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.     

Effects of thromboxane synthase inhibition on air emboli lung injury in sheep

We tested the effects of OKY-046, a thromboxane synthase inhibitor, on lung injury induced by 2 h of pulmonary air infusion (1.23 ml/min) in the pulmonary artery of unanesthetized sheep with chronic lung lymph fistula so as to assess the role of thromboxane A2 (TxA2) in the lung injury. We measured pulmonary hemodynamic parameters and the lung fluid balance. The concentrations of thromboxane B2 (TxB2) and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) in plasma and lung lymph were determined by radioimmunoassay. Air infusion caused sustained pulmonary hypertension and an increase in pulmonary vascular permeability. The levels of TxB2 and 6-keto-PGF1 alpha in both plasma and lung lymph were significantly elevated during the air infusion. TxB2 concentration in plasma obtained from the left atrium was higher than that from the pulmonary artery at 15 min of air infusion. When sheep were pretreated with OKY-046 (10 mg/kg iv) prior to the air infusion, increases in TxB2 were prevented. The pulmonary arterial pressure, however, increased similarly to that of untreated sheep (1.8 X base line). The increase in lung lymph flow was significantly suppressed during the air infusion. Our data suggest that the pulmonary hypertension observed during air embolism is not caused by TxA2.     

Effects of thromboxane synthase inhibition on tumor necrosis factor-induced lung injury in sheep.

To examine the role of thromboxane (Tx) A2 in the pathogenesis of acute lung injury caused by tumor necrosis factor alpha (TNF), we tested the effects of OKY-046, a selective thromboxane synthase inhibitor, on pulmonary hemodynamics, lung lymph balance, circulating leukocytes, arterial blood gas analysis, and TxA2 (as TxB2) and prostacyclin (as 6-keto-prostaglandin F1 alpha) levels in plasma and lung lymph after TNF infusion in awake sheep. Infusion of human recombinant TNF (3.5 micrograms/kg) into a chronically instrumented awake sheep caused a transient increase in pulmonary arterial pressure (Ppa). The Ppa peaked within 15 min of the start of TNF infusion from 23.3 +/- 1.1 (SE) cmH2O of baseline to 42.3 +/- 2.3 cmH2O and then decreased toward baseline. The pulmonary hypertension was accompanied by transient hypoxemia, peripheral leukopenia, and the increases in TxB2 in plasma and lung lymph. These changes were followed by an increase in flow of protein-rich lung lymph, consistent with an increase in pulmonary microvascular permeability. OKY-046 significantly prevented the rises of Ppa and TxB2 concentrations in plasma and lung lymph during early phase after TNF infusion. OKY-046, however, did not attenuate the increase of lung lymph flow, transient hypoxemia, and leukopenia. From these data, and by comparison with our previous studies of OKY-046-pretreated sheep during endotoxemia, we conclude that TxA2 has an important role of the increase in the early pulmonary hypertension, but it is not related to the early hypoxemia, leukopenia, and lung lymph balances in TNF-induced lung injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

Human recombinant tumor necrosis factor alpha infusion mimics endotoxemia in awake sheep

The macrophage-derived cytokine tumor necrosis factor alpha (TNF alpha) has been proposed as the major mediator of endotoxin-induced injury. To examine whether a single infusion of human recombinant TNF alpha (rTNF alpha) reproduces the pulmonary effects of endotoxemia, we infused rTNF alpha (0.01 mg/kg) over 30 min into six chronically instrumented awake sheep and assessed the ensuing changes in hemodynamics, lung lymph flow and protein concentration, and number of peripheral blood and lung lymph leukocytes. In addition, levels of thromboxane B2, 6-ketoprostaglandin F1 alpha, prostaglandin E2, and leukotriene B4 were measured in lung lymph. Pulmonary arterial pressure (Ppa) peaked within 15 min of the start of rTNF alpha infusion [base-line Ppa = 22.0 +/- 1.5 (SE) cmH2O; after 15 min of rTNF alpha infusion, Ppa = 54.2 +/- 5.4] and then fell toward base line. The pulmonary hypertension was accompanied by hypoxemia and peripheral blood and lung lymph leukopenia, both of which persisted throughout the 4 h of study. These changes were followed by an increase in protein-rich lung lymph flow (base-line lymph protein clearance = 1.8 +/- 0.4 cmH2O; 3 h after rTNF alpha infusion, clearance = 5.6 +/- 1.2), consistent with an increase in pulmonary microvascular permeability. Cardiac output and left atrial pressure did not change significantly throughout the experiment. Light-microscopic examination of lung tissue at autopsy revealed congestion, neutrophil sequestration, and patchy interstitial edema. We conclude that rTNF alpha induces a response in awake sheep remarkable similar to that of endotoxemia. Because endotoxin is a known stimulant of TNF alpha production, TNF alpha may mediate endotoxin-induced lung injury.     

