Oxygen-induced lung microvascular injury in neutropenic rabbits and lambs

We did two studies to see if severe neutropenia might reduce the severity or delay development of O2-induced lung microvascular injury. First, we treated 11 rabbits with nitrogen mustard until their circulating neurophil count decreased to less than 50/microliters of blood, after which the rabbits breathed pure O2 until death; nine other rabbits received no nitrogen mustard and had normal numbers of circulating neutrophils during O2 breathing. All rabbits died of respiratory failure with pulmonary edema, and although chemotherapy decreased the number of neutrophils in the lungs by greater than 90%, it did not influence survival time or extravascular lung water content. To see if severe neutropenia might slow the development of O2-induced lung microvascular injury, we assessed the effects of sustained hyperoxia on lung fluid balance in unanesthetized lambs treated with hydroxyurea, so that their absolute neutrophil count was less than 50/microliters of blood. We measured pulmonary arterial and left atrial pressures, cardiac output, lung lymph flow, and concentrations of protein in lymph and plasma during a 2- to 4-h control period and then daily for 2 to 4 h as the lambs continuously breathed pure O2. After 3 days of hyperoxia, lymph flow doubled and the concentration of protein in lymph increased from 3.3 +/- 0.5 to 4.2 +/- 0.3 g/dl. Tracer studies with 125I-albumin before and 3 days after the start of O2 breathing confirmed the development of increased lung vascular permeability to protein. All lambs died of respiratory failure with pulmonary edema after 3-5 days in O2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Failure of therapy with 2,3-dihydroxybenzoic acid to modify the course of sepsis-induced lung injury

Oxidant-induced injury of the pulmonary microvasculature reportedly contributes to an increase in microvascular permeability and pulmonary hypertension, both of which are principal features of acute lung injury (ALI). We tested the hypothesis that antioxidant therapy with 2,3-dihydroxybenzoic acid (DHB), initiated in awake sheep after the development of sepsis-induced ALI, would ameliorate the progression of these lesions. DHB has many actions that suggested to us the potential for demonstrating benefit in ALI complicating sepsis; it is a nontoxic hydroxyl-radical scavenger that also inhibits the cyclooxygenase pathway and acts as a weak iron chelator. In preliminary experiments, we demonstrated that pretreatment with DHB prevented an increase in mean pulmonary arterial pressure, plasma thromboxane A2, measured as its metabolite thromboxane B2, and lymph total protein clearance that otherwise followed an infusion of zymosan-activated plasma (ZAP) in sheep. In subsequent experiments, 12 additional sheep were rendered septic by cecal ligation and perforation. Twenty-four to 36 h after cecal ligation and perforation, an increase in lung microvascular permeability was confirmed, because pulmonary lymph flow had increased by 82% while the mean lymph-to-plasma total protein ratio was unchanged from baseline. At this point, six sheep were then treated with parenteral DHB and six with DHB vehicle for the subsequent 24 h. In contrast to the demonstrated benefit of DHB pretreatment in preventing ALI secondary to an infusion of ZAP, the progressive increase in lymph total protein clearance that complicated septic lung injury in the DHB vehicle group throughout this 24-h study period was not ameliorated in the DHB treatment group. However, DHB did prevent a modest increase in mean pulmonary arterial pressures that was demonstrated in the DHB vehicle group throughout this 24-h treatment period. Although pretreatment prevented ALI after a ZAP infusion, we conclude that DHB only incompletely modified disease progression when administered after the onset of sepsis-induced ALI because it ameliorated the pulmonary hypertensive response without concurrently modifying an increase in lung microvascular fluid flux.     

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.     

Alpha-adrenergic agents have little effect during air embolism lung injury in awake sheep

Since it is not clear whether alpha-adrenergic receptors can modulate lung microvascular liquid and protein leakiness, we studied the effects of alpha-adrenergic receptor stimulation or blockade on lung filtration under base-line conditions and during the acute lung injury caused by a 4-h infusion of venous air emboli in six unanesthetized, chronically instrumented sheep with lung lymph fistulas. During the experiments we continuously infused the alpha-adrenergic receptor agonist phenylephrine hydrochloride (1.0 microgram X kg-1 X min-1 iv) or the alpha-adrenergic receptor antagonist phentolamine mesylate (1.0 mg X kg-1 X min-1 iv), and we measured pulmonary vascular pressures, cardiac output, lung lymph flow, and the lymph-to-plasma protein concentration ratio. During air embolism, alpha-receptor stimulation increased pulmonary vascular resistance and decreased lung lymph flow by 25%; alpha-receptor blockade had the opposite effects. During recovery, neither agent significantly affected pulmonary hemodynamics or lymph flow. Our results indicate that alpha-adrenergic receptors are active during air embolism and modulate pulmonary filtration by causing arteriolar constriction, which reduces the surface area or the perfusion pressure in the pulmonary microvascular bed. They may also affect venous smooth muscle tone. We found no evidence that alpha-adrenergic receptors modulate lung microvascular liquid or protein leakiness directly.     

