Surfactant Subfractions Research Articles

Compositional, structural and functional properties of discrete coexisting complexes within bronchoalveolar pulmonary surfactant

Lung surfactant (LS) stabilizes the respiratory surface by forming a film at the alveolar air-liquid interface that reduces surface tension and minimizes the work of breathing. Typically, this surface-active agent has been isolated from animal lungs both for research and biomedical applications. However, these materials are constituted by complex membranous architectures including surface-active and inactive lipid/protein assemblies. In this work, we describe the composition, structure and surface activity of discrete membranous entities that are part of a LS preparation isolated from bronchoalveolar lavages of porcine lungs. Seven different fractions could be resolved from whole surfactant subjected to sucrose density gradient centrifugation. Detailed compositional characterization revealed differences in protein and cholesterol content but no distinct saturated:unsaturated phosphatidylcholine ratios. Moreover, no significant differences were detected regarding apparent hydration at the headgroup region of membranes, as reported by the probe Laurdan, and lipid chain mobility analysed by electron spin resonance (ESR) in spite of the variety of membranous assemblies observed by transmission electron microscopy. In addition, six of the seven separated LS subfractions formed similar, essentially disordered-like, interfacial films and performed efficient surface activity, under physiologically relevant conditions. Altogether, our work show that a LS isolated from porcine lungs is comprised by a heterogenous population of membranous assemblies lacking freshly secreted unused LS complexes sustaining highly dehydrated and ordered membranous assemblies as previously reported. We propose that surfactant subfractions may illustrate intermediates in sequential structural steps within the structural transformations occurring along the respiratory compression-expansion cycles.

Alveolar macrophage depletion is associated with increased surfactant pool sizes in adult rats

Pulmonary surfactant is a lipid-protein material that is essential for normal lung function. Maintaining normal and consistent alveolar amounts of surfactant is in part dependent on clearance of surfactant by alveolar macrophages (AM). The present study utilized a rat model of AM depletion to determine the impact on surfactant pool sizes and function over time. Male Sprague-Dawley rats were anesthetized and intratracheally instilled with PBS-liposomes (PBS-L) or dichloromethylene diphosphonic acid (DMDP) containing liposomes (DMDP-L) and were killed at various time points up to 21 days for compliance measurements, AM cell counts, and surfactant analysis. AM numbers were significantly decreased 1, 2, and 3 days after instillation in DMDP-L vs. PBS-L, with 72% depletion at 3 days. AM numbers returned to normal levels by 5 days. In DMDP-L rats, there was a rapid increase in surfactant-phospholipid pools, showing a ninefold increase in the amount of surfactant in the lavage 3 days after liposome instillation. Surfactant accumulation progressed up to 7 days, with pools normalizing by 21 days. The increase in surfactant was due to increases in both subfractions of surfactant, the large aggregates (LA) and small aggregates. Surfactant protein A levels, relative to LA phospholipids, were not increased. There was a decreased extent of surfactant conversion in vitro for LA from DMDP-L rats compared with controls. It is concluded that the procedure of AM depletion significantly affects surfactant metabolism. The increased endogenous surfactant must be considered when utilizing the AM depletion model to study the role of these cells during lung insults.

Surfactant Proteins in Innate Host Defense of the Lung

Surfactant proteins A and D (SP-A and SP-D) are members of the collectin family of host defense proteins that are expressed in epithelial cells lining the lung. SP-A and SP-D interact with surfactant lipids in complex ways to determine the structure of tubular myelin, and the ratio of surfactant subfractions that, in turn, influences surfactant uptake and metabolism, respectively. SP-A and SP-D play critical roles in host defense of the lung against diverse viral, fungal, and bacterial pathogens. The collectins bind to the surfaces of microbes via carbohydrate-dependent interaction, aggregating, opsonizing, and enhancing clearance of the organisms by alveolar macrophages in the lung. Pulmonary surfactant proteins A and D play dual roles in pulmonary homeostasis, determining the structure of alveolar lipids and mediating the innate host defense system of the lung.