Dose-dependent effects of a pyridoquinazoline thromboxane synthetase inhibitor on arachidonic acid metabolites and hemodynamics during E. coli endotoxemia in anesthetized sheep

We investigated the effects of a new pyridoquinazoline thromboxane synthetase inhibitor infused before administering Escherichia Coli endotoxin into 18 anesthetized sheep with lung lymph fistulas. In normal sheep increasing plasma Ro 23-3423 concentrations were associated with increased plasma levels of 6-keto-PGF1 alpha, a reduced systemic vascular resistance (SVR, r = -0.80) and systemic arterial pressure (SAP, r = -0.92), the mean SAP falling from 80 to 50 mm Hg at the 20 and 30 mg/kg doses. Endotoxin infused into normal sheep caused transient pulmonary vasoconstriction associated with increased TxB2 and 6-keto-PGF1 alpha levels while vasoconstriction and TxB2 increase were significantly inhibited by pretreatment with Ro 23-3423 in a dose-dependent manner. When compared to controls, plasma and lymph levels of 6-keto-PGF1 alpha, PGF2 alpha and PGE2 after endotoxin infusion were increased several-fold by administering Ro 23-3423 up to plasma levels of 10 micrograms/ml. Doses over 30 mg/kg with blood levels above 10 micrograms/ml reduced plasma and lymph levels of 6-keto-PGF1 alpha, PGF2 alpha and PGE2, suggesting cyclooxygenase blockade at this dose. The peak 6-keto-PGF1 alpha levels at 60 min after endotoxin infusion in sheep with Ro-23-3423 levels below 10 micrograms/ml were associated with the greatest systemic hypotension due to a reduced SVR (r = -0.86). After endotoxin infusion the leukotrienes B4, C4, D4 and E4 in lung lymph were assayed by radioimmunoassay and high pressure liquid chromatography and remained at baseline values.     

Pulmonary vascular response to thrombin: effects of thromboxane synthetase inhibition with OKY-046 and OKY-1581

We examined the effects of thromboxane synthetase inhibition with OKY-1581 and OKY-046 on pulmonary hemodynamics and lung fluid balance after thrombin-induced intravascular coagulation. Studies were made in anesthetized sheep prepared with lung lymph fistulas. Pulmonary intravascular coagulation was induced by i.v. infusion of alpha-thrombin over a 15 min period. Thrombin infusion in control sheep resulted in immediate increases in pulmonary artery pressure (Ppa) and pulmonary vascular resistance (PVR), which were associated with rapid 3-fold increase in pulmonary lymph flow (Qlym) and a delayed increase in lymph-to-plasma protein concentration (L/P) ratio, indicating an increase in the pulmonary microvascular permeability to proteins. Thrombin-induced intravascular coagulation also increased arterial thromboxane B2 (a metabolite of thromboxane A2) and 6-keto-PGF1 alpha concentrations (a metabolite of prostacyclin). Both OKY-1581 and OKY-046 prevented thromboxane B2 and 6-keto-PGF1 alpha generation. The initial increments in Ppa and PVR were attenuated in both treated groups. The increases in Qlym were gradual in the treated groups but attained the same levels as in control group. However, the increases in Qlym were associated with decreases in L/P ratio. In both treated groups, the leukocyte count decreased after thrombin infusion but then increased steadily above the baseline value, whereas the leukocyte count remained depressed in the control group after thrombin. These studies indicate that a part of the initial pulmonary vasoconstrictor response to thrombin-induced intravascular coagulation is mediated by thromboxane generation. In addition, thromboxane may also contribute to the increase in lung vascular permeability to proteins that occurs after intravascular coagulation and this effect may be mediated by a thromboxane-neutrophil interaction.     

