Pulmonary inflammation alters the lung disposition of lipophilic amine indicators.

Many lipophilic amine compounds are rapidly extracted from the blood on passage through the pulmonary circulation. The extent of their extraction in normal lungs depends on their physical-chemical properties, which affect their degree of ionization, lipophilicity, and propensity for interacting with blood and tissue constituents. The hypothesis of the present study was that changes in the tissue composition that occur during pulmonary inflammation would have a differential effect on the pulmonary extraction of lipophilic amines having different properties. If so, measurement of the extraction patterns for a group of lipophilic amines, having different physical-chemical properties, might provide a means for detecting and identifying lung tissue abnormalities. To evaluate this hypothesis, we measured the pulmonary extraction patterns for four lipophilic amines, [(14)C]diazepam, [(3)H]alfentanil, [(14)C]lidocaine, and [(14)C]codeine, along with two hydrophilic compounds, (3)HOH and [(14)C]phenylethylamine, after the bolus injection of these indicators into the pulmonary artery of isolated lungs from normal rabbits and from rabbits with pulmonary inflammation induced by an intravenous injection of complete Freund's adjuvant. The pulmonary extraction patterns, parameterized using a previously developed mathematical model, were, in fact, differentially altered by the inflammatory response. For example, the tissue sequestration rate, k(seq) (ml/s), per unit (3)HOH accessible extravascular lung water volume significantly increased for diazepam and lidocaine, but not for codeine and alfentanil. The results are consistent with the above hypothesis and suggest the potential for using lipophilic amines as indicators for detection and quantification of changes in lung tissue composition associated with lung injury and disease.     

Pulmonary blood volume and edema in postpneumonectomy lung growth in rats

After pneumonectomy in young animals, the contralateral lung undergoes compensatory growth and generally attains the same weight and air space volume as both lungs in age-matched controls. In this study, we determined the contribution of lung edema and increased blood volume to the weight gain in rats. Three weeks after pneumonectomy (n = 18) or sham pneumonectomy (n = 17), the pulmonary blood volume and the extravascular water and albumin were evaluated by use of 51Cr-labeled erythrocytes and 125I-labeled albumin. The air space volume, blood-free lung weights, and DNA and protein content were also compared. The data show that the total pulmonary blood volumes and the blood volume per gram of blood-free dry lung were similar in pneumonectomized and age-matched sham controls. The total extravascular albumin and the extravascular albumin per gram of blood-free dry lung were also similar as well as the extravascular lung water, wet-to-dry weight ratios, DNA and protein content, and air space volumes. These data indicate that the increased weight of the postpneumonectomy lung was due to cellular and stromal proliferation. The blood volume and interstitial fluid increased in proportion to the increase in lung parenchyma. Neither vascular congestion nor increased extravascular protein and water contributed to the observed weight gain.     

Pulmonary angiotensin-converting enzyme substrate hydrolysis during exercise.

We examined exercise-induced changes in indicator-dilution estimates of the angiotensin-converting enzyme first-order kinetic parameter, the ratio of a normalized maximal enzymatic conversion rate to the Michaelis constant (Amax/Km), which, under stable enzymatic conditions, will vary with the pulmonary vascular surface area accessible to vascular substrate, the extravascular lung water (an index of the proportion of lung tissue perfused), and the central blood volume (from pulmonary trunk to aorta). Experiments were performed in 10 mongrel dogs at rest and through two increasing levels of treadmill exercise, with the use of two vascular space tracers (labeled erythrocytes and albumin), a water space tracer ([1,8-14C]-octanediol), and a vascular endothelium surface area marker, benzoyl-Phe-Gly-Pro ([3H]BPGP), which is a pharmacologically inactive angiotensin-converting enzyme substrate. The exercise-induced increase in cardiac output was accompanied by a linear increase in central blood volume, and dilutional extravascular lung water rapidly increased to an asymptotic proportion close to 100% of postmortem vascular lung water. There was an average 55% [3H]BPGP hydrolysis, which did not vary with flow, and the computed Amax/Km increased linearly with exercise. We conclude that exercise results in complete lung tissue recruitment and increases the pulmonary vascular surface area available for BPGP hydrolysis linearly with flow, so that pulmonary vascular recruitment continues after full tissue recruitment.     

