Lung Organ Culture Research Articles

Mechanisms of Phosphatidylcholine Acyl Remodeling by Human Fetal Lung

The molecular specificity of phosphatidylcholine (PC) synthesis by the de novo pathway in postmortem samples of human fetal lung (15 to 20 wk of gestation) was determined from the incorporation pattern in isolated microsomal preparations of CDP:[14C]choline into individual molecular species of PC. These analyses are based on the assumption that the molecular species composition of the pool of endogenous diacylglycerol used for PC synthesis by isolated microsomes reflects that of the authentic pool of diacylglycerol converted to PC by intact cells. Comparison of this microsomal incorporation pattern of radiolabel into PC with tissue PC composition suggested that even at this early stage of gestation 50% of lung dipalmitoyl PC was derived from synthesis de novo, with the remainder coming from acyl remodeling mechanisms. Analysis of PC synthesis de novo by organ cultures of human fetal lung showed that these acyl remodeling mechanisms were lost in culture. Despite evidence for differentiation of type II alveolar epithelial cells in culture, equilibrium labeling of PC with [14C]choline over 18 h resulted in a progressive decline in fractional incorporation into dipalmitoyl PC with time in culture. By 4 days in culture, this value was no different from the fractional incorporation of CDP:[14C]choline into microsomal PC in vitro over 3 h. The pattern of PC synthesized was not altered when total PC synthesis was stimulated by exposure of cultures to dexamethasone and tri-iodothyronine but was readily manipulated by exposure to exogenous fatty acids. These results demonstrate for the first time the activity of PC acyl remodeling mechanisms in human fetal lung, well before the initiation of surfactant production.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of laminin domains involved in branching morphogenesis: Effects of anti-laminin monoclonal antibodies on mouse embryonic lung development

We recently found that polyclonal antibodies to laminin, a basement membrane-related glycoprotein, inhibited murine lung morphogenesis when added to organ cultures of mouse embryonic lung. Using a series of monoclonal antilaminin antibodies with previously characterized subunit specificity (termed AL-1, AL-2, AL-3, AL-4, and AL-5), the deposition and functional involvement of different laminin domains in the developing lung were investigated. By immunohistochemistry the antibodies' reactivity was largely localized to the basement membrane, but was also present diffusely in the extracellular matrix throughout the mesenchyme. Organ cultures of lung explants from Day 12 embryos were cultured for 3 days in the presence of 50–100 μg/ml of each antibody or in the presence of the same concentration of immunoglobulins G and M, laminin-neutralized antibody, or medium alone. Cultures were monitored by phase-contrast microscopy, light microscopy, and immunofluorescence. Although all antibodies penetrated the tissues in culture, only two of them inhibited branching activity. These two antibodies were AL-1, which binds on or near the cross region of laminin, and AL-5, which binds to the lateral short arms at the globular end regions of the B chain of laminin. Inhibition of branching with these two antibodies was dose-dependent and statistically significant for the two concentrations used. AL-2, AL-3, AL-4, laminin-neutralized antibodies and control immunoglobulins did not alter lung morphogenesis. The two domains of laminin that promote lung branching morphogenesis have been reported by others to promote the attachment of a variety of cells and/or bind heparin. These domains of laminin may promote branching morphogenesis by facilitating cell attachment and, consequently, cell proliferation.

Self-differentiation of human fetal lung organ culture: The role of prostaglandins PGE 2 and PGF 2α

Addition of PGE 2, but not PGF 2α, to fetal lung organ cultures accelerates the process of self-differentiation with increased dilatation of terminal airsacs and differentiation of the epithelial lining. Indomethacin reduces the endogenous production by organ cultures of PGE 2, PGF 2α, 13,14-dihydro-15-keto-PGE 2, and 13,14-dihydro-15-keto-PGF 2α and retards the process of self-differentiation. Prolonged exposure of cultures to indomethacin results in cell necrosis. Indomethacin inhibition of self-differentiation can be reversed and accelerated by the addition of PGE 2. Addition of PGF 2α in the presence of indomethacin prevents indomethacin-associated cell necrosis but does not accelerate dilatation or differentiation beyond that of cultures in serafree media without additions. We propose that the endogenous production of PGE 2 is a key process in the mechanism of self-differentiation of human fetal lung in organ culture.

