Leukotriene F4 and the release of arachidonic acid metabolites from perfused guinea pig lungs in vitro

Radioimmunoassay and bioassay techniques have been used to investigate the ability of leukotriene (LT)F4 to release products of arachidonic acid metabolism from guinea pig isolated lungs perfused via the pulmonary artery. Also, the abilities of LTC4, LTD4, LTE4 and LTF4 to contract guinea pig ileal smooth muscle (GPISM) was studied. Each of the LT's contracted GPISM. The rank order of potency was LTD4 greater than LTC4 greater than LTE4 much greater than LTF4 in a ratio of 1:7:170:280 respectively. Bioassay of pulmonary effluents indicated the passage of LTF4 through the lungs caused a contraction of rabbit aorta as well as an FPL-55712 sensitive contraction of GPISM. The contractions of rabbit aorta were inhibited by pretreatment of the lungs with Indomethacin but not with the thromboxane synthetase inhibitor Dazoxiben. Radioimmunoassay of the lung effluents indicated LTF4 to cause a 70-fold increase in thromboxane B2 (TXB2), 4-fold increase in prostaglandin (PG)E2 and a 16-fold increase in 6-keto PGF1 alpha levels. The LTF4-induced increments of these immunoreactive metabolites was inhibited by pretreatment of the lungs with Indomethacin. Pretreatment of lungs with Dazoxiben inhibited the LTF4-induced increment in TXB2 and enhanced the effluent levels of PGE2 24-fold (compared with untreated lungs). There were no detectable differences in either immunoreactive LTC4 or immunoreactive LTB4 levels. It is concluded LTF4 is a relatively weak agonist on GPISM and can induce the release of cyclooxygenase products of arachidonic acid metabolism from guinea pig perfused lung.     

Pulmonary microvascular response to LTB4: effects of perfusate composition

We examined the effects of leukotriene B4 (LTB4) on pulmonary hemodynamics and vascular permeability using isolated perfused guinea pig lungs and cultured monolayers of pulmonary arterial endothelial cells. In lungs perfused with Ringer solution, containing 0.5 g/100 ml albumin (R-alb), LTB4 (4 micrograms) transiently increased pulmonary arterial pressure (Ppa) and capillary pressure (Pcap). Pulmonary edema developed within 70 min after LTB4 injection despite a normal Pcap. The LTB4 metabolite, 20-COOH-LTB4 (4 micrograms), did not induce hemodynamic and lung weight changes. In lungs perfused with autologous blood hematocrit = 12 +/- 1%; protein concentration = 1.5 +/- 0.2 g/100 ml), the increases in Ppa and Pcap were greater, and both pressures remained elevated. The lung weight did not increase in blood-perfused lungs. In lungs perfused with R-alb (1.5 g/100 ml albumin) to match the blood perfusate protein concentration, LTB4 induced similar hemodynamic changes as R-alb (0.5 g/100 ml) perfusate, but the additional albumin prevented the pulmonary edema. LTB4 (10(-11)-10(-6) M) with or without the addition of neutrophils to the monolayer did not increase endothelial 125I-albumin permeability. Therefore LTB4 induces pulmonary edema when the perfusate contains a low albumin concentration, but increasing the albumin concentration or adding blood cells prevents the edema. The edema is not due to increased endothelial permeability to protein and is independent of hemodynamic alterations. Protection at higher protein-concentration may be the result of LTB4 binding to albumin.     

