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Ann Thorac Surg 1997;64:826-829
© 1997 The Society of Thoracic Surgeons

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Original Article: Cardiovascular

Postinjury Thromboxane Receptor Blockade Ameliorates Acute Lung Injury

Departments of Surgery, University of Virginia Health Sciences Center, Charlottesville, and Roanoke Memorial Hospitals, Roanoke, Virginia

Accepted for publication March 29, 1997.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. Acute lung injury is associated with pulmonary hypertension, intrapulmonary shunting, and increased microvascular permeability, leading to altered oxygenation capacity. Thromboxane A₂ has been found to be a central mediator in the development of septic and oleic acid (OA)–induced acute lung injury. Our previous study demonstrated a beneficial effect of preinjury thromboxane A₂ receptor blockade. The current study examines the efficacy of postinjury receptor blockade on oxygenation capacity and pulmonary hemodynamics in an isolated lung model of OA-induced acute lung injury.

Methods. Four groups of rabbit heart-lung preparations were studied for 60 minutes in an ex vivo perfusion-ventilation system. Saline control lungs received saline solution during the first 20 minutes of study. Injury control lungs received an OA-ethanol solution during the first 20 minutes. Two treatment groups were used: T10, in which the thromboxane receptor antagonist, SQ30741, was infused 10 minutes after the initiation of OA infusion; and T30, in which the thromboxane receptor antagonist was infused 30 minutes after OA infusion.

Results. Significant differences were found in oxygenation (oxygen tension in T10 = 62.6 ± 11.7 mm Hg, T30 = 68.2 ± 21.2 mm Hg; injury control = 40.2 ± 9.0 mm Hg, saline control = 123.5 ± 16.01 mm Hg; p < 0.001) and percentile change in pulmonary artery pressure (T10 = 1.1% ± 19.4% increase, T30 = 11.2% ± 7.3% increase; injury control = 47.6% ± 20.5%, saline control = 4.2% ± 6.81%; p < 0.001).

Conclusions. This study demonstrates that blockade of the thromboxane A₂ receptor, even after the initiation of acute lung injury, eliminates pulmonary hypertension and improves oxygenation.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Acute lung injury (ALI) contributes significantly to the high morbidity and mortality of critically ill patients [1, 2]. A variety of diseases and conditions can induce ALI. Despite similarities in clinical presentation, the underlying pathophysiologic mechanisms contributing to the development of ALI are not totally understood. Respiratory dysfunction in ALI results from pathologic changes at the alveolar-capillary membrane, making elucidation of these mechanisms of injury at the cellular level essential in devising effective treatment strategies.

Thromboxane has been implicated as a mediator of ALI. Its active form is thromboxane A₂ (TXA₂), which is produced in the cyclooxygenase pathway of arachidonic acid metabolism. Our previous study [3] proved that TXA₂ receptor blockade pretreatment improved oxygenation in ALI caused by oleic acid (OA) infusion. The current study was designed to determine whether TXA₂ receptor blockade after the initiation of ALI is beneficial, because pretreatment is unlikely in a clinical setting.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
We studied a model of ALI using an apparatus containing ex vivo, isolated, whole-blood–perfused lungs. Our protocol was approved by the University of Virginia Animal Research Committee, and all animals were cared for in accordance with institutional guidelines, as well as those set forth by the National Institutes of Health.

New Zealand White rabbits, each weighing 3 to 4 kg, were anesthetized with intramuscular injections of xylazine (20 mg) and ketamine (200 mg). After tracheostomy, the animals were ventilated mechanically and ear vein cannulation was performed. Median sternotomy was performed, and systemic anticoagulation was achieved with 1,000 U of intravenous heparin. The heart and great vessels were isolated, cannulated, and flushed with saline solution. The entire heart-lung preparation then was explanted en bloc, and was placed immediately into an ex vivo apparatus for study.

The isolated lungs were ventilated continuously by a pressure-controlled small animal ventilator (Kent Scientific, Litchfield, CT) at a rate of 20 breaths/min and an inspired oxygen fraction of 0.21. Continuous blood perfusion was achieved with a Masterflex roller pump (Cole Palmer, Chicago, IL) at a rate of 60 mL/min. Blood was recirculated through a 150-mL reservoir filled with 1,000 U of heparinized blood collected from separate donor rabbits at the time of lung harvest. Perfusate hematocrit was maintained at 25% to 30% for each trial. Infusions entered the circuit through a sideport in the inflow channel and were controlled by a Harvard pump infusion system.