Analysis of pulmonary surfactant by Fourier-transform infrared spectroscopy following exposure to Stachybotrys chartarum (atra) spores

Lung cells are among the first tissues of the body to be exposed to air-borne environmental contaminants. Consequently the function of these cells may be altered before other cells are affected. As gas exchange takes place in the lungs, changes in cellular function may have serious implications for the processes of oxygen uptake and carbon dioxide elimination. In order for these processes to occur, the lung must maintain a high degree of expandability. This latter function is accomplished in part by the pulmonary surfactant which is synthesized and released by alveolar type II cells. Earlier studies have shown that exposure to gas phase materials such as smoke or organic solvents can alter the composition and function of the surfactant. The present study examines the ability of highly toxigenic mold spores to alter surfactant composition. Stachybotrys chartarum spores suspended in saline were instilled into mouse trachea as described earlier. After 24 h, the lungs were lavaged and the different processing stages of surfactant isolated by repeated centrifugation. Intracellular surfactant was isolated from the homogenized lung tissue by centrifugation on a discontinuous sucrose gradient. Samples were extracted into chloroform-methanol, dried and analyzed by Fourier-Transform infrared spectroscopy (FTIR). Exposure to S. chartarum induced an overall reduction of phospholipid among the three surfactant subfractions. The intermediate and spent surfactant fractions in particular were reduced to about half of the values observed in the saline-treated group. The relative distribution of phospholipid was also altered by spore exposure. Within the intracellular surfactant pool, higher levels of phospholipid were detected after spore exposure. In addition, changes were observed in the nature of the phospholipids. In particular strong intramolecular hydrogen bonding, together with other changes, suggested that spore exposure was associated with absence of an acyl chain esterified on the glycerol backbone, resulting in elevated levels of lysophospholipid in the samples. This study shows that mold spores and their products induce changes in regulation of both secretion and synthesis of surfactant, as well as alterations in the pattern of phospholipid targeting to the pulmonary surfactant pools.

Effects of alveolar surfactant aggregates on T-lymphocyte proliferation

The effects of alveolar large aggregate (LA) and small aggregate (SA) surfactant subfractions isolated from healthy adult rats on mitogen-stimulated proliferative responses of human peripheral blood mononuclear cells (PBMC) was examined. Various concentrations of total surfactant suppressed proliferation of stimulated lymphocytes by up to 95% of mitogen-stimulated cells alone. LA subfractions of total surfactant had no effect on proliferation, whereas SA significantly enhanced the lymphocyte proliferation at lower concentrations (7.8 μg/ml) compared to mitogen-stimulated cells alone. Higher concentrations of SA (62.5 μg/ml) inhibited lymphocyte proliferation. This concentration-dependent effect of SA on proliferation of PBMC was also present when cells were stimulated with various lectins including anti-CD3, concanavalin A and phytohemagglutinin. Analysis of the supernatant of mitogen-stimulated cell cultures treated with inhibitory concentrations of SA showed decreased amounts of interleukin (IL)-2, compared to cells alone, which could be reversed by adding exogenous IL-2 to the cell cultures with the SA. These results suggest that alveolar surfactant subfractions have distinct functions within the alveoli, both biophysically and with respect to their effects on the host’s immunomodulatory responses.

Clinical Biological and Genetic Heterogeneity of the Inborn Errors of Pulmonary Surfactant Metabolism

Pulmonary surfactant is a multimolecular complex located at the air-water interface within the alveolus to which a range of physical (surface-active properties) and immune functions has been assigned. This complex consists of a surface-active lipid layer (consisting mainly of phospholipids), and of an aqueous subphase. From discrete surfactant sub-fractions one can isolate strongly hydrophobic surfactant proteins B (SP-B) and C (SP-C) as well as collectins SP-A and SP-D, which were shown to have specific structural, metabolic, or immune properties. Inborn or acquired abnormalities of the surfactant, qualitative or quantitative in nature, account for a number of human diseases. Beside hyaline membrane disease of the preterm neonate, a cluster of hereditary or acquired lung diseases has been characterized by periodic acid-Schiff-positive material filling the alveoli. From this heterogeneous nosologic group, at least two discrete entities presently emerge. The first is the SP-B deficiency, in which an essentially proteinaceous material is stored within the alveoli, and which represents an autosomal recessive Mendelian entity linked to the SFTPB gene (MIM 1786640). The disease usually generally entails neonatal respiratory distress with rapid fatal outcome, although partial or transient deficiencies have also been observed. The second is alveolar proteinosis, characterized by the storage of a mixed protein and lipid material, which constitutes a relatively heterogeneous clinical and biological syndrome, especially with regard to age at onset (from the neonate through to adulthood) as well as the severity of associated signs. Murine models, with a targeted mutation of the gene encoding granulocyte macrophage colony-stimulating factor (GM-CSF) (Csfgm) or the beta subunit of its receptor (II3rb1) support the hypothesis of an abnormality of surfactant turnover in which the alveolar macrophage is a key player. Apart from SP-B deficiency, in which a near-consensus diagnostic chart can be designed, the ascertainment of other abnormalities of surfactant metabolism is not straightforward. The disentanglement of this disease cluster is however essential to propose specific therapeutic procedures: repeated broncho-alveolar lavages, GM-CSF replacement, bone marrow grafting or lung transplantation.

