Eosinophilic "empyema" associated with crack cocaine use.

Smoking of crystalline cocaine, known as "crack" cocaine, has been associated with eosinophilic pneumonitis, but not with pleural effusions. We describe a patient with eosinophilic pneumonitis with an eosinophilic "empyema" after using "crack" cocaine. The illness resolved with corticosteroids. We hypothesised that his effusion would have increased levels of eosinophil cytokines that promote oedema, and found a marked increase in pleural vascular endothelial growth factor (VEGF) and smaller increases in interleukins IL-5, IL-6, and IL-8. In the setting of "crack" use, we suggest that a pleural effusion that appears grossly to be pus should be evaluated for eosinophilic inflammation. Such eosinophilic effusions may respond to corticosteroids alone, consistent with a non-infectious process driven by proinflammatory cytokines.

Resistance of the pulmonary epithelium to movement of buffer ions.

Exposure of the apical surfaces of alveolar monolayers to acidic and alkaline solutions has been reported to have little influence on intracellular pH compared with basolateral challenges (Joseph D, Tirmizi O, Zhang X, Crandall ED, and Lubman RL. Am J Physiol Lung Cell Mol Physiol 282: L675-L683, 2002). We have used fluorescent pH indicators and a trifurcated optical bundle to determine whether the apical surfaces are less permeable to ionized buffers than the membranes that separate the vasculature from the tissues in intact rat lungs. In the first set of experiments, the air spaces were filled with perfusate containing FITC-dextran (mol wt 60000) or 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Air space pH fell progressively from 7.4 to 6.61 +/- 0.03 (mean +/- SE, n = 11, air space buffers at 10 mM). Perfusion for 2 min with 2 mM NH4Cl increased air space pH by 0.142 +/- 0.019 unit, without a subsequent acidic overshoot. Infusions of NaHCO3 and sodium acetate reduced pH without a subsequent alkaline overshoot. In the second set of experiments, cellular pH was monitored in air-filled lungs after perfusion with BCECFAM. Injections of NH4Cl caused a biphasic response, with initial alkalinization of the cellular compartment followed by acidification after the NH4Cl was washed from the lungs. Subsequent return of pH to normal was slowed by infusions of 1.0 mM dimethyl amiloride. These studies suggest that lung cells are protected from air space acidification by the impermeability of the apical membranes to buffer ions and that the cells extrude excess H+ through basolateral Na+/H+ exchangers.

Protection of the lungs from acid during aspiration.

Unlike the thick mucosa that normally covers the upper gastrointestinal tract, the membranes that cover the distal surfaces of the lungs are remarkably attenuated. This permits rapid exchange of gases between the airspaces and pulmonary vasculature, and may make the lungs more susceptible to acid challenges associated with acid reflux and aspiration. Any injury to the alveolar epithelium could result in the movement of solute and water into the airspaces (chemical pneumonia) and impair gas exchange. In this study, we used a fluorescent approach to compare the relative permeability of the apical basolateral surfaces of the lungs to the exchange of the ionic forms of acids and bases. The apical membranes proved to be much less permeable to NH(4)(+) and HCO(3)(+) than the basolateral membranes. This asymmetry in permeability should enhance resistance of the epithelium to inspired acidic challenges by slowing entry of acid into the cells and by linking the intracellular pH of the alveolar cells to that of the plasma, which is a relatively large, well-buffered compartment. Evidence also was obtained that the acid is secreted by the membranes covering the lungs.

Relationship of ultrafiltration and anastomotic flow in isolated rat lungs.

OBJECTIVE: When arterial and venous pressures are increased to equal values in "stop-flow" studies, perfusate continues to enter the pulmonary vasculature from the arterial and venous reservoirs. Losses of fluid from the pulmonary vasculature are due to ultrafiltration and flow through disrupted anastomotic (bronchial) vessels. This study compared the relative sites of ultrafiltration and anastomotic flows at low and high intravascular pressures. METHODS: Isolated rat lungs were perfused for 10 minutes with FITC-dextran, which was used to detect ultrafiltration. Arterial and venous catheters were then connected to reservoirs containing radioactively labeled dextrans at 20 or 30 cm H2O for 10 minutes. The vasculature was subsequently flushed into serial vials, and ultrafiltration and vascular filling during the equal-pressure interval were calculated. RESULTS: Ultrafiltration equaled 0.43 +/- 0.11 mL at 20 cm H2O and was similar to the volume of fresh arterial and venous perfusate which entered and remained in the pulmonary vasculature during the equal-pressure interval (0.45 +/- 0.10 mL). At 30 cm H2O, 0.80 +/- 0.23 mL entered and remained in the vasculature during the equal-pressure interval, replacing the original perfusate, and calculated transudation (0.56 +/- 0.09 mL) was not significantly more than at 20 cm H2O. Fluid also entered the airspaces at 30 cm H2O but not at 20 cm H2O. CONCLUSIONS: At 20 cm H2O, flow through anastomotic vessels occurs at sites that are at the arterial and venous ends of the microcirculation. Flow in exchange vessels remains minimal, permitting measurements of ultrafiltration and exchange. Losses of perfusate from the pulmonary vessels complicate measurements of ultrafiltration at 30 cm H2O.