This circuit allowed direct measurement of tidal volume (in milliliters), pulmonary artery pressure (PAP; in millimeters of mercury), and lung weight (in grams) at 15-second intervals. Pulmonary venous pressure (in millimeters of mercury) also was measured, but it was fixed at 5 mm Hg based on the height of the outflow channel. Calculated variables included pulmonary vascular resistance (PVR; in dynes • second per centimeter quintupled) and dynamic pulmonary compliance. All variables were recorded continuously by computer and displayed on an adjacent monitor. These data were used later to calculate dynamic pulmonary compliance, as well as percentile changes in tidal volume, lung weight, PAP, and PVR. In addition, a separate reservoir of fresh venous blood was used to obtain outflow blood gases at baseline and at 20-minute intervals. These values, along with blood gases obtained simultaneously from the venous reservoir, were used to determine changes in the lungs' capacity to oxygenate. Measurement of oxygenation capacity was calculated as follows: [AVO₂ difference = arterial (outflow) PO₂ - venous (inflow) PO₂]. Percentile change in oxygenation = [AVO₂ (0 minutes) - AVO₂ (30 minutes)]/ AVO₂ (0 minutes), where AVO₂ = arteriovenous oxygen and PO₂ = partial pressure of oxygen.

If tidal volume, PAP, and weight remained constant for 15 minutes after immediate equilibration, the preparations were considered to be stable and further study was undertaken. All lung preparations were assigned to one of four study groups and were studied for a period of 60 minutes. The saline control (SC) group received a continuous infusion of normal saline, which began at 0 minutes and continued at 0.006 mL/min for 20 minutes, for a total infusion volume of 0.12 mL. The injury control (IC) group received a continuous infusion solution of 50% OA and 50% ethanol, which began at 0 minutes and continued at 0.006 mL/min for 20 minutes, for a total infusion volume of 0.12 mL. Ethanol solubilized the OA to provide a diffuse injury. Previous controls demonstrated no hemodynamic or histologic changes when ethanol was used at these volumes. Two treatment groups underwent the same OA infusion as the IC group, but they also received a bolus of 6 mg of the thromboxane receptor antagonist, SQ30741. This was added to the blood perfusate at 10 and then at 30 minutes after the initiation of OA infusion. All variables were recorded as described previously, and blood gases were obtained at 0, 20, and 40 minutes. On completion of the study, tissue samples were taken from all lungs for histologic evaluation of parenchymal injury. The evaluations were performed by a pulmonary pathologist who was blinded to the specimen groups. The tissue samples were examined for edema, capillary thrombi, and hemorrhage.

All data collected from the four study groups were analyzed using analysis of variance. When significant differences existed between the groups, Tukey's Honestly Significant Difference test was used to determine where the differences existed. Each study group consisted of eight isolated lung preparations.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
There were significant differences in the percentile change in PAP at the end of the 60-minute perfusion period (p < 0.001) (Table 1) in the IC group, as compared with the three remaining groups. There was no significant difference between the SC group and the two treatment groups (Fig 1). The oxygenation capacity of the SC group was significantly higher than that of the other groups at 40 and 60 minutes (p < 0.001). The oxygenation capacity of the two treatment groups was significantly higher than that of the IC group at 40 minutes (p < 0.001), but not at 60 minutes, although a trend existed toward improved oxygenation among the treatment groups at 60 minutes (Figs 2, 3).

View larger version (17K): [in this window] [in a new window]   Fig 1. . Percentile change in pulmonary artery pressure (PAP) from baseline to 60 minutes between saline control (SC), oleic acid injury control (IC), and treatment with a thromboxane A2 receptor blocker 10 minutes (T10) and 30 minutes (T30) after oleic acid infusion. (*p < 0.001 compared with SC, T10, and T30 groups.)

View larger version (17K): [in this window] [in a new window]   Fig 2. . Arteriovenous oxygen (AVO2) difference at 40 minutes after the initiation of acute lung injury. (IC = injury control; SC = saline control; T10 = 10 minutes after oleic acid infusion; T30 = 30 minutes after oleic acid infusion; *p < 0.001 versus SC; #p < 0.001 versus IC.)

View larger version (15K): [in this window] [in a new window]   Fig 3. . Arteriovenous oxygen (AVO2) difference 60 minutes after the initiation of acute lung injury. (IC = injury control; saline control (SC); T10 = 10 minutes after oleic acid infusion; T30 = 30 minutes after oleic acid infusion; *p < 0.001 versus SC.)