Bombesin may play a role in fetal lung growth and maturation in utero and in lung organ culture

Bombesin may play a role in fetal lung growth and maturation in utero and in lung organ culture

Bombesin May Play a Role in Fetal Lung Growth and Maturation in Utero and in Lung Organ Culture

Pulmonary neuroendocrine cells containing bombesin occur in relatively high numbers in human fetal lung. We have previously shown that peak levels of gastrin-releasing peptide (GRP) mRNA are expressed during the human fetal midgestational period (wk 20-23). It has long been speculated that GRP, the mammalian homologue of bombesin that is produced by pulmonary neuroendocrine cells, might have a role in promoting lung development.

Bombesin Increases Fetal Lung Growth and Maturation In Utero and in Organ Culture

Pulmonary neuroendocrine cells (PNECs) in fetuses synthesize gastrin-releasing peptide (GRP, or mammalian bombesin) at high levels, but the role of this hormone in lung development has been obscure. The present study demonstrates that bombesin administered for 2 to 4 d toward the end of gestation in utero led to increased DNA (days 17 and 18) and saturated phosphatidylcholine (SPC) synthesis (day 18) in a dose-dependent fashion in fetal lung. These kinetics coincide with the timing of endogenous GRP gene activation in untreated fetal mouse lung, where GRP mRNA is detectable on day 16 and peaks at day 18. Electron microscopy on in vivo bombesin-treated fetal lung showed an increase in the number of cells containing lamellar bodies on both days 17 and 18, consistent with increased growth and/or maturation of type II cells. In mouse fetal lung organ cultures, the addition of bombesin led to accelerated uptake of [3H]thymidine into DNA, [3H]leucine into protein, and [3H]choline into SPC, indicating that increased growth and maturation may be direct effects. Extending these observations to another species, bombesin was found to induce growth and maturation of human fetal lung in organ culture. A monoclonal antibody to bombesin (2A11) prevented bombesin-induced increases in choline and thymidine incorporation in lung organ cultures and also blocked baseline automaturation of control lung organ cultures in serum-free medium. These data suggest that bombesin, and thus PNECs, play a role in normal lung development.

Accelerated fetal lung maturation by estrogen is associated with an epithelial-fibroblast interaction

The role of epithelial-mesenchymal interactions in the stimulation of lung development by estrogen is now investigated using organ cultures of lung from male and female fetal rats taken from Days 17 to 21 of gestation. Estradiol at 1 microgram/ml was found to reduce cell proliferation in explants taken during a rapid growth phase (Day 18) and to stimulate surfactant synthesis in both males and females only in Day 20 explants when cell division is much slower. At this time more epithelial cells from estrogen-treated explants contained lamellar bodies, which were also secreted to fill the air sacs. These cultures also showed a significant increase in the frequency of cell-to-cell contacts between epithelial cells and fibroblasts. Uptake of tritiated estradiol by explants increased from Day 18 onward, and by autoradiography, labeling was located predominantly over fibroblasts. Using pure cultures of fetal and adult cells, uptake of labeled estradiol was significantly higher in fibroblasts than in corresponding epithelial cells, and estradiol did not directly enhance palmitate incorporation into epithelial cells. The results suggest that the earlier maturation and increased surfactant synthesis in female fetal lung is related at least in part to enhanced binding of estrogen by the fibroblast with subsequent transfer of a maturation factor to the fetal epithelium.

