The perfused isolated lung as a possible model for the study of lipid synthesis by type II cells in their natural environment.

The incorporation of radioactively labeled palmitate and acetate into total and disaturated phosphatidylcholines was studied in the perfused whole lung, in surfactant secreted during perfusion, and in isolated alveolar type II cells. Exogenously added palmitate was found to be incorporated preferentially into the 2-position of total and disaturated phosphatidylcholines in all cases. Acetate, when supplied at a high concentration, was incorporated preferentially into the 2-position in all cases. However, acetate supplied at a low concentration was incorporated preferentially into the 2-position in type II cells and in surfactant, but preferentially into the 1-position in the whole lung. The dissimilarity in incorporation of acetate between isolated type II cells and perfused whole lung and the similarity in this respect between isolated type II cells and surfactant indicate that the perfused isolated lung may only be a good model for studying the synthesis of surfactant components by the type II cells in their natural environment if the products of processes in type II cells are separated from products of other cells after the perfusion. Both in surfactant and in lavaged lung tissue, labeled palmitate and acetate incorporated mainly into the 2-position of phosphatidylglycerol. This indicates that remodeling reactions are involved in the synthesis of dipalmitoylphosphatidylglycerol.