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(Chest. 2000;117:1720-1727.)
© 2000 American College of Chest Physicians

Effects of Eicosapentaenoic and {gamma}-Linolenic Acids (Dietary Lipids) on Pulmonary Surfactant Composition and Function During Porcine Endotoxemia*

Michael J. Murray, MD, PhD; Ghassan Kanazi, MD{dagger}; Kamal Moukabary, MD{ddagger}; Henry D. Tazelaar, MD and Stephen J. DeMichele, PhD

* From the Departments of Anesthesiology (Drs. Murray, Kanazi, and Moukabary) and Surgical Pathology (Dr. Tazelaar), Mayo Clinic, Rochester, MN; and Medical Nutritional Research and Development (Dr. DeMichele), Ross Products Division, Abbott Laboratories, Columbus, OH. {dagger} Currently at Department of Anesthesiology, University of Rochester, Rocheter, NY. {ddagger} Currently at Department of Anesthesiology, Kino Community Hospital, Tucson, AZ.

Correspondence to: Michael J. Murray, MD, PhD, 200 1st St SW, Mayo Clinic, Rochester, MN 55905; e-mail: murray.michael{at}mayo.edu


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Study objectives: To investigate whether a diet enriched with fish and borage oils, with their high polyunsaturated fatty acid (PUFA) content, alters surfactant composition and function during endotoxemia.

Design: Prospective, randomized, blinded, controlled animal study.

Setting: Research laboratory at a medical center.

Participants: Thirty-six 15- to 25-kg, disease-free, castrated male pigs.

Diets and measurements: Three groups of pigs (n = 12 per group) were fed for 8 days diets containing either {omega}-6 fatty acids (FAs) (corn oil; diet A), or {omega}-3 FAs (fish oil; diet B), or a combination of {omega}-6 and {omega}-3 FAs (borage and fish oils; diet C). Eight of 12 pigs in each group received a 0.1-mg/kg bolus of Escherichia coli endotoxin followed by a continuous infusion (0.075 mg/kg/h). One lung was subsequently isolated ex vivo, and pressure-volume curves were measured. The contralateral lung was lavaged, and surfactant was analyzed for total and individual phospholipids and FA composition. Minimum and maximum surface tension was measured by bubble surfactometry.

Results: Pigs fed either diet B or C had increased oleic acid (C18:1 {omega}-9), eicosapentaenoic acid (EPA; C20:5 {omega}-3), docosahexaenoic acid (C22:6 {omega}-3), and total {omega}-3 and monounsaturated FAs in their surfactant PUFA pools. The relative percentage of linoleic acid (C18:2 {omega}-6) and total {omega}-6 FAs were significantly lower from pigs fed diets B and C compared with diet A. Palmitic acid (C16:0) concentrations, the primary FA in surfactant, had a tendency to be lower in pigs fed diets B and C. There were no demonstrable effects on surfactant function or pulmonary compliance.

Conclusions: Diets containing EPA or EPA and {gamma}-linolenic acid altered the PUFA composition of pulmonary surfactant, but without demonstrable effects on surfactant function during porcine endotoxemia.

Key Words: acute lung injury • ARDS • borage oil • eicosapentaenoic acid • fish oil • {gamma}-linolenic acid • pulmonary compliance • pulmonary surfactant • sepsis


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Alterations of the alveolar surfactant system have long been implicated in the pathogenesis of the ARDS in adults. Long-chain saturated fatty acids (FAs) are the major FAs found in surfactant phospholipids (PLs).1 The physical properties of these PLs allow for the formation of a homogenous, smooth PL-protein monolayer that lines alveoli in a way that is optimal for increasing surface activity and decreasing surface tension.2

High-fat, low-carbohydrate, enteral diets have been designed to reduce minute ventilation and ventilatory demand by lowering carbon dioxide production in ventilator-dependent patients. However, the lipids found in these formulations may not be optimal for patients at risk of or exhibiting signs of ARDS. Recent advances in nutritional intervention after acute lung injury (ALI) or ARDS include the administration of a specialized diet containing eicosapentaenoic acid (EPA; fish oil) and {gamma}-linolenic acid (GLA; borage oil). The rationale for increasing the amount of EPA and GLA in the diet is that these FAs may decrease the synthesis of proinflammatory eicosanoids while increasing the anti-inflammatory and vasodilatory monoenoic (GLA) and trienoic (EPA) eicosanoids after endotoxemia.