Effect of leukotrienes B4, C4, and D4 on segmental pulmonary vascular pressures

Leukotrienes (LTs) C4 and D4 are vasoconstrictors and are thought to increase both systemic and pulmonary vascular permeability. However, we and others have observed that LTC4 and LTD4 cause pulmonary vasoconstriction but do not increase the fluid filtration coefficient of excised guinea pig lungs perfused with a cell-depleted perfusate. To determine what vascular segments were exposed to an LT-induced increase in intravascular hydrostatic pressure we measured pulmonary arterial (Ppa), pulmonary arterial occlusion (Po,a), venous (Po,v) and double occlusion (Pdo) pressures in isolated guinea pig lungs perfused with a cell-depleted buffered salt solution before and after injecting 4 micrograms of LTB4, LTC4, or LTD4 into the pulmonary artery. All three LTs increased airway pressures and also increased Ppa, Po,a, and Pdo. Histamine (15 micrograms) as well as serotonin (20 or 200 micrograms) had the same effect. In excised rabbit lungs, histamine and serotonin increased only Ppa, and Po,a. LTC4 had no vasoactivity. There are marked species variations with regard to the activity and site of action of histamine, serotonin, and LTC4 on the pulmonary circulation.     

Generation of 5-lipoxygenase metabolites following pulmonary reperfusion in isolated rabbit lungs.

We characterized the release of arachidonic acid (AA) metabolites in lung effluent following lung ischemia-reperfusion since they may contribute to the pathophysiology of reperfusion lung injury. The left pulmonary artery of rabbits (N = 5) was occluded for 24 hrs with a surgically implanted vascular clip. At 24 hrs, the heart and lungs were removed en bloc and perfused with Ringers-albumin (0.5 gm%) at 60 ml/min while statically inflated with 95% O2-5% CO2. The lipid fraction of the lung effluent was concentrated using the Bligh-Dyer extraction and analyzed by gradient RP-HPLC. Samples obtained in the first minute of reperfusion showed significant increases in LTB4 (+180%), LTC4 (+3600%), 15-HETE (+370%), 5-HPETE (+270%), PGE2 (+140%), 6-keto-PGF1 alpha (+110%) and 12-HHT (+160%) compared to the effluent from the right control lung. The reperfusion-induced increases in LTB4, LTC4, LTD4 and 15-HETE were inhibited greater than or equal to 70% by pretreatment with the 5-LO inhibitors L663,536 or L651,392. The increases in lipid concentrations corresponded to significantly increased pulmonary arterial pressure from a baseline value of 9.5 +/- 0.3 to 29.3 +/- 2.9 (cmH2O) during the first min of reperfusion. The pulmonary arterial pressure remained elevated for at least 20 min of reperfusion. Reperfusion also resulted in PMN uptake (assessed by lung tissue myeloperoxidase content) in the reperfused lung versus control lung (25.0 +/- 2.4 vs. 10.5 +/- 2.5 units). The generation of lipoxygenase metabolites during the initial phase of reperfusion may contribute to post-reperfusion PMN uptake and pulmonary vasoconstriction.     

The metabolism of arachidonic acid in isolated perfused fetal and neonatal rabbit lungs

The developmental pattern of fetal and neonatal rabbit lungs to metabolize arachidonic acid (AA) to different cyclo-oxygenase products was studied in isolated rabbit lungs, which were perfused with Krebs bicarbonate buffer. 14C-AA (66 nmol) was injected into the pulmonary circulation and the nonrecirculating perfusion effluent was collected for four minutes. About ten per cent of the injected radioactivity was found in the 0-4 min perfusion effluent. The metabolites of AA in the effluent were analyzed by thin layer chromatography. The major metabolites of AA were PGE2 and its 15-keto-derivates, but also PGF2 alpha and its 15-keto-derivates, TXB2 and 6-keto-PGF1 alpha were found in the effluent. The most drastic developmental change was the increase in the amount of 15-keto-metabolites of PGE2 from late fetal period to the lungs of one day old rabbits (1.8 fold increase between birth and first postnatal day). Smaller changes were detected in the amounts of other cyclo-oxygenase products.     

