Effects of OKY-046, a selective thromboxane synthetase inhibitor, on endotoxin-induced lung injury in unanesthetized sheep

We tested the effects of OKY-046, a selective thromboxane synthetase inhibitor, on endotoxin-induced lung injury in unanesthetized sheep in order to evaluate the role of thromboxane (Tx) in this injury. Escherichia coli endotoxin (1 microgram/kg) infusion produced a biphasic response. The early period (Phase 1) was a transient pulmonary hypertension. The late period (Phase 2) was a more prolonged period characterized by a marked high flow of lung lymph with a high concentration of protein, suggesting increased pulmonary vascular permeability. During Phase 1, there were remarkable increases in TxB2 and 6-keto-PGF1 alpha concentrations in lung lymph and in plasma samples obtained from the pulmonary artery (PA) and the left atrium (LA). The increase in plasma TxB2 level of the LA was greater than that of the PA. During Phase 2, TxB2 levels returned to the baseline values, whereas 6-keto-PGF1 alpha levels remained elevated. Pretreatment with OKY-046 prevented the pulmonary hypertension and increases in TxB2 levels during Phase 1. However, OKY-046 had little effect on lung lymph balance during Phase 2. We conclude that the early pulmonary hypertension induced by endotoxin is mediated mainly by release of TxA2 from the lungs, and TxA2 is not attributed to the increased pulmonary permeability during the late period.     

Increased sheep lung vascular permeability caused by Escherichia coli endotoxin.

We infused Escherichia coli endotoxin, 0.07-1.33 microgram/kg, intravenously into chronically instrumented unanesthetized sheep and measured pulmonary arterial and left atrial pressures, lung lymph flow, lymph and blood plasma protein concentrations, and arterial blood gases. Endotoxin caused a biphasic reaction: an early phase of pulmonary hypertension and a long late phase of steady state increased pulmonary vascular permeability during which pulmonary arterial and left atrial pressures were not increased significantly and lung lymph flow was 5 times the baseline value. Lymph: plasma total protein concentration ratio during the late phase (0.76 +/- 0.04) was significantly (P less than 0.05) higher than during baseline (0.66 +/- 0.03). The lymph response was reproducible. Lung lymph clearance of endogenous proteins with molecular radii (r) 35.5 to 96 A was increased during the steady state late phase of the reaction, but, as during baseline, clearance decreased as r increased. The endotoxin reaction was similar to the reaction to infusing whole Pseudomonas bacteria, except that endotoxin had less effect on pressures during the steady state response and caused a relatively larger increase in lymph clearance of large proteins. We conclude that E. coli endotoxin in sheep causes a long period of increased lung vascular permeability and may have a greater effect on large solute pathways across microvessels than do Pseudomonas bacteria.     

Dibutyryl cyclic AMP attenuates lung responses induced by endotoxin in conscious sheep.

Dibutyryl cyclic AMP (DBcAMP) could inhibit the production of prostanoids and modulate the pulmonary vascular responses induced by endotoxin. Diffuse lung injury after endotoxemia in sheep is accompanied by the production of prostanoids and an increase in endothelial permeability. To determine whether exogenous DBcAMP could prevent the endotoxin responses, we measured pulmonary hemodynamics, gas exchange, and lung lymph responses to an intravenous infusion of Escherichia coli endotoxin (1.0 micrograms/kg over 30 min) in unanesthetized sheep in the presence and absence of DBcAMP (30 micrograms/kg/min) infused intravenously for 6 h beginning 1 h before endotoxin infusion or for 4.5 h after 30 min of treatment with endotoxin infusion. We also measured circulating leukocytes and lung lymph and plasma concentrations of thromboxane B2 (TXB2) and prostacyclin (6-keto-PGF1 alpha) metabolites by radioimmunoassay. DBcAMP infusion before endotoxin infusion decreased endotoxin-induced pulmonary hypertension and hypoxemia and markedly attenuated the increased lung lymph flow and lymph protein clearance. DBcAMP after endotoxin only attenuated the increased lung lymph flow and lymph protein clearance. DBcAMP treatment both before and after endotoxin infusion blocked endotoxin-induced increases in lung lymph and plasma TXB2 and 6-keto-PGF1 alpha. DBcAMP did not affect the number of circulating leukocytes. Although DBcAMP alone did not affect the pulmonary and systemic hemodynamics and lung lymph balance, the potential that DBcAMP directly modulates the pulmonary vascular responses to endotoxin as a vasodilator could be expected. We conclude that DBcAMP infusion attenuates lung dysfunction caused by endotoxemia, possibly by preventing prostanoid release and modulating the pulmonary vascular responses.     

