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

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Abstract

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 A2 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-phenylalanine (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 A2 in granulocyte-endothelial interaction was investigated by pretreatment with the cyclooxygenase inhibitor diclofenac (10 [micro sign]g/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 A2 (>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 [micro sign]g/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 A2. 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. (Crit Care Med 1998; 26:1868-1874)

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