Prostaglandin E2 attenuation of sheep lung responses to endotoxin

Prostaglandin (PG) E2 can inhibit inflammatory responses of neutrophils and lymphocytes, including eicosanoid release. Diffuse lung injury after endotoxemia in sheep is accompanied by sequestration of neutrophils and lymphocytes in the lungs, and eicosanoids mediate some of the pathophysiology of the response. To determine whether exogenous PGE2 could prevent the endotoxin response, we measured pulmonary hemodynamics, gas exchange, and lung lymph responses to infusion of Escherichia coli endotoxin (0.5 micrograms/kg iv over 30 min) in unanesthetized sheep in the presence and absence of PGE2 (0.5 micrograms.kg-1.min-1) infused intravenously for 4 h beginning 0.5 h before endotoxin infusion. We also measured lung lymph concentrations of thromboxane B2 (TxB2) and prostacyclin metabolite, 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), by radioimmunoassay and leukotriene B4 (LTB4) by gas chromatography-mass spectrometry. PGE2 decreased endotoxin-induced pulmonary hypertension and hypoxemia and markedly attenuated the lymph flow and lymph protein clearance responses. PGE2 also attenuated endotoxin-induced increases in lung lymph TxB2 and 6-keto-PGF1 alpha and decreased lymph LTB4 flow after endotoxin without decreasing lymph LTB4 concentrations. We conclude that PGE2 infusion attenuates lung dysfunction caused by endotoxemia, possibly by preventing endogenous release of other eicosanoids.     

Aspirin inhibits arachidonic acid metabolism via lipoxygenase and cyclo-oxygenase in hamster isolated lungs

The effect of aspirin on the fate of exogenous arachidonic acid (AA) was investigated in isolated perfused lungs of female hamsters. During pulmonary infusion of aspirin (10 μM, 100 μM or 1 mM) 45 nmol of ¹⁴C-AA was infused in two minutes into the pulmonary circulation. The nonrecirculating perfusion effluent was collected for 6 minutes after the beginning of the AA infusion. Arachidonate infusion increased the perfusion pressure. This pressor response was completely abolished by 1 mM aspirin. When aspirin was infused into the pulmonary circulation, the amount of radioactivity was increased in the perfused lungs and decreased dose dependently in the nonrecirculating perfusion effluent. The amount of unmetabolized free arachidonate was not changed significantly by aspirin in the perfused lungs or in the perfusion effluent. In the effluent the amounts of all arachidonate metabolites, which were extracted with ethyl acetate first at pH 7.4 and then at pH 3.5 and analysed by thin layer chromatography, were decreased quite similarly by aspirin. The formation of arachidonate metabolites was completely inhibited by 1 mM aspirin. In the perfused lung tissue the amount of ¹⁴C-AA was increased by aspirin in phospholipids and neutral lipids. The present study indicates that the metabolism of arachidonic acid is inhibited by aspirin in hamster lungs not only via cyclo-oxygenase but also via other lipoxygenases.     

Leukotriene E4 causes pulmonary vasoconstriction, not inhibited by meclofenamate

Leukotriene E4 (LTE4) appears to be a rather stable product of the lipoxygenase pathway. Its action in the pulmonary circulation is unknown. Therefore we investigated its effect on the circulation of isolated rat lungs perfused with a cell- and plasma-free solution. Synthetic LTE4 in doses from .15 micrograms to 5 micrograms/.25 ml .9% NaCl injected as a bolus in the pulmonary artery during normoxia caused a fast, transient perfusion pressure increase within seconds. This was followed by a slow rise in baseline perfusion pressure (normoxia) over 25 min. In addition, 5 micrograms LTE4 caused edematogenic lung damage. Injection of 1.5 micrograms LTE4 during hypoxic vasoconstriction caused fast, transient pressure rises, similar to normoxic conditions. 6-keto-PGF1 alpha and TXB2 were measured in the lung effluent before and after LTE4 injection. Neither 6-keto-PGF1 alpha nor TXB2 production changed after LTE4 injection. Meclofenamate (.5 micrograms/ml) increased the fast, transient and the slow, sustained pressure rise. We conclude that LTE4 caused direct pulmonary vasoconstriction unrelated to cyclooxygenase products.     

Endogenous and exogenous catalase in reoxygenation lung injury.