9 Hormonal and developmental regulation of pulmonary surfactant synthesis in fetal lung

Pulmonary surfactant, a unique developmentally regulated, phospholipid-rich lipoprotein, is synthesized by the type II cells of the pulmonary alveolus, where it is stored in organelles termed lamellar bodies. The principal surface-active component of surfactant, dipalmitoylphosphatidylcholine, a disaturated form of phosphatidylcholine, acts in concert with the surfactant-associated proteins to reduce alveolar surface tension. Relatively large amounts of phosphatidylglycerol also are present in lung surfactants of a number of species, including man. The role of phosphatidylglycerol in surfactant function has not been elucidated; however, its presence in increased amounts in pulmonary surfactant is correlated with enhanced fetal lung maturity. Surfactant glycerophospholipid synthesis in fetal lung tissue is regulated by a number of hormones and factors, including glucocorticoids, prolactin, insulin, oestrogens, androgens, thyroid hormones, and catecholamines acting through cyclic AMP. In studies with human fetal lung in organ culture, we have observed that glucocorticoids, in combination with prolactin and/or insulin, increase the rate of lamellar body phosphatidylcholine synthesis and alter lamellar body glycerophospholipid composition to one reflective of surfactant secreted by the human fetal lung at term. Four surfactant-associated proteins, SP-A, SP-B, SP-C and SP-D, have recently been characterized. Recognition of their potential importance in the reduction of alveolar surface tension and in endocytosis and reutilization of secreted surfactant by type II cells has stimulated rapid advancement of knowledge concerning the structures of the surfactant proteins and their genes, as well as their developmental and hormonal regulation in fetal lung tissue. The genes encoding SP-A, SP-B and SP-C are expressed in a cell-specific manner and are independently regulated in fetal lung tissue during development. SP-A gene expression occurs exclusively in the type II cell and is initiated after 75% of gestation is complete. In the human fetus, expression of the SP-B and SP-C genes is detectable much earlier in development than SP-A, before the time of appearance of differentiated type II cells. It is apparent from studies using human and rabbit fetal lung in culture that cyclic AMP and glucocorticoids serve important roles in the regulation of SP-A gene expression. While the effects of cyclic AMP are exerted primarily at the level of gene transcription in human fetal lung tissue, glucocorticoids have stimulatory effects on SP-A gene transcription and inhibitory effects on SP-A mRNA stability. In addition, cyclic AMP and glucocorticoids act synergistically to increase SP-A gene transcription in human fetal lung in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)

Detection of platelet-activating factor in amniotic fluid of complicated pregnancies

The ether phospholipid PAF (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) was originally described as a potent bioactive lipid associated with inflammatory responses. More recently, we have suggested a functional role for PAF in fetal lung maturation and the initiation of parturition. Previously, PAF was detected in the amniotic fluid of women at term during labor. A significant proportion of this PAF was associated with a lamellar body-enriched fraction. In addition, the PAF concentration was elevated in fetal rabbit lung during the latter stages of gestation and in human fetal lung in organ culture. It was therefore concluded that the PAF present in amniotic fluid during labor was, in part, of fetal lung origin. In the reported study, amniotic fluid samples were obtained from a group of patients with uncomplicated pregnancies at term "not in labor" and "in labor" and a group with complicated pregnancies. We found an eightfold greater concentration of PAF in amniotic fluid obtained from the "term, in labor" samples compared with that of the "term, not in labor" samples (40 vs. 312 fmol/ml). A twentyfold elevation in PAF (838 fmol/ml) was evident in the amniotic fluid of patients incurring "preterm labor" with an average gestational age of 32 weeks compared with the "term, not in labor" group. PAF concentrations also were elevated to 756 fmol/ml amniotic fluid in a group of patients with an average gestational age of 31.5 weeks who had premature rupture of membranes. We have previously suggested that a second autacoid, PAF, in addition to eicosanoids, may function in the initiation of parturition at term in uncomplicated pregnancies. On the basis of our findings of a severalfold increase in the PAF concentration in amniotic fluid from complicated pregnancies, it is suggested that this potent activator of myometrial contraction, together with the eicosanoids, may be a contributing factor associated with premature labor.

The α and π isoenzymes of glutathione S-transferase in human fetal lung: in utero ontogeny compared with differentiation in lung organ culture

Polyclonal antisera to the α and π isoenzymes of glutathione S-transferase have been used in immunohistochemical studies of developing human lung. In utero expression of the π set was down-regulated in distal airway cells and the first appearance of π-negative cells coincided with phenotypic differentiation. In contrast, in the early phase of fetal lung organ culture π isoenzyme was detected in all differentiated epithelial cells and only as culture progressed did focal negativity develop. The α set showed no developmental changes in utero or in organ culture.

