Urethane-induced lung hyperplasia: carboxylesterase isozymes as markers in lung pathology

Following a 3- to 5-week exposure to urethane (0.1 per cent in drinking water) a 2-fold increase of total esterase activity per lung was observed. The specific activity of lung esterase was raised from 23 to 31 units per gm. wet weight. Concomitantly, the number of esterase-positive cells (predominately type II alveolar lining cells (pneumocytes and macrophages) increased. As a consequence of urethane treatment, abundant esterase-rich lamellar bodies looked as if they had just been extruded into the alveolar space. This reaction suggests that, even in pathologic states, esterase activity is associated with lamellar bodies. Electrophoretically, esterase-1 was increased and the pattern of esterase-7 was changed, whereas the other isozymes of carboxylesterase did not differ from the control. The hypothesis is made that multilamellar bodies are the subcellular sites of esterase-7 and that macrophages are the location of esterase-1. Since distinct carboxylesterase isozymes seem to be specifically associated with different subcellular structures of the lung and their activity increases in lung hyperplasia, they may be useful marker enzymes for physiologic and pathologic events in lung function.