Disaturated Phosphatidylcholine Levels Research Articles

Identification of sex-specific differences in surfactant synthesis in rat lung.

Delayed lung maturation and lower levels of surfactant phosphatidylcholine have been previously identified in male fetuses compared with female fetuses in several species. We investigated the mechanisms for sex differences in surfactant content by examining parameters of phosphatidylcholine turnover and biosynthesis; the latter was evaluated by measuring metabolic steps within the biosynthetic pathway. Compared with male lung cells, freshly isolated lung cells from female fetuses contained higher levels of disaturated phosphatidylcholine, a marker of surfactant lipid. Female mixed monolayer cultures exhibited a 71% increase in choline incorporation into disaturated phosphatidylcholine compared with male cultures. Male cultures exhibited significantly greater release of [3H]-arachidonic acid into the medium compared with females, suggesting sex differences in phospholipase activity. However, pulse-chase studies showed no sex differences in degradation of disaturated phosphatidylcholine, which was confirmed by assays of phospholipase A2, phosphatidylcholine-specific phospholipase C, and phospholipase D. Female mixed lung cells, however, had greater rates of cellular choline transport and activity of cytidylyltransferase, the rate-regulatory enzyme for phosphatidylcholine synthesis. Separate studies showed that exposure of sex-specific pretype II cell cultures to cortisol-stimulated fibroblast-conditioned medium plus transforming growth factor-beta-neutralizing antibody stimulated cytidylyltransferase activity to a greater extent in male cells compared with female cells. These studies indicate that sex differences in surfactant phospholipid content are not due to differences in phospholipid turnover, but rather differential regulation of specific metabolic steps within the surfactant biosynthetic pathway. The data also support a role for transforming growth factor-beta as a negative regulator of a key surfactant biosynthetic enzyme within male lungs.

Alterations in Lung Surfactant Disaturated Phosphatidylcholine, SP-A, and SP-B in Meconium Injured Rats Lavaged with Perfluorochemical (PFC) or KL4 Surfactant † 1600

Meconium aspiration remains a common cause of respiratory distress from lung injury and surfactant inhibition. Meconium debris in the lung can be removed by lavage with KL4 surfactant, a mixture of phospholipids (PL) and synthetic peptide (Revak, Pediatr Res, 41;264A,1997), or with PFC which are used to maintain gas exchange. In these models, however the status of lung surfactant composition remains unclear. In a rat model of meconium injury, we have evaluated if lung lavage alters the surfactant disaturated phosphatidylcholine (DSPC) and proteins SP-A and SP-B in spontaneously breathing animals. Adult rats were intubated and given 0.3 ml meconium (13.5 mg dry wt) or saline (NS, n=3) endotracheally. Ten minutes later, meconium instilled lungs (Mec) were lavaged (x 3) with 6 ml/kg aliquots of saline (NSL, n=5) or PFC (PFCL, n=5). One group of Mec rats was lavaged twice with saline suspension of KL4 at 2.5 mg/ml, and once at 10 mg/ml (KL4L, n=5); another group was lavaged twice with saline, followed by once with KL4 at 10mg/ml, in order to replenish surfactant washed out with saline lavages (SKL4L, n=5). Animals were extubated after recovering from anesthesia (1-2 hours) to spontaneously breathe room air for 18 hours, a period previously shown to correlate with maximal lung injury in this model. Thereafter, bronchoalveolar lavage fluid (BAL) was obtained on excised lungs and seperated into large(Lag) and small surfactant aggregates. BAL fractions and lung tissue were analyzed for DSPC content and Lag for SP-A and SP-B. DSPC levels (μg lipid phosphorus/lung) were similar in Lag of Mec (12.5±2.1, mean±SE, n=4) and NS animals (9.5±0.2, p=0.06). They were slightly elevated in PFCL group (14.0±0.5, p>0.05, vs Mec) and significantly elevated in KL4L (87±19, p<0.001, vs Mec) and NSKL4L groups (48±8, p<0.001, vs Mec). DSPC levels in the lung tissue were similar in Mec(138±14) and NS animals 189±17, p=0.06). The lungs of KL4L(330±85, p<0.02) and NSKL4L animals (256±42, p<0.05) also showed higher levels of DSPC compared to Mec animals (138±20). In Western blots of Lag, both SP-A and SP-B were decreased in NSL group compared with NS or Mec animals, suggesting that saline lavage depleted SP. Both proteins were elevated in KL4L compared to NSL animals. We speculate that KL4 lavage may lead to metabolic changes that result in increased retention of PL in lung tissue, and may affect SP metabolism to prevent their depletion in lung surfactant. KL4 was a gift of Acute Therapeutics, Inc, Doylestown, Pa.