Effect of progressive exercise on lung fluid balance in sheep

The purpose of this study is to determine the roles of cardiac output and microvascular pressure on changes in lung fluid balance during exercise in awake sheep. We studied seven sheep during progressive treadmill exercise to exhaustion (10% grade), six sheep during prolonged constant-rate exercise for 45-60 min, and five sheep during hypoxia (fraction of inspired O2 = 0.12) and hypoxic exercise. We made continuous measurements of pulmonary arterial, left atrial, and systemic arterial pressures, lung lymph flow, and cardiac output. Exercise more than doubled cardiac output and increased pulmonary arterial pressures from 19.2 +/- 1 to 34.8 +/- 3.5 (SE) cmH2O. Lung lymph flow increased rapidly fivefold during progressive exercise and returned immediately to base-line levels when exercise was stopped. Lymph-to-plasma protein concentration ratios decreased slightly but steadily. Lymph flows correlated closely with changes in cardiac output and with calculated microvascular pressures. The drop in lymph-to-plasma protein ratio during exercise suggests that microvascular pressure rises during exercise, perhaps due to increased pulmonary venous pressure. Lymph flow and protein content were unaffected by hypoxia, and hypoxia did not alter the lymph changes seen during normoxic exercise. Lung lymph flow did not immediately return to base line after prolonged exercise, suggesting hydration of the lung interstitium.     

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)     

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.     

Beta-adrenergic modulation of pulmonary transvascular fluid and protein exchange

We determined in anesthetized sheep whether isoproterenol, a beta-adrenergic agonist, prevents the increases in pulmonary fluid and protein exchange produced by thrombin-induced intravascular coagulation. Seven sheep were infused intravenously with 0.05 micrograms X kg-1 X min-1 isoproterenol before infusion of alpha-thrombin, and six sheep were infused with alpha-thrombin only and served as control subjects. The marked increases in pulmonary lymph flow and lymph protein clearance in the control thrombin group were attenuated (P less than 0.05) in the isoproterenol group in association with a higher pulmonary blood flow (P less than 0.05) and a lower pulmonary vascular resistance (P less than 0.05) in the isoproterenol group and with similar increases in pulmonary arterial and pulmonary arterial wedge pressures in both groups. The decreases in fluid and protein fluxes produced by isoproterenol are related to its beta-adrenergic properties because propranolol, a beta-adrenergic antagonist, blocked the protective effects of isoproterenol in a second group of sheep infused with propranolol, isoproterenol, and thrombin. Raising left atrial pressure to test for changes in vascular permeability increased protein flux to a much greater extent in the thrombin control group than in the isoproterenol group challenged with thrombin. The data suggest that isoproterenol attenuated the increase in fluid and protein fluxes produced by thrombin-induced intravascular coagulation by a permeability-decreasing mechanism.     

Role of circulating platelets and granulocytes in PAF-induced pulmonary dysfunction in awake sheep

The effects of a single intravascular bolus injection of platelet-activating factor (PAF) on pulmonary hemodynamics, lung mechanics, and lung fluid and solute exchange were studied in 13 chronically instrumented unanesthetized sheep. Since PAF has profound effects on both platelets and granulocytes, we investigated the effects of platelet and granulocyte depletion on the sheep's response to exogenous PAF. Sheep received PAF when granulocyte and platelets counts were normal and after platelet depletion with rabbit antisheep platelet antibodies (n = 5) or granulocyte depletion with hydroxyurea (n = 5). Sheep served as their own controls, and the order of experimentation was varied. Bolus injections of PAF had reproducible effects on pulmonary hemodynamics (pulmonary arterial pressure increased acutely to 85 +/- 3.7 cmH2O) and lung mechanics (dynamic compliance of the lungs decreased to 24.5 +/- 3.8% of base line and resistance to airflow across the lungs increased greater than 10-fold) and caused marked increases in lung lymph concentrations of thromboxane B2 and 6-ketoprostaglandin F1 alpha. The single bolus injection of PAF also caused marked prolonged elevations in lung lymph flow and increases in the lymph-to-plasma protein concentration ratio for 3 h after PAF. PAF had profound effects despite platelet and granulocyte depletion. Platelet depletion slightly attenuated the pulmonary hypertension observed after PAF injection. Platelet depletion also attenuated the increases in thromboxane B2 concentrations in lung lymph, and lung mechanics normalized more rapidly in platelet-depleted sheep. There were no statistically significant effects of granulocyte depletion to less than 200 granulocytes/mm3 on any of the measured variables.(ABSTRACT TRUNCATED AT 250 WORDS)     

Development of pulmonary intravascular macrophage function in newborn lambs.

