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.     

Platelet-activating factor increases lung vascular permeability to protein

We studied the effects of platelet-activating factor (PAF) on pulmonary hemodynamics and microvascular permeability in unanesthetized sheep prepared with lung-lymph fistulas. Since cyclooxygenase metabolites have been implicated in mediating these responses, we also examined the role of the cyclooxygenase pathway. PAF infusion (4 micrograms X kg-1 X h-1 for 3 h) produced a rapid, transient rise in pulmonary arterial pressure (Ppa), pulmonary vascular resistance (PVR), plasma thromboxane B2 concentration (TxB2), and pulmonary lymph flow (Qlym). The lymph-to-plasma protein concentration ratio (L/P) did not change from base line. Pretreatment with the cyclooxygenase inhibitor, sodium meclofenamate, prevented the generation of TxB2 and the hemodynamic changes but did not prevent the increase in Qlym. The estimated protein reflection coefficient decreased from a control value of 0.66 +/- 0.04 to 0.43 +/- 0.06 after PAF infusion. We also studied the effects of PAF on endothelial permeability in vitro by measuring the flux of 125I-albumin across cultured bovine pulmonary artery endothelial cells (EC) grown to confluency on a gelatinized micropore filter and mounted within a modified Boyden chemotaxis chamber. PAF (10(-8) to 10(-4) M) had no direct effect on EC albumin permeability, suggesting that the increase in permeability in sheep was not the direct lytic effect of PAF. In conclusion, PAF produces pulmonary vasoconstriction mediated by cyclooxygenase metabolites. PAF also increases pulmonary vascular permeability to protein that is independent of cyclooxygenase products and is not the result of a direct effect of PAF on the endothelium.     

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.     

Prostaglandin synthesis does not mediate the pulmonary vasodilatory effect of acetylcholine.

We wondered if inhibition of hypoxic pulmonary vasoconstriction by acetylcholine was mediated by prostaglandin synthesis. In 5 calves at a simulated altitude of 4,570 m, acetylcholine (10 mug/kg/min) decreased mean pulmonary arterial pressure and total pulmonary resistance by 24 +/- 2 and 35 +/- 3% before and by 21 +/- 2 and 27 +/- 4% after the administration of meclofenamate (2 mg/kg). Since there was no difference in the effect of acetylcholine before and after meclofenamate, it was concluded that pulmonary vasodilation by activation of muscarinic receptors was not dependent on prostaglandin synthesis.     

Chronic propranolol treatment decreases pulmonary artery pressure in conscious dogs

Daily administration of propranolol to 9 chronically instrumented, trained dogs for 2 weeks caused significant (p less than 0.05) decreases in heart rate (70 +/- 8 to 57 +/- 6 beats/min), cardiac output (3.6 +/- 0.3 to 2.9 +/- 0.2 liters/min), pulmonary arterial pressure (15.7 +/- 0.5 to 10.0 +/- 0.5 mm Hg) and total pulmonary vascular resistance (4.6 +/- 0.6 to 3.3 +/- 0.4 units). Nadolol, a structurally dissimilar beta-adrenergic receptor antagonist, caused a similar decrease in total pulmonary resistance. Acute meclofenamate administration did not return to normal pulmonary arterial pressure and resistance in the dogs chronically treated with beta-adrenergic receptor blockers. We therefore conclude that chronic beta-adrenergic receptor blockade lowered pulmonary arterial pressure and resistance by a mechanism independent of cyclooxygenase. In addition, chronic beta-adrenergic receptor blockade did not affect the potential for hypoxic vasoconstriction.     