Reexpansion pulmonary edema parallels reperfusion (reoxygenation) injuries in other organs in that hypoxic and hypoperfused lung tissue develops increased vascular permeability and neutrophil infiltration after reexpansion. This study investigated endogenous lung catalase activity and H2O2 production during hypoxia (produced by lung collapse) and after reoxygenation (resulting from reexpansion), in addition to assessing the effects of exogenous catalase infusion on the development of unilateral pulmonary edema after reexpansion. Lung collapse resulted in a progressive increase in endogenous catalase activity after 3 (14%) and 7 days (23%), while activities in contralateral left lungs did not change (normal left lungs averaged 180 +/- 11 units/mg DNA). Tissue from control left lungs released H2O2 into the extracellular medium at a rate calculated to be 242 +/- 34 nmol.h-1.lung-1. No significant change in extracellular release of H2O2 occurred after 7 days of right lung collapse. However, after reexpansion of the previously collapsed right lungs for 2 h, H2O2 release from both reexpanded right and contralateral left lungs significantly increased (88 and 60%, respectively) compared with controls. Infusion of exogenous catalase significantly increased plasma and lung catalase activities. Exogenous catalase infusion prevented neither the increase in lung permeability nor the infiltration with neutrophils that typically occurs in reexpanded lungs. These data indicate that lung hypoxia/reoxygenation, induced by sequential collapse and reexpansion, has specific effects on endogenous lung catalase activity and H2O2 release. However, exogenous catalase does not prevent reexpansion pulmonary edema, eliminating extracellular (but not intracellular) H2O2 as an important mediator of unilateral lung injury in this model.     

Effects of arachidonic acid and prostaglandin F2 alpha in isolated rat lungs

Isolated rat lungs were ventilated and perfused by saline-Ficoll perfusate at a constant flow. The baseline perfusion pressure (PAP) correlated with the concentration of 6-keto-PGF1 alpha the stable metabolite of PGI2 (r = 0.83) and with the 6-keto-PGF1 alpha/TXB2 ratio (r = 0.82). A bolus of 10 micrograms exogenous arachidonic acid (AA) injected into the arterial cannula of the isolated lungs caused significant decrease in pulmonary vascular resistance (PVR) which was followed by a progressive increase of PVR and edema formation. Changes in perfusion pressure induced by AA injection also correlated with concentrations of the stable metabolites (6-keto-PGF1 alpha: r = -0.77, TxB2: -0.76), and their ratio: (6-keto-PGF1 alpha/TXB2: r = -0.73). Injection of 10 and 100 micrograms of PGF2 alpha into the pulmonary artery stimulated the dose-dependent production of TXB2 and 6-keto-PGF1 alpha. No significant correlations were found between the perfusion pressure (PAP) which was increased by the PGF2 alpha and the concentrations of the former stable metabolites. The results show that AA has a biphasic effect on the isolated lung vasculature even in low dose. The most potent vasoactive metabolites of cyclooxygenase, prostacyclin and thromboxane A2 influence substantially not only the basal but also the increased tone of the pulmonary vessels.     

Pulmonary microvascular responses to arachidonic acid in isolated perfused guinea pig lung

We examined the effects of arachidonic acid (AA) on pulmonary hemodynamics and fluid balance in Ringer- and blood-perfused guinea pig lungs during constant-flow conditions. Mean pulmonary arterial (Ppa), venous (Pv), and capillary pressures (Pcap, estimated by the double-occlusion method) were measured, and arterial (Ra) and venous resistances (Rv) were calculated. Bolus AA injection (500 micrograms) caused transient increases (peak response 1 min post-AA) in Ppa, Pcap, and Rv without affecting Ra in both Ringer- and blood-perfused lungs. The response was sustained in blood-perfused lungs. AA had no effect on the capillary filtration coefficient in either Ringer- or blood-perfused lungs. AA stimulated the release of thromboxane B2 and 6-ketoprostaglandin F1 alpha in both Ringer- and blood-perfused lungs, but the responses were sustained only in the blood-perfused lungs. Meclofenamate (1.5 X 10(-4) M), a cyclooxygenase inhibitor, abolished the AA-induced pulmonary hemodynamic responses in both Ringer- and blood-perfused lungs, whereas U-60257 (10 microM), a lipoxygenase inhibitor, attenuated the response only in the blood-perfused lungs. In conclusion, AA does not alter pulmonary vascular permeability to water in either Ringer- or blood-perfused lungs. AA mediates pulmonary venoconstriction and thus contributes to the rise in Pcap. The venoconstriction results from the generation of cyclooxygenase-derived metabolites from lung parenchymal cells and blood-formed elements. Lipoxygenase metabolites may also contribute to the vasoconstriction in the blood-perfused lungs.     