We sought to determine whether pulmonary intravascular macrophages are involved in pulmonary vascular sensitivity to intravenously injected particles in sheep. We estimated that newborn lambs have few of these macrophages at birth but develop a 10-fold greater density within 2 wk. Awake, chronically instrumented newborn lambs showed no change in pulmonary vascular driving pressure (pulmonary arterial minus left atrial pressure) after injection of either liposomes [2 +/- 3 (SD) cmH2O; n = 5] or Monastral blue particles (3 +/- 2 cmH2O; n = 6) and showed no net pulmonary production of thromboxane B2, the stable metabolite of the vasoconstrictor thromboxane A2. In contrast, five of those lambs 2 wk later showed both an increase in pulmonary vascular driving pressure after injection of liposomes and Monastral blue (20 +/- 16 and 25 +/- 15 cmH2O, respectively; P < 0.05) and net pulmonary production of thromboxane B2 (171 +/- 103 and 429 +/- 419 pg/ml plasma, respectively; P < 0.05). Older lambs (n = 5) had higher pulmonary uptakes than newborn lambs (n = 6) of radioactive liposomes (47 +/- 13 vs. 12 +/- 10%; P < 0.01) and Monastral blue (53 +/- 6 vs. 21 +/- 10%; P < 0.05). We conclude that pulmonary intravascular macrophages are responsible for the sensitivity of sheep to intravenous foreign particles and are essential for a cascade of processes leading to microvascular injury.     

Oleic acid lung injury in sheep

Intravenous infusion of oleic acid into experimental animals causes acute lung injury resulting in pulmonary edema. We investigated the mechanism of oleic acid lung injury in sheep. In experiments with anesthetized and unanesthetized sheep with lung lymph fistulas, we measured pulmonary arterial and left atrial pressures, cardiac output, lung lymph flow, and lymph and plasma protein concentrations. We injured the lungs with intravenous infusions of oleic acid at doses ranging from 0.015 to 0.120 ml/kg. We found that oleic acid caused reproducible dose-related increases in pulmonary arterial pressure and pulmonary vascular resistance, arterial hypoxemia, and increased protein-rich lung lymph flow and extravascular lung water. The lung fluid balance changes were characteristic of increased permeability pulmonary edema. Infusion of the esterified fat triolein had no hemodynamic or lung fluid balance effects. Depletion of leukocytes with a nitrogen mustard or platelets with an antiplatelet serum had no effect on oleic acid lung injury. Treatment of sheep before injury with methylprednisolone 30 mg/kg or ibuprofen 12.5-15.0 mg/kg also had no effects. Unlike other well-characterized sheep lung injuries, injury caused by oleic acid does not require participation of leukocytes.     

Role of anti-L-selectin antibody in burn and smoke inhalation injury in sheep

We hypothesized that the antibody neutralization of L-selectin would decrease the pulmonary abnormalities characteristic of burn and smoke inhalation injury. Three groups of sheep (n = 18) were prepared and randomized: the LAM-(1-3) group (n = 6) was injected intravenously with 1 mg/kg of leukocyte adhesion molecule (LAM)-(1-3) (mouse monoclonal antibody against L-selectin) 1 h after the injury, the control group (n = 6) was not injured or treated, and the nontreatment group (n = 6) was injured but not treated. All animals were mechanically ventilated during the 48-h experimental period. The ratio of arterial PO2 to inspired O2 fraction decreased in the LAM-(1-3) and nontreatment groups. Lung lymph flow and pulmonary microvascular permeability were elevated after injury. This elevation was significantly reduced when LAM-(1-3) was administered 1 h after injury. Nitrate/nitrite (NO(x)) amounts in plasma and lung lymph increased significantly after the combined injury. These changes were attenuated by posttreatment with LAM-(1-3). These results suggest that the changes in pulmonary transvascular fluid flux result from injury of lung endothelium by polymorphonuclear leukocytes. In conclusion, posttreatment with the antibody for L-selectin improved lung lymph flow and permeability index. L-selectin appears to be principally involved in the increased pulmonary transvascular fluid flux observed with burn/smoke insult. L-selectin may be a useful target in the treatment of acute lung injury after burn and smoke inhalation.     