Measurement of lung fluid volumes and albumin exclusion in sheep

A radioactive tracer technique was used to determine interstitial diethylenetriaminepentaacetic acid (DTPA) and albumin distribution volume in sheep lungs. 125I- and/or 131I-labeled albumin were injected intravenously and allowed to equilibrate for 24 h. 99mTc-labeled DTPA and 51Cr-labeled erythrocytes were injected and allowed to equilibrate (2 h and 15 min, respectively) before a lethal dose of thiamylal sodium. Two biopsies (1-3 g) were taken from each lung and the remaining tissue was homogenized for wet-to-dry lung weight and volume calculations. Estimates of distribution volumes from whole lung homogenized samples were statistically smaller than biopsy samples for extravascular water, interstitial 99mTc-DTPA, and interstitial albumin. The mean fraction of the interstitium (Fe), which excludes albumin, was 0.68 +/- 0.04 for whole lung samples compared with 0.62 +/- 0.03 for biopsy samples. Hematocrit may explain the consistent difference. To make the Fe for biopsy samples match that for homogenized samples, a mean hematocrit, which was 82% of large vessel hematocrit, was required. Excluded volume fraction for exogenous sheep albumin was compared with that of exogenous human albumin in two sheep, and no difference was found at 24 h.     

The use of an "internal standard" for control of the recovery in microdialysis

Microdialysis of intravenously injected theophylline in blood and in lung tissue was performed in two rats during anaesthesia. The recovery (dialysate extraction fraction) in blood was greater than the recovery in lung tissue and there was a change in recovery with time both in blood and in lung. The concentrations of theophylline in the dialysates were corrected for the recovery using caffeine as an "internal standard" in the perfusate as well as tritiated water injected into the rats. There was excellent agreement between the two different methods. Furthermore, the corrected concentration of unbound theophylline in the blood was in accordance with the simultaneously measured total concentration of theophylline in plasma when binding to plasma proteins was taken into account. The conclusion is that an "internal standard" for correction of the recovery is a useful method to approach the true concentrations of compounds in the extracellular water. The "internal standard" must be as equal as possible to the substance of interest.     

Toluidine blue O and methylene blue as endothelial redox probes in the intact lung

There is increasing evidence that the redox activities of the pulmonary endothelial surface may have important implications for the function of both lungs and blood. Because of the inherent complexity of intact organs, it can be difficult to study these activities in situ. Given the availability of appropriate indicator probes, the multiple-indicator dilution (MID) method is one approach for dealing with some aspects of this complexity. Therefore, the objectives of the present study were to 1) evaluate the potential utility of two thiazine redox indicators, methylene blue (MB) and toluidine blue O (TBO), as MID electron acceptor probes for in situ pulmonary endothelium and 2) develop a mathematical model of the pulmonary disposition of these indicators as a tool for quantifying their reduction on passage through the lungs. Experiments were carried out using isolated rabbit lungs perfused with physiological salt solution with or without plasma albumin over a range of flow rates. A large fraction of the injected TBO disappeared from the perfusate on passage through the lungs. The reduction of its oxidized, strongly polar, relatively hydrophilic blue form to its colorless, highly lipophilic reduced form was revealed by the presence of the reduced form in the venous effluent when plasma albumin was included in the perfusate. MB was also lost from the perfusate, but the fraction was considerably smaller than for TBO. A distributed-in-space-and-time model was developed to estimate the reduction rate parameter, which was approximately 29 and 1.0 ml/s for TBO and MB, respectively, and almost flow rate independent for both indicators. The results suggest the utility particularly of TBO as an electron acceptor probe for MID studies of in situ pulmonary endothelium and of the model for quantitative evaluation of the data.     

Influence of size of emboli on extravascular lung water

We examined the influence of the size of emboli on the vascular volume (QL) and extravascular volume (Qev) accessible to 3HOH during a single pass through an isolated dog lung lobe using the double indicator-dilution method with 125I-human serum albumin as the vascular indicator. As successively more beads of a given diameter (58, 548, or 3,175 microns) were introduced into a lung lobe, a linear relationship between QL and Qev was obtained as they both decreased. The slope of the graph of QL vs. Qev with progressive embolism was directly proportional to the bead diameter. This suggested an approach for estimating the total vascular volume in vessels smaller than the diameter of the beads before embolization, referred to as Qm. If it is assumed that most of the transvascular diffusional exchange of 3HOH occurs in vessels smaller than the smallest beads (mainly capillaries) and that vessel obstruction does not change the ratio of Qev to the perfused capillary volume, the slope of the plot of QL vs. Qev is an estimate of the fraction, Qm/QL, of the total vascular volume in vessels smaller than the bead diameter. In the dog lung lobes studied, Qm/QL was approximately 0.64 for 58-microns vessels, 0.75 for 548-microns vessels, and 0.82 for 3,175-microns vessels. The results suggest that, with occlusion of vessels greater than or equal to 58 microns, 3HOH does not diffuse significantly into unperfused regions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional extravascular and interstitial lung water in normal dogs

