M. B. Perlman

Superoxide dismutase prevents the thrombin-induced increase in lung vascular permeability: role of superoxide in mediating the alterations in lung fluid balance.

We investigated the effects of superoxide dismutase (SOD) and SOD linked to Ficoil (mol. wt = 400,000) on the changes in pulmonary transvascular fluid and protein exchange following pulmonary microembolism induced with α-thrombin. Studies were made in chronically prepared unanesthetized sheep with lung lymph fistulas. Control thrombin challenged sheep (n = 5) were compared to animals infused with SOD (the SOD-thrombin group, n = 5) or animals infused with SOD linked to high molecular weight Ficoil (the Ficoll-SOD-thrombin group, n = 6). The Ficoll-SOD-thrombin animals were also compared to animals infused with Ficoil alone (the Ficoll-thrombin group, n = 4) In the control-thrombin group, thrombin induced sustained increases in the pulmonary transvascular protein clearance (pulmonary lymph flow × lymph/plasma protein concentration ratio) and pulmonary vascular resistance (PVR). In the SOD-thrombin group, thrombin initially increased both pulmonary transvascular protein clearance and PVR; however, the later increases in protein clearance and PVR were blunted. The pulmonary reflection coefficients for total protein (σ), a measure of vascular permeability to protein, decreased from a value of 0.70 ± 0.03 in normal sheep to 0.60 ± 0.01 following thrombin challenge (p < 0.05) indicating an increase in lung vascular permeability. The σ value in the SOD-treated animals was 0.70 ± 0.02, indicating a protective effect of SOD. The infusion of the Ficoll-SOD complex also attenuated the increases in pulmonary transvascular protein clearance and PVR after thrombin. However, the infusion of Ficoil alone induced a similar protection. The lymph from the SOD-thrombin and Ficoll-SOD-thrombin groups prevented the reduction of ferricytochrome C by xanthine/xanthine oxidase, whereas, the lymph from the Ficoll-thronibln animals did not have this effect, indicating SOD activity was present in the animals receiving the enzyme but not in the group infused with Ficoil alone. Differences in the degree of intravascular coagulation could not explain the response to Ficoil since the decreases in fibrinogen concentration following the thrombin were similar in all the groups. Since Ficoil and related dextrans may modify neutrophil function, in particular neutrophil adherence to the endothelium, we examined the effects of Ficoil on neutrophil adherence. The results indicated that when Ficoil was added to the endothelial medium Ficoil reduced the increase adherence of neutrophils to the endothelial cell monolayer. Therefore, Ficoil as a carrier for SOD may provide a direct protection in models of lung vascular injury that are dependent on neutrophils. The infusion of SOD prevents the thrombin-induced increase in lung vascular permeability and reduces the pulmonary vasoactive response to thrombin-induced pulmonary intravascular coagulation. The results indicate that superoxide generation contributes to the increases in lung vascular permeability to protein and PVR following thrombin.

Lipoxygenase products induce neutrophil activation and increase endothelial permeability after thrombin-induced pulmonary microembolism.

We examined the mechanism of the neutrophil (PMN)-dependent increase in pulmonary vascular permeability to protein after thrombin-induced pulmonary microembolism. Humoral factors that activate PMNs after thrombin-induced pulmonary microemboUsm were characterized in pulmonary lymph obtained from unanesthetized sheep challenged with intravenous infusion of α-thrombin. Tune-dependent increases in PMN migration, aggregation, and superoxide anion (O2-) generation were induced by the puhnonary lymph obtained within 20 minutes after thrombin infusion. The puhnonary lymph neutrophil activating factors present in ether extracts of lymph had retention times of leukotriene B4 (LTB4) and monohydroxyeicosatetraenoic acids (HETEs) by high-performance liquid chromatography. The postthrombin lymph samples containing the LTB4 and HETEs increased PMN O2- generation and endothelial monolayer permeability to 125I-albumin in the presence of PMNs layered on the endothelial monolayers. Control lymph samples replete with LTB4, 5-HETE, and 15-HETE induced increases in PMN O2- generation and endothelial monolayer permeability to I25I-albumin in the presence of PMNs layered on the endothelial monolayers. Maximal increases in PMN O2-production and endothelial permeability occurred when LTB4, 5-HETE, and 15-HETE were coincubated with PMNs, indicating a synergistic action of these mediators in inducing PMN activation. Endothelial monolayer permeability to 125I-albumin did not increase with postthrombin lymph samples obtained after pretreatment with the 5-lipoxygenase inhibitor, L-651, 392. The results indicate that lipoxygenase products generated in the lungs after thrombin-induced microembolism contribute to increased endothelial permeability secondary to PMN activation.