Sequential release of eicosanoids during endotoxin-induced shock in anesthetized pigs

The release of eicosanoids during endotoxin shock was investigated in anesthetized pigs receiving 5 micrograms/kg Escherichia coli lipopolysaccharide (LPS) over 60 min into the superior mesenteric artery. TXB2, 6-keto PGF1 alpha and LTB4 concentrations in blood obtained from the superior mesenteric vein (SMV), right ventricle (RV) and aorta, during LPS infusion and an additional period of 2 h, were assessed along with hemodynamic variables, blood gases and pH and laboratory parameters. Half of the animals died within 30 min after termination of LPS infusion (non-survivors, n = 8), while the other half survived the experimental period of 3 h, though in a shock state (survivors, n = 9). The non-surviving pigs demonstrated progressively reduced cardiac output, hypotension and hypoperfusion in all organs. The surviving pigs demonstrated also a reduced cardiac output, which however was compensated by an elevated systemic vascular resistance resulting in a maintenance of arterial blood pressure. After exhausting this compensation the flow to non-vital organs increased and consequently arterial blood pressure was reduced resulting in hypoperfusion. In survivors a marked, though, transient increase was measured in concentrations of TXB2 and 6-keto PGF1 alpha level. A significant increase was measured in plasma concentration of LTB4 in SMV without any elevation in RV and aorta. LTB4 production started when prostanoid release had decreased. In contrast to survivors, no changes could be observed in eicosanoid release for non-survivors. A correlation was observed between systemic vascular resistance and TXB2 to 6-keto PGF1 alpha ratio.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Comparison of umbilical vein models for measurement of relative prostacyclin and thromboxane production

There is growing evidence that blood vessels generate TXA2 in addition to PGI2. We examined effluents from continuously perfused human umbilical vein and supernatants from umbilical vein rings for TXB2 and 6-keto-PGF1 alpha measurements (stable metabolites of TXA2 and PGI2, respectively). TXB2 and 6-keto-PGF1 alpha were identified in all samples. 6-keto-PGF1 alpha to TXB2 ratio was higher in intact vein effluents than in the venous ring supernatants (112:1 and 28:1, respectively, P less than 0.01). Arachidonate stimulation increased 6-keto-PGF1 alpha and TXB2 levels similarly in the intact vein effluent. In contrast, stimulation of the venous rings resulted in a relatively larger increase in TXB2 than in 6-keto-PGF1 alpha. This caused 6-keto-PGF1 alpha to TXB2 ratio to decline (p less than 0.01). The identity of TXB2 was confirmed in several different ways. These data suggest that 1) human umbilical veins produce TXA2 in addition to PGI2, 2) TXA2 release is more by venous rings than by the intact vein probably reflecting contribution from non-endothelial layers, and 3) arachidonate stimulation causes relatively greater release of TXA2 than of PGI2 from the venous rings, whereas release of PGI2 and TXA2 is similar from the intact vein.     