Localization of a candidate surfactant convertase to type II cells, macrophages, and surfactant subfractions.

Pulmonary surfactant exists in the alveolus in several distinct subtypes that differ in their morphology, composition, and surface activity. Experiments by others have implicated a serine hydrolase in the production of the inactive small vesicular subtype of surfactant (N. J. Gross and R. M. Schultz. Biochim. Biophys. Acta 1044: 222-230, 1990). Our laboratory recently identified this enzyme in the rat as the serine carboxylesterase ES-2 [F. Barr, H. Clark, and S. Hawgood. Am. J. Physiol. 274 (Lung Cell. Mol. Physiol. 18): L404-L410, 1998]. In the present study, we determined the cellular sites of expression of ES-2 in rat lung using a digoxygenin-labeled ES-2 riboprobe. ES-2 mRNA was localized to type II cells and alveolar macrophages but not to Clara cells. Using a specific ES-2 antibody, we determined the protein distribution of ES-2 in the lung by immunohistochemistry, and it was found to be consistent with the sites of mRNA expression. Most of the ES-2 in rat bronchoalveolar lavage is in the surfactant-depleted supernatant, but ES-2 was also consistently localized to the small vesicular surfactant subfraction presumed to form as a consequence of conversion activity. These results are consistent with a role for endogenous lung ES-2 in surfactant metabolism.

Effects ofStachybotrys chartarum (atra) conidia and isolated toxin on LungSurfactant production and homeostasis

This study evaluated the effects of Stachybotrys chartarum conidia and a trichothecene, isosatratoxin-F, on choline incorporation into DSPC by fetal rabbit alveolar type II cells and on alveolar surfactant subtypes in mice. Exposure of fetal rabbit type II cells to S. chartarum conidia at concentrations of 10(3) to 10(6) conidia ml(-1) significantly depressed [3H] choline incorporation after 24 h of exposure. Exposure of the rabbit cells to 10(5) to 10(6) conidia ml(-1) also resulted in significantly depressed [3H] choline uptake after 48 h. Additionally, fetal rabbit alveolar type II cells exposed to isosatratoxin-F in concentrations ranging from 10(-9) to 10(-4) M showed a significant reduction in [3H] choline incorporation into DSPC. Alveolar surfactant phospholipid concentrations in the different metabolic subfractions of lung lavage fluid of mice intratracheally exposed to either 50 microl of 10(7) ml(-1) S. chartarum conidia or 50 microl 10(-7) M isosatratoxin-F showed some significant changes at 12, 24, 48, and 72 h post-exposure, compared to the surfactant subfractions of control mice which were either untreated, exposed to saline or to 50 microl of 10(-7) ml(-1) Cladosporium cladosporioides conidia. In both the S. chartarum- and the isosatratoxin-F-treated mice, exposure significantly increased P10, P100, and S100 phospholipid concentrations, while the P60 phospholipid concentrations were depressed. In contrast, C. cladosporioides-treated mice showed only one significant change in subfraction phospholipid concentration: P60 was depressed at 48 h post-exposure. These results reveal that alveolar type II cells are sensitive to exposure to S. chartarum conidia and to isosatratoxin F. Sensitivity is manifest by alterations in the normal metabolic processing of alveolar surfactant. In exposed mice, this effect appears to involve a significant increase in newly secreted surfactant and an accumulation of the used surfactant forms.