Histologically, six of eight preparations from the SC group showed no evidence of injury, as compared with one of eight preparations from the IC group. Three of seven preparations from the T10 group (one specimen was lost) and three of eight from the T30 group showed no evidence of injury (no significant differences except between IC and SC groups).

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Acute lung injury, as manifested clinically by adult respiratory distress syndrome in the critically ill patient, continues to be a difficult disease process to manage, despite the many recent technologic advances in intensive care medicine. To develop new treatment options and improve patient outcome, it is necessary (1) to create an animal model that mimics the pathologic and physiologic processes present in human ALI, and (2) to use pharmacologic interventions to delineate the molecular and cellular pathways that contribute to the initiation and progression of ALI, which are complex and poorly understood. Both local and systemic inflammatory factors may play a role in the evolution of adult respiratory distress syndrome.

Adult respiratory distress syndrome, as seen clinically, is a difficult process to re-create experimentally in animal models. Oleic acid infusion is a widely used and accepted model for studying the effects of ALI in experimental animal models [4–8]. As pointed out by Schuster [4], OA-induced ALI produces many pathologic and nonpathologic features that are similar to the findings in adult respiratory distress syndrome. Among these similarities is increased thromboxane production [4, 9, 10]. Thromboxane A₂, a byproduct of the cyclooxygenase pathway, is a potent vasoconstrictor that promotes platelet aggregation and increases airway resistance [11]. Fourfold to fivefold increases in thromboxane B₂ (the stable metabolite of TXA₂) have been reported in dogs and rabbits after OA injury [12–14]. Stephenson and colleagues [15] and Schuster and associates [16] found that the spontaneous perfusion redistribution that occurred after OA injury primarily is due to increased levels of TXA₂. Thus, TXA₂ is believed to be the preponderate eicosanoid in OA-induced ALI. Thromboxane A₂ also plays a role in ALI induced experimentally by staphylococcal toxin [17], ischemia-reperfusion [18], lipopolysaccharide [19], hydrogen peroxide [20], and arachidonic acid induction [21]. Therefore, OA-induced ALI results in thromboxane generation, which causes pulmonary hypertension with enhanced edema formation. Kukkonen and colleagues [22] found that thromboxane receptor blockade did not ameliorate the pulmonary hypertension or decrease in oxygenation found in porcine lungs after transplantation.

Our previous studies have shown a salutary effect of pretreatment with a thromboxane receptor antagonist, improving pulmonary hypertension and oxygenation, as well as the pathologic changes seen after OA-induced ALI [3]. Because pretreatment is unlikely in most clinical situations, we investigated the effect of posttreatment on lung injury. We found that postinjury treatment had a beneficial effect on oxygenation and pulmonary hypertension when compared with IC. Histologically, there was a trend toward less interstitial edema, capillary thrombi, and hemorrhage among the treatment groups. However, the protection afforded was significantly less than that seen when pretreatment was used. A likely explanation is that OA exerts a direct toxic effect on the alveolar-capillary interface, as well as the vascular endothelium, which is mediated partly, but not completely, by TXA₂. The finding that oxygenation was affected, even though PAPs between the treatment groups and the SC group were not significantly higher, supports this explanation. This suggests that the effect of OA, and possibly other mediators of ALI, is not caused solely by elevation of PAP, elevation of hydrostatic pressure, and subsequent intraalveolar edema. A direct effect on the capillary-alveolar interface also is present and plays a significant role. Of interest is the finding that treatment with a thromboxane receptor antagonist as long as 30 minutes after OA infusion can prevent the pulmonary hypertension seen in the IC group. Thus, it is evident that the effect of OA on thromboxane production is either persistent or that the thromboxane generated remains active after the OA infusion is stopped.

In this experiment, we found that posttreatment with a thromboxane receptor antagonist abolished the changes in PAP found after OA infusion, but did not block completely their deleterious effect on oxygenation. These results lead us to conclude that thromboxane plays a role in the change in pulmonary vascular reactivity that occurs after OA infusion, as well as a possible role in the endothelial injury that leads to interstitial edema formation and impaired oxygenation. Thromboxane A₂ receptor blockade may provide an effective treatment modality in ameliorating ALI in the clinical setting.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Address reprint requests to Dr Young, Department of Surgery, University of Virginia Health Sciences Center, PO Box 10005, Charlottesville, VA 22906-0005.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