Effect of catalase on endotoxin-induced acute lung injury in unanesthetized sheep

Administration of endotoxin intravenously to unanesthetized sheep causes an acute lung injury characterized by increased microvascular barrier permeability and subsequent pulmonary edema. Endotoxin-induced sheep lung injury can be attenuated by leukocyte depletion, and may be mediated by toxic metabolites of oxygen. We studied effects of administering catalase, which catalyzes conversion of hydrogen peroxide to oxygen and water, to sheep subsequently infused with endotoxin to test the hypothesis that hydrogen peroxide plays a role in the pathogenesis of lung injury. We found that infusions of endotoxin (1 microgram/kg) into untreated sheep caused the expected biphasic response, a transient, early, marked pulmonary arterial hypertension followed by a prolonged increase in protein-rich lung lymph flow characteristic of increased microvascular permeability filtration in the lungs. Intraperitoneal injections of catalase (50 mg/kg) prior to infusing endotoxin in these same sheep resulted in substantial catalase activity in plasma and in lung lymph, and attenuated the expected changes in pulmonary arterial pressure, lung lymph flow, and arterial leukocyte counts and oxygen tension after endotoxin infusions. Furthermore, mechanical elevation of hydrostatic pressure in the lungs of a catalase-treated sheep infused with endotoxin resulted in increased lung lymph flow with a decreased protein concentration, indicating that the microvascular barrier to fluid and protein was functionally intact. Administration of catalase that was inactivated by reaction with hydrogen peroxide in the presence of aminotriazole or administration of the catalase vehicle, thymol, had no effects on the sheep responses to endotoxin. We conclude that hydrogen peroxide plays a role in the pathogenesis of endotoxin-induced acute lung injury in sheep.     

Effect of sulfidopeptide leukotriene receptor antagonists on endotoxin-induced pulmonary dysfunction in awake sheep.

We studied the effects of two structurally unrelated sulfidopeptide leukotriene receptor antagonists on endotoxin-induced pulmonary dysfunction in chronically instrumented unanesthetized sheep. The agents employed were L-660,711 (MK-571) (Merck-Frosst, Canada) and SK&F 104,353 (Smith Kline and French, King of Prussia, PA). The efficacy and specificity of the agents were verified in sheep by administering boluses of exogenous leukotrienes (LTB4, LTC4, LTD4, and LTE4) in doses as great as 100 micrograms while monitoring lung mechanics and vascular pressures. The antagonists blocked the changes in lung mechanics and pulmonary hemodynamics induced by the sulfidopeptide leukotrienes (LTC4, LTD4, and LTE4) while having no effect on the animals' responses to LTB4. The endotoxin studies were performed by administering endotoxin alone (Escherichia coli endotoxin 0.75 microgram/kg) or endotoxin after pretreatment with one of the sulfidopeptide leukotriene receptor antagonists. In control studies, each animal received a continuous infusion of one of the receptor antagonists for a duration identical to that of the endotoxin studies. Neither L-660,711 nor SK&F 104,353 significantly altered the endotoxin-induced changes in pulmonary hemodynamics, lung mechanics, lung fluid and solute exchange, oxygenation, or leukopenia. Peak lung lymph thromboxane B2 levels were significantly lower in sheep pretreated with L-660,711. When the antagonists were given alone, no effects were seen. We conclude that (1) sulfidopeptide leukotrienes do not measurably contribute to endotoxin-induced pulmonary dysfunction in chronically instrumented sheep; (2) sulfidopeptide leukotrienes may contribute to thromboxane release after endotoxin.     