Effects of Stachybotrys chartarum atra conidia and isolated toxin on LungSurfactant production and homeostasis

This study evaluated the effects of Stachybotrys chartarum conidia and a trichothecene, isosatratoxin-F, on choline incorporation into DSPC by fetal rabbit alveolar type II cells and on alveolar surfactant subtypes in mice. Exposure of fetal rabbit type II cells to S. chartarum conidia at concentrations of 103 to 106 conidia ml−1 significantly depressed [3H] choline incorporation after 24 h of exposure. Exposure of the rabbit cells to 105 to 106 conidia ml−1 also resulted in significantly depressed [3H] choline uptake after 48 h. Additionally, fetal rabbit alveolar type II cells exposed to isosatratoxin-F in concentrations ranging from 10−9 to 10−4 M showed a significant reduction in [3H] choline incorporation into DSPC. Alveolar surfactant phospholipid concentrations in the different metabolic subfractions of lung lavage fluid of mice intratracheally exposed to either 50 μl of 107 ml−1 S. chartarum conidia or 50 μl 10−7 M isosatratoxin-F showed some significant changes at 12, 24, 48, and 72 h post-exposure, compared to the surfactant subfractions of control mice which were either untreated, exposed to saline or to 50 μl of 10−7 ml−1 Cladosporium cladosporioides conidia. In both the S. chartarum- and the isosatratoxin-F-treated mice, exposure significantly increased P10, P100, and S100 phospholipid concentrations, while the P60 phospholipid concentrations were depressed. In contrast, C. cladosporioides-treated mice showed only one significant change in subfraction phospholipid concentration: P60 was depressed at 48 h post-exposure. These results reveal that alveolar type II cells are sensitive to exposure to S. chartarum conidia and to isosatratoxin F. Sensitivity is manifest by alterations in the normal metabolic processing of alveolar surfactant. In exposed mice, this effect appears to involve a significant increase in newly secreted surfactant and an accumulation of the used surfactant forms. Copyright © 1998 John Wiley & Sons, Ltd.

Surfactant subfractions during nosocomial infection in ventilated preterm human neonates.

Long after resolution of the neonatal respiratory distress syndrome, deterioration of respiratory function in ventilated premature infants during severe nosocomial infections is commonly observed. Based on an increased oxygen demand and ventilatory support, impairment of the pulmonary surfactant system was hypothesized to occur. The clinical course of 10 premature neonates (764 +/- 57 g, 26.6 +/- 0.4 wk) with nosocomial infection mainly due to Staphylococcus epidermidis was divided into four periods in each individual patient: "before deterioration" (average 8 to 11 d of life), "deterioration" (11 to 17 d), "peak" (17 to 22 d), and "recovery" (22 to 24 d). A total of 810 airway specimens were obtained by small volume lavage (1 ml/kg bw), pooled to yield appropriate amounts for differential centrifugation into two distinct subfractions known as large surfactant aggregates (LA) and small surfactant aggregates (SA). "Before deterioration" the amount of phospholipids recovered was constant, and the two fractions were characterized by electron microscopic morphology and biochemical analysis. In the LA fraction lamellar body-like lipid structures were demonstrated, and the phospholipid composition was typical of pulmonary surfactant in premature neonates with a high content of phosphatidylcholine and phosphatidylinositol. With "deterioration" and "peak" the masses of total phospholipids and of phosphatidylcholine recovered were reduced (p < 0.05). At the same time the mass ratio of SA/LA for phosphatidylcholine decreased from 0.32 +/- 0.10 to 0.18 +/- 0.03, indicating a more pronounced decrease of the SA fraction (p < 0.05). The phospholipid composition in the LA fraction did not change during the course of nosocomial infection. In the SA fraction a decrease of phosphatidylcholine and a concomitant increase in lysophosphatidylcholine were observed at the "peak" of the infection. We concluded that, in ventilated premature neonates during nosocomial infection and respiratory deterioration, changes in phospholipid subfractions occur, possibly indicating impairment of pulmonary surfactant metabolism. These findings may be important when considering treatment of acute lung injury with nebulized exogenous surfactant.

Roles of SP-A, SP-B, and SP-C in modulation of lipid uptake by pulmonary epithelial cells in vitro.