547 RETRANSFER (RT) IS A SAFE AND COST-EFFECTIVE MEANS OF IMPROVING NEONATAL INTENSIVE CARE UNIT (NICU) UTILIZATION

During an 18 mo. period, 1255 neonates were admitted to the only Level III (LIII) NICU in a 50,000 sq. mi. service area with 26,000 live births/yr and having 33 Level I (LI) and 5 Level II (LII) referring hospitals. 739 of 1255 patients were transported from referring hospitals. 524 were neonatal transports (NT) and 215 maternal transports (MT). 641 of 739 survived and were eligible for RT to referring hospitals after stabilization. 225/641 (35%) underwent RT; only 4 required NICU readmission. Duration of hospitalization was greater for infants < 2000 gms. birthweight (BW). Analysis of transport and RT patterns is shown below.Rates of RT to LI or LII were all < 50%; when used, RT safely decreased duration of NICU hospitalization.Conclusions: at an average LIII cost of

EFFECTS OF CYCLOOXYGENASE INHIBITORS ON LUNG MICROVASCULAR INJURY FOLLOWING PULMONARY INTRAVASCULAR COAGULATION |[lpar]|PIC|[rpar]|

800/day and an LI/LII cost of

1815 PULMONARY VASCULAR PERMEABILITY TO PROTEINS INCREASES AFTER THROMBIN-INDUCED INTRAVASCULAR COAGULATION

400/day, RT represents

1814 MEDIATORS AFFECTING NEUTROPHIL (PMN) FUNCTION ARE RELEASED AFTER PULMONARY INTRAVASCULAR COAGULATION

770,000 in potential annual savings. As shown here, analysis of regional referral patterns and use of RT aids optimal use of limited NICU resources.

Pulmonary microvascular effects of arachidonic acid metabolites and their role in lung vascular injury

We compared the effects of cyclooxygenase inhibitors, meclofenamate (MEC) and ibuprofen (IBU) on the development of lung mcirovascular injury after PIC induced by i.v. thrombin (T) infusion (80 U/kg). Studies were made in awake (n=10) sheep with lung lymph fistulas. The animals were pretreated with either MEC or IBU. Lung lymph flow (Qlym) lymph-to-plasma protein concentration ratio (L/P), and transvascular protein clearance (L/P × Qlym) were determined. MEC and IBU prevented the increases in the cyclooxygeanse end-products, thromboxane B2 and 6-keto-PGF1α after T. T resulted in 6-fold increases in Qlym and protein clearance, indicating lung microvascular injury. MEC attenuated the initial rises in Qlym and protein clearance after T, while IBU prevented both initial and steady-state responses. IBU but not MEC reduced the increases in pulmonary arterial pressure and PVR after T. In another group (n=11), lung PMN uptake after T was determined by infusing homologous 111-Indium oxine labeled PMN and measuring lung activity with a gamma camera. PMN uptake increased by 11% over baseline after T in controlas, compared to 4.1% in MEC group and none in IBU group. Conclusion: IBU has a greater protective effect in preventing thrombin-induced lung vascular injury than MEC. The protective effect is independent of inhibition of cyclooxygenase but may be related to inhibition of neutrophil margination. (HL-17355 and HL-26551)

Thrombin-induced alterations in lung fluid balance in awake sheep.

Since intravascular coagulation is a proposed etiologic factor in acute lung injury, we examined whether thrombininduced intravascular coagulation results in increased lung vascular permeability to proteins. Sheep (n=5) were prepared with lung lymph fistulas and balloon-tipped left atrial catheters. The sheep were studied in the unanesthetized state. The left atrial balloon was inflated to produce step increases in left atrial pressure (Pla) to a maximum of 25 Torr. Pulmonary lymph flow (Qlym) and lymph-to-plasma protein concentration ratio (L/P) were measured. The protein reflection coefficient (σd), a measure of pulmonary vascular permeability, was determined by increasing Pla until Qlym approached the filtration-independent state; i.e. further increases in Qlym did not further decrease L/P and σd approached (1–L/P). α −thrombin (80 U/kg) was then infused and a new steady-state Qlym was reached to allow σd to be determined after thrombin. (σd=1 indicates complete impermeability to proteins and d=0 indicates complete permeability). In the present study, σdd before thrombin was 0.70±0.03 (mean±SE) and decreased to 0.59±0.01 after thrombin (p<0.05). We conclude that pulmonary intravascular coagulation increases pulmonary vascular permeability to proteins and that this may be a factor in mediating acute lung injury. (Supported by HL17355, HL26551 and GM07033).

Ibuprofen prevents thrombin-induced lung vascular injury: mechanism of effect

Awake sheep (n=4) with lung lymph fistulas were infused with thrombin (T)(80U/kg). Lung lymph was collected before and at 5 to 60 min. after T. PMN were isolated from donor sheep. Lymph chemotaxis was measured by chemotaxis under agarose. Superoxide anion (O2−) release by PMN incubated with lymph was measured by difference in ferricy tochrome C reduction with and without superoxide dismutase. PMN aggregation was measured on an aggregometer. Data are shown as mean ± SEMAddition of hirudin (a thrombin inactivator) to lymph did not reduce chemotaxis indicating that responses were not due to T.Conclusion. Thrombin-induced intravascular coagulation causes time-dependent intrapulmonary generation of mediatorsoof PMN chemotaxis, aggregation and O2− production. These may be important in PMN-dependent acute long injury in the patient with disseminated intravascular coagulation. (Supported by HL-17355, HL-26551, HL-31359 and HL-07529).