Endotoxin-induced changes in pulmonary hemodynamics and respiratory mechanics. Role of lipoxygenase and cyclooxygenase products

We investigated the role of leukotrienes and cyclooxygenase products in endotoxin-induced pulmonary vascular and airway changes. In 11 conscious sheep, measurements of pulmonary vascular resistance (PVR), lung resistance (RL), arterial PO2, leukocyte count (WBC), and plasma thromboxane B2 (TxB2), 6-keto-PgF1 alpha and PgF2 alpha were obtained, before and at predetermined intervals after a 10-min infusion of E. coli endotoxin (0.3 microgram/kg). On a separate occasion, 5 sheep received an infusion of the leukotriene end-organ receptor antagonist FPL-57231 (0.7 to 1 mg/kg/min), before and for as long as 4 h after endotoxin infusion; and 6 sheep received a single injection of the cyclooxygenase inhibitor indomethacin (2 mg/kg) 1 h before endotoxin infusion. Endotoxin caused a biphasic response with an increase in mean PVR and RL to 441 and 353% of baseline, respectively, during the early phase (0 to 1 hr), and lesser increases to 168 and 195% of baseline during the late phase (1.5 to 4 h). These changes were associated with mild hypoxemia, marked leukopenia, and marked increases in plasma TxB2, 6-keto-PgF1 alpha and PgF2 alpha. The FPL-57231 completely blocked the endotoxin-induced changes in PVR, RL, and PaO2 during both phases without preventing the increases in TxB2; however, it partly attenuated the increases in 6-keto-PgF1 alpha and enhanced the generation of PgF2 alpha. Indomethacin, which blocked the endotoxin-induced increases in TxB2, 6-keto-PgF1 alpha, PgF2 alpha, and RL, only partly blocked the increase in PVR during the early phase, followed by an exaggerated increase of PVR during the late phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of hemorrhagic shock on endotoxin-induced pulmonary hypertension and increased vascular permeability in unanesthetized sheep

The lung is very susceptible to sepsis or endotoxin injury in the trauma patient. We studied the effect of an episode of hemorrhagic shock and resuscitation on the prostaglandin-induced pulmonary hypertension and leukocyte-induced increased permeability phase of endotoxin lung injury. Eight unanesthetized sheep with chronic lung lymph fistula were bled 50% of blood volume for 2 hr, then resuscitated. Thromboxane, TxA2, levels increased from 0.1 to 0.6 ng/ml during shock, while blood white cell count decreased. Both parameters returned to baseline while lung lymph flow increased twofold during resuscitation with lymph being protein-poor, indicating no increase in permeability. Lung water was not increased but some pulmonary leukostasis was evident histologically after resuscitation. We then studied the effect of this process on all immediate endotoxin insult. Seven unanesthetized sheep were given 0.7 microgram/kg E. coli endotoxin alone, and again after shock and resuscitation, in paired studies performed 3 days apart. There was no difference in either the early pulmonary hypertension or the later increased permeability phase of endotoxin lung injury when comparing the paired studies, as measured by lymph flow and protein flux. Hemorrhagic shock, despite producing a transient increase in thromboxane and pulmonary leukocyte sequestration, does not accentuate the lung injury of endotoxin if the shock state is adequately resuscitated.     