Mechanism of peptidoleukotriene-induced increases in pulmonary transvascular fluid filtration

We examined the effects of leukotrienes C4 (LTC4) and D4 (LTD4) (1 microgram) on the pulmonary vascular filtration coefficient, a measure of vessel wall conductivity to water, and the alterations in pulmonary vascular resistance (PVR) in isolated-perfused guinea pig lungs. We also assessed whether LTC4 and LTD4 increased the permeability to albumin in cultured monolayers of pulmonary artery endothelial cells. In Ringer-perfused and blood-perfused lungs, LTC4 resulted in increases in pulmonary arterial pressure (Ppa) and the pulmonary capillary pressure (Pcap) measured as the equilibration pressure after simultaneous pulmonary arterial and venous occlusions. Pulmonary venous resistance (Rv) increased to a greater extent than arterial resistance (Ra) in both Ringer-perfused and blood-perused lungs challenged with LTC4. The greater increase in PVR in blood-perfused lungs corresponded with a greater elevation of lung effluent thromboxane B2 (TxB2) concentration. The LTC4-stimulated increase in PVR was prevented by pretreatment with meclofenamate (10(-4) M). LTD4 also induced rapid increases in Ppa and Pcap in both Ringer-perfused and blood-perfused lungs; however, Ppa decreased before stabilizing at a pressure higher than base line. The increases in Rv with LTD4 were greater than Ra. The LTD4-stimulated increases in Ra and Rv also paralleled the elevation in TxB2 concentration. As with LTC4, the increases in Ppa, Pcap, PVR, and TxB2 concentration were greater in blood-perfused than in Ringer-perfused lungs. Pretreatment with meclofenamate reduced the magnitude of the initial increase in Ppa, but did not prevent the response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pulmonary microcirculatory responses to leukotrienes B4, C4 and D4 in sheep

The pulmonary microvascular responses to leukotrienes B4, C4, and D4 (total dosage of 4 micrograms/kg i.v.) were examined in acutely-prepared halothane anesthetized and awake sheep prepared with lung lymph fistulas. In anesthetized as well as unanesthetized sheep, LTB4 caused a marked and transient decrease in the circulating leukocyte count. Pulmonary transvascular protein clearance (pulmonary lymph flow X lymph-to-plasma protein concentration ratio) increased transiently in awake sheep, suggesting a small increase in pulmonary vascular permeability. The mean pulmonary artery pressure (Ppa) also increased. In the acutely-prepared sheep, the LTB4-induced pulmonary hemodynamic and lymph flow responses were damped. Leukotriene C4 increased Ppa to a greater extent in awake sheep than in anesthetized sheep, but did not significantly affect the pulmonary lymph flow rate (Qlym) and lymph-to-plasma protein concentration (L/P) ratio in either group. LTD4 increased Ppa and Qlym in both acute and awake sheep; Qlym increased without a significant change in the L/P ratio. The LTD4-induced rise in Ppa occurred in association with an increase in plasma thromboxane B2 (TxB2) concentration. The relatively small increase in Qlym with LTD4 suggests that the increase in the transvascular fluid filtration rate is the result of a rise in the pulmonary capillary hydrostatic pressure. In conclusion, LTB4 induces a marked neutropenia, pulmonary hypertension, and may transiently increase lung vascular permeability. Both LTC4 and LTD4 cause a similar degree of pulmonary hypertension in awake sheep, but had different lymph flow responses which may be due to pulmonary vasoconstriction at different sites, i.e. greater precapillary constriction with LTC4 because Qlym did not change and greater postcapillary constriction with LTD4 because Qlym increased with the same rise in Ppa.     

Effect of inhibition of 5-lipoxygenase metabolism of arachidonic acid on response to endotoxemia in sheep

