Disaturated Phosphatidylcholine Content Research Articles

Altered surfactant homeostasis and recurrent respiratory failure secondary to TTF-1 nuclear targeting defect

BackgroundMutations of genes affecting surfactant homeostasis, such as SFTPB, SFTPC and ABCA3, lead to diffuse lung disease in neonates and children. Haploinsufficiency of NKX2.1, the gene encoding the thyroid transcription factor-1 (TTF-1) - critical for lung, thyroid and central nervous system morphogenesis and function - causes a rare form of progressive respiratory failure designated brain-lung-thyroid syndrome. Molecular mechanisms involved in this syndrome are heterogeneous and poorly explored. We report a novel TTF-1 molecular defect causing recurrent respiratory failure episodes in an infant.MethodsThe subject was an infant with severe neonatal respiratory distress syndrome followed by recurrent respiratory failure episodes, hypopituitarism and neurological abnormalities. Lung histology and ultrastructure were assessed by surgical biopsy. Surfactant-related genes were studied by direct genomic DNA sequencing and array chromatine genomic hybridization (aCGH). Surfactant protein expression in lung tissue was analyzed by confocal immunofluorescence microscopy. For kinetics studies, surfactant protein B and disaturated phosphatidylcholine (DSPC) were isolated from serial tracheal aspirates after intravenous administration of stable isotope-labeled 2H2O and 13C-leucine; fractional synthetic rate was derived from gas chromatography/mass spectrometry 2H and 13C enrichment curves. Six intubated infants with no primary lung disease were used as controls.ResultsLung biopsy showed desquamative interstitial pneumonitis and lamellar body abnormalities suggestive of genetic surfactant deficiency. Genetic studies identified a heterozygous ABCA3 mutation, L941P, previously unreported. No SFTPB, SFTPC or NKX2.1 mutations or deletions were found. However, immunofluorescence studies showed TTF-1 prevalently expressed in type II cell cytoplasm instead of nucleus, indicating defective nuclear targeting. This pattern has not been reported in human and was not found in two healthy controls and in five ABCA3 mutation carriers. Kinetic studies demonstrated a marked reduction of SP-B synthesis (43.2 vs. 76.5 ± 24.8%/day); conversely, DSPC synthesis was higher (12.4 vs. 6.3 ± 0.5%/day) compared to controls, although there was a marked reduction of DSPC content in tracheal aspirates (29.8 vs. 56.1 ± 12.4% of total phospholipid content).ConclusionDefective TTF-1 signaling may result in profound surfactant homeostasis disruption and neonatal/pediatric diffuse lung disease. Heterozygous ABCA3 missense mutations may act as disease modifiers in other genetic surfactant defects.

Effects of terbutaline on lung surfactant components in fetal lung tissue, fetal lung washing and amniotic fluid in pregnant rabbit.

Synopsis Terbutaline (0.1 mg/kg) was given intramuscularly once or 3 times at intervals of 12 hours to pregnant rabbits. Fetuses were delivered at 28 days of gestation by cesarean section 4 hours after the last administration. In the 3-dose group, there were no changes in concentration of disaturated phosphatidylcholine in fetal lung tissue or of total phospholipid in the lung washing. Nor was there an increased number of lamellar bodies in type-II pneumocytes, but total phosphatidylcholine levels in amniotic fluid showed a significant increase (2.4 times the control group). In the single-dose group, levels of both total phospholipids and total phosphatidylcholine increased significantly, while lamellar bodies in type-II pneumocytes showed a significant decrease. This suggests that terbutaline is not involved in the synthesis of lung surfactant but enhances secretion and exerts a beneficial action upon fetal lung adaptability to the outside uterine environment through alveolar stabilization.

Effects of age and smoking on the disaturated phosphatidylcholine content of broncho-alveolar lavage fluid

Effects of age and smoking on the disaturated phosphatidylcholine content of broncho-alveolar lavage fluid

Diminished lung compliance and elevated surfactant lipids and proteins in nutritionally obese young rats.