Effect of endotoxemia on hypoxic pulmonary vasoconstriction in unanesthetized sheep

This study examined the effect of acute endotoxemia on hypoxic pulmonary vasoconstriction (HPV) in awake sheep. Thirteen sheep were chronically instrumented with Silastic catheters in the pulmonary artery, left atrium, jugular vein, and carotid artery; with a Swan-Ganz catheter in the main pulmonary artery; with a chronic lung lymph fistula; and with a tracheostomy. Base-line HPV was determined by measuring the change in pulmonary vascular resistance (PVR) while sheep breathed 12% O2 for 7 min. Concentrations of immunoreactive 6-keto-PGF1 alpha and thromboxane B2 (TXB2) were measured in lung lymph during the hypoxic challenge. Escherichia coli endotoxin (0.2-0.5 micrograms/kg) was infused intravenously. Four hours after endotoxemia, HPV was measured. In five sheep, meclofenamate was infused at 4.5 h after endotoxemia and HPV measured again. During the base-line hypoxic challenge, PVR increased by 36 +/- 9% (mean +/- SE). There was no significant change in lung lymph 6-keto-PGF1 alpha or TXB2 levels with hypoxia. Twelve of the 13 sheep showed a decrease in HPV 4 h after endotoxemia; the mean change in PVR with hypoxia was -8 +/- 5%, which was significantly (P less than 0.05) reduced compared with base-line HPV. The infusion of meclofenamate at 4.5 h after endotoxin did not restore HPV.     

Thromboxane A2 and prostacyclin do not modulate pulmonary hemodynamics during exercise in sheep

The purpose of this study was to determine the role of thromboxane and prostacyclin in modulating pulmonary hemodynamics during maximal cardiopulmonary stress in the healthy lung. We studied 11 yearling sheep in paired studies during progressive maximal treadmill exercise with and without meclofenamate (n = 5), ibuprofen (n = 6), or UK38485 (n = 2). We also studied five sheep during hypoxia and hypoxic exercise, and six sheep during prolonged steady-state treadmill exercise for 45-60 min with and without drug treatment. We measured the metabolites of thromboxane A2 (thromboxane B2, TxB2) and prostacyclin (6-ketoprostaglandin F1 alpha, 6-keto-PGF1 alpha) in blood plasma and lung lymph in each protocol. We found that progressive exercise significantly reduced pulmonary vascular resistance but that cyclooxygenase or thromboxane synthesis blockade did not alter the change. Plasma TxB2 rose minimally but significantly during maximal exercise, but 6-keto-PGF1 alpha did not change. During continuous hypoxia, exercise reduced pulmonary vascular resistance nearly to base-line levels, but the degree of reduction was also unchanged by drug treatment. There were also no significant changes in lymph or plasma TxB2 or 6-keto-PGF1 alpha during 45-60 min of continuous moderate exercise. We conclude that neither TxB2 nor prostacyclin modulate pulmonary hemodynamics in the normal lung during maximal exercise, prolonged moderate exercise, or exercise-induced reductions in vascular resistance during hypoxia.     