Role of circulating granulocytes in sheep lung injury produced by phorbol myristate acetate

Phorbol myristate acetate (PMA) and endotoxin cause pulmonary granulocyte sequestration and alteration in lung fluid and solute exchange in awake sheep that are felt to be analogous to the adult respiratory distress syndrome in humans. The basic hypothesis that PMA causes lung injury by activating circulating granulocytes has never been tested. The effects of infused PMA on lung mechanics and the cellular constituents of lung lymph have also not been reported. We therefore characterized the effects of intravenous PMA, 5 micrograms/kg, on lung mechanics, pulmonary hemodynamics, lung fluid and solute exchange, pulmonary gas exchange, blood and lymph leukocyte counts, and plasma and lymph cyclooxygenase products of arachidonate metabolism in 10 awake sheep with normal granulocyte counts and after granulocyte depletion with hydroxyurea. PMA significantly altered lung mechanics from base line in both nongranulocyte depleted and granulocyte-depleted sheep. Dynamic compliance decreased by over 50% and resistance to airflow across the lungs increased over threefold acutely following PMA infusion in both sets of experiments. Changes in lung mechanics, pulmonary hemodynamics, lung fluid and solute exchange, pulmonary gas exchange, and plasma and lymph arachidonate metabolites were not significantly affected by greater than 99% depletion of circulating granulocytes. We conclude that the lung injury caused by PMA in chronically instrumented awake sheep probably is not a result of activation of circulating granulocytes.     

Effects of inspiratory resistance loading on lung fluid balance in awake sheep

Because pulmonary edema has been associated clinically with airway obstruction, we sought to determine whether decreased intrathoracic pressure, created by selective inspiratory obstruction, would affect lung fluid balance. We reasoned that if decreased intrathoracic pressure caused an increase in the transvascular hydrostatic pressure gradient, then lung lymph flow would increase and the lymph-to-plasma protein concentration ratio (L/P) would decrease. We performed experiments in six awake sheep with chronic lung lymph cannulas. After a base-line period, we added an inspiratory load (20 cmH2O) and allowed normal expiration at atmospheric pressure. Inspiratory loading was associated with a 12-cmH2O decrease in mean central airway pressure. Mean left atrial pressure fell 11 cmH2O, and mean pulmonary arterial pressure was unchanged; calculated microvascular pressure decreased 8 cmH2O. The changes that occurred in lung lymph were characteristic of those seen after other causes of increased transvascular hydrostatic gradient, such as increased intravascular pressure. Lung lymph flow increased twice base line, and L/P decreased. We conclude that inspiratory loading is associated with an increase in the pulmonary transvascular hydrostatic gradient, possibly by causing a greater fall in interstitial perimicrovascular pressure than in microvascular pressure.     

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.     

Role of sulfidopeptide leukotrienes in synthetic smoke inhalation injury in sheep

Acute lung injury with smoke inhalation results in significant morbidity and mortality. Previously we have shown that synthetic smoke composed of carbon and acrolein, a common component of smoke, causes delayed-onset noncardiogenic pulmonary edema. To study the possible role of the vasoactive and edemagenic sulfidopeptide leukotrienes (SPLT) in smoke inhalation injury, we measured pulmonary hemodynamics, lung lymph flow, and SPLT and leukotriene (LT) B4 in lung lymph before and after 10 min of synthetic acrolein smoke exposure. After smoke exposure there was a significant rise in pulmonary vascular resistance caused by a rise in pulmonary arterial pressure, a fall in cardiac output, and no change in pulmonary capillary wedge pressure. This was accompanied by an increase in total systemic vascular resistance (P less than 0.05), lung lymph flow (P less than 0.05), and extravascular lung water-to-lung dry weight ratio (P less than 0.05). Both SPLT and LTB4 clearance rose significantly (P less than 0.05), but there was a 10-fold increase in SPLT over LTB4 clearance. In sheep pretreated with FPL55712, a SPLT antagonist, the early rise in pulmonary vascular resistance was attenuated, and the rise in systemic vascular resistance was blocked. This was associated with an attenuated and delayed fall in cardiac output. FPL55712 had no effect on lung lymph flow or extravascular lung water-to-dry weight ratio. SPLT, and especially LTD4, may have a role in increased pulmonary and systemic vascular resistance after smoke inhalation injury but does not appear to affect vascular permeability.     