For example, GLA is a precursor for dihomo-{gamma}-linolenic acid, which is not further desaturated by {Delta}5-desaturase because of the inhibitory effects of EPA. Dihomo-{gamma}-linolenic acid, when released by phospholipases, can be subsequently metabolized to prostaglandin E1, a known pulmonary vasodilator.

Previously, we have shown that short-term feeding (8 days) of a specialized enteral diet containing EPA and GLA improved gas exchange and oxygen delivery in a porcine model of ALI, presumably in part through modifications in eicosanoid production, with a decrease in pulmonary vascular resistance and an increase in cardiac output.3 Additional studies in animal models of sepsis-induced ARDS from other laboratories have shown reduced pulmonary neutrophil accumulation,4 reduced severity of pulmonary microvascular protein permeability,5 6 reduced synthesis of proinflammatory eicosanoids of lung injury,4 5 6 and rapidly displaced arachidonic acid from lung and alveolar macrophage PLs.7 8

Changing the type and amount of lipid in the diet alters the FA composition of surfactant,9 which may change the physical and physiologic properties of surfactant10 and the alveolar surface tension.11 12 Fish and borage oil have high amounts of polyunsaturated fatty acids (PUFAs) and, therefore, have the potential to alter pulmonary surfactant composition and decrease compliance. Endotoxemia increases the content of PUFAs in pulmonary surfactant,13 with the potential to decrease pulmonary compliance. This is of concern because of the increasing body of evidence that particular long-chain PUFAs of the {omega}-3 (EPA) and {omega}-6 (GLA) families may be beneficial after ALI or ARDS.3 4 5 6 7 8 Any benefit from the anti-inflammatory properties of EPA and GLA might be offset by changes in the FA composition of surfactant and alterations in surface tension and compliance.

The present study was designed to investigate whether a diet enriched with fish and borage oils, with their high PUFA content, would alter surfactant composition and function during the early, acute phase of endotoxemia.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Conclusion
 References
 
After approval from the Institutional Animal Care and Use Committee and following the National Institutes of Health Guidelines for Care and Use of Laboratory Animals, 36 disease-free, castrated male pigs (Sus scrofa, mixed breeds) weighing 15 to 25 kg were studied. Pigs were divided into three groups of 12 pigs each. All pigs were fed eucaloric and isonitrogenous enteral diets (Table 1 ) for 8 days. The diets were supplemented with either linoleic acid (LA; diet A), EPA (diet B), or a combination of EPA and GLA (diet C) (Table 2 ). The latter diet was supplemented with antioxidants, including vitamins E and C, and B-carotene. Diets provided 55% of calories from corn oil (diet A), fish oil (diet B), or fish and borage oil (diet C). Each pig received 175 kcal/kg/d of the enteral diets from a specially made liquid feeding device. Pigs were periodically checked to assure that the feed was consumed. All liquid diets were formulated and manufactured by Ross Products Division, Abbott Laboratories, Columbus, OH.


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  		Table 1.. Composition of Enteral Diets*

 

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  		Table 2.. Fatty Acid Profiles of Enteral Diets*

 
On the eighth day, the pigs were fed only in the morning, and 6 h later were anesthetized with 25 mg/kg ketamine and 0.6 mg atropine given intramuscularly. Between 1.0 and 1.5% halothane was administered through a face mask for maintenance of anesthesia, and femoral venous and arterial cannulas were placed. After the procedure, the animals were allowed to recover from the anesthetic for 18 h before being placed unanesthetized in a standing harness. Eight of 12 pigs in each group received an IV bolus of 0.1 mg/kg Escherichia coli endotoxin (Sigma Chemical Co; St. Louis, MO), with continuous infusion of endotoxin for 4 h at 0.075 mg/kg/h.