Diethylcarbamazine on pulmonary vascular response to endotoxin in awake sheep

Diethylcarbamazine (DEC) is an inhibitor of lipoxygenase, with protective effects in several experimental models of anaphylaxis and lung dysfunction. The hypothesis of this study was that DEC would alter the pulmonary response to endotoxin infusion, especially the prolonged pulmonary hypertension, leukopenia, hypoxemia, and high flow of protein-rich lung lymph. We prepared sheep for chronic measurements of hemodynamics and collection of lung lymph. In paired studies we gave six sheep endotoxin (0.5 micrograms/kg iv) either with or without DEC. DEC was given (80-100 mg/kg iv) over 30 min followed by a continuous infusion at 1 mg X kg-1 X min-1. Endotoxin was given after the loading infusion of DEC, and variables were monitored for 4 h. The response to endotoxin was characterized by pulmonary hypertension, leukopenia, hypoxemia, and elevations of thromboxane B2 and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha). Lymph flow and protein content reflected hemodynamic and permeability changes in the pulmonary circulation. DEC did not significantly modify the response to endotoxin by any measured variable, including pulmonary arterial and left atrial pressures, cardiac output, lymph flow and protein content, alveolar-to-arterial PO2 difference, blood leukocyte count, and lymph thromboxane B2 and 6-keto-PGF1 alpha. We could not find evidence of release of leukotriene C4/D4 by radioimmunoassay in lung lymph after endotoxin infusion with or without DEC treatment. We conclude that lipoxygenase products of arachidonic acid may not be a major component of the pulmonary vascular response to endotoxin.     

Production of arachidonic acid metabolites by endothelial cells in hyperoxia

This study investigated the response of bovine pulmonary artery endothelial cells to incubation in hyperoxia (95% O2-5% CO2). Changes in cell number and morphology, release of lactate dehydrogenase, and production of arachidonic acid metabolites were assessed during continuous exposure of confluent endothelial monolayers to air (air-5% CO2, "controls") or O2 (95% O2-5% CO2, "O2-exposed") for periods of 12-72 h. Control monolayer cell numbers remained constant (approximately 2,000,000 cells/flask), whereas the number of cells in O2-exposed monolayers decreased progressively to 30% of controls (P less than 0.01) by 72 h. As assessed by radioimmunoassay, both control and O2-exposed cells produced the prostacyclin metabolite, 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha), and prostaglandin F2 alpha (PGF2 alpha), but no thromboxane metabolite (TxB2) was detected. The O2-exposed cells released significantly more 6-keto-PGF1 alpha and PGF2 alpha than control cells when apparent net production rates over the entire 72-h period were compared. In addition, both control and O2-exposed (48 h) endothelial monolayers released immunoreactive leukotriene B4 (LTB4) on stimulation with calcium ionophore (10 microM A23187). As with the cyclooxygenase products, O2-exposed cells released more immunoreactive LTB4 than did controls. Both cyclooxygenase and lipoxygenase metabolites of arachidonic acid are released by cultured endothelial cells during the development of O2 toxicity.     

Thromboxane release from irradiated perfused rat lungs: role of oncotic agents

Isolated lungs from 20 Gray (Gy) whole body irradiated rats were perfused with Krebs-Ringer bicarbonate plus 3% bovine serum albumin (KRB-BSA). The pulmonary effluent showed a 99% (p less than .05) increase in immunoassayable thromboxane B2 (iTXB2) release compared with non-irradiated lungs. Since both arachidonic acid and cyclooxygenase products bind to albumin, studies were performed to determine if omission or substitution of this protein oncotic agent would alter the radiation-induced increase in pulmonary iTXB2 release. Irradiated, isolated lungs perfused with media from which the BSA was omitted (KRB) did not demonstrate the radiation-induced increase in pulmonary iTXB2 release. Similarly, irradiated lungs perfused with media in which Dextran 70 (KRB plus 3% Dextran 70, KRB-Dextran 70) was substituted for BSA also did not show the radiation-induced increase in pulmonary effluent iTXB2 levels. These studies demonstrate the importance of including albumin as the oncotic agent in perfused organ systems when studying cyclooxygenase product release.     