Response of the lungs to aspiration.

Aspiration of acid from the stomach and water from the mouth can cause significant lung injury. Animal experiments suggest that acid entering the lungs is normally neutralized by bicarbonate derived from the plasma. It is hypothesized that this process may be impaired in patients with cystic fibrosis and that some of the airway injury that they experience may be related to this defect. This disease is characterized by abnormalities in the cystic fibrosis transmembrane conductance regulator, which normally conducts bicarbonate and chloride exchange. Evidence is discussed regarding the role of water channels (aquaporins) in transporting water from the airspaces into the vasculature.

Airway synthesis of 20-hydroxyeicosatetraenoic acid: metabolism by cyclooxygenase to a bronchodilator.

Rabbit airway tissue is a particularly rich source of cytochrome P-4504A protein, but very little information regarding the effect(s) of 20-hydroxyeicosatetraenoic acid (20-HETE) on bronchial tone is available. Our studies examined the response of rabbit bronchial rings to 20-HETE and the metabolism of arachidonic acid and 20-HETE from airway microsomes. 20-HETE (10(-8) to 10(-6) M) produced a concentration-dependent relaxation of bronchial rings precontracted with KCl or histamine but not with carbachol. Relaxation to 20-HETE was blocked by indomethacin or epithelium removal, consistent with the conversion of 20-HETE to a bronchial relaxant by epithelial cyclooxygenase. A cyclooxygenase product of 20-HETE also elicited relaxation of bronchial rings. [14C]arachidonic acid was converted by airway microsomes to products that comigrated with authentic 20-HETE (confirmed by gas chromatography-mass spectrometry as 19- and 20-HETE) and to unidentified polar metabolites. [3H]20-HETE was metabolized to indomethacin-inhibitable products. These data suggest that 20-HETE is an endogenous product of rabbit airway tissue and may modulate airway resistance in a cyclooxygenase-dependent manner.

Stop-flow studies of solute uptake in rat lungs.

Stop-flow studies were used to characterize solute uptake in isolated rat lungs. These lungs were perfused at 8 or 34 ml/min for 10-28 s with solutions containing 125I-albumin and two or more of the following diffusible indicators: [3H]mannitol, [14C]urea, 3HOH, 201Tl+, or 86Rb+. After this loading period, flow was stopped for 10-300 s and then resumed to flush out the perfusate that remained in the pulmonary vasculature during the stop interval. Concentrations of 201Tl+ and 86Rb+ in the venous outflow decreased after the stop interval, indicating uptake from exchange vessels during the stop interval. The amount of these K+ analogs lost from the circulation during the stop interval was greater when the intervals were longer. However, losses of 201T1+ at 90 s approached those at 300 s. Because extraction continued after the vasculature had been flushed, vascular levels had presumably fallen to negligible levels during the stop interval. By 90 s of stop flow the vascular volume that was cleared of 201T1+ averaged 0.657 +/- 0.034 (SE) ml in the experiments perfused at 8 ml/min and 0.629 +/- 0.108 ml in those perfused at 34 ml/min. Increases in perfusate K+ decreased the cleared volumes of 201T1+ and 86Rb+. Uptake of [3H]mannitol, [14C]urea, and 3HOH during the stop intervals was observed only when the lungs were loaded at high flow for short intervals. Decreases in 201T1+ and 86Rb+ concentrations in the pulmonary outflow can be used to identify the fraction of the collected samples that were within exchange vessels of the lung during the stop interval and may help determine the distribution of solute and water exchange along the pulmonary vasculature.

Tissue sources of cytochrome P450 4A and 20-HETE synthesis in rabbit lungs.