From previous experience, we know that the mortality rate after 6 h in this model is >= 30%; because death is not an acceptable end point in animal studies, we terminated the experiments after an additional 2 h of monitoring in the interest of animal welfare.

BAL
The animals then received an overdose of IV pentobarbital followed by a lethal dose of potassium chloride. The chest was immediately opened, and the right and left lungs isolated. A small clamp was placed in the distal aspect of the right middle lobe, and a 3- to 5-g segment of lung was removed for studies of lung pathology. Specimens were placed in formalin, fixed overnight, stained with hematoxylin and eosin, embedded in paraffin, and cut with a microtome. The specimens were reviewed in a randomized fashion by one of us (H.D.T.) who was unaware of which diet each animal received. Specimens were graded for degree of leukocyte infiltration, edema, and hemorrhage, using a range of 0 to 3, with 0 representing no abnormalities and 3 representing the most severe abnormality.

The right mainstem bronchus was intubated, the air evacuated, and buffered lavage fluid instilled from a deformable plastic reservoir attached to the bronchial tube to form a closed system. The lavage buffer was 10 mM Tris-HCl, pH 7.4, 0.01 mM CaCl2, and 0.01 mM MgCl2 in 0.9% NaCl. Five hundred milliliters of lavage fluid was used, with the fluid instilled and retrieved three times by gravitational flow. This fluid was then centrifuged within 30 min of the lavage at 500g for 10 min at 4°C to remove the cell pellet. The supernatant of the low-speed centrifugation was frozen and stored under nitrogen at -70°C until subsequent analyses.

Pulmonary Compliance
The left lung was excised, air was removed in a vacuum for 5 min, the left mainstem bronchus was cannulated, and the lung was inflated to 30 cm H2O pressure as measured by a water manometer. The lung was then deflated in 20-mL increments, and the airway pressure was recorded after 10 s. When the functional residual capacity was reached (defined as atmospheric airway opening pressure), the bronchus was occluded. The lung was then weighed, and the lung volume was measured by water displacement, assuming a tissue density of 1.065 g/mL. The total lung capacity was calculated as the sum of the functional residual capacity and the amount of air removed during the deflation maneuver. Volumes were not corrected for gas compression.

The pressure-volume (P-V) curve of the lung was then measured while the lung was distended with saline to negate the effects of surfactant on the P-V characteristics of the lung. Air was removed from the lung, and normal saline was infused to achieve an airway opening pressure of 10 cm H2O. The saline was then removed in 10-mL increments, and the pressure was recorded until functional residual capacity was reached. The BAL supernatant from the low-speed centrifugation was thawed, mixed, and centrifuged at 48,000g for 60 min at 4°C. The high-speed centrifuged supernatant was decanted, and the crude surfactant pellet was resuspended in 200 µL of saline containing 5 mM CaCl2 and analyzed for total protein, total PL, individual PLs, and biophysical activity.

Lavage and Surfactant Analyses
Surface tension was analyzed using a pulsating bubble surfactometer14 with all samples adjusted (when possible) to 1.5 mM phosphorus concentration in saline containing 5 mM CaCl2.

Total PLs were extracted by the method of Bligh and Dyer.15 A trace amount of radiolabeled disaturated phosphatidylcholine (PC) was added to quantify recovery. Total protein was determined on an aliquot of each sample by a modification of the method of Lowry as described by Peterson16 and was expressed per milliliter of resuspended crude surfactant pellet. Total PL was quantified by assaying organic phosphorus as described by Dittmer and Wells17 and was expressed per milliliter of resuspended crude surfactant pellet. The individual PLs were separated according to Coorthuis et al.18 Each PL was assayed by directly digesting the gel, with the exception of PC, which was extracted from the silica. The PL profile represents the percentage of each of the PLs present on the thin-layer chromatography plate. Disaturated PC was determined on an aliquot of the extracted PC according to a modification of Mason et al19 as described by Tsai et al.20

Total lipids were extracted from the lavage fluid using three volumes of CHCl3/CH3OH (2:1) by the method of Folch et al.21 The chloroform extract was concentrated by evaporation under reduced pressure. The surfactant lipids were stored as a CHCl3 solution at -20°C under nitrogen until thin-layer chromatography was performed.

