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)     

Thrombin-induced alterations in lung fluid balance in awake sheep

We examined the effect of fibrinolysis depression on thrombin-induced pulmonary microembolism in awake sheep prepared with chronic lung lymph fistulas. Fibrinolysis was depressed by an intravenous infusion (100 mg) of tranexamic acid [trans-4-(Aminomethyl)cyclohexanecarboxylic acid]. Pulmonary microembolism was induced by an intravenous infusion of alpha-thrombin (80 NIH U/kg) in normal (n = 7) and in tranexamic acid-treated (n = 6) sheep. Thrombin immediately increased pulmonary lymph flow (Qlym) in both groups. The increased Qlym was not associated with a change in the lymph-to-plasma protein concentration (L/P) ratio in the control group and with a small decrease in the tranexamic acid-treated group. The increases in Qlym and pulmonary transvascular protein clearance (Qlym X L/P ratio) in the tranexamic acid-treated group were greater and sustained at four- to fivefold above base line for 10 h after the thrombin and remained elevated at twofold above base line even at 24 h. In contrast, Qlym and protein clearance were transiently increased in the control group. The mean pulmonary arterial pressure (Ppa) and pulmonary vascular resistance (PVR) increased after thrombin in tranexamic acid-treated group; the increases in Ppa and PVR in the control group were transient. Protein reflection coefficient as determined by the filtration independent method decreased after thrombin in tranexamic acid-treated sheep (n = 5), indicating an increased vascular permeability to proteins. We conclude that prolongation of microthrombi retention in the pulmonary circulation results in an increased vascular permeability to proteins. Both increased vascular permeability and vascular hydrostatic pressure are important determinants of the increases in Qlym and transvascular protein clearance after thrombin-induced pulmonary microembolism.     

Thromboxane increases pulmonary vascular resistance and transvascular fluid and protein exchange after pulmonary microembolism

We compared the effects of inhibition of thromboxane synthetase with antagonism of thromboxane A2 (TxA2)/prostaglandin H2 receptors on the changes in pulmonary hemodynamics and pulmonary transvascular fluid and protein exchange following thrombin-induced pulmonary microembolism. Studies were made in chronically instrumented unanesthetized sheep prepared with lung lymph fistulas. Control thrombin challenged sheep (n = 5) were compared to animals pretreated with Dazoxiben (the Dazoxiben-thrombin group, n = 8) or animals pretreated with L-640,035 (the L-640,035-thrombin group, n = 5). In the control-thrombin sheep, plasma TxA2 concentration rose after thrombin and the response was inhibited in the Dazoxiben-thrombin group. The rise in the plasma TxA2 concentration was greater in the L-640,035-thrombin group than in the control-thrombin group. In the control-thrombin group, thrombin produced a sustained increase in the pulmonary transvascular protein clearance (pulmonary lymph flow x lymph/plasma protein concentration ratio) and pulmonary vascular resistance (PVR). In the Dazoxiben-thrombin group, increases in both pulmonary transvascular protein clearance and PVR after thrombin were less than in the control-thrombin group. In the L-640,035-thrombin group, thrombin initially increased pulmonary transvascular protein clearance and PVR to the same levels as the control group; however, both protein clearance and PVR declined with time, in contrast to the sustained responses in the control-thrombin group. These differences may be related to the initially greater increase in plasma TxA2 concentrations after thrombin in the L-640,035-treated animals. The results indicate that TxA2 plays a role in mediating the increases in PVR and contributes to increases in pulmonary transvascular fluid and protein exchange after thrombin-induced pulmonary microembolism.     