The effects of the surfactant proteins (SP)-A, SP-B, and SP-C on binding and endocytosis of fluorescently labeled lipid vesicles were studied in rat type II epithelial cells and in MLE-12 cells, a pulmonary adenocarcinoma cell line with alveolar cell characteristics. Incorporation of SP-C in lipid vesicles markedly stimulated binding to the cell membrane at 4 degrees C and endocytosis of lipids at 37 degrees C. SP-C enhanced lipid uptake in MLE-12 cells, type II cells, and NIH 3T3 cells. SP-B stimulated lipid uptake in MLE-12 cells, but to a lesser degree. SP-B decreased the amount of lipid uptake stimulated by SP-C, SP-A did not increase endocytosis of lipids by MLE-12 cells or type II cells, but aggregates of lipid were observed associated with the cell surface in the presence of SP-A. Maintenance of active surfactant in the lung may be achieved through the selective uptake and degradation of surfactant subfractions depleted in SP-A and SP-B.

Pulmonary surfactant subfractions in patients with the acute respiratory distress syndrome.

Changes in the surfactant system have been observed in patients with acute respiratory distress syndrome (ARDS). These alterations in surfactant are thought to contribute to lung dysfunction in this disease. In this report we describe the changes in surfactant subfractions in bronchoalveolar wash obtained from five patients with established ARDS compared with five non-ARDS patients. Our results show that, in addition to the changes in surfactant composition and yield reported previously, the ratio of small to large surfactant aggregates is significantly increased in patients with ARDS compared with non-ARDS patients (0.48 +/- 0.09 versus 0.20 +/- 0.05 respectively [p < 0.05]). This increased ratio was associated with a decreased level of SP-A in the large aggregate fraction. We suggest that this increased ratio represents a marker for surfactant alterations in ARDS that is independent of lavage technique and can be measured in a very small surfactant sample.

Alveolar surfactant subfractions differ in their lipid composition

Alveolar surfactant consists of subfractions which are generated during normal lung function. Although subfractions obtained by differential centrifugation of lung lavage differ in structure, function and protein content, the phospholipid-pattern shows only minor differences. To correlate possible differences in composition between subfractions to their functional properties we did a more detailed analysis of lipid pattern. Subfractions of lung lavages from Wistar rats were obtained by differential centrifugation, lipid classes were separated by thin layer chromatography (TLC). Fatty acids and plasmalogens were determined as methylester and dimethylacetals by gas chromatography, respectively. Cholesterol and vitamin E were determined enzymatically and by HPLC, respectively. The patterns of fatty acids of total lipids and of the molecular species of phosphatidylcholine and phosphatidylethanolamine were very similar among the subfractions. The distribution of individual lavage lipids varied considerably. Three types of subfractions can be distinguished: The two dense subfractions (1000 g and 60,000 g) contain 70–88% of total phospholipids, dipalmitoylphosphatidylcholine, polyunsaturated phospholipids and polyunsaturated fatty acids present in lung lavage. The less dense subfraction (100,000 g) contains 44–60% of total cholesterol, choline plasmalogen, ethanolamine plasmalogen and vitamin E. The 100,000 g supernatant contains 40–50% of total tri-, diacylglycerols and free fatty acids. Our results support the concept that the 1000 g subfraction contains freshly secreted surfactant. The 60,000 g subfraction likely contains the monolayer and freshly secreted surfactant. The 100,000 g pellet probably contains material “squeezed out” from the monolayer at expiration. Most likely, the supernatant contains material destined for removal from the airspace.

Surface activity of rabbit pulmonary surfactant subfractions at different concentrations in a captive bubble.

This study investigates the surface activity of rabbit pulmonary surfactant subfractions at different concentrations in a new pressure-driven captive bubble surfactometer, which provides more rigorous testing conditions than heretofore applied to this material. Subfractions were separated by centrifugation of lavage return into a third (P3; 1,000 x average g, 20 min), a fourth (P4; 60,000 x average g, 60 min), and a fifth (P5; 100,000 x average g, 16 h) pellet. At 2.0 mg phospholipid/ml, P3 and P4 demonstrated more rapid adsorption, lower minimum surface tensions on first and subsequent compressions, and lower monolayer compressibilities than did P5. This surface activity of P3 and P4 increased with concentration between 0.1 and 2.0 mg phospholipid/ml. Adsorption rate constants were approximately 10,000 times faster than desorption constants. We conclude that, in a normal lung, components of P3 and P4 determine alveolar surface tension. We speculate that under special circumstances even the less surface active P5 could have an important influence at the air-water interface.