Low-dose PGI2 prevents monocrotaline-induced thromboxane production and lung injury

In animals, monocrotaline induces an acute lung injury secondary to capillary endothelial damage. To date, no reports have appeared dealing with the role of prostaglandins in monocrotaline-induced injury. Our studies, in dogs, revealed that monocrotaline (30 mg/kg iv) caused an acute and persistent thrombocytopenia, lung platelet deposition, pulmonary hypertension, and increased extravascular lung water (EVLW). The pulmonary hypertensive response was biphasic. Thromboxane B2 levels were similarly biphasic, peaking at 5 min and 2 h. The levels of 6-keto-PGF1 alpha peaked at 30 min and returned to base line at 3 h. Pulmonary vascular resistance paralleled thromboxane levels. Infusion of prostacyclin (PGI2) at 50 ng X kg-1 X min-1 effectively prevented the thrombocytopenia, lung platelet deposition, pulmonary hypertension, and increased EVLW; and it decreased excess thromboxane production by 79%. These results suggest that platelet activation and lung sequestration play a role in acute lung injury due to monocrotaline, and that the resultant thromboxane production may contribute to the pulmonary hypertension. PGI2 ameliorates monocrotaline-induced injury, perhaps by preventing platelet activation.     

Effects of dibutyryl cAMP on pulmonary air embolism-induced lung injury in awake sheep

To assess the role of intracellular adenosine 3',5'-cyclic monophosphate (cAMP), we tested the effects of dibutyryl cAMP (DBcAMP), an analogue of cAMP, on lung injury induced by pulmonary air embolism in awake sheep with chronic lung lymph fistula. We infused air (1.23 ml/min) in the pulmonary artery for 2 h in untreated control sheep. In DBcAMP-pretreated sheep DBcAMP was infused (1 mg/kg bolus and 0.02 mg.kg-1.min-1 constantly for 5 h); after 1 h from beginning of DBcAMP administration the air infusion was started. After the air infusion, pulmonary arterial pressure (Ppa) and lung lymph flow rate (Qlym) significantly increased in both groups. DBcAMP-pretreated sheep showed significantly lower responses in Qlym (2.7 X base line) compared with untreated control sheep (4.6 X base line); however, Ppa, left atrial pressure, and lung lymph-to-plasma protein concentration ratio were not significantly different between the two groups. Although plasma and lung lymph thromboxane B2 and 6-ketoprostaglandin F1 alpha concentrations increased significantly during the air infusion, DBcAMP-pretreated sheep showed significantly lower responses. Thus DBcAMP infusion attenuated pulmonary microvascular permeability induced by air embolism. We conclude that pulmonary vascular permeability is in part controlled by the intracellular cAMP level.     

Endotoxin-induced lung injury in rats: role of eicosanoids

We studied lung vascular injury and quantitated lung eicosanoids in rats after intraperitoneal injection of Salmonella enteritidis endotoxin. Within 40 min after endotoxin injection (20 mg/kg), lung tissue thromboxane B2 doubled, although 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) increased by 8- to 10-fold. Lung 5-hydroxyeicosatetraenoic acid and leukotriene C4 were variably increased by endotoxin. The levels of all eicosanoids returned to base line 6 h after endotoxin challenge. Lung vascular injury, as assessed by the extravascular accumulation of 125I-albumin and water in isolated perfused lungs, was observed 90 min after endotoxin injection (0.02-20 mg/kg) in vivo. Inhibition of the cyclooxygenase pathway with indomethacin and the lipoxygenase pathway with diethylcarbamazine and 2-(12-hydroxydodeca-5,10-dinyl)-3,5,6-trimethyl-1,4-benzoqui none failed to attenuate endotoxin-induced lung injury. In addition, essential fatty acid deficiency, which markedly reduced lung tissue levels of 6-keto-PGF1 alpha, thromboxane B2, and leukotriene C4, did not protect against endotoxin injury. We conclude that although lung eicosanoids are activated during endotoxemia, they do not play a crucial role in the development of acute lung vascular injury in rats.     