Dietary-induced obesity is associated with increases in lung weight, lung volume, alveolar surface area, and number of lamellar bodies in alveolar epithelial type II cells. This suggests that alterations in lung compliance and surfactant content may also occur. The effects of dietary-induced obesity on lung function and surfactant composition were studied in newborn male rats raised in (1) small litters until weaning and then fed a high fat diet (Obese Group, n = 23) and (2) normal-sized litters until weaning and subsequently fed a normal rat diet (Control Group, n = 29). At age 8 weeks, lung function was measured in anesthetized, spontaneously breathing rats, and surfactant composition was analyzed in lung tissue and lavage fluid. The 8-week-old obese rats had a higher body weight (31%) and fat pad weight/body weight ratio (224%) than the Control Group. When compared with control animals, obese rats had an increased respiratory rate, reduced tidal volume, and decreased lung compliance (dynamic and specific). Disaturated phosphatidylcholine (DSPC) in lung tissue and surfactant pellets (large aggregates) and SP-A and SP-B levels in large aggregates were higher in obese than control rats. Phospholipid, DSPC, and triglyceride contents were also elevated in lung tissue in obese rats, suggesting intracellular lipid accumulation, but low relative to alveolar surface area. Thus, alterations in lung function and surfactant lipids and proteins occur in dietary-induced obesity in young rats. We speculate that intrapulmonary lipid deposition and possible surfactant deficiency relative to alveolar surface area may contribute to the reduction in lung compliance in obese rats.

Surfactant therapy in neonates with respiratory failure due to haemorrhagic pulmonary oedema.

We studied the clinical and biochemical factors associated with surfactant dysfunction and factors affecting the responsiveness to exogenous surfactant among 27 neonates with haemorrhagic pulmonary oedema (HPE). HPE was defined as the presence of a large amount of blood-stained lung effluent and respiratory failure which was difficult to differentiate from respiratory distress syndrome. Among the neonates, 33% had very low birth weight, 96% were preterm, 70% were delivered by caesarean section, and 44% had delivery room intubation. The onset of HPE was at 1.5+/-0.1 h (mean +/- SEM) after birth. In 26 cases, surfactant was administered at 3.0+/-1.3 h after the onset of HPE. The concentrations of surfactant protein A (SP-A), disaturated phosphatidylcholine (DSPC), and albumin in the epithelial lining fluid were determined using the first lung effluent from the patients. The level of inhibitory activity against pulmonary surfactant in the effluent was determined in vitro. Surfactant inhibitory activity was associated with lower birth weight, earlier gestational age, delivery room intubation, earlier onset of HPE, and lower SP-A or DSPC concentration. A good response to exogenous surfactant, which was defined as ventilatory index <0.047 at 1 h after surfactant administration, was seen in 82% of cases, and was associated with lower serum albumin, lower birth weight, and earlier gestational age. Cases with higher DSPC concentration prior to surfactant administration and shorter interval between the onset of HPE and surfactant administration showed an immediate response to surfactant, followed by no increase in ventilatory index for 24 h after surfactant administration. exogenous surfactant appeared to be a useful adjunctive therapy for overcoming surfactant inhibition and normalising the respiratory status of infants with haemorraghic pulmonary oedema. Surfactant treatment for this indication awaits further investigations including a randomised controlled study.

Effects of intratracheal instillation of TNF-alpha on surfactant metabolism.

Tumor necrosis factor-alpha (TNF-alpha) has been shown to play an integral role in the pathogenesis of the acute respiratory distress syndrome. This disorder is characterized by a deficiency of alveolar surfactant, a surface-active material that is composed of key hydrophobic proteins and the major lipid disaturated phosphatidylcholine (DSPC). We investigated how TNF-alpha might alter DSPC content in rat lungs by instilling the cytokine (2.5 microg) intratracheally for 10 min and then assaying parameters of DSPC synthesis and degradation in alveolar type II epithelial cells, which produce surfactant. Cells isolated from rats given TNF-alpha had 26% lower levels of phosphatidylcholine compared with control. TNF-alpha treatment also decreased the ability of these cells to incorporate [(3)H]choline into DSPC by 45% compared with control isolates. There were no significant differences in the levels of choline substrate or choline transport between the groups. However, TNF-alpha produced a 64% decrease in the activity of cytidylyltransferase, the rate-regulatory enzyme required for DSPC synthesis. TNF-alpha administration in vivo also tended to stimulate phospholipase A(2) activity, but it did not alter other parameters for DSPC degradation such as activities for phosphatidylcholine-specific phospholipase C or phospholipase D. These observations indicate that TNF-alpha decreases the levels of surfactant lipid by decreasing the activity of a key enzyme involved in surfactant lipid synthesis. The results do not exclude stimulatory effects of the cytokine on phosphatidylcholine breakdown.