Mouse alveolar surfactant: Characterization of subtypes prepared by differential centrifugation

To characterize the properties of alveolar surfactant subfractions obtained from mouse lung by differential centrifugation, lavage fluid, following a preliminary centrifugation at 140 x g for 5 min to yield a cellular pellet (Pc), was sequentially centrifuged at 10,000 x g for 30 min, 60,000 x g for 60 min and 100,000 x g for 15 h; and the resultant pellets, respectively referred to as P10, P60 and P100, were harvested for electron microscopy, phospholipid analysis and surface tension measurements. Ultrastructural differences were observed, in that P10 contained large multilamellated structures which were typical of newly secreted surfactant, P100 contained small unilamellar vesicular structures, typical of catabolic end products of alveolar surfactant and P60 appeared to contain a mixture of structures present in P10 and P100 in addition to numerous, large unilamellar vesicles which were not present in either P10 or P100. Slight but significant differences were found in the phospholipid compositions of the three subfractions but not in the fatty acid composition of their phosphatidylcholine (PC) component. There were no significant differences in their disaturated PC/total PC ratios, but significant differences in their phospholipid/protein ratios. P60 had the highest proportion of phospholipid to protein. P10 and P60 demonstrated surface activity but P100 did not. Total alveolar surfactant phospholipid was evenly distributed among the three fractions. This pattern of distribution was significantly different from that observed in rabbit subfractions prepared by the same procedure. These data indicate that mouse alveolar surfactant consists of three distinct subfractions or subtypes which can be separately and quantitatively isolated by differential centrifugation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Pulmonary Toxicity of Aerosolized Oil-Based Aminocarb Insecticide: Early Responses of the Pulmonary Surfactant

AbstractThe pulmonary toxicity of aerosolized oil-formulated aminocarb (Matacil) insecticide was assessed in acutely treated rats in relation to pulmonary surfactant (SF). Time- and dose-dependent changes in biochemical markers [alkaline phosphatase (AKP), acid phosphatase (ACP), β-N-acetyl glucosaminidase (β-NAG) and lactic dehydrogenase (LDH), protein and phospholipid contents] were analyzed in four pulmonary surfactant compartments: (1) the lavaged lung tissue, (2) the cell-free bronchoalveolar lavage (BAL) and its surfactant subfractions obtained by centrifugation, namely, (3) the common myelin figure (CMF) fraction or surfactant proper and (4) the tubular myelin figure (TMF) fraction. Air control groups were used for comparison for every treatment time period. Aerosol deposition was estimated by mathematical calculation. First, groups of animals were treated for 1 hr with a high-concentration aerosol (134 mg aminocarb/m3 air; MMAD 3.6 μm; GSD 2.4 μm) and studied at 1, 3, and 14 days postexposure. Aft...

Altered surfactant function and metabolism in rabbits with acute lung injury

Lung injury was induced in rabbits with N-nitroso-N-methylurethane (NNNMU), and saturated phosphatidylcholine (Sat PC) pool sizes and phospholipid compositions were measured in alveolar wash subfractions isolated by differential centrifugation (large and small surfactant aggregates). Surfactant metabolism also was studied using intravascular and intratracheal radiolabels. Protein permeability, gas exchange, and compliance were significantly abnormal as lung injury progressed. At peak injury, there was a decrease in the large aggregate Sat PC pool size in alveolar wash accompanied by increased uptake of Sat PC from the air space and increased specific activity of both intravascular and intratracheal radiolabels in lamellar bodies. This was followed by a marked rise in the small aggregate pool size in the alveolar wash and increased secretion of Sat PC into the air spaces. Phospholipid compositions, total phospholipid-to-protein ratios, and in vivo functional studies using a preterm ventilated rabbit model were abnormal for both large and small aggregate surfactant fractions from the lung-injured rabbits. These studies characterize quantitative, qualitative, and functional changes of alveolar wash surfactant subfractions in NNNMU-injured lungs.