Antioxidant enzyme activities in organ cultures of human fetal lung

Conference Article| August 01 1989 Antioxidant enzyme activities in organ cultures of human fetal lung MARY C. McELROY; MARY C. McELROY 1Child Health and Human Nutrition, Level G, Centre Block, Southampton General Hospital, Tremona Road, Southampton SO9 4XY, U.K. Search for other works by this author on: This Site PubMed Google Scholar FRANK J. KELLY; FRANK J. KELLY 1Child Health and Human Nutrition, Level G, Centre Block, Southampton General Hospital, Tremona Road, Southampton SO9 4XY, U.K. Search for other works by this author on: This Site PubMed Google Scholar ANTHONY D. POSTLE ANTHONY D. POSTLE 1Child Health and Human Nutrition, Level G, Centre Block, Southampton General Hospital, Tremona Road, Southampton SO9 4XY, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1989) 17 (4): 699–700. https://doi.org/10.1042/bst0170699 Article history Received: November 24 1988 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation MARY C. McELROY, FRANK J. KELLY, ANTHONY D. POSTLE; Antioxidant enzyme activities in organ cultures of human fetal lung. Biochem Soc Trans 1 August 1989; 17 (4): 699–700. doi: https://doi.org/10.1042/bst0170699 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search Keywords: AOE, antioxidant enzyme, CAT, catalase, GSH-Px, glutathione peroxidase, SOD, superoxide dismutase This content is only available as a PDF. © 1989 Biochemical Society1989 Article PDF first page preview Close Modal You do not currently have access to this content.

Effect of fatty acid supplementation on phosphatidylcholine synthesis by organ cultures of human fetal lung

Conference Article| August 01 1989 Effect of fatty acid supplementation on phosphatidylcholine synthesis by organ cultures of human fetal lung PETULA A. CAESAR; PETULA A. CAESAR 1Child Health, University of Southampton, Southampton SO9 4XY, U.K. Search for other works by this author on: This Site PubMed Google Scholar ANTHONY D. POSTLE ANTHONY D. POSTLE 1Child Health, University of Southampton, Southampton SO9 4XY, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1989) 17 (4): 730–731. https://doi.org/10.1042/bst0170730 Article history Received: November 24 1988 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation PETULA A. CAESAR, ANTHONY D. POSTLE; Effect of fatty acid supplementation on phosphatidylcholine synthesis by organ cultures of human fetal lung. Biochem Soc Trans 1 August 1989; 17 (4): 730–731. doi: https://doi.org/10.1042/bst0170730 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1989 Biochemical Society1989 Article PDF first page preview Close Modal You do not currently have access to this content.

Sex hormones influence growth and surfactant production in fetal lung explants.

Sex-related differences may be present during fetal lung growth and at the onset of surfactant synthesis. In this study we investigated the role of dihydrotestosterone (DHT) and estrogen (EST) on cell division and on labeled palmitate incorporation into disaturated phosphatidylcholine (DSPC) at various times of gestation. Using organ cultures of fetal rat lung from sexed littermates, it was shown that both DHT and EST reduce DNA synthesis only in tissue taken during the rapid growth phase from day 16 to 19 of gestation. From autoradiographic counts, epithelial cell division was most affected. Both hormones reduced DSPC synthesis in explants prepared at day 18, when levels are normally low. At day 19, DHT reduced palmitate incorporation into DSPC of female explants to the male level; subsequently DHT had no effect on any tissue. In contrast, the addition of EST stimulated DSPC synthesis 40% above controls in both male and female explants taken at day 20 only. The results suggest that sex differences seen in late fetal lung development may arise from the combined effects of slowed epithelial growth induced by these hormones followed by inhibition of DSPC synthesis by DHT and acceleration by EST at the crucial period when surfactant synthesis begins.

Glucocorticoid regulation of the major surfactant associated protein (SP-A) and its messenger ribonucleic acid and of morphological development of human fetal lung in vitro.