We measured the regional distribution of pulmonary extravascular and interstitial water to examine the possibility that regional differences in microvascular pressure or tissue stress may cause regional differences in lung water. We placed chloralose-anesthetized dogs in an upright (n = 6) or supine (n = 7) position for 180 min. We injected 51Cr-labeled EDTA to equilibrate to the extracellular space and 125I-labeled albumin to equilibrate with plasma. At the end of the experiment, the lungs were removed, passively drained of blood, and inflated before rapid freezing. Lungs were divided into horizontal slices, and extravascular, interstitial, and plasma water, red cell volume, and dry lung weight were determined for each slice. We found that regional extravascular and interstitial water were constant throughout the lungs in both groups and that there were no significant differences between upright and supine dogs. There were no significant differences in hematocrit between slices. We conclude that gravity and body position have no measurable effect on either the total size of the extravascular and interstitial compartments or their regional distribution.     

Alveolar vessel behavior in the zone 2 lung inferred from indicator-dilution data

To gain insight into the changes occurring in alveolar vessels when alveolar pressure exceeds venous pressure at the downstream end of the alveolar vessels (zone 2), we compared the uptake of serotonin and the extravascular volume accessible to 3HOH (Qev) under zone 2 and 3 conditions in isolated dog lung lobes. We also examined the influence of occluding some of the small pulmonary arteries with 58- to 548-micron-diam beads on the serotonin uptake and Qev. We found that, with the bead embolization, both the serotonin uptake and the Qev were reduced, whereas the change from zone 3 to 2 reduced serotonin uptake but did not change Qev. A plausible explanation for these observations is that the beads occluded vessels that were relatively large compared with those in which significant transvascular 3HOH exchange and serotonin uptake take place. Perfusion ceased in the collection of capillaries normally served by the obstructed arteries. Thus the extravascular water and the serotonin uptake sites downstream from the obstructions were not accessible to the indicators during the short time interval of the indicator passage through the lung. On the other hand, the change from zone 3 to zone 2 resulted in the collapse of small individual capillary segments within the alveolar vessel bed. Since the serotonin does not readily diffuse from the vessels through the tissue, it could not reach the endothelial cells of the collapsed capillaries. However, since the distances for diffusion between collapsed capillaries and neighboring perfused capillaries were small, the more highly diffusible 3HOH had access to the same Qev under both zone 2 and 3 conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Vascular permeability and late radiation fibrosis in mouse lung

It has been suggested that fibrosis which develops after irradiation is caused by increases in vascular permeability. Plasma proteins leak into irradiated tissue where fibrinogen may be converted into fibrin which is gradually replaced by fibrous tissue. Vascular and fibrotic changes in mouse lung were investigated after X irradiation of the right hemithorax. Blood volume and accumulation of extravascular proteins were measured using indium (111In)-labeled red cells, iodinated (131I) albumin, and iodinated (125I) fibrinogen. Tracers were injected 1-47 weeks after irradiation and lungs were excised 24 or 96 hr later to determine radioactivity. The amount of collagen was estimated by measuring the hydroxyproline content. During the first few months after X rays, lung blood volume decreased to a plateau which depended on radiation dose (10-25 Gy). Small increases in extravascular albumin and fibrinogen occurred at 1-12 weeks after 10-25 Gy. Subsequently, protein returned to normal after 10 Gy, remained elevated after 15 Gy, and increased after 20 and 25 Gy. Hydroxyproline per gram of dry irradiated lung was increased at 18 weeks after 15-25 Gy. Subsequently it showed little change although both total hydroxyproline content and dry weight decreased after 20 and 25 Gy. Support for the hypothesis was that hydroxyproline per gram only increased after X-ray doses which caused marked extravasation of protein. There was no evidence, however, for deposition of 125I-fibrin or for a gradual increase in fibrosis corresponding to the prolonged excess of extravascular protein.     