Alveolar fluid reabsorption is impaired by increased left atrial pressures in rats

Cardiogenic pulmonary edema results from increased hydrostatic pressures across the pulmonary circulation. We studied active Na(+) transport and alveolar fluid reabsorption in isolated perfused rat lungs exposed to increasing levels of left atrial pressure (LAP; 0--20 cmH(2)O) for 60 min. Active Na(+) transport and fluid reabsorption did not change when LAP was increased to 5 and 10 cmH(2)O compared with that in the control group (0 cmH(2)O; 0.50 +/- 0.02 ml/h). However, alveolar fluid reabsorption decreased by approximately 50% in rat lungs in which the LAP was raised to 15 cmH(2)O (0.25 +/- 0.03 ml/h). The passive movement of small solutes ((22)Na(+) and [(3)H]mannitol) and large solutes (FITC-albumin) increased progressively in rats exposed to higher LAP. There was no significant edema in lungs with a LAP of 15 cmH(2)O when all active Na(+) transport was inhibited by hypothermia or amiloride (10(-4) M) and ouabain (5 x 10(-4) M). However, when LAP was increased to 20 cmH(2)O, there was a significant influx of fluid (-0.69 +/- 0.10 ml/h), precluding the ability to assess the rate of fluid reabsorption. In additional studies, LAP was decreased from 15 to 0 cmH(2)O in the second and third hours of the experimental protocol, which resulted in normalization of lung permeability to solutes and alveolar fluid reabsorption. These data suggest that in an increased LAP model, the changes in clearance and permeability are transient, reversible, and directly related to high pulmonary circulation pressures.     

Selective inhibition by antiflamrnin-2 of thromboxane B(2) release from isolated and perfused guinea-pig lung

Antiflammin-2 (AF2) is a nonapeptide corresponding to the amino acid residues 246-254 of lipocortin-1 showing anti-inflammatory activity both in vitro and in vivo. The effect of AF2 on the thromboxane B(2) (TXB(2)) and histamine release from isolated and perfused guinea-pig lungs has been studied. AF-2 (10-100 nM) inhibited leukotriene C(4)- (LTC(4)) (3 ng) and antigen-induced (ovalbumin, 1 mg) TXB(2) release in normal and sensitized lungs, respectively. In contrast AF-2 (100 nM) did not modify TXB(2) release induced by histamine (5 mug) or bradykinin (5 mug) in normal lungs. Antigen-induced histamine release was not affected by 100 nM AF-2 infusion. When tested in chopped lung fragments AF-2 (0.1-25 muM) did not modify the release of histamine and TXB(2) induced by antigen (ovalbumin, 10 mug ml(-1)) or calcium ionophore A 23187 (1 muM). Our results show that the inhibitory effect of AF-2 on TXB(2) release is selective and depends on the stimulus applied. In this respect AF-2 mimics, at least in part, the actions of both glucocorticoids and lipocortin-1.     

The metabolism of arachidonic acid to an antiaggregatory compound in isolated lungs of fetal and neonatal rabbits

The developmental pattern of fetal and neonatal rabbit lungs to generate an antiaggregatory compound from arachidonic acid (AA) was studied in isolated rabbit lungs, which were perfused with Krebs bicarbonate buffer. The antiaggregatory effect of the nonrecirculating perfussion effluent was tested by adding a small portion of the effluent to human platelet rich plasma (PRP) in a Born-type aggregometer before the aggregation was induced by ADP. The production of an antiaggregatory compound was minimal, when exogenous AA was not infused into the pulmonary circulation. When arachidonate (40 nmol/min) was infused into the pulmonary circulation of rabbits which were 1 day or 1 week old, the perfusion effluent significantly inhibited the ADP induced aggregation of PRP. Perfused lungs from fetal rabbits (gestation age 28–31 days) formed also an antiaggregatory compound fro AA, but the antiaggregatory effect was not as great as 1 day after birth. It seems that neonatal rabbit lungs metabolize AA more to an antiaggregatory compound than late fetal lungs. The fact that the AA induced production of an antiaggregatory compound is inhibited by simultaneous infusion of indomethacin favours the hypothesis that this antiaggregatory compound could he PGI₂.