Pulmonary hypertensive response to foreign body microemboli

Pulmonary hypertension and foreign body granulomas are recognized sequelae of chronic intravenous drug abuse. We have recently described the development of transient pulmonary hypertension and increased permeability pulmonary edema after the intravenous injection of crushed, suspended pentazocine tablets in both humans and dogs. To determine the role of vasoactive substances in the development of this transient pulmonary hypertension, we measured pulmonary hemodynamics and accumulation of arachidonic acid metabolites in dogs during the infusion of indomethacin, a cyclooxygenase inhibitor, diethylcarbamazine (DEC), a lipoxygenase inhibitor, and FPL 55712, a receptor antagonist for leukotriene C4/D4 (LTC4/D4). Following the intravenous administration of crushed, suspended pentazocine tablets (3-4 mg/kg of body weight), mean pulmonary artery pressure increased from 14 +/- 2 mmHg to 30 +/- 6 mmHg (p less than 0.05) at 60 secs with a concomitant increase in plasma concentrations of 6-keto-PGF1 alpha from 187 +/- 92 pg/ml to 732 +/- 104 pg/ml and thromboxane B2 from 206 +/- 83 pg/ml to 1362 +/- 117 pg/ml (both p less than 0.05). Indomethacin prevented the increase in both cyclooxygenase metabolites, but had no effect on the pulmonary hypertension. In contrast, DEC had no effect on the increase in cyclooxygenase products, but blocked the pulmonary hypertension. FPL 55712 did not effect either the increase in cyclooxygenase metabolites or the pulmonary hypertension. We conclude that the transient pulmonary hypertension, induced by the intravenous injection of crushed, suspended pentazocine tablets, is not mediated by cyclooxygenase products but may be mediated by lipoxygenase product(s) other than LTC4/D4.     

Role of platelet-activating factor in the ovine heparin-protamine reaction.

Platelet-activating factor (PAF) infusion into sheep, as well as protamine reversal of heparin anticoagulation, causes thromboxane release into plasma, pulmonary hypertension, hypoxemia, and leukopenia. We investigated the possible role of PAF in the heparin-protamine reaction. Intravenous protamine was administered to neutralize heparin anticoagulation in five awake sheep and caused an increase of mean pulmonary arterial pressure from 16.6 +/- 1 (SE) mmHg at base-line to 47 +/- 9 mmHg at 1 min after protamine injection (P < 0.01) because of a 4.5-fold increase of pulmonary vascular resistance. This neutralization reaction induced a 25% reduction of circulating leukocyte count and arterial PO2. Undetectable blood levels of PAF were measured by bioassay and high-performance liquid chromatography during these heparin-protamine reactions. Infusion of BN 52021 (20 mg/kg), a PAF receptor antagonist, before rechallenging the same sheep with heparin and then protamine did not reduce the level of peak pulmonary hypertension or the degree of hypoxemia and leukopenia. We conclude that the leukopenia and thromboxane-mediated pulmonary vasoconstriction occurring after rapid intravascular formation of heparin-protamine complexes in sheep are not due to the release of PAF.     

Verapamil attenuates lung vascular responses to endotoxin in sheep

Experiments were conducted on five chronically instrumented unanesthetized sheep to determine the effects of verapamil, a calcium channel inhibitor, on the pulmonary hemodynamic and microvascular permeability responses to endotoxemia. Paired control endotoxemia experiments (E) and endotoxemia with verapamil treatment (30-60 micrograms.kg-1.min-1) experiments (V + E) were conducted on each sheep in random order. In the V + E experiments sheep were pretreated with a continuous intravenous infusion of verapamil 1.5-2.0 h before endotoxin infusion (1.0 microgram/kg, given over 15 min). Verapamil significantly increased base-line pulmonary arterial pressure, left atrial pressure, lung lymph flow rate, and circulating blood leukocyte levels and significantly decreased base-line cardiac output. During the endotoxin response, verapamil significantly attenuated both phase I pulmonary arterial hypertension and phase II lung lymph flow rate compared with control endotoxin experiments. The results indicate that verapamil attenuates both the pulmonary hemodynamic and increased lung microvascular permeability response to endotoxin in sheep. In a series of in vitro experiments, verapamil was found to be a potent inhibitor of phorbol myristate acetate-induced superoxide production in isolated sheep granulocytes. These data suggest that the beneficial in vivo effects of verapamil during endotoxemia may in part be due to its inhibition of increased free cytosol calcium concentration and/or inhibition of toxic O2 metabolite production.     