Influence of hypoxia on the longitudinal distribution of pulmonary vascular resistance

We have examined the influence of hypoxia on the longitudinal distribution of vascular resistance and intravascular pressure in isolated cat lungs using the low-viscosity bolus technique. Hypoxia increased total vascular resistance, decreased total lung blood volume, and moved the maximum local resistance downstream away from the main pulmonary artery. The circumference of the main pulmonary artery was increased and the extravascular lung water (double indicator dilution technique) was decreased by hypoxia. Thus, it would appear that distension of the large pulmonary arteries and a decrease in the amount of lung tissue perfused contributed to the change in resistance distribution brought about by hypoxia.     

Carbonic anhydrase activity of rabbit lungs

Pulmonary carbonic anhydrase (CA) activity was studied in rabbit lungs perfused with solutions containing no CA. Measurements were made of the amount of 14CO2 appearing in the expired gas following injections of H14CO3(-), 14CO2, or a 20:1 mixture of each into the pulmonary artery. The fraction of the injected label in the expired gas was only 17% greater for 14CO2 than for the mixture, suggesting that equilibration between H14CO3(-) and 14CO2 was nearly complete during the capillary transit time. Inhibition of pulmonary CA decreased excretion of H14CO3(-) and the mixture by 40 and 49% and increased the excretion of 14CO2 by 96%. Addition of CA to the perfusate had no effect. Thus, CO2 exchange is not significantly limited by pulmonary CA if inhibitors are absent. Tissue binding of [3H]acetazolamide injected into the pulmonary artery was diminished by 50% when acetazolamide concentrations reached 0.13 x 10(-6) M. Each liter of extravascular lung water contained 1.25 x 10(-6) mol of receptors for acetazolamide that were accessible to plasma during a single circulation. Binding of [3H]acetazolamide was also observed in lungs of anesthetized rabbits, suggesting that pulmonary CA is accessible to plasma in vivo as well as in situ.     

Mechanisms of extracellular reactive oxygen species injury to the pulmonary microvasculature.

We investigated the effect of xanthine (X) plus xanthine oxidase (XO) on pulmonary microvascular endothelial permeability in isolated rabbit lungs perfused with Krebs buffer containing bovine serum albumin (5 g/100 ml). Addition of five mU/ml XO and 500 microM X to the perfusate caused a twofold increase in the pulmonary capillary filtration coefficient (Kf,c) 30 min later without increasing the pulmonary capillary pressure. This increase was prevented by allopurinol or catalase but not by superoxide dismutase or dimethyl sulfoxide. Because these data implicated hydrogen peroxide (H2O2) as the injurious agent, we measured its concentration in the perfusate after the addition of X and XO for a 60-min interval. In the absence of lung tissue and albumin, H2O2 increased with time, reaching a concentration of approximately 250 microM by 60 min. If albumin (5 g/100 ml) was added to the perfusate, or in the presence of lung tissue, the corresponding values were 100 microM and less than 10 microM, respectively. To understand the mechanisms of H2O2 scavenging by lung tissue, we added a 250 microM bolus of H2O2 to the lung perfusate. We found that H2O2 was removed rapidly, with a half-life of 0.31 +/- 0.04 (SE) min. This variable was not increased significantly by inhibition of lung catalase activity with sodium azide or inhibition of the lung glutathione redox cycle with 1-chloro-2,4-dinitrobenzene. However, inhibition of both enzymatic systems increased the half-life of H2O2 removal to 0.71 +/- 0.09 (SE) min (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Reliability of extravascular lung thermal volume measurements by thermal conductivity technique in sheep.

We tested the accuracy, sensitivity, and reproducibility of a new lung water computer, based on the thermal conductivity technique, in 22 anesthetized closed-chest ventilated sheep with different treatments: 1) controls (n = 8), 2) 0.05 ml/kg of oleic acid + 100 ml/kg of lactated Ringer solution (n = 6), and 3) airway instillation of saline [3.1 +/- 1.3 (SD) g/kg, n = 8]. After 4 h, we determined the extravascular lung water gravimetrically. We found a significant overall correlation between the final extravascular lung thermal volume and the gravimetric extravascular lung mass (P < 0.001). Although the average ratio of extravascular lung thermal volume to extravascular lung mass was 0.97 +/- 0.25 ml/g for all groups, the computer overestimated extravascular lung mass in controls by 10% (17 g) and underestimated it in sheep with oleic acid by 15% (95 g) and in sheep with airway instillation by 8% (37 g). The computer also underestimated the small quantities of saline placed via the airway in the alveolar space by 75% (61 g). Reproducibility of three consecutive measurements was 4.3% (SE). We conclude that the thermal conductivity technique has an ability to detect the baseline extravascular lung mass but has a poor ability to detect an accurate increment of the extravascular lung water under poor tissue perfusion in anesthetized ventilated sheep.     