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.

Differential Effects in Vivo of Thyroid Hormone on the Expression of Surfactant Phospholipid, Surfactant Protein mRNA and Antioxidant Enzyme mRNA in Fetal Rat Lung

Antenatal administration of triiodo-L-thyronine (T3) to late gestation rats resulted in decreased lung antioxidant enzyme (AOE) activity but increased surfactant phospholipids. In fetal rat lung explant cultures, T3 decreased the expression of surfactant proteins (SP) A and B. There have been no reported studies of the simultaneous in vivo developmental influence of T3 on both pulmonary AOE and SP gene expression. We hypothesized that antenatal T3 treatment would cause differential regulation of surfactant phospholipid, SP, and AOE genes in the late gestation fetal rat. Timed pregnant rats received intramuscular injections of either T3 (7 mg/kg) or placebo on days 19 and 20 of gestation and fetuses were delivered on day 21. Fetal lung SP-A, SP-B, SP-C, and AOE mRNA levels were studied by Northern analysis. AOE mRNA levels were further quantitated by solution hybridization. Total lung phospholipids (TPL) and disaturated phosphatidylcholine (DSPC) content were quantitated by a phosphorus assay. T3 significantly increased TPL and DSPC content, and significantly decreased the expression of SP-A, SP-C, CuZnSOD, and catalase genes. Because of a crucial interplay of these factors for normal lung function at the time of birth, the molecular mechanisms by which these apparently opposing changes are accomplished warrant further investigation

Content of dipalmitoyl phosphatidylcholine in lung surfactant: ramifications for surface activity.

The content of dipalmitoyl phophatidylcholine (DPPC) in the phosphatidylcholine (PC) fraction of calf lung surfactant extract (CLSE) is measured by gas chromatography (GC) and estimated from the widely used osmium tetroxide assay for disaturated phosphatidylcholine (DSPC). The surface-active properties of model phospholipid/apoprotein surfactants with varying DPPC content are also defined and compared relative to CLSE. GC analysis of fatty acids in PC isolated from CLSE indicated a possible range of 30 to 65% for DPPC content depending on C16:0 fatty chain mismatching, and further studies using phospholipase A2 treatment indicated an actual DPPC content < or = 41%. The osmium tetroxide assay gave a very high value of 70% for the DSPC content of surfactant PC, and experiments with synthetic phospholipids demonstrated that this assay responded inappropriately in the presence of monounsaturated PC, leading to falsely elevated DSPC values. The influence of DPPC content on adsorption and film behavior was investigated in model surfactants containing 40, 60, and 80% DPPC (DPPC/egg PC/egg PG, 40:50:10, 60:30:10, and 80:10:10 by mol) combined with 1.3% hydrophobic surfactant protein (SP)-B and -C. The biophysical properties of the model surfactant with 40% DPPC were found to be closer to CLSE than those of mixtures with 60 or 80% DPPC. The adsorption of dispersions containing 40% DPPC with 1.3% SP-B, C was almost identical to CLSE and was improved in rate and magnitude compared with the mixtures with higher DPPC content (60 or 80%). In Wilhelmy balance studies of cycled films, respreading was increased and maximum surface pressure was decreased for the 40% versus higher DPPC content mixtures, again approaching CLSE in behavior. All synthetic phospholipid (SPL):SP mixtures lowered surface tension to < 1 mN/m in oscillating bubble studies at physiologic cycling rate (20 cpm), but the 40% DPPC mixture had a time dependent most closely matching that of CLSE. Our measured DPPC content near 40% for lung surfactant PC, and the similarly high activity of a related synthetic phospholipid/apoprotein model mixture, suggest that exogenous surfactants with relatively low DPPC contents might be important for future study and development.

Fetal mouse lung ultrastructural maturation is accelerated by maternal thyrotropin-releasing hormone treatment.