The lipid extracts of lung surfactant were separated into the major constituent lipid classes, PLs, free FAs, triglycerides, and cholesterol esters, by thin-layer chromatography on 250 silica gel H µm plates. The running solvent was Skelly F (petroleum ether [boiling point 30 to 60°C]/CH3OCH3/acetic acid, 80:20:1). Surfactant PC and phosphatidylglycerol subfractions were separated by thin-layer chromatography as described elsewhere.22 The plates were sprayed with 1,7-dichlorofluorescein, viewed under a short-wavelength ultraviolet light, and scraped to isolate the individual lipid classes.

The FAs of the lipid classes were esterified or transesterified using 10% HCl in CH3OH at 98°C for 90 min. The fatty acid methyl esters (FAMEs) were extracted into heptane. The FAMEs were stored under nitrogen at -20°C until gas chromatography (GC) analysis. FAMEs were separated and quantified by GC on a 30 m x 0.53 mm internal diameter, free-FA phase, wall-coated, open tubular capillary column with a flame ionization detector. The carrier gas was helium at 23.5 mL/min. The analysis was temperature programed from 145 to 200°C at 1.75°C/min with a 5-min initial hold and a 15-min final temperature hold. The signal from the flame ionization detector was integrated by a Hewlett Packard 5840A GC integrator (Avondale, PA). FAMEs were identified by comparison with relative retention times of a known standard (GC standard; Nu-Chek Prep; Elysian, MN).

Statistical Analysis
The data were analyzed as a one-way analysis of variance. This allowed for examination of the comparison of interest (between the endotoxin groups) and within each dietary group, examining for the effect of diet and for all possible comparisons among the groups. For all analyses, after a significant t test, Tukey’s least significant difference was used to determine where the differences occurred. Data that were not normally distributed were analyzed with a Kruskal-Wallis test. The P-V curves for the two groups of animals were compared with each other at total lung capacity and at 10% of total lung capacity decrements by unpaired t tests. Results were considered to be statistically significant when the overall significance level was < 5%.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Conclusion
 References
 
Oxygenation
We observed that pigs given endotoxin had a 26% decrease in the PaO2 within 20 min of receiving the bolus of endotoxin, with a 129% increase in the alveolar-arterial oxygen gradient, which over the 4 h of the experiment abated to a 15.2% decrease in PaO2 and a 66.7% increase in the alveolar-arterial oxygen gradient. The changes were associated with an 87.4% increase in pulmonary arterial pressure and an 11.6% decrease in mean systemic arterial pressure.

Pulmonary Surfactant Composition and Function
The composition and function of pulmonary surfactant isolated from pigs given endotoxin are shown in Tables 3 and 4 and Figure 1 . Within each group, the pigs that did not receive endotoxin had pulmonary surfactant similar to other pigs in their group without significant differences in function (data not shown). Total protein, total PLs, and PL/protein ratio were not significantly different between the three dietary groups 2 h after endotoxin was discontinued (Table 3) . The individual PL composition, expressed as the percentage of total PLs recovered from the thin-layer chromatography plate, showed no significant differences between all groups for PC, disaturated PLs, phosphatidylglycerol, phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, and sphingomyelin (Table 4) .


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  		Table 3.. Surfactant PL and Protein Composition 4 h After Endotoxin Infusion*

 


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  		Figure 1.. The mean maximum surface tension (dynes/cm) (top) and the mean minimum surface tension (dynes/cm) (bottom) in the three groups of pigs 2 h after the endotoxin infusion was discontinued are plotted. No statistically significant differences were found among groups. Values are mean ± SD.

 

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  		Table 4.. Surfactant PL Chemical Composition 2 h After Endotoxin Infusion Was Discontinued*

 
Minimum and maximum surface tensions were measured by bubble surfactometry as an indicator of surfactant function (Fig 1) . No significant differences in minimum surface tension and maximum surface tension were noted between the three diets 4 h postendotoxin infusion.