Surfactant protein B and disaturated phosphatidylcholine levels in Survanta treated premature infants. 1457

Premature infants are routinely treated with multiple doses of exogenous surfactant to ameliorate their respiratory distress, but the status of surfactant in such infants has not been determined. This study evaluated disaturated phosphatidylcholine (DSPC) and SP-B levels in tracheal washings of four infants (27 wks gestation) before and after Survanta treatments (arrows). Tracheal washings were obtained by suctioning following instillation of normal saline (0.7 ml) at indicated intervals (Fig.). The pre-treatment levels of SP-B and DSPC in tracheal washings were 1.93 ± 1.22 μg/mg protein and 8.25 ± 3.2 μg phosphorous (Pi)/mg protein, respectively. Two hours after Survanta instillation, the levels for both were higher (4-7 fold) and were unchanged after 10 hours. These results suggest that a single application of Survanta is sufficient to raise the DSPC and SP-B to a steady state and that these two are cleared very slowly. A second dose did not change the SP-B levels. In comparison, the DSPC levels were further increased by ≈50% but later returned to pre-second dose levels. We speculate that excess surfactant protein and lipids may be cleared independently to maintain individual steady state levels.

Activity loss on room temperature storage of Survanta®, a bovine lung extract based surfactant

The rapid loss in Survanta®, a bovine lung extract based surfactant, activity upon storage at 30°C is investigated. During 3 months, the minimum surface tension as measured by both Wilhelmy plate and pulsating bubble methods rose by 8–9 mN/m. Additionally, a decrease in the in situ rat lung bioactivity of approximately 40% was observed. Disaturated phosphatidylcholine levels decreased while free fatty acid levels increased under the same storage conditions. Thus, the presence of both lysolecithins and additional free fatty acids is believed to result in the loss in activity.

Hyperoxia-induced alterations of rat alveolar lavage composition and properties.

Although lethal exposures of most animal species to oxygen result in a reduced amount of surfactant phospholipids (PL), hyperoxia in rats leads to elevated levels of PL on the alveolar surface. Because of this different response, a study was made of the amount, composition, surface properties, and subfraction distribution (obtained by differential centrifugation) of alveolar lavage materials from rats exposed to > 95% oxygen for 64 h. The exposures lead to severe lung damage, which includes the appearance of pleural effusion, pulmonary edema, and increased protein levels on the alveolar surface. However, the PL levels of lavage fluid are increased two- to threefold, and the PL composition is altered. In O2-exposed rats, only 39(+/- 1)% of the phospholipid is disaturated phosphatidylcholine (DSPC), the major surface active component of surfactant, as compared to 46(+/- 1)% DSPC in lavage from control animals. The distribution of PL and DSPC in subfractions of lavage materials obtained by differential centrifugation is approximately reversed following hyperoxia. In lavage from control animals, 36% of the PL is in the heavier, more dense subfractions and 64% is in the lighter, less dense subfractions, while 72% is heavier and 28% lighter in lavage from O2-exposed animals. Measurements of surface properties with the Wilhelmy balance indicate that the ability of the lavage materials to reduce surface tension is impaired following hyperoxia. Thus, lethal exposures of rats to oxygen lead to increased amounts of surfactant on the alveolar surface, but the surface properties of the surfactant are impaired, probably due to reduced levels of DSPC, increased amounts of protein, and alterations in its physical form.

Regulation of CTP:choline-phosphate cytidylyltransferase by polyunsaturated n-3 fatty acids