Maternal administration of thyrotropin-releasing hormone, alone or in combination with corticosteroid, accelerates functional, morphologic and biochemical fetal lung maturation. However, the dose-response relationship of maternal thyrotropin-releasing hormone treatment and acceleration of fetal lung ultrastructural maturation or disaturated phosphatidylcholine content has not been investigated. We administered (i.p.) saline or thyrotropin-releasing hormone (0.2, 0.4 or 0.6 mg/kg/dose) to the pregnant Balb/c mouse on days 16 and 17 (b.i.d.) and on day 18 of gestation (1 h prior to killing). Morphometric ultrastructural analysis and quantitation of disaturated phosphatidylcholine content was done on the 18-day gestation fetal lung. Maternal thyrotropin-releasing hormone treatment resulted in an increase in the number of lamellar bodies and depletion of glycogen in fetal lung type II cells, and an increase in the lung airspace to parenchymal ratio. In addition, a striking difference in the pattern of lung growth was noted in the thyrotropin-releasing-hormone-treated (0.4 and 0.6 mg/kg/dose) groups. These lungs had larger air spaces, thinner alveolar septae and more air-blood barriers. Maternal thyrotropin-releasing hormone treatment did not influence fetal lung disaturated phosphatidylcholine content. We conclude that in the mouse, maternal thyrotropin-releasing hormone treatment enhances fetal lung structural maturation and propose that thyrotropin-releasing hormone plays a role in mammalian fetal lung growth.

Biochemical and Biophysical Characterization of Pulmonary Surfactant in Rats Exposed Chronically to Cigarette Smoke

Biochemical and Biophysical Characterization of Pulmonary Surfactant in Rats Exposed Chronically to Cigarette Smoke. Subramaniam, S., Bummer, P., and Gairola, C. G. (1995). Fundam. Appl. Toxicol. 27, 63-69. The pulmonary surfactant plays an important role in the gas exchange functions of the lungs. Although previous studies suggest that cigarette smoking alters the pulmonary surfactant system in human smokers, the nature of such changes is poorly understood. The aim of the present study was to determine if biochemical and biophysical properties of pulmonary surfactant are affected in rats following chronic exposure to cigarette smoke. Female Sprague-Dawley rats were exposed daily to smoke from the University of Kentucky high tar/high nicotine reference cigarettes, twice a day, for 60 weeks in a nose-only exposure system. Blood carboxyhemoglobin, plasma cotinine, and pulmonary aryl hydrocarbon hydroxylase activity measurements showed that animals effectively inhaled smoke during exposures. At termination, the bronchoalveolar lavage fluids (BALF) and the lung tissues were collected for biochemical and biophysical analyses of surfactant. The total phospholipid content of the BALF and the lung tissues from room control (RC), sham-treated (SH), and smoke-exposed (SM) animals were the same among the different groups. However, disaturated phosphatidylcholine (DSPC) levels in the BALF were significantly decreased in SM rats compared to RC or SH groups. In contrast, the lung tissue DSPC content in SM rats was not significantly different from that of control groups. Phospholipid profile analysis of the BALF also did not reveal any significant differences among other major constituents of surfactant from control and SM animals. The organic extracts of BALF obtained from different animal groups were assessed for surface activity using a Wilhelmy balance. The results showed an increase in surface compressibility and a reduction in respreadability index in SM group. In contrast, the stability indices of surfactant films obtained from different groups were the same. These observations suggest that decreased DSPC content in SM rats plays a role in altering the biophysical characteristics of surfactant. It is concluded that chronic exposure to cigarette smoke adversely affects the pulmonary surfactant system of rats.

Effects of Maternal Administration of Dexamethasone and Thyrotropin-Releasing Hormone on Fetal Rat Pulmonary Surfactant Synthesis

To determine the effects of maternal administration of dexamethasone (DEX) and thyrotropin-releasing hormone (TRH) on fetal lung maturation, 16 pregnant rats were divided into the following four groups: 20 micrograms/kg TRH twice a day was given intraperitoneally to the TRH group rats, 0.5 mg/kg/day DEX to the DEX group and both DEX and TRH to the DEX + TRH group for 3 consecutive days from gestational day 17. The control rats were given an equivalent volume of saline. The pregnant rats were sacrificed on gestational day 20 and the fetal lungs were removed. The relative amounts of surfactant protein A (SP-A), B (SP-B) and C (SP-C) mRNAs were analyzed by Northern blotting and the total lung disaturated phosphatidylcholine (DSPC) contents were determined using an enzymatic method. The SP-B and -C mRNA and DSPC contents in the DEX and DEX + TRH groups were significantly higher than those in the control group, whereas the SP-A mRNA levels did not differ significantly among the four groups. The SP-B and -C mRNA and DSPC contents in the DEX and DEX + TRH groups did not differ significantly. These findings suggest that TRH has no effects on the regulation of surfactant protein mRNAs or DSPC contents in the fetal rat lung and has no additive effects when combined with DEX.

