Beneficial effects of inhaled nitric oxide (iNO) on arterial oxygenation in acute lung injury (ALI) suggest the presence of vasoconstriction in ventilated lung regions and this may be influenced by endothelin-1 (ET-1). We studied a possible interaction between ET-1 and iNO in experimental ALI. Sixteen piglets were anesthetized and mechanically ventilated (inspired O2 fraction, 1.0). After induction of ALI by surfactant depletion, animals were randomly assigned to either inhale 30 ppm NO (iNO group, n = 8), or to receive no further intervention (controls, n = 8). Measurements were performed during the following 4 hrs. In all animals, induction of ALI significantly decreased arterial oxygen tension (PaO2) from 569 +/- 15 (prelavage) to 58 +/- 3 mm Hg. Inhaled NO significantly increased PaO2 when compared with controls (iNO group: 265 +/- 51 mm Hg; controls: 50 +/- 4 mm Hg, values at 4 hrs, P < 0.01). Prelavage ET-1 plasma levels were comparable between groups (iNO: 0.74 +/- 0.03, controls: 0.71 +/- 0.03 fmol/ml, NS). During the protocol, the ET-1 levels increased and were different at 3 hrs (iNO: 0.93 +/- 0.06, controls: 1.25 +/- 0.09 fmol/ml; P < 0.05). PaO2 changes induced by iNO revealed a moderate and significant correlation with ET-1 plasma levels (R = 0.548, P = 0.001). Our data suggest that endogenous ET-1 production influences the efficacy of iNO in ALI. Furthermore, iNO reduced ET-1 plasma levels, possibly indicating anti-inflammatory properties of iNO in the early phase of ALI.