Disaturated phosphatidylcholine (DSPC) is the most distinctive surface-active lipid in pulmonary surfactant. The feeding of docosahexanoic acid (DHA) 22:6 n-3 has recently been described to elevate the levels of DSPC in rodent lung. The purpose of the present study was to determine the mechanisms by which this n-3 fatty acid might regulate CTP:choline-phosphate cytidylyltransferase, a key enzyme required for phosphatidylcholine (PC) synthesis. Cytidylyltransferase exists in lung cytosol as a large lipid-associated aggregate (H form) which is active, and as an inactive, low-molecular-weight species (L form). Fatty acids in vitro stimulate and aggregate the inactive L form to the active H form. Short-term (2-h) and long-term (24-h) exposure of fetal lung explants to DHA (150 microM) stimulated choline incorporation into PC by 54 and 64%, respectively. The fatty acid also enhanced DSPC synthesis by 88%. These changes were associated with an increase in the activity of cytidylyltransferase by 63% after addition of DHA to the explant medium. In vitro, DHA (50 microM) stimulated L form nearly 15-fold and appeared to be a more potent activator and aggregator of the enzyme than either linoleic 18:2 n-6 or arachidonic 20:4 n-6 acids. The effect of DHA on L-form activation was comparable, however, with other members of the n-3 family. Kinetic studies revealed that DHA increased the maximum velocity of enzyme reaction for cytidylyltransferase, although it did not alter the Michaelis constant of the enzyme for CTP. These observations provide in vitro evidence that n-3 fatty acids may play an important role in the regulation of surfactant PC biosynthesis.

Reversal of Lung Maturational Delay in the Fetus of the Diabetic Rat Using Triiodothyronine or Dexamethasone

Administration of glucocorticoids and thyroid hormone can accelerate fetal lung development. To investigate whether the delayed fetal lung maturation seen in the diabetic rat gestation could be reversed by dexamethasone (DEX) or triiodothyronine (T3), control and streptozotocin-diabetic dams were injected daily from day 18 of gestation with either saline, 0.5 mg/kg DEX, or 1 mg/kg T3 until sacrifice on day 21 or day 22. While DEX did not change glucose levels in diabetic animals, T3 resulted in a slight reduction in both maternal (474 +/- 25 vs. 539 +/- 17 mg%; p < 0.07) and fetal (354 +/- 43 vs. 404 +/- 26 mg%; p < 0.05) serum glucose concentrations. DEX therapy exaggerated the reduction in body and lung weight seen in fetuses of streptozotocin-diabetic dams. Fetal lung phosphatidylcholine and disaturated phosphatidylcholine levels were significantly reduced in saline-treated diabetic animals as compared with controls. However, fetuses of T3- or DEX-treated diabetic rats had significantly increased lung phosphatidylcholine and disaturated phosphatidylcholine levels were significantly reduced in saline-treated diabetic animals as compared with controls. However, fetuses of T3- or DEX-treated diabetic rats had significantly increased lung phosphatidylcholine and disaturated phosphatidylcholine levels as compared with fetuses of untreated diabetic rats; these data suggest that maternal DEX or T3 therapy reverses the delayed fetal lung maturation seen in the diabetic rat gestation. Since glucocorticoids can exacerbate maternal diabetes, treatment with thyroid hormone may be more appropriate, although risks must be weighed against potential benefits.

反復性中耳炎の成因について

Recurrent acute otitis media (rAOM) is one of the most common pediatric diseases. Klein reported that the criteria for rAOM are three or more documented episodes of AOM in 6 months or four episodes in 12 months. Freijd A et al have reported subtle immunologic defects, i. e., IgG2 subclass deficiency in rAOM. The pathogenesis of rAOM, however, is still poorly understood.We examined 136 patients with rAOM aged 1 to 20 years who were attending our ENT clinic in Hokkaido. There was a higher incidence of rAOM in the younger children. Males had significantly more episodes than did females.To clarify the pathogenesis of rAOM, both secretory IgA and surfactant were analyzed in the present study. Secretory IgA is related to decreased bacterial adherence. Surfactant is composed mainly of phospholipid, i. e., DSPC (disaturated phosphatidylcholine), and has the definite function of lowering surface tension. Middle ear effusion samples were obtained from patients with OME (otitis media with effusion). OME patients with four or more episodes of AOM during a 12-month period were defined as the (rAOM +OME) group, and OME patients without a previous episode of AOM were in the OME group.Both secretory IgA and DSPC levels were lower in the (rAOM+OME) group than in the OME group. These results suggest that both immunologic disturbance and eustachian tube dysfunction play important roles in the pathogenesis of rAOM.

