The catabolism of lung surfactant by alveolar macrophages.

Surfactant was isolated from lung tissue of normal and chlorocyclizine-fed rats. Chlorocyclizine surfactant contained 2.5-3.4 times more phospholipids per mg protein than normal surfactant. Alveolar macrophages, incubated in vitro with normal and chlorocyclizine surfactants hydrolyzed the surfactant phospholipids and incorporated the fatty acids into cellular triacylglycerol. Employing [3H]palmitate-labeled surfactant, it was shown that cells incubated with chlorocyclizine surfactant incorporated 46.2-73.0 nmol of fatty acids per mg protein and were transformed into foam cells. Employing fluorescein or 125I-labeled surfactant, the uptake of surfactant protein by macrophages was shown. No significant differences between protein uptake from normal and chlorocyclizine surfactants were observed. These results suggest that the surfactant phospholipids and protein were catabolized independently.