at birth, phospholipid patterns in tracheal or pharyngeal aspirates of 54 newborn infants were analyzed by two-dimensional thin-layer chromatography. The compositions of phospholipids and their surface tension-lowering abilities were assessed after gestations with various complications. Preterm infants with respiratory distress syndrome (RDS) lacked phosphatidylglycerol and had lower lecithin/sphingomyelin ratios than infants without RDS. An acceleration of both phosphatidylcholine (lecithin) and phosphatidylglycerol concentrations was observed in 21 preterm infants born after prolonged rupture of the membranes and treatment with isoxuprine. In these infants, the phospholipid pattern of lung effluent was similar to that of term infants even at gestational ages less than or equal to 30 weeks. Biochemical lung maturation was delayed in aneccephalic infants, infants of diabetic mothers, and one infant of a mother with hypothyroidism.

Characterization of the forward and reverse reactions catalyzed by CDP-diacylglycerol:inositol transferase in rabbit lung tissue

CDPdiacylglycerol:inositol transferase activity in rabbit lung tissue has been characterized and the optimum conditions for assaying this enzyme in vitro were determined. Rabbit lung tissue CDPdiacylglycerol:inositol transferase activity was found primarily in the microsomal fraction. The pH optimum of the enzyme activity was between 8.8 and 9.4, and the reaction was dependent on either Mn2+ or Mg2+. Detergents and Ca2+ inhibited the activity of the enzyme. The apparent Km values of the enzyme for CDPdioleoylglycerol and myoinositol were 0.18 mM and 0.10 mM, respectively. The reversibility of the reaction catalyzed by CDPdiacylglycerol:inositol transferase in microsomes prepared from rabbit lung tissue was demonstrated by the synthesis of [3H]CMPdiacylglycerol when [3H]CMP and phosphatidylinositol were present in the incubation mixture. The reverse reaction was characterized and its importance in the regulation of the acidic phospholipid composition of surfactant during lung development is discussed. The pH optimum for the reverse reaction was 6.2, and the reverse reaction was also dependent on Mn2+ or Mg2+. The apparent Km value of CDPdiacylglycerol:inositol transferase for CMP was found to be 2.8 mM.

Antepartum aminophylline treatment for prevention of the respiratory distress syndrome in premature infants

The frequency of idiopathic respiratory distress (IRD) among premature offspring born of women who were given aminophylline before the thirty-fourth week of pregnancy was evaluated. Sixty-seven premature deliveries were included in the aminophylline group and 75 in the control group. The perinatal death rate was 7.1% in the aminophylline group and 17.9% in the control group (p less than 0.05). A statistically significant difference was noted between the aminophylline and control groups in the frequency of IRD which was three times lower (10%) in the aminophylline group than in the control group (29.5%) for the total of premature infants. If the time of rupture of membranes is taken into consideration, a significant decrease in the frequency of IRD following aminophylline administration is noted in the infants, whose mothers had ruptured membranes for more than 24 hours. No complications or side effects of aminophylline administration were noted in the mothers or their infants.

Glucocorticoid induction of pulmonary maturation in the rabbit fetus. The effect of maternal injection of betamethasone on the activity of enzymes in fetal lung