In the present study we investigated the effects of dexamethasone (DEX) on the accumulation of the major pulmonary surfactant-associated protein (SP-A), a glycoprotein of about 35,000 mol wt, and on the levels of mRNA encoding this protein in human fetal lung in organ culture. In addition, the effects of DEX on the structural development of the fetal lung tissue was investigated using morphometric techniques. We observed that DEX had a biphasic effect on the accumulation of SP-A and its mRNA; at concentrations of 10(-10) and 10(-9) M, a stimulatory effect was observed, while at concentrations of 10(-8) M or greater, the glucocorticoid was markedly inhibitory. The inhibitory effect of DEX (10(-7) M) was evident at all time points of incubation and was apparent within 24 h of its addition to the medium at any time during the culture period. In addition, DEX (10(-7) M) antagonized the stimulatory effects of (Bu)2cAMP on the accumulation of SP-A and its mRNA. DEX also had pronounced effects on the morphological development of human fetal lung tissue. At a concentration of 10(-7) M or greater, DEX caused a marked reduction of alveolar lumen size compared to that of fetal lung explants maintained in control medium. A biphasic effect of DEX on the volume density of type II cells in fetal lung explants was observed; at a concentration of 10(-10) M, DEX significantly increased the volume density of type II cells, whereas at a concentration of 10(-7) M or more, the glucocorticoid significantly reduced the volume density of type II cells compared to that of control explants. These findings suggest that synthetic glucocorticoids at concentrations of 10(-10) and 10(-9) M are stimulatory whereas elevated levels are inhibitory of SP-A synthesis and morphological development of the human fetal lung.

Dose-dependent effect of benz(a)pyrene on embryonic lung organ cultures from mice resistant and predisposed to pulmonary neoplasia

Dose-dependent effect of benz(a)pyrene on embryonic lung organ cultures from mice resistant and predisposed to pulmonary neoplasia

Adult peripheral lung organ culture—A model for respiratory tract toxicology

This report describes procedures to culture 1- to 2-mm-thick cross sections of lung lobes for periods of 4 to 6 weeks. Normal morphologic and macromolecular composition are maintained. Previous attempts to maintain adult peripheral lung cultures for periods beyond 7–10 days or to examine respiratory disorders in vitro other than acute changes have been generally unsuccessful. Eight different, supplemented, serum-free media, mixed with heated liquid agarose were infused into the airways of hamster and rat lungs. Cross sections were explanted onto squares of porous surgical packing material, placed in medium, and incubated for 4 to 6 weeks. The ability of each medium to maintain normal lung was assessed microscopically by quantitative image analysis and by biochemical analyses. The optimal medium formulation for each species is described. The adult peripheral lung culture system may provide toxicologists with a unique model for mechanistic and safety evaluations of potential lung toxicants.

Evidence for the existence of three chick lung tropoelastins

Three tropoelastin polypeptides are identified among the cell-free translation products of chick embryo lung mRNAs and organ cultures extracts. The tropoelastins are distinguished by one and two dimensional gel electrophoretic systems and are all immunoreactive with monospecific chick tropoelastin antiserum. The ratio of the three tropoelastins does not vary significantly between 10 and 16 days of lung embryogenesis. The third tropoelastin (c) is found to co-migrate with tropoelastin b on SDS-polyacrylamide gel electrophoresis but is visible after cyanogen bromide cleavage of reticulocyte lysate proteins. Immunoprecipitates from lung organ culture also contain tropoelastins a, b and c.

β-ADRENERGIC AGONISTS AND cAMP ANALOGUES MARKEDLY INCREASE THE LEVELS OF SURFACTANT APOPROTEIN AND ITS mRNA AND INDUCE DRAMATIC MORPHOLOGIC CHANGES IN HUMAN FETAL LUNG IN VITRO

The use of β-adrenergic agonists for treatment of preterm labor is associated with a decreased incidence of RDS in premature newborns. In the present study, antibodies and a cDNA probe specific for the major surfactant apoprotein were used to evaluate the effects of Bt2 cAMP and the β-agonist, terbutallne, on the levels of surfactant apoproteln and its mRNA in human fetal lung in organ culture, using Western and Northern blotting. A marked stimulatory effect of Bt2 cAMP on the levels of surfactant apoproteln and mRNA in the fetal lung tissue was observed within 48 h of its addition to the medium. Terbutaline caused a dose-dependent increase in surfactant apoproteln and mRNA to levels comparable to those observed after treatment with Bt2cAMP. Using light and electron microscopy, we found that after 48 h incubation with Bt2cAMP, a significantly greater proportion of the ductular epithelium of the fetal lung explants was comprised of type II cells; these ducts were enlarged greatly and the interalveolar connective tissue reduced as compared to control explants. Abundant secretory material (lamellar bodies and tubular myelin) was observed within the ducts of the Bt2cAMP-treated tissue; little secretory material was observed in control tissues. Thus, catecholamines acting through β-adrenergic receptors and cAMP, may serve an important role in surfactant apoprotein gene expression and in morphologic development of the human fetal lung.