We studied the effects of a 5-lipoxygenase inhibitor, L-651,192, on the pulmonary dysfunction caused by endotoxemia in chronically instrumented unanesthetized sheep. The efficacy and selectivity of L-651,392 were tested by measuring in vivo production of leukotriene B4 (LTB4) and cyclooxygenase products of arachidonic acid after endotoxemia before and after pretreatment with L-651,392 and ex vivo from granulocytes and whole blood stimulated with calcium ionophore from sheep before and 24 h after pretreatment with L-651,392. A novel assay for LTB4 by high-performance liquid chromatography/gas chromatography/mass spectrometry techniques was developed as a measure of 5-lipoxygenase metabolism of arachidonic acid. L-651,392 proved to be an effective in vivo 5-lipoxygenase inhibitor in sheep. L-651,392 blocked the increase in LTB4 observed in lung lymph after endotoxemia in vivo in sheep as well as inhibited by 80% the ex vivo production of LTB4 by granulocytes removed from sheep treated 24 h earlier with L-651,392. Although L-651,392 blocked the increase in cyclooxygenase products of arachidonic acid observed in lung lymph after endotoxemia in vivo in sheep, the drug probably did not function directly as a cyclooxygenase inhibitor. L-651,392 did not attenuate the ex vivo production of thromboxane B2 by whole blood from sheep treated 24 h earlier with the drug. L-651,392 attenuated the alterations in pulmonary hemodynamics, lung mechanics, oxygenation, and lung fluid and solute exchange observed after endotoxemia in sheep. We speculate that 5-lipoxygenase products are a major stimulus for cyclooxygenase metabolism of arachidonic acid after endotoxemia in sheep.     

Pulmonary hypertension and increased vasoreactivity caused by repeated indomethacin in sheep

Six chronically catheterized awake sheep were given the cyclooxygenase inhibitor indomethacin (5 mg/kg) twice a day over a 3-wk period. Three sheep receiving vehicle alone served as controls. Pulmonary arterial, left atrial, and systemic arterial pressures, cardiac output, blood gases, and pH were measured biweekly. Pulmonary vasoreactivity to 12% O2 and an analogue of prostaglandin H2 (PGH2-A) was also assessed. As a percent of base line, indomethacin caused a doubling in pulmonary vascular resistance (3 wk = 190 +/- 26%, mean +/- SE) and a 50% increase in pulmonary arterial pressure (3 wk = 151 +/- 9%). Vasoreactivity to 12% O2 increased approximately fourfold during the 1st wk of treatment and then declined. Vasoreactivity to PGH2-A increased steadily, nearly doubling by 3 wk. Light-microscopic counts of peripheral lung biopsy tissue revealed marked sequestration of granulocytes. Morphometric techniques applied to lungs removed at autopsy and fixed with the pulmonary arteries distended with barium gelatin mixture showed a significant reduction in number of barium-filled peripheral arteries and reduction in their external diameter. We conclude that repeated administration of indomethacin alters pulmonary vasoreactivity and causes sustained pulmonary hypertension. Structural studies reveal peripheral lung inflammation and changes in the arterial circulation that are perhaps more consistent with maintained vasoconstriction than chronic pulmonary hypertension.     

Leukotriene B4 increases pulmonary transvascular filtration by a neutrophil-independent mechanism

We examined the role of circulating granulocytes in the pulmonary microvascular response to leukotriene B4 (LTB4) by prior depletion of circulating granulocytes using hydroxyurea. LTB4 (2 micrograms/kg injection followed by infusion of 2 micrograms/kg over 15 min) produced transient increases in pulmonary arterial pressure and pulmonary vascular resistance, indicating that neutrophils were not required for the pulmonary hemodynamic effects of LTB4. Infusion of LTB4 in granulocyte-depleted sheep also resulted in transient increases in pulmonary lymph flow (QL) with no significant change in the lymph-to-plasma protein concentration ratio (L/P), findings similar to those in control animals. In vitro studies indicated that LTB4 (10(-7) or 10(-9) M) produced a transient adherence of neutrophils to cultured pulmonary artery endothelial monolayers. Maximal responses occurred at 10 min after the addition of LTB4 to the endothelial cell-neutrophil coculture system, and the adherence decreased to base line within 60 min. LTB4 infusion in sheep also produced a transient uptake of autologous 111In-oxine-labeled neutrophils. The results indicate that LTB4-mediated increase in pulmonary transvascular protein clearance (QL x L/P) is independent of circulating granulocytes.     

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.     