Tracing the leukocyte marker protein in lung fluids and lung-draining lymph nodes during endotoxemia in sheep

Infusion of Escherichia coli endotoxin into sheep produces a form of acute lung injury that resembles the adult respiratory distress syndrome (ARDS). A large portion of the physiologic derangements produced by E. coli endotoxin in this model is thought to be granulocyte-dependent. We measured the level of L1, a granulocyte and monocyte marker protein, in various tissues and fluids after infusion of E. coli endotoxin into sheep. In an acute study, sheep received saline or 1.25 microgram/kg E. coli endotoxin dissolved in saline, or endotoxin after hydroxyurea-induced granulocytopenia. L1 was measured by radioimmunoassay in efferent lymph from the caudal mediastinal lymph node collected between 5 and 6 h after infusion. In addition, L1 was visualized in both lung-draining and extrapulmonary lymph nodes by indirect immunofluorescence. In a chronic study, sheep were prepared with lung lymph fistulas, and L1 was measured in draining pulmonary lymph, plasma, and bronchoalveolar lavage (BAL) fluid, serially, over a 24-h period after infusion. Mean L1 level in pulmonary lymph in the acute study was 6 times higher by absolute concentration, and 19 times higher when lymph flow rates were taken into account, in the sheep that received endotoxin than in saline-infused sheep or endotoxin-infused, granulocytopenic sheep. Fluorescence was greater in the outer cortical region adjacent to subcapsular, afferent sinuses of lung draining-lymph nodes of endotoxin-treated sheep than in the comparable nodes of saline-infused sheep and endotoxin-infused granulocytopenic sheep. In endotoxin-treated sheep, extrapulmonary lymph nodes were less reactive than lung-draining nodes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the cardiopulmonary responses to single bolus and continuous infusion of endotoxin in an ovine model

We compared the cardiopulmonary responses to a single bolus (1.5 microgram/kg) vs. continuous infusion of endotoxin (LPS) (24 ng/kg/hr) in unanesthetized sheep. A single bolus produced an initial marked increase in pulmonary arterial pressure and plasma thromboxane levels and an elevated flow rate of lung lymph low in protein. Concomitantly, the cardiac output dropped and systemic vascular resistance rose. In the animals that received a continuous infusion of LPS, only very small changes in these variables were noted during this early period. Later, lung lymph flow rate and protein flux were elevated in both groups with a greater response in the bolus group. At 6 hr after LPS, the systemic vascular resistance fell in both groups, but to a greater extent in the bolus group, whereas the cardiac output rose to the same extent. Plasma levels of neutrophils, lymphocytes, and plasma prekallikrein levels decreased in both groups; neutropenia was more pronounced in the bolus group. The most important difference between both endotoxemia models during this phase was the reduction of the stroke work index in the bolus model, which was not observed with the continuous infusion. The apparent myocardial depression, the early reduction in cardiac output, and eicosanoid mediated pulmonary hypertension are the major differences between the two responses.     

Influence of steroidal and nonsteroidal anti-inflammatory agents on the accumulation of arachidonic acid metabolites in plasma and lung lymph after endotoxemia in awake sheep. Measurements of prostacyclin and thromboxane metabolites and 12-HETE

The influence of methylprednisolone and meclofenamate on endotoxin-induced release of 3 arachidonic acid metabolites was studied in unanesthetized sheep. Concentrations in plasma and lung lymph of prostacyclin and thromboxane (Tx) A2 metabolites (6-keto-PGF1 alpha and TxB2, respectively) were measured by radioimmunoassay. Concentrations of 12-HETE in lung lymph were measured by stable isotope dilution assay employing gas chromatography-mass spectroscopy. Thromboxane B2 concentrations increased quickly to peak values during the first hour after endotoxin infusion, then decreased to baseline by 1.5 hr. 6-keto-PGF1 alpha concentrations increased more gradually to peak values between 1 and 2 h after endotoxin infusion and remained elevated at 2.5 h. Lymph concentrations of both cyclooxygenase metabolites exceeded those in blood plasma. Methylprednisolone significantly inhibited accumulation of 6-keto-PGF1 alpha in lymph and plasma, but did not significantly inhibit accumulation of TxB2 in lymph or plasma. The combination of meclofenamate and methylprednisolone completely inhibited accumulation of TxB2 and 6-keto-PGF1 alpha in lymph and plasma. The concentration of 12-HETE in lung lymph increased significantly to peak values by 2.5 h after endotoxemia, and methylprednisolone, with or without meclofenamate, inhibited accumulation of 12-HETE in lung lymph. These data support participation of TxA2 in acute pulmonary hypertension after endotoxemia. That methylprednisolone treatment inhibited accumulation of 6-keto-PGF1 alpha and prevented the increase in lung vascular permeability suggests that prostacyclin production is a consequence of lung vascular injury. Increased lung lymph concentrations of the lipoxygenation product, 12-HETE, were coincident with physiologic evidence of increased lung vascular permeability, but whether release of lipoxygenase products after endotoxemia contributes to or results from lung vascular injury remains to be established.     

