Endothelin-1 and thromboxane A2 increase pulmonary vascular resistance in granulocyte-mediated lung injury.

Objective: To examine the pathophysiologic role of vasoactive eicosanoids and endothelin-1 in granulocyte-mediated effects in the pulmonary vasculature. Design: Prospective experimental study in rabbits. Setting: Experimental laboratory in a university teaching hospital. Subjects: Thirty adult rabbits. Interventions: The experiments were performed on 30 isolated and ventilated rabbit lungs that were perfused with a cell- and plasma-free buffer solution. Measurements and Main Results: The pulmonary arterial pressure and the lung weight gain were continuously registered. Intermittently perfused samples were taken to determine endothelin-1 and thromboxane A 2 concentrations. Six experiments without intervention served as the sham group. The granulocytes in the pulmonary circulation were stimulated with N-formyl-L-leucin-methionyl-L-phenylaianine (FMLP; 10 -6 M; control, n = 6). To investigate whether activated granulocytes influence the pulmonary vasculature via endothelin-1, the endothelin-A receptor antagonist LU135252 (10 -6 M) was added to the perfusate before FMLP injection (n = 6). The potential involvement of thromboxane A 2 in granulocyte-endothelial interaction was investigated by pretreatment with the cyclooxygenase inhibitor diclofenac (10 μg/mL; n = 6). Activation of granulocytes resulted in an acute increase in pulmonary arterial pressure (>9 mm Hg), which was followed by a second delayed pressure increase after 60 mins (>14 mm Hg) and was paralleled by a massive generation of thromboxane A 2 (>250 pg/ mL). Fifteen minutes after FMLP-injection, endothelin-1 was detectable in the perfusate. Pretreatment with the selective endothelin-A antagonist LU135252 significantly (p <.01) reduced the initial pressure response after FMLP stimulation, while diclofenac significantly reduced (p <.05) the delayed pressure increase. Using diclofenac (10 μg/mL) in conjunction with LU135252 (10 -6 M; n = 6) before FMLP injection significantly reduced the early and the delayed pressure increase. Conclusions: Activated granulocytes seem to enhance pulmonary vascular resistance via endothelin-1 and thromboxane A 2 . The endothelin-1 effects are probably mediated via endothelin-A receptors since the endothelin-A receptor antagonist LU135252 was able to suppress the early pressure reaction after FMLP injection, whereas the cyclooxygenase inhibitor diclofenac was able to reduce the second pressure increase.