Induction of Surfactant Protein (SP-A) Biosynthesis and SP-A mRNA in Activated Type II Cells during Acute Silicosis in Rats

The synthesis of the major surfactant protein, SP-A, was studied in activated alveolar type II cells isolated from the lungs of rats exposed to silica by intratracheal instillation. Exposure of rats to silica resulted in large increases in the levels of disaturated phosphatidylcholine and SP-A in the extracellular and intracellular surfactant compartments. Isolated type II cells were used to determine if the observed increases in SP-A were associated with increased SP-A synthesis. Type II cells were isolated by a combination of elastase digestion, centrifugal elutriation, and differential adherence on IgG-coated petri dishes. Type II cells from silica-treated lungs were separated into two populations, designated type IIA and type IIB. The type IIB, or activated population, consisted of type II cells that were larger than normal type II cells and, in addition, contained larger and more numerous lamellar bodies than normal type II cells. Type IIB cells contained 4.3-fold higher levels of SP-A compared to normal type II cells. SP-A synthesis was measured by incubating freshly isolated cells with [35S]Translabel (70% [35S]methionine, 15% [35S]cysteine) for up to 4 h in methionine-free medium, followed by immunoprecipitation of newly synthesized protein. The rate of SP-A synthesis was increased approximately 6.7-fold in the activated type II cells. Analysis of the newly synthesized protein by one-dimensional SDS-PAGE indicated three intracellular forms of SP-A with molecular weights of approximately 26,000, 30,000, and 34,000. In type II cells from control rats, the 34-kD protein accounted for approximately 93% of the newly synthesized SP-A after 4 h of incubation; only a small amount of radioactivity was associated with the lower molecular weight species. The increased biosynthesis of SP-A in the activated type II cells was associated with a 7.3-fold increase in the level of SP-A mRNA. These results indicate that the content and synthesis of SP-A are both highly elevated in activated type II cells and that these increases may be due to increased levels of SP-A mRNA.

Comparison of Amniotic Fluid Disaturated Phosphatidylcholine, Phosphatidylglycerol and Lecithin/Sphingomyelin Ratio in Predicting the Risk of Developing Neonatal Respiratory Distress Syndrome

One hundred forty-one amniotic fluid samples were analyzed for disaturated phosphatidylcholine (DSPC), phosphatidylglycerol (PG) and the lecithin/sphingomyelin (L/S) ratio. The L/S ratio was measured by two-dimensional thin layer chromatography. Mature levels (positive) were defined as an L/S ratio of 2:1 or more, a DSPC level of 100 micrograms/ml or more and a detectable level of PG. The DSPC value agreed with the L/S ratio in 114 samples (80.9%). Fourteen of 17 infants with respiratory distress syndrome (RDS) (82.4%) had immature L/S ratios and immature DSPC levels. RDS developed in 16 of 40 (40%) children with immature L/S ratios, and in 15 of 33 (45.5%) children with immature DSPC levels. The true-positive rates of the L/S ratio and DSPC levels were 99.0 and 98.1%, respectively. PG had a low true-negative rate, as only 17 of 67 (25.4%) samples without detectable levels of PG were associated with RDS. However, when PG was present, it had a 100% predictive value of no-RDS. In conclusion, DSPC is nearly equal to the L/S ratio measured by two-dimensional as concerns diagnostic accuracy. PG is useful as an additional index for predicting lung maturation.

Determination of phosphatidylcholine and disaturated phosphatidylcholine content in lung surfactant by high performance liquid chromatography.

A rapid isocratic method for determining the total phosphatidylcholine and disaturated phosphatidylcholine levels in lung surfactant preparations by high performance liquid chromatography (HPLC) is described. The analysis was performed on a 3.9 x 300 mm mu-Porasil column with detection by refractive index. The lipids were eluted with a solvent system of chloroform-acetonitrile-methanol-water-85% phosphoric acid 650:650:500:130:2 (v/v/v/v/v). A 4.6 x 30 mm silica guard column was used in place of an injector loop which served as a sample concentrator and purifier. Phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, and phosphatidylglycerol, all known components of lung surfactants, were eluted from the loop column and were prevented from reaching the analytical column. Sphingomyelin and lysophosphatidylcholine elute later than the phosphatidylcholines on the analytical column. The method was developed so that phosphatidylcholines elute as a single peak regardless of the fatty acid chain length (C12-C20). When the sample was first oxidized with a potassium permanganate-potassium metaperiodate solution, and potentially interfering oxidation products were removed by extraction into a basic aqueous phase, then only the disaturated phosphatidylcholines were analyzed.

Effect of oxygen exposure on ATP content of rat bronchoalveolar lavage.