Effect of complement depletion on lung fluid balance after thrombin

We examined the effect of complement depletion on lung fluid and protein exchange after thrombin-induced pulmonary thromboembolization. Sheep were prepared with lung lymph fistulas to assess pulmonary transvascular fluid and protein dynamics. Studies were made in three groups: in group I (n = 5) pulmonary thromboembolization (PT) was induced by an iv infusion of thrombin (55.0 +/- 12.9 NIH U/kg); in group II (n = 6) cobra venom factor (CVF) was given ip (94.5 +/- 18.8 U/kg/day) for 2 days to deplete complement, and then thrombin (66.4 +/- 37.0 NIH U/kg) was infused to raise pulmonary vascular resistance to the same level as in group I; in group III (n = 10) left atrial pressure (Pla) was increased by 10-15 Torr in normal animals by inflation of a Foley balloon catheter. In group I, thrombin infusion caused an increase in pulmonary lymph flow (Qlym) with a gradual increase in the lymph-to-plasma protein concentration ratio (L/P). In complement-depleted sheep, thrombin caused a transient increase in Qlym, which was associated with a decrease in L/P. In group I an increase in Pla further increased Qlym but without a change in L/P, indicating an increase in lung vascular permeability to proteins; whereas in the decomplemented-thrombin sheep raising Pla increased Qlym but decreased L/P. Results in the latter group were similar to those obtained in normal animals after left atrial hypertension (group III). Therefore the complement system participates in the increase in lung vascular permeability following thrombin-induced microembolization.     

Effect of prostacyclin on pulmonary vascular response to thrombin in awake sheep

We determined the effects of infusion of prostacyclin (PGI2) and 6-alpha-carba-PGI2 (6-cPGI2), a stable PGI2 analogue, on pulmonary transvascular fluid and protein fluxes after intravascular coagulation induced by thrombin. Studies were made in control awake sheep prepared with lung lymph fistulas (n = 6) and in similarly prepared awake sheep pretreated with either 6-cPGI2 (n = 5) or PGI2 (n = 5). Both prostacyclin compounds (500 ng X kg-1 X min-1) were infused intravenously. All groups were challenged with 80 U/kg thrombin. Pulmonary arterial pressure (Ppa), pulmonary vascular resistance (PVR), pulmonary lymph flow (Qlym), lymph protein clearance (Qlym X lymph/plasma protein concentration ratio), and neutrophil and platelet counts were determined. In vitro tests assessed sheep neutrophil chemotaxis and chemiluminescence and platelet aggregation. In both 6-cPGI2 and PGI2 groups, the increases in Qlym after thrombin were less than those in the control group. The increase in lymph protein clearance in the 6-cPGI2 group was the same as that in control, whereas the increase in clearance in the PGI2 group was reduced. PVR and Ppa increased to a greater extent in the 6-cPGI2 group than in the control group, whereas the increases in PVR and Ppa were inhibited in the PGI2 group. Neutrophil and platelet counts decreased after thrombin in PGI2 and 6-cPGI2 groups, as they did in the control group. Neither 6-cPGI2 altered neutrophil chemotaxis induced by thrombin and chemiluminescence induced by opsonized zymosan. Both prostacyclin compounds inhibited platelet aggregation induced by ADP or thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of alpha- and gamma-thrombin on lung fluid balance in anesthetized sheep

We examined the effects of varying dosages of thrombin on lung fluid balance in halothane-anesthetized sheep prepared with lung lymph fistulas. A 15-min iv infusion of sublethal doses of alpha-thrombin (2.5 clotting units/micrograms), the native enzyme, at 0.6 or 1.1 nmol active enzyme/kg body wt increased the mean pulmonary arterial pressure (Ppa) and pulmonary vascular resistance (PVR) two- to threefold. Neither parameter increased in a dose-dependent manner. Platelet counts decreased 50% with both dosages. Leukocyte counts decreased 35 and 75% from base line in the low- and high-dosage groups, respectively, and reached comparable levels of 50% below base line at 60-min postinfusion in both groups. Plasma fibrinogen concentrations decreased in a dose-dependent manner preceding dose-dependent increases in pulmonary lymph flow (Qlym) and lymph protein clearance (Clym). Fibrin deposition in pulmonary vessels was greater at 30 than at 180 min postinfusion. In contrast, a 15-min iv infusion of gamma-thrombin (0.002 clotting units/micrograms), which lacks the fibrinogen recognition site, at 1.2 nmol active enzyme/kg produced no significant increases in PVR, Ppa, Qlym, or Clym. The fibrinogen concentration did not change significantly, whereas platelet and leukocyte counts decreased 25% within 15 min. Fibrin microthrombi were less prominent in pulmonary vessels. Fibrin deposition associated with intravascular coagulation may be an important factor mediating thrombin-induced increases in pulmonary transvascular fluid and protein exchange.     

