We determined aortic plasma endothelin (ET-1) concentration in juvenile pigs during six hours after acute lung injury induced by meconium aspiration. Twelve 10 week-old pigs received 3 ml/kg 20% human meconium via endotracheal tube. Six pigs were pretreated with 30 mg/kg methylprednisolone i.v. known to attenuate the acute lung injury. Another six pigs served as controls and received endotracheally 3 ml/kg sterile saline. Ventilator settings were adjusted to avoid hypoxemia.

Meconium aspiration induced a biphasic increase in pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR) during the 6 hour observation period. A simultaneous biphasic increase detected in ET-1 concentration. Further, this increase correlated well with the increase in PVR(r=0.76). In contrast, endothelin concentration tended to decrease in the control group.

Methylprednisolone prevented significantly the second phase (1-6h) progressive rise in PAP, PVR, and ET-1. However, the decrease in ET-1 concentration was not statistically significant when compared to the meconium group.

We conclude, that meconium aspiration induces an acute lung injury characterized by a biphasic hypertensive pulmonary response and an increase in endothelin concentration suggesting an inportant role of this vasoactive mediator in the pathophysiology of pulmonary hypertension.