Biochemical and Biophysical Characterization of Pulmonary Surfactant in Rats Exposed Chronically to Cigarefte Smoke

The pulmonary surfactant plays an important role in the gas exchange functions of the lungs. Although previous studies suggest that cigarette smoking alters the pulmonary surfactant system in human smokers, the nature of such changes is poorly understood. The aim of the present study was to determine if biochemical and biophysical properties of pulmonary surfactant are affected in rats following chronic exposure to cigarette smoke. Female Sprague-Dawley rats were exposed daily to smoke from the University of Kentucky high tar/high nicotine reference cigarettes, twice a day, for 60 weeks in a nose-only exposure system. Blood carboxyhemoglobin, plasma cotinine, and pulmonary aryl hydrocarbon hydroxylase activity measurements showed that animals effectively inhaled smoke during exposures. At termination, the bronchoalveolar lavage fluids (BALF) and the lung tissues were collected for biochemical and biophysical analyses of surfactant. The total phospholipid content of the BALF and the lung tissues from room control (RC), sham-treated (SF), and smoke-exposed (SM) animals were the same among the different groups. However, disaturated phosphatidylcholine (DSPC) levels in the BALF were significantly decreased in SM rats compared to RC or SH groups. In contrast, the lung tissue DSPC content in SM rats was not significantly different from that of control groups. Phospholipid profile analysis of the BALF also did not reveal any significant differences among other major constituents of surfactant from control and SM animals. The organic extracts of BALF obtained from different animal groups were assessed for surface activity using a Wilhelmy balance. The results showed an increase in surface compressibility and a reduction in respreadability index in SM group. In contrast, the stability indices of surfactant films obtained from different groups were the same. These observations suggest that decreased DSPC content in SM rats plays a role in altering the biophysical characteristics of surfactant. it is concluded that chronic exposure to cigarette smoke adversely affects the pulmonary surfactant system of rats.

Retinoids control surfactant phospholipid biosynthesis in fetal rat lung.

Vitamin A (retinol) may play an important role in lung maturation: 1) premature delivery is simultaneously a source of vitamin A deficiency and increased risk of neonatal respiratory distress syndrome and subsequent bronchopulmonary dysplasia (BPD), due to deficit in pulmonary surfactant; 2) neonatal supplementation with retinol reduces the risk of BPD; and 3) fetal rat lung stores retinol in late gestation just before the onset of surfactant synthesis. To test the hypothesis of an implication of retinoids in the control of pulmonary surfactant synthesis, experiments were designed in the pregnant rat, aiming either at enhancing fetal lung vitamin A stores, bringing the active metabolite of vitamin A, retinoic acid (RA), or inhibiting the conversion of retinol to RA with aid of citral. Maternal administration of a single dose of 50,000 IU of retinyl palmitate on day 16 (term 22 days) increased 22 and 29%, respectively, the total phospholipid (TPL) and disaturated fraction of phosphatidylcholine (PC) in extracted fetal surfactant on day 19 but did not change surfactant protein (SP) A concentration. Chronic administration of retinyl palmitate to the mother from day 16 through 20 increased disaturated PC content on day 21 but decreased SP-A concentration. Fetal lung surfactant phospholipids were increased by chronic administration of RA and considerably reduced by citral (-31 and -35% for TPL and PC concns, respectively). RA also enhanced labeled choline incorporation into fetal lung PC on day 20. Given once on day 17, it accelerated the appearance of surfactant precursors on day 18.(ABSTRACT TRUNCATED AT 250 WORDS)

Antenatal glucocorticoid corrects pulmonary immaturity in experimentally induced congenital diaphragmatic hernia in rats.