Pulmonary Surfactant FA Composition
The total FA composition was determined from total surfactant PLs (Fig 2 ) and from the main surfactant PL, PC (Table 5 ), 2 h after the discontinuation of the endotoxin infusion. Pigs fed either diet B or C had changes within both surfactant PUFA pools, as evidenced by significant increases in oleic acid (C18:1 {omega}-9), EPA (C20:5 {omega}-3), and docosahexaenoic acid (C22:6 {omega}-3), and total {omega}-3 and monounsaturated FAs compared with diet A. The relative percentages of LA (C18:2 {omega}-6) and total {omega}-6 FAs were significantly lower in the total PLs and PC from pigs fed diets B and C compared with diet A. However, despite these changes within the total PUFAs in both surfactant pools, total PUFAs remained similar among the diet groups. The percentage of palmitic acid (C16:0), the primary FA associated with surfactant, and the total percentage of saturated FAs were lower (not significant) in total PL and PC fractions from pigs fed diets B and C compared with diet A.



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  		Figure 2.. The FA composition of total surfactant PL 2 h after the endotoxin infusion was discontinued in the pigs fed the three different diets is plotted. Top: the total saturated FAs, the total monounsaturated FAs, and the total PUFAs are plotted. Bottom: the total {omega}-6 and {omega}-3 FAs are plotted. Middle: palmitic acid (C16:0), oleic acid (C18:1 {omega}-9), LA (C18:2 {omega}-6), and EPA (C20:5 {omega}-3) are plotted. *p < 0.05 vs diet A. **p < 0.05 comparing diet B with C.

 

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  		Table 5.. FA Composition of Surfactant PC 2 h After Endotoxin Was Discontinued*

 
Pulmonary Compliance
Pulmonary compliance as determined by P-V curves was measured in all pigs 2 h after endotoxin administration was discontinued (Fig 3 ). P-V curve analysis did not show any significant differences in pulmonary compliance among the three groups, nor among these groups and the group of animals that did not receive endotoxin.



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  		Figure 3.. Airway pressures are depicted on the x-axis, and lung volumes are depicted on the y-axis. Measurements were made on lungs 2 h after the infusion of endotoxin or placebo was discontinued. The P-V curves are almost identical. No statistically significant differences were found.

 
Pathology
The lung specimens were examined by a pathologist (H.D.T.), who had no knowledge of the purpose of the experiment or the group to which the animal belonged. There was 1 to 3+ edema, hemorrhage, and inflammation (polymorphonucleocytes and leukocytes) in all tissue specimens without any evidence of differences among the three groups. This is in contrast to the groups that received no endotoxin, in which none of the animals had evidence of edema, hemorrhage, or inflammation.


   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Conclusion
 References
 
In the present study, we were able to demonstrate that short-term feeding of diets containing EPA or EPA and GLA altered the lipid composition of pulmonary surfactant. The FA composition of total surfactant PLs showed significant increases in monounsaturated FAs, predominantly from oleic acid (C18:1 {omega}-9) and total {omega}-3 FA, particularly from EPA, in pigs fed diets enriched with either EPA or EPA and GLA when compared with a diet enriched with LA. Significant decreases in total {omega}-6 FAs, with predominantly decreased LA (C18:2 {omega}-6), were observed in pigs fed diets B and C when compared with pigs fed diet A.

Despite these changes within the PUFA pool, the PLs and total PUFAs in pulmonary surfactant did not differ significantly between the groups. PC is the most abundant and important component of pulmonary surfactant. Its FA composition was changed the most by diet B (enriched with EPA), with significant decreases in LA and total {omega}-6 PUFAs. Conversely, there were significant increases in oleic acid, EPA, and docosahexaenoic acid. Diet C (enriched with EPA and GLA) had similar decreases in LA and total {omega}-6 PUFAs, but no significant increases in EPA or docosahexaenoic acid, although oleic acid was almost twice that found in animals fed diet A. It is important to note that despite changes in the PUFA composition of the PLs in surfactant, levels of total saturated FAs and palmitic acid (C16:0) were lower but not statistically different in pigs fed diets B and C compared with pigs fed diet A. These changes in specific FAs suggest that short-term enteral feeding with specific diets can influence the alveolar type II epithelial cell to produce surfactant that reflects the FA composition of the diet. This is in agreement with a study by Palombo et al,9 who showed that significant changes in the FA composition of rat lung surfactant could be rapidly achieved by continuous feeding of an enteral diet containing fish oil.