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 lyng lymph fistulas. Pulmonary intravascular coagulation was induced by i.v. infusion of α-thrombin over a 15 min period. Thrombin infusion in control sheep resulted in immediate increases in pulmonary artery pressure (P ) and pulmonary vascular resistance (PVR), which associated with rapid 3-fold increase in pulmonary lymph flow (Q̇lym) 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 alos increased arterial thromboxane B₂ (a metabolite of thromboxane A₂) and 6-keto-PGF_1α concentrations (a metabolite of prostacyclin). Both OKY-1581 and OKY-046 prevented thromboxane B₂ and 6-keto-PGF_1α generation. The initial increments in P and PVR were attenuated in both treated groups. The increases in Q̇lym were gradual in the treated groups but attained the same levels as in control group. However, the increases in Q̇lym 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.     

Effects of beta-adrenergic agents in lungs of normal and air-embolized awake sheep

It is unclear whether beta-adrenergic agonists or antagonists affect lung liquid and protein exchange by changing pulmonary hemodynamics or microvascular leakiness. In 23 unanesthetized, instrumented sheep with long-term lung lymph fistulas, we assessed the effect of the beta-agonist terbutaline or the beta-antagonists propranolol, nadolol, and atenolol, all infused intravenously, on lung lymph flow under base-line conditions and during the acute lung injury caused by 4 h of venous air embolism. Under base-line conditions, neither beta-stimulation nor blockade had any effect. During air embolism, terbutaline decreased pulmonary vascular resistance and lymph flow by 25%. Propranolol and nadolol (non-selective beta 1,beta 2-antagonists) but not atenolol (selective beta 1-antagonist) also decreased lymph flow by 22% on average. We favor the more conservative (hemodynamic) over the more liberal (altered permeability) explanation for our results. First, beta-stimulation clearly caused vasodilation, which lowered the pulmonary microvascular pressure at the site of injury. beta-blockade caused changes similar to alpha-stimulation (J. Appl. Physiol. 62: 2147-2153, 1987). We therefore interpret the beta-blockade as unmasking pulmonary arterial alpha-receptors stimulated by the air-embolism injury, thus allowing vasoconstriction upstream to the site of injury. We do not believe the explanation of the beta-agent effects requires any modulation of lung microvascular leakiness by beta-adrenergic agents.     

Inspiratory airway obstruction does not affect lung fluid balance in lambs

The purpose of this study was to examine the effects of inspiratory airway obstruction on lung fluid balance in newborn lambs. We studied seven 2- to 4-wk-old lambs that were sedated with chloral hydrate and allowed to breathe 30-40% O2 spontaneously through an endotracheal tube. We measured lung lymph flow, lymph and plasma protein concentrations, pulmonary arterial and left atrial pressures, mean and phasic pleural pressures and airway pressures, and cardiac output during a 2-h base-line period and then during a 2- to 3-h period of inspiratory airway obstruction produced by partially occluding the inspiratory limb of a nonrebreathing valve attached to the endotracheal tube. During inspiratory airway obstruction, both pleural and airway pressures decreased 5 Torr, whereas pulmonary arterial and left atrial pressures each decreased 4 Torr. As a result, calculated filtration pressure remained unchanged. Inspiratory airway obstruction had no effect on steady-state lung lymph flow or the lymph protein concentration relative to that of plasma. We conclude that in the spontaneously breathing lamb, any decrease in interstitial pressure resulting from inspiratory airway obstruction is offset by a decrease in microvascular hydrostatic pressure so that net fluid filtration remains unchanged.     

Hypoxia and angiotensin II infusion redistribute lung blood flow in lambs

To assess the effects of alveolar hypoxia and angiotensin II infusion on distribution of blood flow to the lung we performed perfusion lung scans on anesthetized mechanically ventilated lambs. Scans were obtained by injecting 1-2 mCi of technetium-labeled albumin macroaggregates as the lambs were ventilated with air, with 10-14% O2 in N2, or with air while receiving angiotensin II intravenously. We found that both alveolar hypoxia and infusion of angiotensin II increased pulmonary vascular resistance and redistributed blood flow from the mid and lower lung regions towards the upper posterior region of the lung. We assessed the effects of angiotensin II infusion on filtration pressure in six lambs by measuring the rate of lung lymph flow and the protein concentration of samples of lung lymph. We found that angiotensin II infusion increased pulmonary arterial pressure 50%, lung lymph flow 90%, and decreased the concentration of protein in lymph relative to plasma. These results are identical to those seen when filtration pressure increases during alveolar hypoxia. We conclude that alveolar hypoxia and angiotensin II infusion both increase fluid filtration in the lung by increasing filtration pressure. The increase in filtration pressure may be the result of a redistribution of blood flow in the lung with relative overperfusion of vessels in some areas and transmission of the elevated pulmonary arterial pressure to fluid-exchanging sites in those vessels.