1. Taylor RW, Norwood SH. The adult respiratory distress syndrome. In: Civetta JM, ed. Critical care. Philadelphia: Lippincott, 1992:1237.
2. Rochon RB, Rice CL, Carroci CJ. Adult respiratory distress syndrome. In: Shields TW, ed. General thoracic surgery, 4th ed. Baltimore: Williams & Wilkins, 1994:788.
3. Thies SD, Corbin RS, Goff CD, et al. Thromboxane receptor blockade improves oxygenation in an experimental model of acute lung injury. Ann Thorac Surg 1996;62:1453–7.
4. Schuster D. ARDS: clinical lessons from the oleic acid model of acute lung injury. Am J Respir Crit Care Med 1994;149:245–60.[Medline]
5. Leeman M, Lejeune P, Closset J, et al. Nature of pulmonary hypertension in canine oleic acid pulmonary edema. J Appl Physiol 1990;69:293–8.[Abstract/Free Full Text]
6. Leeman M, Lejeune P, Melot C, Naerje R. Pulmonary vascular pressure-flow plots in canine oleic acid pulmonary edema. Am Rev Respir Dis 1988;138:362–7.[Medline]
7. Tomashefski JF. Pulmonary pathology of the adult respiratory distress syndrome. Clin Chest Med 1990;11:593–619.[Medline]
8. Derks CM, Jacobovitz-Derks D. Embolic pneumopathy induced by oleic acid. Am J Pathol 1977;87:143–58.[Abstract]
9. Maarek JM, Grimbert F. Segmental pulmonary vascular resistances during oleic acid lung injury in rabbits. Respir Physiol 1994;98:179–91.[Medline]
10. Deby-Dupont G, Braun M, Lamy M, et al. Thromboxane and prostacyclin release in adult respiratory distress syndrome. Intensive Care Med 1987;13:167–74.[Medline]
11. Buzzard CJ, Pfister SL, Campbell WB. Endothelium-dependent contractions in rabbit pulmonary artery are mediated by thromboxane A2. Circ Res 1993;72:1023–34.[Abstract/Free Full Text]
12. Katz SA, Halushka PV, Wise WC, Cook JA. Oleic acid induces pulmonary injury independent of eicosanoids in the isolated, perfused rabbit lung. Circ Shock 1987;22:221–30.[Medline]
13. Olanoff LS, Reines HD, Spicer KM, Halushka PV. Effects of oleic acid on pulmonary capillary leak and thromboxanes. J Surg Res 1984;36:597–605.[Medline]
14. Tachmes L, Adler H, Wolozsyn TT, et al. Role of arachidonic acid metabolites in oleic acid induced pulmonary injury in a canine model: effects of ketoconazole (thromboxane synthetase inhibitor). Am Surg 1991;3:171–7.[Medline]
15. Stephenson AH, Lonigro AJ, Holmberg SW, Schuster DP. Eicosanoid balance and perfusion redistribution of oleic-acid induces acute lung injury. J Appl Physiol 1992;73:2126–34.[Abstract/Free Full Text]
16. Schuster DP, Sandoferd P, Stephenson AH. Thromboxane receptor stimulation/inhibition and perfusion redistribution after acute lung injury. J Appl Physiol 1993;75:P2069–78.
17. Seeger W, Baner M, Bhakdi S. Staphylococcal alpha-toxin elicits hypertension in isolated rabbit lungs. J Clin Invest 1984;74:849–59.[Medline]
18. Zamora CA, Baron DA, Heffner JE. Thromboxane contributes to pulmonary hypertension in ischemia-reperfusion lung injury. J Appl Physiol 1993;231:13–21.
19. Arimura A, Asanuma F, Yagi H, Kurosawa A, Harada M. Involvement of thromboxane A2 in bronchial hyperresponsiveness but not lung inflammation induced by bacterial lipopolysaccharide in guinea pigs. Eur J Pharmacol 1993;231:13–21.[Medline]
20. Corten I, Peeters FAM, Rampart M, et al. Ridogrel prevents the thromboxane-mediated pressor response and oedema induced by hydrogen peroxide in isolated rabbit lungs. Eur J Pharmacol 1991;201:83–90.[Medline]
21. Littner MR, Lott FD. Edema from cyclooxygenase products of endogenous arachidonic acid in isolated lung. J Appl Physiol 1989;67:846–55.[Abstract/Free Full Text]
22. Kukkonen S, Heikkila L, Verkkala K, Mattila S, Toivonen H. Thromboxane receptor blockade does not attenuate pulmonary pressor response in porcine single lung transplantation. J Heart Lung Transplant 1996;15:409–14.[Medline]

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Curtis G. Tribble Irving L. Kron Jeffrey S. Young Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Goff, C. D. Articles by Young, J. S. Search for Related Content PubMed PubMed Citation Articles by Goff, C. D. Articles by Young, J. S.