Prostaglandin E1 prevents increased lung microvascular permeability during intravascular complement activation in sheep

Prostaglandin E1 (PGE1) inhibits a variety of functions of activated neutrophils including respiratory burst, release of leukotriene B4, and adherence to endothelial cells. To determine if PGE, alters the pathophysiology of complement-induced lung vascular injury, experiments were conducted in anesthetized sheep with lung lymph fistulas given a 1-hour infusion of zymosan-activated plasma. PGE1 (30 ng/min/kg) or its saline vehicle was infused intravenously for 90 minutes beginning 30 minutes before the infusion of activated plasma. PGE1 had no effect on leukocyte count, the initial hypoxemia and thromboxane A2 release, or the development of acute pulmonary hypertension. However, PGE1 prevented steady-state increases in lung lymph flow that in vehicle-treated sheep signaled an increase in lung microvascular permeability. Furthermore, extraction of PGE1 by pulmonary endothelial cells was unaffected by the infusion of activated plasma. We propose that PGE1 prevented the increase in lung vascular permeability by inhibiting adherence of activated neutrophils to endothelial cells.     

Prevention of release of granulocyte aggregants into sheep lung lymph following endotoxemia by N-acetylcysteine

Interactions of granulocytes with the lungs are altered by endotoxemia and may be critical in the pathogenesis of endotoxin-induced lung injury. In chronically instrumented unanesthetized sheep, we measured the ability of lung lymph to aggregate normal sheep neutrophils in vitro. We found a marked increase in lung lymph aggregating activity beginning within 1 hour after endotoxin infusion and persisting for several hours. When n-acetylcysteine was administered to the animals before endotoxin infusion, neutrophil aggregating activity in lung lymph after endotoxin infusion was markedly reduced. N-acetylcysteine did not affect neutrophil aggregation, adherence, or leukotriene B4 production in vitro and did not prevent complement activation at concentrations achieved in vivo. It is concluded that endotoxemia causes release from the lungs of substance(s) that activate granulocytes, and that this response is prevented by n-acetylcysteine, possibly as a result of the antioxidant properties of the drug.     

Imbalance between plasma levels of thromboxane B2 and 6-keto-prostaglandin F1 alpha during subacute endotoxin-induced hyperdynamic sepsis or multiple organ failure syndrome in sheep.