Pulmonary fibrin microembolism with Echis carinatus venom in dogs: effects of a synthetic thrombin inhibitor

We produced pulmonary fibrin microembolism using an infusion of a prothrombin activator (Echis carinatus venom, 30 min, 0.5 NIH thrombin equivalent units/kg) in open-chest mongrel dogs. To determine the nonclotting effects of this venom on edemagenesis we infused an irreversible thrombin inhibitor, D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (PPACK, 57 nmol X kg-1 X min-1 for 120 min), alone (n = 5) or with venom (Echis + PPACK, n = 5). The control group (n = 5) was given 1 ml of 0.9% NaCl. A decline in left atrial pressure (means +/- SE, 5.3 +/- 0.4 to 4.0 +/- 0.5 mmHg, P less than 0.05) and cardiac index (149 +/- 10 to 82 +/- 13 ml X min-1 X kg-1, P less than 0.01) in association with a marked increase in pulmonary arterial pressure (14.5 +/- 0.6 to 26.6 +/- 2.5 mmHg, P less than 0.001) and pulmonary vascular resistance (64 +/- 5 to 304 +/- 42 mmHg X ml-1 X min-1 X kg-1, P less than 0.001) was observed after 20 min of venom infusion. During this interval, pulmonary artery wedge pressure increased (4 +/- 1 to 12 +/- 4 mmHg, P less than 0.01) in four of eight animals. Fibrinogen declined below measurable levels and fibrin microemboli were seen in many pulmonary arterioles. These changes were not observed in the Echis + PPACK, PPACK, or control groups. Leukopenia and thrombocytopenia were observed in the Echis and Echis + PPACK groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

CVF-induced decomplementation: effect on lung transvascular protein flux after thrombin

We examined the effects of cobra venom factor (CVF) on the changes in pulmonary hemodynamics and transvascular fluid and protein exchange following thrombin-induced pulmonary microembolism. Studies were made in unanesthetized sheep prepared with lung lymph fistulas. The animals received tranexamic acid (100 mg) to suppress fibrinolysis and were then challenged with an intravenous infusion of alpha-thrombin (80 U/kg). Control-thrombin challenged sheep were compared with the CVF-treated sheep challenged with the same thrombin dosage. CVF treatment (187 U X kg-1 X day-1 for 4 days) decreased the total hemolytic complement activity by 45% of control. Thrombin infusion in control sheep increased the mean pulmonary arterial pressure (Ppa), pulmonary vascular resistance (PVR), and lymph protein clearance (pulmonary lymph flow X lymph-to-plasma protein concentration ratio, Clym). Thrombin infusion in CVF-treated sheep produced smaller increments in Ppa, PVR, and Clym. Pulmonary lymph obtained from control-thrombin and CVF-thrombin sheep induced migration of granulocytes obtained from normal unchallenged sheep. The granulocytes obtained from CVF-treated sheep responded relatively less to the migratory and O-2-generating stimuli (i.e., zymosan-treated serum, pulmonary lymph from sheep after thrombin challenge, and plasma from sheep after CVF treatment) compared with normal granulocytes. The attenuation of the thrombin-induced increases in Ppa, PVR, and lung transvascular fluid and protein exchange by CVF treatment may be the result of impaired function of granulocytes.     