Diet can alter surfactant composition by several mechanisms. A lack of nutrients, ie, starvation, can affect the lipid composition and surface activity of surfactant.23 24 25 Garbagni et al23 studied the effects of daily ingestion of cream vs fasting on pulmonary surface activity in rabbits. Fasting control rabbits had a decrease in surface activity compared with cream-fed rabbits. In this study, however, the PL composition of the surfactant was not measured. Gross et al24 examined the effects of five different diets on PL content of developing rat lung. There was a control group; a fasting group; and a glucose-protein-fat-diet enriched group. Only the control and fast groups had their lungs lavaged and PL content of the surfactant analyzed. The authors concluded that fasting affected the lungs by decreasing lung cell size, not the total number of cells. The total PL and phosphatidyl content in lung tissue and lung lavage was decreased, but not per unit cell mass or per unit protein. Bruno et al,25 also in a study of fasting rats, noted that choline deficiency affected the hepatic concentrations of PC. They did not specifically examine the effects of fasting on FA composition of PLs or on the function of pulmonary surfactant. It is concluded from these three studies that fasting, by decreasing surfactant substrate, alters pulmonary surfactant, with a change in surface activity within the lung. These findings, although of interest, are probably not applicable to humans inasmuch as adipose stores in rodents are small compared with those in humans, and even a brief fast would be anticipated to have more of an effect in this animal model than it would in humans, in which one might expect to see alterations only after long-term starvation.

Additional proof of the effect of diet on surfactant comes from studies in which the addition of exogenous palmitate increased choline incorporation into PC (25% increase).26 Several other studies have demonstrated that alterations in the surfactant substrate pool (by the addition of different lipid precursors) can alter the FA composition of surfactant.27 28 29 In a study of rats, examining specifically the effects of fish (menhaden) oil on fetal lung PL content, significant differences in concentrations of {omega}-6 and {omega}-3 FAs were noted.27 Swanson et al29 noted that the FA composition of surfactant in mice could be altered by consumption of menhaden oil, but continual ingestion was necessary to maintain the modifications and FA composition of PLs that they measured. Baybutt et al,30 in a study of rats, suggested that dietary {omega}-3 FAs stimulate synthesis and/or inhibit degradation of lung surfactant without altering surfactant secretion in alveoli. In another rat study, Archer et al31 fed rats a fish oil-supplemented diet for 1 month. They found an increase in {omega}-3 FAs in lung PLs, but without any effect on cardiopulmonary function.

Others, however, have noted effects of dietary alteration on the mechanical properties of the lungs; posttraumatic rats fed parenterally had an improvement in their static lung compliance and total lung capacity if lipids were infused as part of the nutrition regimen.32

Why the observed changes in surfactant did not lead to changes in function, as observed in these other studies, may be explained by the fact that in our study, animals had endotoxin administered for 4 h and an additional 2 h elapsed before an assessment of pulmonary surfactant or of pulmonary function. The half-life of pulmonary surfactant is reported to be between 6 and 14 h in several species.33 Endotoxin has the potential to shorten the half-life of surfactant by a variety of mechanisms, including an elevation in catecholamines34 and free FAs.35 If endotoxin increases the turnover of surfactant, then the newly formed surfactant might more reflect the current blood lipid profile, also known to be altered by {omega}-3 diets.3

Although we did see a change in FA composition of the pulmonary surfactant, we did not see an alteration in the P-V curves of the lungs. It is known that ALI will affect P-V curves,36 but in our study, all three groups of animals were given endotoxin. Although endotoxin may have altered P-V curves, there were no differences among groups, independent of the changes we saw in the FA composition of the pulmonary surfactant. Nor did we see an alteration in the surface tension of isolated surfactant. The lipid composition of the surfactant can affect the physical properties of surfactant, but we did not see such changes.