Lymphokine-activated killer cells with interleukin-2: dose toxicity and localization in isolated perfused rat lungs

Lymphokine-activated killer (LAK) cells combined with recombinant interleukin-2 (rIL-2) can produce tumor regression in murine models and in patients with pulmonary metastatic disease. However, the dose escalations of rIL-2 required for optimal therapeutic effect often result in increased vascular permeability ("vascular leak syndrome") and other toxic systemic consequences. To avoid systemic distribution, lung perfusion was used to administer LAK and rIL-2 locally. Preliminary to using these agents to treat tumor-bearing lungs, we used a nonblood-perfused isolated rat lung model to study the localization of radiolabeled rIL-2 and LAK and to characterize effects on normal lung tissue of increasing dosages and exposure times of rIL-2 and LAK cells, individually and combined. Lung function or permeability was assessed by measuring lung weight gain and pulmonary arterial pressure during the perfusion, extravascular lung water by double indicator dilution techniques, and wet weight to dry weight ratio. After perfusion for 1 hour using 200,000 U (1,300 U/ml) rIL-2, injury was detected as visible pulmonary edema, weight gain and increases in wet to dry weight ratio, and extravascular lung water; no injury was detected at lower, clinically appropriate dosages. When 1 X 10(8) LAK cells combined with 100,000 U rIL-2 (666 U/ml) were perfused for up to 2 hours, no injury was ascertained. Uptake and distribution of the radiolabeled rIL-2 or LAK was uniform to all lung lobes and corresponded to the decrease of 12% of the rIL-2 or 50% of the LAK from the perfusate after 1-hour perfusion.     

Spontaneous resolution of pulmonary edema caused by short periods of cyclic overinflation.

Mechanical ventilation with high or even moderate peak inspiratory pressure produces pulmonary permeability edema. Besides the level of overinflation, duration may affect both severity and type of edema. We studied the effect of 2 min of 35-mmHg peak pressure mechanical ventilation (HV) on microvascular permeability and deep lung fluid balance in rats. It resulted in increased extravascular lung water (+50%), bloodless dry lung weight (+25%), and albumin uptake in lungs (+450%). The increase in dry lung weight and albumin uptake compared with that of lung water suggested major permeability alterations. Ultrastructural examination showed the presence of numerous endothelial blebs. Epithelial lining fluid (ELF) volume, its potassium and protein concentrations, and cellular composition were assessed by bronchoalveolar lavage. There was an increase in ELF volume (+180%), a decrease in ELF potassium concentration (-50%), and an increase in ELF protein content (+76%). A few blood cells were recovered, suggesting the presence of a few large epithelial breaks. Some animals were allowed to recover for periods less than or equal to 180 min after HV. Extravascular lung water, dry lung weight, and albumin distribution space returned to control levels within 45 min. ELF volume diminished but remained larger than in controls, and ELF protein concentration increased probably because of alveolar fluid resorption. No further hemorrhage was observed. These results indicate that periods of HV as short as 2 min transiently alter microvascular permeability in rats.     

Transalveolar osmotic and diffusional water permeability in intact mouse lung measured by a novel surface fluorescence method

A surface fluorescence method was developed to measure transalveolar transport of water, protons, and solutes in intact perfused lungs. Lungs from c57 mice were removed and perfused via the pulmonary artery (approximately 2 ml/min). The airspace was filled via the trachea with physiological saline containing a membrane-impermeant fluorescent indicator (FITC-dextran or aminonapthalene trisulfonic acid, ANTS). Because fluorescence is detected only near the lung surface due to light absorption by lung tissue, the surface fluorescence signal is directly proportional to indicator concentration. Confocal microscopy confirmed that the fluorescence signal arises from fluorophores in alveoli just beneath the pleural surface. Osmotic water permeability (Pf) was measured from the time course of intraalveolar FITC-dextran fluorescence in response to changes in perfusate osmolality. Transalveolar Pf was 0.017 +/- 0.001 cm/s at 23 degrees C, independent of the solute used to induce osmosis (sucrose, NaCl, urea), independent of osmotic gradient size and direction, weakly temperature dependent (Arrhenius activation energy 5.3 kcal/mol) and inhibited by HgCl2. Pf was not affected by cAMP activation but was decreased by 43% in lung exposed to hyperoxia for 5 d. Diffusional water permeability (Pd) and Pf were measured in the same lung from intraalveolar ANTS fluorescence, which increased by 1.8-fold upon addition of 50% D2O to the perfusate, Pd was 1.3 x 10(-5) cm/s at 23 degrees C. Transalveolar proton transport was measured from FITC-dextran fluorescence upon switching perfusate pH between 7.4 and 5.6; alveolar pH half-equilibrated in 1.9 and 1.0 min without and with HCO3-, respectively. These results indicate high transalveolar water permeability in mouse lung, implicating the involvement of molecular water channels, and establish a quantitative surface fluorescence method to measure water and solute permeabilities in intact lung.     