Thrombin is present in the lungs of patients with primary extremity osteosarcoma and pulmonary metastases

Osteosarcoma is a rare cancer, which metastasizes to the lung in up to 80% of cases. Thrombin is involved in metastasis and is present in the lungs of patients with pulmonary metastases (PM). To identify its role in PM and osteosarcoma, we measured thrombin levels in the bronchoalveolar lavage fluid (BALF) of 15 patients. BALF was collected at different stages of the disease and correlated with the diagnosis of PM. We also assessed fibrinogen overexpression in the tumors. We found that 11/15 (73%) patients with high thrombin levels in the lungs developed PM within the first 12 months from primary surgery. The median thrombin concentration in the BALF of these patients increased up to 8x10(-9) M (range, 3x10(-9)M-15x10(-9)M), which represents a more than 100-fold increase compared to patients without PM (p<0.0001). Eight of 15 (53%) primary and 11/15 (73%) metastatic samples showed fibrinogen overexpression. A significant difference between high thrombin levels, fibrinogen overexpression and PM was found compared to patients without PM (p=0.00073 and p=0.025). These results show that thrombin levels are increased in the lungs of patients with primary osteosarcoma and a high risk of developing PM. They suggest that thrombin may be involved in the development of PM.     

Effects of coronary ischemia on lung fluid balance in conscious sheep

It has been suggested that coronary ischemia increases extravascular lung water. To determine whether pulmonary microvascular permeability is increased by coronary ischemia, we measured pulmonary hemodynamics, lung lymph flow (QL), and lymph-to-plasma protein concentration ratio (L/P) in 12 sheep with chronic lung lymph fistulas. Studies were done in 3 groups: in group 1 (n = 7) a marginal branch of the left circumflex artery (Lcx) was occluded, in group 2 (n = 5) left atrial pressure (Pla) was mechanically raised by 10 mmHg, and in group 3 (n = 5) Lcx was occluded and Pla was raised by 10 mmHg. In group 1, coronary occlusion increased QL (4.6 +/- 0.4 to 8.3 +/- 2.6 ml/h) without changes in L/P. In group 2, elevated Pla increased QL (5.1 +/- 1.2 to 10.1 +/- 3.0 ml/h) with decreases in L/P (0.71 +/- 0.02 to 0.61 +/- 0.02). In group 3, coronary occlusion with elevated Pla caused a further increase in QL (5.0 +/- 1.5 to 16.9 +/- 4.6 ml/h) without significant decreases in L/P (0.71 +/- 0.01 to 0.65 +/- 0.06). Lung lymph concentrations of 6-keto-prostaglandin F1 alpha (a degradation product of prostacyclin) increased transiently after coronary occlusion. These results indicate that coronary occlusion can increase transcapillary protein transport in lungs of conscious sheep and simultaneously increase prostacyclin production in the lung.     

Pulmonary neutrophil kinetics after thrombin-induced intravascular coagulation

Previous studies have indicated that neutrophils are required for the development of increased lung vascular permeability after thrombin-induced pulmonary microembolization. In this study, we examined neutrophil kinetics and uptake in the sheep lung before and after lung vascular injury. Sheep neutrophils were isolated by a Percoll-gradient method and labeled with indium-111 oxine. A maximum lung activity of 40% of the injected indium-111 neutrophil activity was attained 8-12 min after the injection. The calculated half-lives of both circulating and pulmonary neutrophils were 700 min. The rate of washout of labeled neutrophils from the lungs was the same as the loss of the peripheral blood activity, indicating removal of neutrophils from the lung and blood by a common pathway (e.g., liver and spleen). Intravenous infusion of alpha-thrombin resulted in an immediate uptake of neutrophils of 14% above the base-line activity. The increased uptake was associated with an immediate decrease in the blood activity, indicating sequestration of the neutrophils in the pulmonary circulation. The neutrophil uptake after alpha-thrombin was transient, reaching a maximum 15 min after infusion. Neutrophil uptake did not occur with alpha-thrombin (which lacks the fibrinogen recognition site), suggesting that the uptake was secondary to intravascular coagulation. An increase in the pulmonary blood volume cannot explain the increased neutrophil sequestration because pulmonary blood volume determined by [99mTc]pertechnetate-labeled erythrocytes did not increase after the alpha-thrombin infusion. Therefore, alpha-thrombin results in a transient neutrophil sequestration in the lung, and the response is secondary to the intravascular coagulation induced by the alpha-thrombin.     