We believe this information is significant because the pig diets that were supplemented with EPA and GLA have been demonstrated to have a beneficial metabolic effect in animal models of sepsis-induced ARDS3 4 5 6 7 8 and in patients with or at risk of ARDS who were fed diets supplemented with GLA and EPA.37 The fact that these diets do affect the physiologic profile of pigs and humans during ALI indicates that the diets were working by mechanisms independent of changes in surfactant.

Finally, we note that in the present study, discrete subpopulations of surfactant, eg, lamellar tubular myelin, were not examined, only total surfactant.1 Isolation of discrete subpopulations may demonstrate that the FA changes we found in total surfactant were not found in the surface film and, therefore, could not affect surface tension. Whatever the changes in FA composition of total surfactant or of lamellar surfactant, we are confident that the dietary changes we induced did not affect the surface activity of the surfactant or the physical properties of the surfactant in terms of the P-V curves that we measured.


   Conclusion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
References
 
Diets containing EPA or EPA and GLA have the potential to alter the PUFA composition of pulmonary surfactant, but without demonstrable effects on surfactant function during early endotoxemia


   Acknowledgements
 
The authors thank Lynn Harstad for her superb technical assistance and Kathy Dailey and Robin Williams for their excellent secretarial assistance in the preparation of the manuscript.


   Footnotes
 
Abbreviations: ALI = acute lung injury; EPA = eicosapentaenoic acid; FA = fatty acids; FAME = fatty acid methyl esters; GC = gas chromatography; GLA = {gamma}-linolenic acid; LA = linoleic acid; PC = phosphatidylcholine; PL = phospholipid; PUFA = polyunsaturated fatty acids; P-V = pressure-volume

Supported by Ross Products Division and Mayo Foundation.

Received for publication March 11, 1998. Accepted for publication December 8, 1999.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 

  1. King, RJ, Clements, JA (1985) Lipid synthesis and surfactant turnover in the lungs. Fishman, AP Fisher, AB eds. Handbook of physiology: the respiratory system ,309-336 American Physiological Society Bethesda, MD.
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  6. Mancuso, P, Whelan, J, DeMichele, SJ, et al (1997) Effects of eicosapentaenoic and gamma-linolenic acid on lung permeability and alveolar macrophage eicosanoid synthesis in endotoxic rats. Crit Care Med 25,523-532[CrossRef][ISI][Medline]
  7. Palombo, JD, DeMichele, SJ, Lydon, E, et al (1996) Rapid modulation of lung and liver macrophage phospholipid fatty acids in endotoxemic rats by continuous enteral feeding with {omega}-3 and gamma-linolenic fatty acids. Am J Clin Nutr 63,208-219[Abstract/Free Full Text]
  8. Palombo, ID, DeMichele, SJ, Lydon, E, et al (1997) Cyclic vs continuous enteral feeding with {omega}-3 and gamma-linolenic fatty acids: effect on modulation of phospholipid fatty acids in rat lung and liver macrophages. JPEN J Parenter Enteral Nutr 21,123-132[Abstract]
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  11. Baritussio, A, Enzi, G, De Biasi, D, et al (1978) The elastic properties of the lung in hyperlipidemias. Crepaldi, G Lefebvre, PJ Alberti, KLMM eds. Diabetes, obesity and hyperlipidemias ,325-329 Academic Press London.
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  13. Wright, JR, Clements, JA (1987) Metabolism and turnover of lung surfactant. Am Rev Respir Dis 135,426-444[ISI][Medline]
  14. Enhorning, G (1977) Pulsating bubble technique for evaluating pulmonary surfactant. J Appl Physiol 43,198-203[Abstract/Free Full Text]
  15. Bligh, EG, Dyer, WJ (1959) A rapid method of total lipid extraction and purification. Can J Biochem Physiol 37,911-917
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