We compared the time course of plasma and pulmonary lymph levels of thromboxane B2 (TxB2) and 6-keto-prostaglandin (PG)F1 alpha during the development of either the hyperdynamic phase of sepsis or of the multiple organ failure syndrome (MOFS) associated with sepsis in 26 chronically instrumented awake sheep with intravascular catheters and a chronic pulmonary lymph fistula. Using a continuous i.v. infusion of Escherichia coli endotoxin administered at a rate of 20 ng.kg-1.min-1 (group E20, n = 9) resulted in hyperdynamic septic shock with more than 75% of animals surviving after 72 h of continuous endotoxin administration. Infusing endotoxin at a higher dosage (40 ng.kg-1.min-1; group E40, n = 9) resulted in the development of respiratory failure and MOFS with death occurring within 55 hr of endotoxemia. Eight similarly instrumented sheep served as controls. Administration of endotoxin produced within 4 hr in both endotoxin groups a significant increase in arterial plasma concentration of TxB2, which was not significantly different between both endotoxin groups. Thereafter, plasma TxB2 concentrations progressively decreased in the E20 group to reach at 36 hr values significantly lower than those measured in control sheep not given endotoxin. In the E40 group, plasma TxB2 concentrations returned to baseline values during the development of a MOFS. The time course of TxB2 concentrations in pulmonary lymph in both endotoxin groups was similar to that measured in each group in plasma. 6-Keto-PGF1 alpha concentrations in arterial plasma and pulmonary lymph were significantly higher than in controls during the first 20 hr following the start of endotoxin infusion in both endotoxin groups and were not different between these groups. Thereafter, plasma and pulmonary lymph 6-keto-PGF1 alpha concentrations progressively returned to baseline values in the E20 group and remained at these levels up to the end of the study period (72 hr). In the E40 group, plasma 6-keto-PGF1 alpha concentrations also decreased to baseline values during the second day of endotoxemia but then significantly increased in sheep that survived more than 36 hr and developed a hypodynamic septic state. During the first 24 hr of endotoxemia, the plasma TxB2/6-keto-PGF1 alpha ratio was similar in controls and in both endotoxin groups. During the second study day, TxB2/6-keto-PGF1 alpha ratio progressively decreased in both endotoxin groups to reach and maintain values significantly lower than those measured in controls at 36 hr in the E40 group and at 52 hr in E20 group.(ABSTRACT TRUNCATED AT 400 WORDS)     

A 21-aminosteroid, U-74006F, attenuates endotoxin-induced lung injury in awake sheep

The purpose of the present study was to examine the efficacy of U-74006F, a 21-aminosteroid, on lung dysfunction induced by endotoxaemia in awake sheep with lung lymph fistula and haemodynamic monitoring. We measured pulmonary haemodynamics, lung lymph balance, circulating leucocyte count, arterial blood gas tensions, and levels of thromboxane (Tx) B2 and 6-keto-prostaglandin (PG) F1 alpha in plasma and lung lymph. We performed two experiments. In experiment 1 (n = 6), we intravenously infused Escherichia coli lipopolysaccharide endotoxin (1 microgram/kg) over 30 min and observed the parameters over 5 h. In experiment 2 (n = 6), we pretreated sheep with an intravenous bolus of U-74006F (2 mg/kg) 30 min before the infusion of endotoxin in the same manner of experiment 1, and continuously infused U-74006F (0.5 mg/kg per h) over 5 h after the bolus during the experiment. The U-74006F significantly suppressed the early pulmonary hypertension, the late increase in pulmonary permeability and the elevations of TxB2 and 6-keto-PGF1 alpha levels in plasma and lung lymph during the early period following endotoxaemia, although the compound did not change the time course of leucocytopenia and hypoxaemia. These findings suggest that the administration of U-74006F attenuates the lung dysfunction induced by endotoxaemia in awake sheep.     

Timing of corticosteroid treatment. Effect of lung lymph dynamics in air injury in awake sheep

In paired experiments, we studied the effects of high-dose methylprednisolone on the acute pulmonary injury caused by 4 h of venous air embolization in 19 chronically instrumented, unanesthetized sheep with lung lymph fistulas. We compared the effect of methylprednisolone (30 mg/kg intravenous bolus) given before embolization, early (1 H) in the course of embolization, late (3 h) in the course of embolization, or after embolization (at the beginning of the recovery period). We measured pulmonary hemodynamics and lymph dynamics. In six sheep we also fixed lung tissue for semiquantitative histology, and in some we measured leukocyte concentrations in blood and in pulmonary lymph. Methylprednisolone did not significantly affect pulmonary hemodynamics but it largely prevented lung injury when it was given before embolization. It also lessened the degree of lung injury when it was given during embolization, although this effect became less marked as treatment was delayed. Methylprednisolone had no effect on lung injury when given after embolization was completed (4 h). We found fewer leukocytes attached to air emboli and fewer endothelial cell gaps in the lungs of sheep given methylprednisolone as prophylaxis. Leukocyte counts were lower in lung lymph and higher in the circulating blood of methylprednisolone-treated sheep. We conclude that methylprednisolone has a preventive effect on air embolism lung injury, such that its effect is greater when given earlier during the development of injury.     