Effect of thrombomodulin on specific thrombin functions: fibrinogen coagulation and thrombocyte aggregation

The effect of thrombomodulin (TM), prepared from rabbit lungs, on fibrinogen clotting and platelets aggregation by alpha-thrombin has been investigated. It has been established that TM caused a dose-dependent decrease in fibrinogen-clotting activity of thrombin (Ki = 14.7 +/- 1.24 nM). TM was shown to reduce thrombin-induced platelet aggregation but not to alter ADP-induced one. It was found that the kinetic parameters for hydrolysis of synthetic substrates by alpha-thrombin were not altered by TM.     

Sympathetic nervous activity decreases during head-down bed rest but not during microgravity.

We tested the hypothesis that sympathoadrenal activity in humans is low during spaceflight and that this effect can be simulated by head-down bed rest (HDBR). Platelet norepinephrine and epinephrine were measured as indexes of long-term changes in sympathoadrenal activity. Ten normal healthy subjects were studied before and during HDBR of 2-wk duration, as well as during an ambulatory study period of a similar length. Platelet norepinephrine concentrations (half-life = 2 days) were studied in five cosmonauts, 2 wk before launch, within 12 h after landing after 11-12 days of flight, and at least 2 wk after return to Earth. Because of the long half-life of platelet norepinephrine, data obtained early after landing would still reflect the microgravity state. Platelet norepinephrine decreased markedly during HDBR (P < 0.001), whereas there were no significant changes when subjects were ambulatory. Platelet epinephrine did not change during HDBR. During microgravity, platelet norepinephrine and epinephrine increased in four of the five cosmonauts. Platelet norepinephrine concentrations expressed in percentage of preflight and pre-HDBR values, respectively, were significantly different during microgravity compared with HDBR [153 +/- 28% (mean +/- SE) vs. 60 +/- 6%, P < 0.004]. Corresponding values for platelet epinephrine were also significant (293 +/- 85 vs. 90 +/- 12%, P < 0.01). The mechanism of the platelet norepinephrine and epinephrine response during spaceflight flight is most likely related to the concomitant decrease in plasma volume. HDBR cannot be applied to simulate changes in sympathoadrenal activity during microgravity.     

Elevation of superior vena caval pressure increases extravascular lung water after endotoxemia

In many sheep Escherichia coli endotoxin results in pulmonary hypertension, increased microvascular permeability, pulmonary edema, and increased central venous pressure. Since lung lymph drains into the systemic veins, increases in venous pressure may impair lymph flow sufficiently to enhance the accumulation of extravascular fluid. We tested the hypothesis that, following endotoxin, elevating the venous pressure would increase extravascular fluid. Thirteen sheep were chronically instrumented with catheters to monitor left atrial pressure (LAP), pulmonary arterial pressure (PAP), and superior vena caval pressure (SVCP) as well as balloons to elevate LAP and SVCP. These sheep received 4 micrograms/kg endotoxin, and following the pulmonary hypertensive spike the left atrial balloon was inflated so that (PAP + LAP)/2 = colloid osmotic pressure. It was necessary to control PAP + LAP in this way to minimize the sheep-to-sheep differences in the pulmonary hypertension. We elevated the SVCP to 10 or 17 mmHg or allowed it to stay low (3.2 mmHg). After a 3-h period, we killed the sheep and removed the right lungs for determination of the extravascular fluid-to-blood-free dry weight ratio (EVF). Sheep with SVCP elevated to 10 or 17 mmHg had significant increases in EVF (5.2 +/- 0.1 and 5.6 +/- 1.2) compared with the sheep in which we did not elevate SVCP (EVF = 4.5 +/- 0.4). These results indicate that sustained elevation in central venous pressure in patients contributes to the amount of pulmonary edema associated with endotoxemia.     

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.     