1. Maternal administration of betamethasone (0.2 mg/kg) on day 25 or 26 of gestation produced a significant decrease in the lung/body weight ratio of the rabbit fetuses within 24 h. 2. The incorporation of [14C]choline but not [14C]ethanolamine into the lipids of fetal lung slices was significantly increased, indicating that there was a specific effect on phosphatidylcholine synthesis. 3. The activities of a number of marker enzymes for subcellular organelles were elevated, especially in the lungs of fetuses delivered on day 26. The increases in monoamine oxidase (mitochondrial outer membrane), beta-glycerophosphatase and aqueously dispersed phosphatidic acid-dependent phosphatidic acid phosphohydrolase (lysosomal) activities were significant. 4. Although the activity of cholinephosphotransferase was not affected by glucocorticoid treatment, the activities of glycerol-3-phosphate phosphatidyltransferase and the activities of two enzymes in the auxiliary pathways for the production of disaturated phosphatidylcholine (lysophosphatidylcholine:lysophosphatidylcholine transacylase and lysophosphatidylcholine:acyl-CoA acyl-transferase) were significantly increased. 5. Membrane-bound phosphatidic acid-dependent phosphatidic acid phosphohydrolase activity was elevated to a lesser extent than the aqueously dispersed phosphatidate-dependent activity and this increase was not significant. 6. The incorporation of E135S]methionine into protein by slices of fetal lung was significantly reduced after maternal treatment with betamethosone. 7. These results are consistent with the general view that glucocorticoids can induce pulmonary maturation and surfactant production in the rabbit fetus but indicate that some of the former hypotheses regarding the mechanism by which lipid synthesis is accelerated must be reevaluated.

Effects of betamethasone on phospholipid content, composition and biosynthesis in the fetal rabbit lung

Administration of betamethasone (0.2 mg/kg, intramuscularly) to pregnant rabbits had the following effects on the fetal lung at 26--27 days gestation. It increased the amount of phosphatidylcholine in lung lavage by 70% and almost doubled the phosphatidylcholine/sphingomyelin ratio, it increased the rate of incorporation of choline into phosphatidylcholine in fetal lung slices by up to 90%, it increased the activities of pulmonary cholinephosphate cytidylyltransferase and phosphatidate phosphatase by 50% and it reduced the amount of lung glycogen to 60% of the amount in the controls. Betamethasone had no effect on the activities of pulmonary cholinephosphotransferase or lysolecithin: lysolecithin acyltransferase but it slightly decreased the activity of choline kinase. Betamethasone administration to the doe did not increase the amount of surfactant phospholipid in fetal lung lavage to as great an extent as did direct administration of cortisol to the fetuses. Neither did betamethasone stimulate the activity of pulmonary cholinephosphotransferase. These data suggest that agents other than glucocorticoids mediate the stress-induced acceleration of fetal lung maturation and surfactant production.

Factors influencing surfactant composition in the newborn infant

In order to evaluate the surfactant maturation of the neonate, tracheal aspirates were analyzed in 84 newborn infants with 12h of birth. Using 2-dimensional thin-layer chromatography, 9 different phospholipids were identified. Dynamic surface tension measurements were performed with a modified Wilhelmy balance. Five different groups of infants with typical phospholipid patterns were characterized: i.e., 1. Normal term newborn. 2. RDS in the preterm infant. 3. Acceleration of lung maturity in preterm infants without RDS. 4. Retardation in term infants with RDS. 5. Therapeutic induction of pulmonary maturity in preterm infants following maternal glucocorticoid administration. Mature lung effluent contains high concentrations of phosphatidylcholine (PC) and phsophatidylglycerol (PG). In infants with RDS, PC is low and PG absent. Accelerated lung maturity was observed after chronic prenatal stress, such as prolonged rupture of the membranes, chronic vaginal bleeding, and maternal hepatitis or drug addiction. Retardation of pulmonary maturity was seen in infants with alpha-1-AT-deficiency, maternal diabetes and maternal hypothyroidism. Administration of methylprednisolone to the mother 24 h to 72h before birth induced both the synthesis of PC and PG in the preterm infants, resulting in an almost full-term phospholipid pattern as early as 31 weeks of gestation. The significance of these factors on the pathogenesis of RDS is discussed.