Exogenous ATP stimulates surfactant phospholipid secretion in vitro through binding to P2-purinoceptors on the surface of the alveolar type II cell. To determine whether ATP is present in the bronchoalveolar space at concentrations sufficient to stimulate phospholipid secretion, we determined bronchoalveolar lavage ATP content in rats exposed to different inspired oxygen concentrations. Bronchoalveolar lavage ATP content of control animals exposed to room air was 155 +/- 12 nmol ATP/lavage (n = 17) and fell in a dose-dependent fashion to 34 +/- 5 nmol ATP/lavage in animals exposed to 85% oxygen for 72 h (n = 17). Airway content of ATP metabolites fell in a similar fashion in response to oxygen exposure. The decrease in airway ATP content after oxygen exposure was also time-dependent. ATP content in young adult male rats exposed to 85% oxygen decreased from a mean of 236 nmol ATP/lavage on d 1 of exposure to 18 nmol ATP/lavage after 4 d. There was no further decrease in bronchoalveolar lavage ATP content after 4-7 d of oxygen exposure. Despite the fall in airway levels of ATP, disaturated phosphatidylcholine levels increased. Rat bronchoalveolar lavage contained measurable concentrations of ATP, indicating the presence of ATP in the airway at levels which modulate surfactant phospholipid secretion from isolated alveolar type II cells in vitro. Bronchoalveolar lavage ATP content decreased significantly with exposure to oxygen, whereas disaturated phosphatidylcholine content increased.

Postnatal development of rat lung following retarded fetal lung growth.

Postnatal lung development was examined in rats born with smaller than normal lungs after either prenatal exposure to glucocorticoid or to an inhibitor of collagen synthesis. At birth, treated animals had lower than normal lung weights, lung to body weight ratios, hydroxyproline (HYP) levels, total DNA; and rates of DNA synthesis. Rats exposed to steroid showed a rapid recovery in growth during the normal postnatal cell proliferative phase from 4 to 11 days, though collagen levels did not return to normal until 3 weeks of age. Rats exposed to a prenatal proline analog showed a much slower rise in lung weight and total DNA, and these levels were still much below normal at 2-3 weeks when the cell proliferation phase was completed. Levels of disaturated phosphatidylcholine were significantly below normal up to 11 days, whereas total HYP was significantly reduced and less fibrillar collagen was seen in the lung throughout the study. The results indicate that the smaller but mature lungs at birth after antenatal steroid show a growth rebound and quickly become structurally normal. In contrast, inhibition of fibroblast growth and collagen deposition produces small lungs at birth, which continue to show inhibited growth and development at least up to 3 weeks of age, when the cell division phase is over.

Profile of phospholipase A 2 activity in subcellular fractions and lamellar bodies of developing, neonatal and adult rabbit lung. Correlation with intracellular levels of disaturated phosphatidylcholine

Phospholipase A 2 activity was determined in subcellular fractions and lamellar bodies of fetal, neonatal and adult rabbit lungs. Specific activity in most fractions decreased from the 24th to the 28th day of gestation. All fractions except the mitochondrial and the nuclear fractions exhibited a sharp increase in activity in the newborn lung. Specific activity in the adult lung generally declined in comparison to neonatal values. During gestation total enzyme activity per gram of lung was concentrated in the cytosolic fraction. With the exception of the lamellar body fraction, the total content of phospholipase A 2 activity increased dramatically in all fractions from the neonatal lung. The lamellar body fractions displayed both low specific activity and low total enzyme activity during gestation. Specific activity increased dramatically in the neonatal and adult lung but still accounted for only a small fraction of the activity in comparison to the other subcellular fractions. The subcellular content of disaturated phosphatidylcholine (PC) appeared to correlate well with the activity of phospholipase A 2 in the neonatal mitochondrial, microsomal and cytosolic fractions. Since decreasing prenatal enzyme levels are associated with increasing disaturated PC content, the alkaline and calcium-dependent phospholipase A 2 may not be directly involved in disaturated PC synthesis in the fetus. However, postnatally, the correlation between the pattern of production of disaturated PC and the activity of the phospholipase A 2 indicates a role for this enzyme in surfactant-related disaturated PC synthesis.

Epithelial-mesenchymal interactions in postnatal rat lung growth.