Nafamstat mesilate attenuates pulmonary hypertension in heparin-protamine reactions

Rapid protamine reversal of heparin anticoagulation in awake sheep caused, after 1 min, a approximately 15-fold increase of arterial plasma thromboxane B2 (TxB2) levels, a 4-fold rise of pulmonary vascular resistance (PVR), a 2-fold rise of pulmonary arterial pressure, and after 3 min, a 2-fold rise of ovine arterial plasma complement C3a levels (P less than 0.05). Infusion of nafamstat mesilate (FUT-175), a protease and complement pathway inhibitor, before protamine reduced these increases by approximately 60-90% (P less than 0.05). FUT-175 did not modify heparin + protamine-induced leukopenia, suggesting that FUT-175 incompletely blocked C5a production. We also learned that infusing protamine first and heparin 5 min later did not increase either plasma C3a or TxB2 levels or PVR while the activated clotting time increased only minimally. Thus, in awake sheep, the sequence of heparin and protamine infusion influences complement activation and pulmonary vasoconstriction. FUT-175 pretreatment reduces thromboxane release and pulmonary vasoconstriction probably by limiting complement activation.     

Cyclooxygenase blockers inhibit ethanol-induced pulmonary vasoconstriction in lambs

We investigated the mechanism of ethanol-induced pulmonary vasoconstriction in lambs, by a pharmacological approach. We chronically instrumented 28 lambs to determine whether phentolamine (alpha-block), propranolol (beta-block), promethazine and cimetidine (H1- and H2-block), high-dose indomethacin, or low- and high-dose meclofenamate (cyclooxygenase block) altered the vasoconstriction. Ethanol alone increased pulmonary vascular resistance from 0.14 to 0.49 Torr.ml-1.kg-1.min (U). Only indomethacin (7-8 mg/kg po) and high-dose meclofenamate (7-8 mg/kg iv) abolished the pulmonary vascular response to ethanol infusion. Pulmonary vascular resistance was 0.14 U after ethanol plus indomethacin and was 0.2 U after ethanol plus high-dose meclofenamate (P = NS vs. base line). Low-dose meclofenamate (2 mg/kg) attenuated the vasoconstrictor response. Systemic vascular resistance increased moderately after ethanol and had a similar pattern of inhibition by cyclooxygenase blockade. Cardiac output and heart rate decreased nearly significantly after ethanol (P less than 0.06), a tendency that was also ablated by cyclooxygenase inhibition. Thus the acute cardiocirculatory response to ethanol involves an intact prostaglandin synthase system in lambs. To our knowledge, these data are the first documentation that cyclooxygenase enzyme blockade can eliminate the acute cardiac and vascular effects of ethanol in a whole-animal system.     

Enhancement of plasma levels of biologically active leukotriene B compounds during anaphylaxis in guinea pigs pretreated by indomethacin or by a fish oil-enriched diet

The changes in arterial plasma concentrations of immunoreactive leukotriene B (LTB) were compared after antigen challenge of two groups of sensitized, mepyramine-treated, and mechanically ventilated guinea pigs, one fed a diet enriched with fish oil and the other a control diet enriched with beef tallow. The lung tissue of animals fed a fish oil-enriched diet (FFD) for 9 to 10 wk incorporated eicosapentaenoic acid (EPA) and docosahexaenoic acid to constitute 8 to 9% of total fatty acid content, whereas these alternative fatty acids constituted less than 1% of the total fatty acid content of the lung tissue of animals on a beef tallow-supplemented diet (BFD). The maximum increase after antigen challenge in immunoreactive LTB4 from 0.16 +/- 0.04 ng/ml to 0.84 +/- 0.25 ng/ml in BFD animals and from 0.47 +/- 0.11 to 5.1 +/- 1.4 ng/ml immunoreactive LTB (LTB4 and LTB5) in FFD animals was significant (p less than 0.02) for each. Furthermore, the increase in total immunoreactive LTB in mepyramine-treated FFD animals was significantly greater than the increase in LTB4 in mepyramine-treated BFD guinea pigs at 2 to 8 min after antigen challenge (p less than 0.05). Resolution of arterial plasma immunoreactive LTB from pooled samples by reverse-phase high-performance liquid chromatography demonstrated that the sum of LTB4 and LTB5 in FFD animals exceeded that of LTB4 in BFD animals and that the quantity of LTB4 in the FFD animals was at least as great as that in the BFD animals during anaphylaxis. The products eluting at the retention times of LTB4 and LTB5 exhibited the chemotactic activity of their respective synthetic standards. The combination of indomethacin and mepyramine markedly augmented the antigen-induced increase in arterial plasma immunoreactive LTB4 concentrations in BFD animals, but had no effect on immunoreactive LTB levels in FFD animals. Limited in vivo measurements showing a lesser increase of plasma immunoreactive thromboxane B2 in the FFD relative to the BFD animals during anaphylaxis and ex vivo measurements showing a decreased LTB4-stimulated (cyclooxygenase product-dependent) contractile response of pulmonary parenchymal strips from the FFD relative to the BFD animals provide evidence for blockade in the cyclooxygenase pathway in the FFD animals. The measurements of arterial plasma LTB indicate that indomethacin treatment alone, which inhibits cyclooxygenase activity, and FFD treatment each augment the metabolism of arachidonic acid by the 5-lipoxygenase pathway in animals pretreated with mepyramine.(ABSTRACT TRUNCATED AT 400 WORDS)     