Congenital diaphragmatic hernia, a highly lethal condition, displays at term the pulmonary biochemical and morphologic immaturity characteristic of premature delivery. We hypothesized that antenatal glucocorticoid, now the standard treatment to prevent hyaline membrane disease in premature human beings, might correct the parameters of the pulmonary biochemical and morphologic immaturity in severe congenital diaphragmatic hernia. A total of 112 fetal rats with or without nitrofen-induced congenital diaphragmatic hernias from 34 pregnancies were treated antenatally with either saline or dexamethasone. Antenatal dexamethasone increased the lung disaturated phosphatidylcholine content, reduced the lung glycogen concentration, reduced the saccular septal thickness, and increased the mean saccular size and volume fraction of saccules in the lungs of rats with large congenital diaphragmatic hernia in comparison with similar rats not so treated. All differences were statistically significant. Antenatal glucocorticoid therapy was efficacious in treating rats with nitrofen-induced congenital diaphragmatic hernia. This encouraging finding warrants further investigation in a large animal model with surgically created congenital diaphragmatic hernia.

Combined antenatal thyrotropin-releasing hormone and low-dose glucocorticoid therapy improves the pulmonary biochemical immaturity in congenital diaphragmatic hernia

The lungs of patients born with severe congenital diaphragmatic hernia (CDH) are biochemically and morphologically immature. Because antenatal glucocorticoid therapy can accelerate pulmonary maturation in premature neonates who have respiratory distress syndrome, we hypothesized that it may correct the pulmonary biochemical and morphological immaturity associated with CDH. We showed in previous experimental studies that antenatal low-dose dexamethasone improved the biochemical and morphological parameters of pulmonary immaturity in rats that had severe CDH. Somatic and pulmonary growth were inhibited with high doses of dexamethasone. In the present study, we examined the effects of antenatal low-dose dexamethasone and thyrotropin-releasing hormone (TRH), alone or in combination, on the pulmonary maturation in CDH. Combined antenatal low-dose dexamethasone and TRH significantly reduced mean lung glycogen concentration ( P = .001), and increased mean disaturated phosphatidylcholine content ( P < .005) to better than that observed with either therapy alone, without changing mean body or lung weight. Combined TRH and low-dose glucocorticoid as an antenatal therapy may reduce the morbidity and mortality of CDH.

Antenatal Cocaine Exposure Produces Accelerated Surfactant Maturation without Stimulation of Antioxidant Enzyme Development in the Late Gestation Rat

Antenatal cocaine administration is associated with increases in catecholamines and glucocorticoids and results in fetal hypoxemia, with the speculated potential for increased free radical formation in the fetus. Because of this, we hypothesized that antenatal cocaine exposure would produce not only accelerated pulmonary surfactant maturation, but also stimulation of antioxidant enzyme (AOE) system maturation and the ability to mount a protective AOE response to hyperoxia as well. Seventy-two, 48, and 24 h before delivery at either 20, 21, or 22 d of gestation, pregnant rats received twice daily s.c. injections of cocaine hydrochloride (40 mg/kg) or saline. Off-spring demonstrated growth retardation with significant reduction in body weight at all 3 gestational d studied that persisted to the 5th postnatal d. Serum corticosterone and total catecholamines were elevated from 50 to 200% in cocaine-exposed adult rats and pups. Advanced surfactant development in cocaine-exposed fetal offspring was apparent at d 21 of gestation, with significant increases in lung disaturated phosphatidylcholine content in cocaine (3.94 +/- 0.67 mg/g lung) versus control (3.25 +/- 0.64) offspring (p < 0.01). No increases in AOE maturation were found in cocaine-exposed fetuses at all 3 gestational d studied, whereas a significant decrease was demonstrated in glutathione peroxidase activity at d 20 and 22 of gestation in cocaine-exposed fetuses. In addition, cocaine newborns manifested a protective AOE response to hyperoxia of a magnitude similar to that of control newborns.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of insulin and glucose on pulmonary insulin receptors in late gestation fetal rats.