Effect of Pattern of Breathing on Subfractions of Surfactant in Tissue and Alveolar Compartments of the Adult Rat Lung

We have used tow previously characterized models of hyperpnea in vivo and different modes of ventilation in the isolated perfused rat lung to investigate changes in the phospholipid content of tubular myelin-rich (PLalv-1) and -poor (PLalv-2) fractions isolated from lavaged material and of two lamellar body subfractions. A vesicular lamellar body subfraction (lbB) was preferentially released during 30-min swimming. However, during the subsequent 3-h recovery period there was a preferential supplementation of the classic-appearing lamellar body fraction (lbA). Hyperpnea induced by exposure to 5% CO2/13% O2/82% N2 led to an increase in lbA after 12 h and in lbB after 48 h. Whereas PLalv-2 was elevated above control values after 8 h, PLalv-1 remained unchanged until 24 h. In the perfused lung isolated from rats infused with [methyl-3H]choline chloride 3 h previously, salbutamol, a deep breath, and increased tidal volume (VT) all increased total alveolar phospholipids; however, the pattern of change was very different. Salbutamol markedly elevated PLalv-1 and increased the specific activity of both alveolar fractions. In contrast, a single deep breath increased PLalv-2 while slightly increasing the specific activity of PLalv-1. Finally, an increased VT decreased PLalv-1 while inducing a large increase in PLalv-2; it increased specific activity in both alveolar fractions. Both salbutamol and an increased VT decreased phospholipids in lbA. We conclude that lbA and lbB vary in their response to different stimuli. In vivo, PLalv-1, the tubular myelin-rich fraction, remains very constant, a fact consistent with its being the controlled variable in surfactant homeostasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Surfactant metabolism in surfactant-treated preterm ventilated lambs.

Preterm lambs were delivered at 132 days gestational age, treated with 100 mg/kg radiolabeled natural sheep surfactant or Surfactant TA, and ventilated for times up to 24 h. Compared with an untreated group that developed respiratory failure by 5 h, both surfactant-treated groups had stable respiratory function to 24 h. Although only approximately 13% of the labeled surfactant phosphatidylcholine was recovered by alveolar wash at 24 h, there was no significant loss of the labeled phosphatidylcholine from the lungs. Labeled palmitic acid intravascularly injected at 1 h of age comparably labeled lung phosphatidylcholine in the three groups of lambs at 5 h; however, only approximately 0.5% of the labeled phosphatidylcholine was secreted to the air spaces of surfactant-treated lambs at 24 h. Labeled lysophosphatidylcholine given with the natural sheep surfactant was taken up by the lungs, converted to phosphatidylcholine with 30-40% efficiency, and resecreted to the air spaces, demonstrating recycling of a phospholipid. The large surfactant aggregates recovered from alveolar washes by centrifugation were surface active and contained approximately 76% of the air-space phosphatidylcholine in both surfactant-treated groups. Although clinical status was comparable, alveolar washes and surfactant subfractions from Surfactant TA-treated lambs had better surface properties than did sheep surfactant-treated lambs. These studies identified no detrimental effects of surfactant treatments on endogenous surfactant metabolism and indicated that the surfactants used for treatments were recycled by the preterm ventilated lamb lung.

Effect of lung collapse on alveolar surfactant in rabbits subjected to unilateral pneumothorax.

To determine whether atelectasis might modify lung surfactant, we injected N2 into the right pleural space of adult rabbits. Daily, under sedation, pleural gas volume and pressure were measured and adjusted to 20 ml/kg and 0 to +2 cm H2O with N2. On the sixth day, pHa, PaCO2, PaO2, and FRC were measured. Pressure-volume diagrams or bronchoalveolar lavages (BAL) were performed separately on right and left lungs. Surfactant subfractions were obtained from BAL fluid, and total protein, LDH, and cell counts were determined. Phospholipid (PL) was assayed in lung homogenate, BAL fluid, and subfractions, and PL composition was determined on the largest BAL subfraction (P4). On the sixth day the pleural gas volume was 19.7 +/- 2.7 (SD) ml/kg, and PaO2 and FRC were significantly decreased. Air volume in excised right lungs at 30 cm H2O was 13.1 +/- 2.8 (SE) ml/kg with pneumothorax (PN) and 22.8 +/- 1.9 (SE) ml/kg in controls. Total PL was decreased 43% in BAL and 59% in P4 of collapsed lungs. Phosphatidylglycerol to phosphatidylinositol (PI) plus phosphatidylserine (PS) ratio of P4 was substantially decreased in both lungs of PN animals. Cell counts, LDH, and protein in BAL did not suggest inflammation or epithelial damage. We conclude that pneumothorax decreases the quantity of alveolar surfactant in the collapsed lung and alters its phospholipid composition toward the fetal pattern in both lungs, possibly due in part to the proliferative response of the lungs to pneumothorax.