Rat lung surfactant kinetics biochemical and morphometric correlation.

Biochemical and morphometric techniques were combined to estimate the distribution and flux or rat lung disaturated phosphatidylcholine (DSPC) in surfactant pathways. We found 126 +/- 8 X 10(6) alveolar epithelial type II (AEP II) cells per lung, each containing 150 +/- 30 lamellar bodies (LB). High yields of LB were isolated by centrifugation of lung homogenates with a discontinuous sucrose density gradient. Measurement of DSPC in LB and alveolar lavage (LV) material demonstrated that only 30% (LB 14%, LV 16%) of lung DSPC was present in these surfactant compartments. Radiolabeling of lung DSPC with [14C]palmitate demonstrated a product-precursor-relationship between LB and LV and a surfactant-associated DSPC flux of 90 microgram-lung-1 X h-1. We conclude that, although only 16% of lung DSPC is in an intracellular surfactant pathway at any time, all this DSPC is ultimately secreted onto the alveolar surface.