Evaluating flux of labeled albumin into the pulmonary interstitium of sheep lungs.

A noninvasive method was used to measure the movement of 131I-labeled albumin across the pulmonary microvascular barrier of a blood-perfused in situ sheep lung lymph preparation. After injection of labeled albumin into the blood, external measurements of gamma activity were taken for 2 h. The interstitial concentrations were calculated by applying the external activities and sampled lung lymph concentrations to a mass transport model. For the external activities and lymph activities to yield the same quantitative results, two modifications were necessary. First, lymph concentrations were corrected for transport delay from the lymphatic system. Second, externally detected radioactivity had to be corrected for the contribution of unbound nuclide. Application of a mathematical model to the data indicated the extravascular distribution volume for albumin was 79% of the pulmonary blood volume, and the extravascular distribution volume for radiolabeled iodide was 4.42 times greater than the pulmonary blood volume. The permeability-surface area product for iodide in the lung was estimated to be 0.274 ml.min-1.g blood-free dry lung wt-1. The transport delay in the lymphatic system was approximately 30-45 min and represented a volume of 1.44-2.80 ml.     

Effects of sulfhydryl and other reagents on the diffusional permeability of dog erythrocytes to small solutes

The effects of p-chloromercuriphenylsulfonic acid (PCMBS), 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB), phloretin and thiourea on the diffusional permeability of dog erythrocytes to tritiated water and to small 14C-labeled lipophilic and hydrophilic solutes were measured at 37 degrees C by means of the linear diffusion technique. Permeability to 3HHO was significantly decreased by PCMBS but was not affected by the other reagents. The permeability to the small hydrophilic solutes acetamide and urea was decreased by phloretin and thiourea but only the permeability to acetamide was reduced to a statistically significant extent by PCMBS. The permeability to the lipophilic solutes methanol, ethanol and antipyrine was not affected by any of these agents. We interpret these results as an indication that the small lipophilic solutes probably move through lipid areas, that the small hydrophilic solutes probably move through protein associated areas in the erythrocyte membrane and that pathways for the small hydrophilic solutes are distinct from those for water. While the pathways for water may be associated with membrane protein they do not appear to be associated specifically with band 3 protein as has been suggested for human erythrocytes. Diffusional water movement through the dog erythrocyte occurs by two distinct pathways.     

Edema from cyclooxygenase products of endogenous arachidonic acid in isolated lung

We infused A23187, a calcium ionophore, into the pulmonary circulation of dextran-salt-perfused isolated rabbit lungs to release endogenous arachidonic acid. This led to elevations in pulmonary arterial pressure and to pulmonary edema as measured by extravascular wet-to-dry weight ratios. The increase in pressure and edema was prevented by indomethacin, a cyclooxygenase enzyme inhibitor, and by 1-benzylimidazole, a selective inhibitor of thromboxane (Tx) A2 synthesis. Transvascular flux of 125I-albumin from vascular to extravascular spaces of the lung was not elevated by A23187 but was elevated by infusion of oleic acid, an agent known to produce permeability pulmonary edema. We confirmed that A23187 leads to elevations in cyclooxygenase products and that indomethacin and 1-benzylimidazole inhibit synthesis of all cyclooxygenase products and TxA2, respectively, by measuring perfusate levels of prostaglandin (PG) I2 as 6-ketoprostaglandin F1 alpha, PGE2, and PGF2 alpha and TxA2 as TxB2. We conclude that release of endogenous pulmonary arachidonic acid can lead to pulmonary edema from conversion of such arachidonic acid to cyclooxygenase products, most notably TxA2. This edema was most likely from a net hydrostatic accumulation of extravascular lung water with an unchanged permeability of the vascular space, since an index of permeability-surface area product (i.e., transvascular albumin flux) was not increased.