[OBJECTIVE] To evaluate (1) whether alveolar macrophages are activated as a consequence of acute pancreatitis (AP), (2) the implication of inflammatory factors released by these macrophages in the process of neutrophil migration into the lungs observed in lung injury induced by AP, and (3) the role of the liver in the activation of alveolar macrophages.[SUMMARY BACKGROUND DATA] Acute lung injury is the extrapancreatic complication most frequently associated with death and complications in severe AP. Neutrophil infiltration into the lungs seems to be related to the release of systemic and local mediators. The liver and alveolar macrophages are sources of mediators that have been suggested to participate in the lung damage associated with AP.[METHODS] Pancreatitis was induced in rats by intraductal administration of 5% sodium taurocholate. The inflammatory process in the lung and the activation of alveolar macrophages were investigated in animals with and without portocaval shunting 3 hours after AP induction. Alveolar macrophages were obtained by bronchoalveolar lavage. The generation of nitric oxide, leukotriene B4, tumor necrosis factor-alpha, and MIP-2 by alveolar macrophages and the chemotactic activity of supernatants of cultured macrophages were evaluated.[RESULTS] Pancreatitis was associated with increased infiltration of neutrophils into the lungs 3 hours after induction. This effect was prevented by the portocaval shunt. Alveolar macrophages obtained after induction of pancreatitis generated increased levels of nitric oxide, tumor necrosis factor-alpha, and MIP-2, but not leukotriene B4. In addition, supernatants of these macrophages exhibited a chemotactic activity for neutrophils when instilled into the lungs of unmanipulated animals. All these effects were abolished when portocaval shunting was carried out before induction of pancreatitis.[CONCLUSION] Lung damage induced by experimental AP is associated with alveolar macrophage activation. The liver mediates the alveolar macrophage activation in this experimental model.Supported by 1996 Research Grant Program of the Hospital Clinic, University of Barcelona.Peer reviewed