Role of subcutaneous tissue endotoxin in the production of prostanoid-induced lung injury: comparison with intravenous endotoxin response

Local injection of endotoxin into soft tissues of the flank results in hypoxia and pulmonary hypertension. Our purpose was to determine whether this was caused by tissue prostanoid production or production by the lung as is seen with endotoxemia. Twenty-six sheep were prepared with lung and flank tissue lymph fistulae. Thirteen sheep were given 2 micrograms/kg Escherichia coli endotoxin into the flank soft tissue, six of which were pretreated with ibuprofen, 12.5 mg/kg. Thirteen sheep were given intravenous endotoxin, 2 micrograms/kg, with six pretreated with ibuprofen. An early hypertensive phase was noted with both insults characterized by pulmonary hypertension, hypoxia, and increased lung lymph flow (QL). With subcutaneous tissue endotoxin, there was a significant increase in tissue lymph TxB2 and 6-keto-PGF1 alpha when compared to lung lymph and increased values in venous plasma compared to arterial plasma, indicating tissue to be the source. With intravenous endotoxin, lung lymph and aortic plasma levels were significantly higher than tissue lymph and venous plasma, respectively. The hypoxia, hypertension and increased prostanoids were prevented using ibuprofen. An increased lung permeability phase was noted with intravenous endotoxin but not with tissue endotoxin. As expected, this phase was not inhibited with ibuprofen and, therefore, not prostanoid-induced.     

TNF- and LPS-induced changes of lung vascular permeability: studies in unanesthetised sheep

There have been reports that the administration of TNF produces many of the cardiopulmonary changes seen with endotoxin (LPS). We asked whether all of LPS effects can be mimicked by TNF infusion. The effects of infusion of (human recombinant) TNF (50 micrograms/kg/30 min) and LPS (3 micrograms/kg/30 min) on permeability characteristics of sheep lungs were compared. Thirteen sheep were chronically instrumented for cardiopulmonary studies including lung lymph data. Infusion of LPS and TNF result in an increase of body temperature and lung lymph protein clearance (measured as the product of Lymph Flow and Lymph/Plasma Protein Ratio). The two responses had entirely different time courses. This might be related to the significantly longer period of pulmonary hypertension (MPAP) with LPS, which was only transient with TNF. Similar differences in plasma levels of thromboxane B2 (TxB2) were also noted. There were also differences in leukocyte kinetics, arterial blood gases, and plasma lactate levels. This indicates that although TNF infusion results in an increased pulmonary microvascular permeability, this event occurs without concomitant changes in thromboxane metabolism and exhibits time characteristics somewhat different from endotoxin.     

Pulmonary vascular response to endotoxin in normal and lymphocyte depleted sheep.

The cardiopulmonary effects of intravenously administered Escherichia coli endotoxin were studied in unanesthetized sheep. One group of animals was depleted of circulating T-lymphocytes while a non-depleted group served as control. T-lymphocyte depletion was accomplished by chronic thoracic duct drainage of lymph, removal of lymphocytes by continuous flow centrifugation and return of the cell free lymph intravenously. The T-lymphocyte depleted sheep demonstrated markedly obtunded increases in pulmonary arterial pressure and pulmonary vascular resistance following endotoxin when compared to the effects of the lipopolysaccharide in control animals. additionally, the lymphocyte depleted group showed a significant augmentation of myocardial contractility which occurred at the same time as marked systemic hypotension. This period of extreme hypotension following endotoxin is presumed to be accompanied by a reflex increase in the activity of the sympathetic nervous system. The control sheep, although equally hypotensive at this time, did not demonstrate a significant increase in myocardial contractility from the preendotoxin value. The results of these experiments indicate that T-lymphocytes may mediate some of the pathophysiological effects of bacterial endotoxin on the cardiovascular system.     