Endotoxemia produces an increase in arterial but not venous lipid peroxides in sheep

Our purpose was to determine the effect of an endotoxin-induced lung injury on circulating lipid peroxides. We measured both malondialdehyde (MDA) and conjugated dienes (as optical density at 233 nm) in aortic and venous plasma and lung lymph in 10 unanesthetized sheep given 1 microgram/kg of Escherichia coli endotoxin. Total lipids and prostanoids 6-ketoprostaglandin F1 alpha and thromboxane B2 were also measured. Six control sheep were also studied. Animals were monitored for a 12-h period and then killed, and lung tissue MDA was determined. A two-phase endotoxin response was noted with an initial pulmonary hypertension followed by a steady-state increase in protein-rich lung lymph flow (QL) between a 3- and 6-h period. Aortic plasma MDA was significantly increased from a base line of 4.8 +/- 1.4 to 8.9 +/- 1.6 and 7.5 +/- 1.3 nmol/ml at 1 and 4 h post-endotoxin. Aortic plasma conjugated dienes increased in all 10 sheep post-endotoxin. Venous levels of both MDA and conjugated dienes were not significantly increased. Lung QL increased two- to three-fold. Lung lymph MDA increased significantly at 1 h post-endotoxin. Lymph conjugated dienes decreased. Plasma and lymph lipid peroxide levels returned to base line by 12 h in most animals. However, tissue MDA remained significantly increased in all sheep from base line of 45 +/- 9 to 85 +/- 14 nmol/g tissue. We conclude that both MDA and conjugated dienes are transiently released into aortic plasma during endotoxin-induced oxidant lung injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pulmonary vascular response to leukotriene D4 in unanesthetized sheep: role of thromboxane

We examined the pulmonary vascular response to an intravenous leukotriene D4 (LTD4) injection of (1 microgram X kg-1 X min-1 for 2 min) immediately followed by infusion of 0.133 microgram X kg-1 X min-1 for 15 min in awake sheep prepared with lung lymph fistulas. LTD4 resulted in rapid generation of thromboxane A2 as measured by an increase in plasma thromboxane B2 concentration. The thromboxane B2 generation was associated with increases in pulmonary arterial and pulmonary arterial wedge pressures while left atrial pressure did not change significantly. Pulmonary lymph flow (Qlym) increased (P less than 0.05) transiently from base line 6.87 +/- 1.88 (SE) ml/h to maximum value of 9.77 +/- 1.27 at 15 min following the LTD4 infusion. The maximum increase in Qlym was associated with an increase in the estimated pulmonary capillary pressure. The increase in Qlym was not associated with a change in the lymph-to-plasma protein concentration (L/P) ratio. Thromboxane synthetase inhibition with dazoxiben (an imidazole derivative) prevented thromboxane B2 generation after LTD4 and also prevented the increases in pulmonary vascular pressures and Qlym. We conclude that LTD4 in awake sheep increases resistance of large pulmonary veins. The small transient increase in Qlym can be explained by the increase in pulmonary capillary pressure. Thromboxane appears to mediate both the pulmonary hemodynamic and lymph responses to LTD4 in sheep.     

Intravascular macrophage depletion attenuates endotoxin lung injury in anesthetized sheep.

We recently showed that we can selectively and safely deplete most (average 85%) of the pulmonary intravascular macrophages in sheep by intravenously infusing liposomes containing dichloromethylene bisphosphonate. After a 1-h stable baseline, we made a 6-h comparison after a 30-min intravenous endotoxin infusion (1 microg/kg) between six anesthetized control lambs and six anesthetized lambs in which the intravascular macrophages had been depleted 24 h previously. Three of the control lambs had been macrophage depleted and allowed to recover their intravascular macrophage population for >/=2 wk. After depletion, both the early and late pulmonary arterial pressure rises were dramatically attenuated. Our main interest, however, was in the acute lung microvascular injury response. The early and late rises in lung lymph flow and the increase in lung lymph protein clearance (lymph flow x lymph-to-plasma protein concentration ratio) were >90% attenuated. We conclude the pulmonary intravascular macrophages are responsible for most of the endotoxin-induced pulmonary hypertension and increased lung microvascular leakiness in sheep, although the unavoidable injury of other intravascular macrophages by the depletion regime may also contribute something.     