Optimization of fetal lung organ culture for surfactant biosynthesis.

Lung organ culture has been a widely used system for studying differentiation and maturation of alveolar epithelium through various culture conditions. The purpose of this work was to carefully characterize in vitro lung biochemical differentiation through isolation of surfactant fraction from tissue and to search for optimal culture conditions. Fetal rat lung was explanted on the 18th gestational day for studying glycogen storage, and on the 20th gestational day for studying surfactant accretion, and cultivated for 48 h. Morphologic differentiation was studied by electron microscopy on tissue explanted on the 17th or 18th gestational days and cultivated for various times. Glycogen storage was greater on fluid medium, although less than occurring in vivo. Cellular integrity and surfactant accumulation were maximal on a semisolid medium containing 0.5% agar. Use of O2-CO2 instead of air-CO2 for gassing the explants slightly decreased phospholipid accumulation. Among media used in previous lung culture studies, Waymouth MB 752/1 was the only one to allow net glycogen accumulation in vitro. The most favorable media for surfactant phospholipid accretion were Waymouth MB 752/1, Eagle's minimum essential and its Dulbecco's modification, CMRL 1066, and NCTC 109. They allowed a 12- to 14-fold increase of surfactant fraction phospholipids in vitro, which is similar to the increase occurring in vivo during the same period. Ham's F10 and F12 media allowed a six fold increase. RPMI 1640 and medium 199 (M199) allowed only a three fold increase. Phospholipid concentration in nonsurfactant fraction only doubled during culture, and differences between various media were much less marked. DNA concentration changed little during culture. Morphologic differentiation of epithelial cells was advanced as compared with in vivo timing in a medium allowing maximal surfactant accretion (Waymouth MB 752/1) but not in a medium allowing low surfactant increase (RPMI 1640). The possible role of compositional differences between media is discussed.

The development of surfactant synthesis in fetal rabbit lung organ culture exhibits a sex dimorphism

Sex differences in amniotic fluid and lung lavage surfacant have been found. Although these studies suggest that augmented fetal surfactant synthesis occurs earlier in the female fetus, there is little direct evidence for a sex difference in fetal surfactant synthesis. We studied the synthesis of surfactant by evaluating the appearance of labelled phospholipids in lamellar bodies recovered from sex-specific organ culture of fetal rabbit lungs. Furthermore, we studied the ability of dexamethasone to stimulate surfactant synthesis in male and female fetal lungs. Organ culture was begun on day 21 gestation. After 5 days the incorporation of [1,3- 14C]glycerol into phosphatidylcholine (PC), disaturated phosphatidylcholine, phosphatidylinositol (PI), and phosphatidylglycerol was studied. Female lungs in organ culture synthesized more disaturated PC per milligram protein than male lungs. In the presence of dexamethasone (10 −8 M) and dihydrotestosterone (10 −8 M) an increased synthesis was noted in the female cultures of PC (270%), disaturated PC (234%), PI (281%), and phosphatidylglycerol (754%). No significant increase in the synthesis of PC or disaturated PC was observed in the male cultures. However in the male cultures smaller increases in the synthesis of PI (193%) and of phosphatidylglycerol (360%) were observed. Overall, dexamethasone stimulated synthesis in females but not in males such that significant differences in the synthesis of all phospholipids were found in the presence of 10 −8 M dexamethasone. These studies show that the synthesis of surfactant in the fetal lung is sexually dimorphic, as is the ability of dexamethasone to regulate synthesis. An understanding of the mechanism which causes these differences may provide important insight into the control of the developmental clock which regulates the orderly progression of development.