Permeability of barriers to albumin flux in lungs of sheep resuscitated from hemorrhagic shock

We assessed pulmonary endothelial and epithelial permeability and lung lymph flow in nine adult sheep under base-line conditions and after resuscitation from profound hemorrhagic shock. Animals were mechanically ventilated and maintained on 1% halothane anesthesia while aortic pressure was held at 40 Torr for 3 h. Systemic heparin was not used. After reinfusion of shed blood, sheep recovered from anesthesia and we measured lung lymph flow (QL), lymph-to-plasma concentration ratio for proteins, and time taken to reach half-equilibrium concentration of intravenous tracer albumin in lymph (t1/2). Twenty-four hours after bolus injection of radio-albumin we lavaged subsegments of the right upper lobe and determined fractional equilibration of the tracer in the alveolar luminal-lining layer. In each sheep we had measured these parameters 7 days earlier under base-line conditions. Animals were killed, and the lungs were used for gravimetric determination of extravascular lung water (gravimetric extravascular lung water-to-dry weight ratio) 24 h after resuscitation from shock. Pulmonary endothelial injury after resuscitation was evidenced by marked increase in QL, without fall in lymph-to-plasma ratio. Time taken to reach half-equilibrium concentration fell from 169 +/- 47 (SD) min in base-line studies to 53 +/- 33 min after shock. There was no evidence of lung epithelial injury. Gravimetric extravascular lung water-to-dry weight ratio was significantly increased in these animals killed 24 h after resuscitation (4.94 +/- 0.29) compared with values in our laboratory controls (4.13 +/- 0.09, mean +/- SD). These data demonstrate a loss of lung endothelial integrity in sheep after resuscitation from profound hemorrhagic shock.     

Increases in lung expansion alter pulmonary hemodynamics in fetal sheep.

Prolonged increases in fetal lung expansion stimulate fetal lung growth and development, but the effects on pulmonary hemodynamics are unknown. Our aim was to determine the effect of increased fetal lung expansion, induced by tracheal obstruction (TO), on pulmonary blood flow (PBF) and vascular resistance (PVR). Chronically catheterized fetal sheep (n = 6) underwent TO from 120 to 127 days of gestational age (term approximately 147 days); tracheas were not obstructed in control fetuses (n = 6). PBF, PVR, and changes to the PBF waveform were determined. TO significantly increased lung wet weight compared with control (166.3 +/- 20.2 vs. 102.0 +/- 18.8 g; P < 0.05). Despite the increase in intraluminal pressure caused by TO (5.0 +/- 0.9 vs. 2.4 +/- 1.0 mmHg; P < 0.001), PBF and PVR were similar between groups after 7 days (TO 28.1 +/- 3.2 vs. control 34.1 +/- 10.0 ml.min(-1).100 g lung wt(-1)). However, TO markedly altered pulmonary hemodynamics associated with accentuated fetal breathing movements, causing a reduction rather than an increase in PBF at 7 days of TO. To account for the increase in intraluminal pressure, the pressure was equalized by draining the lungs of liquid on day 7 of TO. Pressure equalization increased PBF from 36.8 +/- 5.2 to 112.4 +/- 22.8 ml/min (P = 0.01) and markedly altered the PBF waveform. These studies provide further evidence to indicate that intraluminal pressure is an important determinant of PBF and PVR in the fetus. We suggest that the increase in PBF associated with pressure equalization following TO reflects an increase in growth of the pulmonary vascular bed, leading to an increase in its cross-sectional area.     

Pulmonary neutrophil kinetics in sheep: effects of altered hemodynamics

We investigated the effect of elevated left atrial pressure and reduced cardiac output on pulmonary neutrophil kinetics in the sheep. Sheep neutrophils were isolated, labeled with 111In-oxine, and reinfused. Erythrocytes were labeled with [99mTc]pertechnetate. A gamma camera measured the lung activities of the labeled neutrophils and erythrocytes. The results indicated that 38.5% of the total injected neutrophils marginated in the lung. Pulmonary hemodynamics were altered by inflating a left atrial balloon three times in each sheep for 15-30 min to achieve 5- to 25-mmHg increments in pulmonary arterial wedge pressure. At least a 30-min recovery period was allowed between inflations. After each left atrial balloon inflation, neutrophil uptake remained unchanged from base line, despite decreased mean cardiac output to 0.67 +/- 0.24 (+/- SD) 1/min and increased pulmonary blood volume. The absence of pulmonary neutrophil uptake was confirmed by arterial-venous measurements. Increased pulmonary blood volume had little effect on lung neutrophil uptake, suggesting that most of the pulmonary neutrophils are marginated. We conclude that the lungs have a large marginated neutrophil pool compared with the circulating pool and that reduced cardiac output and elevated left atrial pressure have no effect on pulmonary neutrophil kinetics in the sheep.     