Effects of thromboxane synthase and cyclooxygenase inhibition on PAF-induced changes in lung function and arachidonic acid metabolism.

PAF was administered as an intravenous bolus (0.1 micrograms/kg) to eight chronically instrumented awake sheep. The effects of pretreatment with an inhibitor of cyclooxygenase (meclofenamate) on PAF-induced changes in lung function were compared to those observed with a specific inhibitor of thromboxane synthase (DP1904). Each animal was studied four times in varied order: PAF alone, PAF + DP1904, PAF + meclofenamate, and DP1904 alone. Saline alone (control), DP1904 alone, and meclofenamate alone did not cause changes in any of the measured variables. DP1904 and meclofenamate significantly attenuated the PAF-induced fall in lung compliance, elevation in peak pulmonary artery pressure, and increased lung lymph flow. Both drugs abolished the PAF-induced increases in lung lymph thromboxane B2 concentrations. Meclofenamate, but not DP1904, blocked the rise in lymph 6-keto-PGF1 alpha. Although meclofenamate blocked the rise in lymph PGE2, DP1904 resulted in levels 2.7 times higher than PAF alone. We conclude that: (1) inhibition of thromboxane synthase is as effective as inhibition of cyclooxygenase in attenuating PAF-induced changes in lung function, and (2) thromboxane synthase inhibition results in augmented production of PGE2 following PAF administration in vivo.     

Pulmonary response to group B streptococcal toxin in young lambs

Marked respiratory distress is seen in severe early onset group B beta-hemolytic streptococcal (GBS) disease in newborn infants. To investigate the pathophysiological effects of a polysaccharide toxin from GBS type III cultures, obtained from an infant who died from this disease, young chronically instrumented, unanesthetized lambs were studied with measurements of lung mechanics, lung volumes, ventilation, hemodynamics, and lung vascular permeability. Intravenously administered GBS toxin resulted in a biphasic response with an early threefold increase in total lung resistance, 40% decrease in dynamic lung compliance, and 30% increase in minute ventilation coinciding with hypoxemia, pulmonary hypertension, and fever. A second phase of the response followed consisting of less prominent changes in these variables as well as increased lung lymph protein clearance compatible with increased vascular permeability. The temporal close relationship between marked leukopenia and increased lung lymph thromboxane B2 concentrations to the simultaneously occurring pulmonary hypertension and changes in lung mechanics suggests that leukocytes and thromboxane A2 may be mediators of these GBS toxin-induced effects.     

Effect of LY171883 on endotoxin-induced lung injury in pigs

We evaluated the role of sulfidopeptide leukotrienes as mediators of endotoxin-induced respiratory failure in pigs. Escherichia coli endotoxin (055-B5) was infused intravenously into anesthetized 10- to 14-wk-old pigs at 5 micrograms/kg the 1st h followed by 2 micrograms.kg-1.h-1 for 3 h in the presence and absence of LY171883, a specific leukotriene D4 (LTD4)/LTE4 receptor antagonist. Endotoxin caused hemoconcentration, granulocytopenia, decreased cardiac index, systemic hypotension, pulmonary hypertension, increased pulmonary vascular resistance, bronchoconstriction, hypoxemia, increased permeability of the alveolar-capillary membrane, pulmonary edema, and increased plasma concentrations of thromboxane B2 (TxB2), prostaglandin F2 alpha (PGF2 alpha), and 6-keto-PGF1 alpha. LY171883 did not modify endotoxin-induced cardiopulmonary and hematologic abnormalities, except for a modest attenuation of pulmonary hypertension (at 1 h) and increased pulmonary vascular resistance (at 1-2 h). Ex vivo stimulation of whole blood with calcium ionophore caused large increases in plasma concentrations of TxB2, PGF2 alpha, and LTB4. These increases were not significantly modified in blood derived from pigs treated with LY171883, indicating no inhibition of cyclooxygenase or 5-lipoxygenase. We conclude that LTD4 and LTE4 are not important mediators of endotoxin-induced lung injury in anesthetized pigs, although they may contribute modestly to pulmonary vasoconstriction.