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.     

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.     

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)     

OKY-046 prevents increases in LTB4 and pulmonary edema in phorbol ester-induced lung injury in dogs.

Thromboxanes (Txs) were implicated as possible participants in the altered microvascular permeability of acute lung injury when the Tx synthase inhibitor, OKY-046, was reported to prevent pulmonary edema induced by phorbol myristate acetate (PMA). Recently, however, we found that OKY-046, at a dose just sufficient to block Tx synthesis in intact dogs, did not prevent PMA-induced pulmonary edema but rather merely reduced it modestly. The present study was designed to explore other mechanisms whereby OKY-046 might prevent PMA-induced pulmonary edema. The finding that 5-lipoxygenase (5-LO) metabolites of arachidonic acid were increased within the lung after PMA administration, coupled with the report that OKY-046 inhibited slow-reacting substance of anaphylaxis formation, permitted formulation of the hypothesis that OKY-046, at a dose in excess of that required to inhibit Tx synthesis, inhibits the formation of a product(s) of 5-LO and, thereby, prevents edema formation. In vehicle-pretreated pentobarbital-anesthetized male mongrel dogs (n = 4), PMA (20 micrograms/kg i.v.) increased pulmonary vascular resistance (PVR) from 4.4 +/- 0.3 to 26.3 +/- 8.8 mmHg.l-1 x min (P < 0.01) and extravascular lung water from 6.7 +/- 0.5 to 19.1 +/- 6.2 ml/kg body wt (P < 0.05). Concomitantly, both TxB2 and leukotriene B4 (LTB4) were significantly increased in the lung. Pretreatment with OKY-046 (100 mg/kg i.v., n = 8) prevented PMA-induced increases in TxB2, LTB4, and pulmonary edema formation but did not prevent the increase in PVR.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of platelet depletion on lung vasoconstriction in heparin-protamine reactions

In six awake sheep the control heparin-protamine reaction was associated with a 150-fold rise in arterial plasma thromboxane B2 (TxB2) levels, a 4.5-fold increase in pulmonary vascular resistance, a 20% decrease in cardiac output, a 30% decrease in arterial PO2, and a 30% reduction in arterial white blood cell concentrations. Depletion of 99% of circulating platelets by antibodies did not prevent either acute and severe pulmonary hypertension or increased plasma TxB2 levels induced by heparin-protamine administration. We produced sheep platelet aggregation in vitro with bovine thrombin and measured marked TxB2 release (36.3 +/- 16.3 ng/10(9) platelets). In contrast, neither heparin, protamine, nor heparin-protamine complexes over a 10,000-fold range of concentrations induced platelet aggregation and release of thromboxane in vitro. Therefore sheep platelets are not the source of thromboxane production associated with acute pulmonary hypertension during the heparin-protamine reaction, and other cells must produce the thromboxane.     

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.