Effects of recombinant human tumor necrosis factor alpha, lymphotoxin, and Escherichia coli lipopolysaccharide on hemodynamics, lung microvascular permeability, and eicosanoid synthesis in anesthetized sheep

We infused recombinant human tumor necrosis factor alpha (rhTNF alpha), lymphotoxin (rhLT), and Escherichia coli 0111:B4 lipopolysaccharide (LPS) into anesthetized sheep with a lung lymph fistula to compare their effects on systemic and pulmonary hemodynamics, lung lymph dynamics, and eicosanoid release. rhTNF alpha (25-150 micrograms/kg, n = 6 sheep), but not rhLT (25 micrograms/kg, n = 3), rapidly increased lung lymph and plasma levels of 6-keto-prostaglandin F1 alpha (6-k-PGF1 alpha) and caused profound systemic vasodilation and hypotension. Meclofenamate pretreatment (10 mg/kg) of three other sheep given 25 micrograms/kg rhTNF alpha prevented the increase of lymph and plasma 6-k-PGF1 alpha levels, systemic vasodilation, and the early (less than 2 hrs) but not the late (4-6 hours) hypotension caused by rhTNF alpha. LPS (1 micrograms/kg, n = 11) induced a briefer increase of lymph 6-k-PGF1 alpha levels than did rhTNF alpha while plasma 6-k-PGF1 alpha levels did not increase. LPS induced more gradual hypotension than did rhTNF alpha but did not cause systemic vasodilation. LPS and rhTNF alpha, but not rhLT, increased lymph thromboxane B2 (TXB2) levels during the first hour of study, whereas only LPS acutely increased plasma TXB2 levels. LPS caused acute pulmonary vasoconstriction and greater acute pulmonary artery hypertension than did either rhTNF alpha or rhLT. Whereas LPS-treated sheep required less fluid transfusion than rhTNF alpha-treated sheep to maintain mean systemic arterial pressure greater than 50 mm Hg, LPS infusion caused a greater increase of lung lymph protein clearance. rhTNF alpha caused minimal alterations of lung microvascular permeability. We conclude that eicosanoid mediators contribute importantly to differences of systemic and pulmonary hemodynamics caused by these agents in sheep. rhTNF alpha cannot account for all of the LPS-induced hemodynamic, lung lymph, and eicosanoid responses in sheep.     

Salicylate pulmonary edema: the mechanism in sheep and review of the clinical literature.

Several clinical reports of salicylate-induced pulmonary edema led us to investigate the mechanism in a chronic unanesthetized sheep preparation. We infused an aspirin-buffer solution intravenously at rates up to 1,200 mg of aspirin per hour and compared effects on lung lymph flow and lymph protein concentration to those seen after mechanical elevation of pulmonary vascular pressures. Aspirin had little effect on lung vascular pressures but caused lung lymph flow to increase an average of greater than twice baseline. Because lymph protein concentrations were higher for a given lymph flow with aspirin than during mechanical pressure elevation, lymph protein (lymph flow X lymph to plasma protein concentration) increased much more with aspirin. Thus, aspirin appears to cause increased permeability to fluid and protein in the pulmonary vascular bed. Aspirin caused arterial PO2 to decrease from 83 +/- 3 SE mm Hg to 74 +/- 3 mm Hg (P less than 0.05) and caused postmortem extravascular lung water to increase. These findings are supported by a review of the clinical literature, indicating that salicylate pulmonary edema in humans is noncardiac in origin and may occur at doses considered therapeutic for some diseases as well as after overdose.