Epithelial-mesenchymal interactions have been implicated in epithelial cell differentiation in fetal lung. The role of such intercellular communication during postnatal lung growth is now evaluated to correlate intercellular contacts with cell division and with biochemical function of epithelial and interstitial cells. Sexed newborn rats, killed at frequent intervals to 8 weeks, received 3H-thymidine 1 h before death. A period of rapid cell proliferation between 3 and 10 days involved a five-fold increase in labeling index of both interstitial and type 2 epithelial cells. Hydroxyproline levels increased rapidly as interstitial cell division slowed, and epithelial growth was associated with elevated levels of disaturated phosphatidylcholine. Compared to the time of birth when epithelial cell division was slow, continuous basement membrane (BM) was more frequently found beneath type 2 cells during the postnatal proliferative phase, and fewer foot processes (FP) penetrated the BM; type 1 cells had few FP and uninterrupted BM. The number of intercellular contacts between type 2 cells and interstitial cells, one per two epithelial cell profiles at birth, decreased rapidly during the postnatal proliferative phase. There was a subsequent increase between 2 and 4 weeks that may reflect postmitotic epithelial differentiation. These observations support the hypothesis that transfer of mesenchymal factors may be important in the control of pulmonary epithelial growth and differentiation. The low incidence of cell-cell contacts seen after 4 weeks, one per five epithelial cell profiles, may reflect base levels of communication necessary to retain type 2 cell function in a resting cell population.

Morphologic disturbance of lung maturation in fetuses of alloxan diabetic rabbits.

Maturation of lungs was studied morphologically in fetuses of does made diabetic with alloxan. The lungs of fetuses of does treated with alloxan 24 h after mating appeared to be less mature than control lungs, as shown by significant decrease in areal density of air space (p < 0.01) and by increases in areal density of alveolar epithelium and capillaries (p < 0.02). In alloxan fetuses, ultrastructural techniques revealed that type II cells had 10 times the control value for areal density of glycogen (p < 0.01) and 2.5 times that of rough endoplasmic reticulum (p < 0.05), but the proportion of type II cells and the number of lamellar bodies per type II cell profile were similar in both groups. Ultrastructural examination of capillaries demonstrated that their migration and the fusion of their basement membrane with that of alveolar epithelium did not occur as frequently in alloxan fetuses as in control fetuses. Biochemically, the lungs of alloxan fetuses contained significantly more glycogen and protein (p < 0.01) than control lungs, but the deoxyribonucleic acid was similar. The alloxan fetuses had a disturbance of lung structural maturation that was consistent with our previous findings of delayed functional maturation without accompanying change in disaturated phosphatidylcholine levels and ratio of lecithin to sphingomyelin.

Delayed fetal pulmonary maturation in a rabbit model of the diabetic pregnancy.

A rabbit model for the diabetic pregnancy was used to investigate the etiology of delayed pulmonary maturation observed in infants of diabetic mothers. Pregnant rabbit does were made glucose intolerant and insulinopenic by injection of alloxan, a pancreatic beta-cell cytotoxin. At 28 d (term approximately 31 d) fetuses of these animals were hyperglycemic, but were not hyperinsulinemic and did not demonstrate tissue overgrowth. Fetal pulmonary maturity was assessed by measurement of pressure-volume relationships on the fetal lungs. Fetuses of glucose-intolerant does demonstrated less retention of air on deflation. Phospholipid components of pulmonary surfactant were assayed on fluid obtained from lavage of the fetal lungs. Levels of disaturated phosphatidylcholine (per-cent total-lavage phospholipids) were diminished in fetuses of glucose-intolerant does compared to control fetuses (20.5 +/- 4.2 vs. 38.0 +/ 4.3%; P less than 0.01). Lecithin/sphingomyelin ratios were similar in both groups and phosphatidylglycerol was not detected in either group. There was a direct correlation between the percentage of alveolar disaturated phosphatidylcholine and retention of air on lung deflation. These findings suggest that in this model pulmonary instability was a result of diminished alveolar disaturated phosphatidylcholine, and this diminution did not result from fetal hyperinsulinemia.

Regulation of phosphatidylcholine metabolism by cyclic AMP in a model alveolar type 2 cell line.

The influence of cyclic AMP on the metabolism of phosphatidylcholine, the major component of pulmonary surfactant was examined in a cell line (A549) with type 2 pneumonocyte characteristics. It was found that cyclic AMP increased both the total amount of phosphatidylcholine and disaturated phosphatidylcholine as well as the incorporation of [3H]choline into these fractions. The effect was specific for cyclic AMP since 5'-AMP, adenosine, and cyclic GMP did not alter phosphatidylcholine or disaturated phosphatidylcholine levels. Cyclic AMP had no effect on phosphatidylcholine and disaturated phosphatidylcholine metabolism in another non-type 2 human epithelial cell line (MA-160). Since the ability of various cyclic AMP analogs to increase phosphatidylcholine and disaturated phosphatidylcholine levels was correlated with their ability to activate protein kinase, it seems likely that a protein phosphorylation mechanism is involved in controlling phosphatidylcholine metabolism.