We previously reported that 20-hydroxyeicosatetraenoic acid (20-HETE) is an endogenous cytochrome P450 (cP450) 4A metabolite of arachidonic acid (AA) in human lung tissue, and is a potent cyclooxygenase-dependent vasodilator of isolated pulmonary arteries. In the present investigations, we identified sources of cP450 4A immunospecific protein, messenger RNA (mRNA), and 20-HETE synthesis in rabbit lungs. Microsomes of peripheral lung tissue, airways, small and large vessels, and lysates of alveolar macrophages all express proteins of approximately 50 kD which cross-reacted with a primary antibody raised against rat liver cP450 4A1. Peripheral lung tissue, small and large pulmonary arteries, airways, and isolated vascular smooth muscle cells from small pulmonary arteries produced 20-HETE when incubated with AA. Expression of cP450 4A6/4A7 mRNA was readily detectable by reverse transcription-polymerase chain reaction using isoform-specific probes and 5 microg total RNA extracted from microdissected small pulmonary arteries. These data demonstrate that small pulmonary arteries express cP450 4A proteins and vascular smooth muscle cells derived from these arteries synthesize 20-HETE. Furthermore, cP450 4A appears to be widely distributed in rabbit tissue, raising the possibility that 20-HETE generated from nonvascular tissue could serve as a paracrine factor in the pulmonary circulation.

Stop-flow studies of distribution of filtration in rat lungs.

The stop-flow approach was used to investigate where filtration occurs in the pulmonary vasculature after elevation of left atrial pressure and aspiration of HCl. Rat lungs were perfused for 11 min at zero left atrial pressures, and then flow was stopped for 10 min and left atrial pressures were increased to 20 cmH2O. Thereafter, 3HOH was instilled into the air spaces, and the pulmonary vasculature was flushed by perfusing it from the pulmonary artery to left atrium (anterograde flush) or in the opposite direction (retrograde flush). Increases in fluorescein isothiocyanate (FITC)-dextran (molecular weight 2,000,000) indicated filtration, and these preceded increases in 3HOH after anterograde but not retrograde flushes. This suggests that some filtration occurred through vessels that were relatively venous compared with those through which 3HOH exchange had occurred. Filtration increased fivefold after instillation of 0.1 N HCl in isotonic saline into the air spaces before perfusion. Increases in Evans blue-labeled albumin concentrations were < 40% those of FITC-dextran, indicating loss from the vasculature, but increases in unlabeled albumin and FITC-albumin were comparable.

Water transport and the distribution of aquaporin-1 in pulmonary air spaces.

Recent evidence suggests that water transport between the pulmonary vasculature and air spaces can be inhibited by HgCl2, an agent that inhibits water channels (aquaporin-1 and -5) of cell membranes. In the present study of isolated rat lungs, clearances of labeled (3HOH) and unlabeled water were compared after instillation of hypotonic or hypertonic solutions into the air spaces or injection of a hypotonic bolus into the pulmonary artery. The clearance of 3HOH between the air spaces and perfusate after intratracheal instillation and from the vasculature to the tissues after pulmonary arterial injections was invariably greater than that of unlabeled water, indicating that osmotically driven transport of water is limited by permeability of the tissue barriers rather than the rate of perfusion. Exposure to 0.5 mM HgCl2 in the perfusate and air-space solution reduced the product of the filtration coefficient and surface area (PfS) of water from the air spaces to the perfusate by 28% after instillation of water into the trachea. In contrast, perfusion of 0.5 mM HgCl2 in air-filled lungs reduced PfS of the endothelium by 86% after injections into the pulmonary artery, suggesting that much of the action of this inhibitor is on the endothelial surfaces. Confocal laser scanning microscopy demonstrated that aquaporin-1 is on mouse pulmonary endothelium. No aquaporin-1 was found on alveolar type I cells with immunogold transmission electron microscopy, but small amounts were present on some type II cells.

Human pulmonary arteries dilate to 20-HETE, an endogenous eicosanoid of lung tissue.

We investigated the effect of 20-hydroxyeicosatetraenoic acid (20-HETE), an arachidonic acid metabolite of the cytochrome P-450 (cP450) 4A pathway, on human pulmonary arterial tone. 20-HETE elicited a dose-dependent and indomethacin-inhibitable vasodilation of isolated small pulmonary arteries. Whole lung microsomes metabolized [24C]arachidonic acid into 20-HETE and a variety of leukotrienes, epoxyeicosatrienoic acids, and prostanoids. Indomethacin blocked formation of prostanoids without effects on the conversion of arachidonate into 20-HETE, 20-HETE was converted by lung microsomes into prostanoids, raising the possibility that 20-HETE may be metabolized by cyclooxygenase enzymes in vascular tissue to a vasodilatory compound. Western blots probed with a polyclonal antibody to cP450 4A identified a protein of approximately 50 kDa immunologically similar to the cP450 4A in rat liver. We conclude that small arteries from human lungs dilate upon exposure to 20-HETE in a cyclooxygenase-dependent manner and that the proteins and enzymatic activity required to synthesize this product are present in lungs. Our observations suggest that cP450 enzyme products could be endogenous modulators of pulmonary vascular tone.