Bradykinin is degraded in hypoxic lungs and does not affect epithelial permeability

To investigate the effect of intravenous infusions of bradykinin (BK) on the permeability of the hypoxic pulmonary epithelium to small solutes, experiments (n = 7) were performed in yearling sheep with chronic vascular catheters. Sheep were anesthetized, intubated, paralyzed, and ventilated. After establishing stable and normal base-line pulmonary hemodynamics and blood gas tensions, the lungs were insufflated with a submicronic aerosol of technetium-99m-labeled diethylenetriaminepentaacetate (99mTc-DTPA, mol wt = 492). Radioactivity arising from the right hemithorax was measured by an NaI probe with a parallel-holed collimator. The base-line pulmonary clearance rate (k) for 99mTc-DTPA was 0.51 +/- 0.09% (SE)/min, while the sheep were ventilated with a fractional concentration of inspired O2 (FIO2) of 0.5 [arterial partial pressure of O2 (PaO2) = 196 +/- 11.4 (SE) Torr]. Clearance of 99mTc-DTPA was unaffected by hypoxia alone or BK infusions in nonhypoxic lungs. The combination of an intravenous infusion of BK at either 1.2 (n = 3) or 2.4 micrograms . kg-1 . min-1 (n = 4) and alveolar hypoxia [FIO2 = 0.11, PaO2 = 28 +/- 1.6 (SE) Torr] did not affect pulmonary clearance of 99mTc-DTPA [k = 0.43 +/- 0.08% (SE)/min]. In contrast, a 0.05-ml/kg intravenous infusion of oleic acid increased clearance 10-fold in one sheep. During combined hypoxia and BK infusion the pulmonary arterial BK concentration (radioimmunoassay) increased from 0.82 +/- 0.16 (SE) to 7.05 +/- 1.86 ng/ml (P less than 0.001), but the systemic arterial concentrations were unchanged [0.67 +/- 0.19 (SE) to 0.66 +/- 0.09 ng/ml].(ABSTRACT TRUNCATED AT 250 WORDS)     

Airway responsiveness to inhaled and intravenous carbachol in sheep: effect of airway mucus

Excessive airway mucus can alter both the mass and site of aerosol deposition, which, in turn, may affect airway responsiveness to inhaled materials. In six prone sheep, we therefore measured pulmonary airflow resistance (RL) and cumulative aerosol deposition during five standard breaths (AD5) at base line and 3 min after inhalation challenge with 2% carbachol in buffered saline (10 breaths, tidal volume = 500 ml) or after an intravenous loading dose of carbachol (3 micrograms/kg) followed by a constant infusion of 0.3 micrograms.kg-1.min-1 with and without instillation of 20 ml of a mucus simulant (MS) into the distal end of each of the main bronchi or 30 ml of MS into the right main bronchus only by means of a flexible fiber-optic bronchoscope. Before carbachol challenge, RL did not change with MS into either both lungs or one lung only. AD5 increased from 36 +/- 2% (SE) before to 42 +/- 2% after MS instillation into both lungs (P less than 0.05) but remained unchanged after MS into one lung. After carbachol inhalation, RL increased significantly by 154 +/- 20 before and 126 +/- 25% after MS into both lungs and 162 +/- 24 before and 178 +/- 31% after MS into one lung (P less than 0.05). When the percent increase in RL was normalized for total aerosol deposition (% delta RL/AD5), the normalized values were lower after MS (3.0 +/- 0.5) than before MS (4.4 +/- 0.3) into both lungs (P less than 0.05) but were not significantly different before and after MS into the right lung only.(ABSTRACT TRUNCATED AT 250 WORDS)