Early effects of TNF, LPS and thromboxane on pulmonary microvascular dysfunction

Introduction: TNF, LPS and thromboxane A₂ (TXA₂) are known mediators of acute lung injury characterized by increased airway pressure, decreased compliance, altered gas exchange and increased pulmonary microvascular permeability. This study examines the early (15-20 min) effects of TNF, LPS and U46619 (a TXA₂ receptor agonist) on the capillary filtration coefficient, K_f, in an isolated perfused lung model, given either in the perfusate or intra-tracheally. Methods: Mechanically ventilated lungs of Wistar rats were perfused ex-vivo in Krebt-Henseleit buffer with 100 ng/ml recombinant rat TNF, 400 ug/ml LPS, or 7 × 10^-8 M U46619 in the perrusate or 1.23 ug TNF, 5 mg LPS or 7 × 10^-8 M U46619 intratracheally. To determine whether there were any effects mediated by circulating blood elements, the experiments were repeated with the addition of 20% heparinized aucologous whole blood to the perfusate. After equilibration and 15 minutes of treatment, K_f is calculated according to the method described by Drake and Zanaboni. Data reported as mean±sem, analyzed by ANOVA, Fisher's PLSD. Results: K_f (gm/min/mm Hg/100 gm body wt) Treatment Perfusate Intra-tracheal Blood Perfusate Control 5.7 ± 0.5 5.3 ± 0.6 3.2± 0.3 TNF 6.8 ± 0.7 12.2 ± 6.0 4.0 ± 0.3 LPS 12.2± 0.4*1 19.9 ± 7.0**4.6 ± 0.4 U46619 33.2 ± 3.4*36.2 ± 15.9*4.4 ± 0.6*p<0 05 vs control 1 p<0.05 vs U46619 n≥5 for all groups Conclusions: It has been a widely held belief that TNF, LPS and TXA₂ play a prominent role in mediating early pulmonary microvascular dysfunction. In this model of acute lung injury, LPS or a thromboxane A₂ receptor agonist administered in the bloodless perfusate or intra-tracheally increased the capillary filtration coefficient, while TNF had no effect despite a supraphysiologic dose. Until now the influence of these mediators early in acute lung injury had not been defined. We have shown that LPS and TXA₂ have significant effects on the capillary filtration coefficient, yet TNF docs not induce any changes in K_f within 20 minutes even in combination with circulating blood elements such as neutrophils and platelets. This observation suggests that TNF does not exert any early direct or indirect effects on pulmonary capillary permeability.