Studies on pulmonary surfactant. Effects of cortisol administration to fetal rabbits on lung phospholipid content, composition and biosynthesis

Corticosteroids are known to accelerate maturation of the fetal lung and production of surfactant. We examined the effect of cortisol administration to fetal rabbits on the phospholipid content and composition of lung lavage and lung tissue, as well as on the activities of enzymes involved in the synthesis of phosphatidylcholine and phosphatidylglycerol, the major surface-active components of surfactant. Cortisol was administered by intrauterine injection at 25 days' gestation and the fetuses were delivered at 27 days (full term, 31 days). Saline-injected fetuses, littermates of the cortisol-treated as well as non-littermates, were used as controls. The amount of phospholipid in lung lavage from the hormone-treated fetuses was almost double that of the saline-injected controls and was similar to that of an untreated fetus of more than 30 days' gestation. Similarly, the phospholipid composition of lung lavage from the hormone-treated fetuses was similar to that of an untreated fetus at a greater gestational age. These data, therefore, suggest that cortisol acts by accelerating physiological development. Cortisol administratration stimulated the activity of cholinephosphate cytidylyltransferase and lysolecithin acyltransferase to a small, but statistically significant extent. This is also consistent with an acceleration of normal development. The stimulation of lysolecithin acyltransferase is of interest, since this enzyme is believed to be involved in the synthesis of dipalmitoylglycerophosphocholine, the major surface-active species of phosphatidylcholine. Cortisol administration had no effect on the activities of pulmonary choline kinase, cholinephosphotransferase, lysophosphatidic acid acyltransferase and glycerolphosphate phosphatidyltranferase, although we have previously shown the latter enzyme to be stimulated following a longer period of exposure to the hormone. Saline injection produced some maturational effects presumably as a result of stress, which may be mediated by corticosteroids or other hormones.

The influence of postnatal nutritional deprivation on the phospholipid content of developing rat lung

It has been previously reported that fasting may result in decreased lung surfactant production. In order to investigate this relationship and the role of nutrition in lung phospholipid synthesis, 21-day-old rats were exposed for 60 h to one of five dietary regimens: standard rat chow (controls), fasting, pure glucose, pure fat, or pure protein. After the period of fasting there was a 33% decrease in lung protein content, but there was no change in DNA content. Exposure to any of the experimental diets resulted in a decrease in tissue total phospholipid and phosphatidylcholine content per lung, but not per unit lung protein. Similarly lung lavage phospholipid and phosphatidylcholine content was decreased by 25% after fasting when expressed per lung or per unit DNA, but not per unit protein. Pulmonary cholinephosphotransferase (EC 2.7.8.2) activity was decreased in the fasted animals and those fed the protein diet, but not in the glucose or fat-fed animals. The activities of acetyl-CoA carboxylase (EC 6.4.1.2) and microsomal fatty acid elongation were decreased in all the experimental groups except for the glucose-fed group. It is concluded that fasting results in a decrease in lung cell size but not in lung cell number. Total phospholipid and phosphatidylcholine content in lung tissue and lung lavage is decreased per cell but not per unit cell mass.

Phospholipid content, composition and biosynthesis during fetal lung development in the rabbit

The phospholipid content and composition of lung wash and lung tissue as well as the activities of the enzymes involved in the synthesis of phosphatidylcholine and phosphatidylglycerol (the major surface active components of pulmonary surfactant) were studied in the rabbit during fetal lung development. In lung wash the amount of phospholipid increased four-fold during the period 27-31 day's gestation. There was a further ten-fold increase following the onset breathing. During the same period the amount of phosphatidylcholine in lung wash increased from 29% of the total phospholipid to 80% while the amount of sphingomyelin decreased from 38% to 2%. The amount of phosphatidylcholine in lung tissue also increased during development but to a much lesser extent. During fetal lung development the activities of choline kinase and cholinephosphate cytidyltransferase changed little, cholinephosphotranserase decreased while lysophosphatidic acid acyltransferase and lysolecithin acyltransferase increased. There was a postnatal increase in the activities of cholinephosphate cytidyltransferase, cholinephosphotransferase and both acyltransferases. The amount of phosphatidylglycerol, as a percentage of the total phospholipid, in lung wash and lung tissue as well as the activity of pulmonary glycerolphosphate phosphatidyltransferase did not change appreciably during development.