The effects of high glucose and insulin concentrations on fetal lung insulin receptors and tyrosine kinase activity were studied in an in vitro system utilizing 19- or 20-d fetal rat lung explants. Exposure of the explants to 100 mM glucose and insulin (0.1 unit/mL) for 72 h resulted in a significant decrease in specific binding of insulin to partially purified receptors [5.78% +/- 0.66 (SEM) vs. 9.64% +/- 1.68; P less than .01] when compared with lung explants exposed to 10 mM glucose alone. When individual effects of high insulin and glucose were studied, down-regulation of specific insulin binding was also observed, but to a lesser extent than that observed using both high glucose and insulin. Differences in insulin receptor affinity were not noted. Insulin receptor tyrosine kinase activity was also significantly decreased (52% of control values) under high-glucose/high-insulin conditions. Total phosphatidylcholine and disaturated phosphatidylcholine concentrations were significantly decreased in explants grown under high-glucose/high-insulin conditions, consistent with delayed pulmonary maturation. High glucose and insulin levels thus result in down-regulation of fetal lung insulin receptors and insulin receptor tyrosine kinase activity late in gestation. These results may have implications for substrate availability in the developing fetal lung.

Prenatal Hormone Treatment with Thyrotropin Releasing Hormone and with Thyrotropin Releasing Hormone Plus Dexamethasone Delays Antioxidant Enzyme Maturation but Does Not Inhibit a Protective Antioxidant Enzyme Response to Hyperoxia in Newborn Rat Lung

Whereas glucocorticoid administration to pregnant rats produces parallel acceleration of lung surfactant and antioxidant enzyme system maturation in late gestation, prenatal thyroid hormone treatment results in acceleration of surfactant maturation, with a paradoxical decrease in antioxidant enzyme (AOE) development. In these studies, we tested whether prenatal thyroid releasing hormone (TRH) treatment would act like prenatal thyroid hormone on pulmonary surfactant and AOE system maturation and whether combined prenatal treatment with TRH plus dexamethasone (DEX) would alter these effects. Secondly, we tested whether prenatal TRH and prenatal TRH plus DEX would inhibit the ability of newborn rats to respond to hyperoxia with protective increases in AOE activities. Results of the developmental studies revealed significantly increased fetal lung disaturated phosphatidylcholine content with significantly decreased pulmonary AOE activities as a result of prenatal TRH treatment that was not reversed with the addition of DEX. Combined TRH plus DEX treatment resulted in statistically significant decreases in body weight, lung weight, and lung weight to body weight ratios at both 21 and 22 d of gestation; growth effects were not seen with TRH alone. In terms of hyperoxic AOE response, despite being born with lower baseline AOE levels, the newborn animals prenatally treated with TRH or TRH plus DEX were able to induce a normal pulmonary AOE response to high O2 exposure. Although requiring further investigation, this reassuring finding suggests that clinical prenatal therapy with TRH or the combination of TRH plus DEX is not contraindicated for those infants delivered prematurely who go on to require intensive hyperoxic therapy.

Surfactant Content and Type II Cell Development in Fetal Guinea Pig Lungs during Prenatal Starvation

Prenatal caloric restriction in guinea pigs causes intrauterine growth retardation and reduced neonatal viability and surfactant phospholipid (PL). We report here fetal surfactant levels in this model, and correlate total lung PL with ultrastructural maturation of surfactant type II cells and lamellar bodies (LB). Pregnant guinea pigs were fed ad libitum throughout their 68-d gestation (control), or fed 50% rations from d 45 until term (starved). Fetal lungs were examined at d 55, 60, and 65 for PL content and composition, including disaturated phosphatidylcholine (DPC), and compared with neonates for both groups. Lung lobes were analyzed ultrastructurally in d 65 fetuses for the numerical, volume, and surface densities of type II cells and the volume densities of LB. Prenatal starvation caused significant intrauterine growth retardation at all ages; body and dry lung weights were reduced on d 65 by 26 and 23%, respectively. By d 55 and thereafter, starvation decreased total lung PL by 43-45% but did not alter PL composition. On d 65, the total lung volumes and relative numbers, surface densities, and volumes of type II cells in tissue and the relative volumes of LB within type II cells did not differ by caloric regimen. Thus, starved and control fetuses had similar total volumes of LB per lung (13-15 microL), although starved animals had significantly less lung DPC. Although the total volume of LB per lung correlated well with total lung DPC from d 55 through birth in controls, starvation led to a significant departure from this relationship.(ABSTRACT TRUNCATED AT 250 WORDS)