Nonspecificity of elevated angiotensin-converting enzyme activity in bronchoalveolar lavage fluid from high permeability lung edema states.

Elevated levels of angiotensin-converting enzyme activity (ACE) in bronchoalveolar lavage fluid (BAL) have been used as a specific marker for pulmonary endothelial cell injury associated with high permeability lung edema. Alternatively, however, BAL-ACE elevations might reflect a nonspecific leak of plasma proteins into bronchoalveolar spaces. To investigate the cause of BAL-ACE elevations in high permeability lung injury states, we measured ACE and protein concentrations in BAL from isolated perfused rabbit lungs injured with oleic acid or hyperoxia. Although BAL-ACE was elevated, we found no increase in the BAL-ACE:protein ratio over values from control preparations, despite the presence of marked nonhydrostatic lung edema. We conclude that, in the experimental setting of nonhydrostatic lung edema, BAL-ACE elevations are no more helpful in identifying acute lung injury than are elevated BAL-protein levels.