Influence of phosphatidylglycerol on the uptake of liposomes by alveolar cells and on lung function. The effect of phosphatidylglycerol on the uptake of surfactant-like liposomes by alveolar type II cells and alveolar macrophages as well as the effect on endogenous surfactant function was studied in vivo. Healthy ventilated rats were intratracheally instilled with fluorescent labeled liposomes with different concentrations of phosphatidylglycerol. Lung function was determined by monitoring

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... ial oxygenation and, at the end of the experiment, by recording static pressure-volume curves. In addition, alveolar cells were isolated, and cell-associated fluorescence was determined using flow cytometry. The results show that, in the presence of cofactors (Ca 2ϩ , Mg 2ϩ ), phosphatidylglycerol stimulates the uptake by alveolar macrophages but hardly affects the uptake by alveolar type II cells. High concentrations of phosphatidylglycerol reduce the number of alveolar macrophages in the alveolar space and deteriorate lung function. On the other hand, the presence of cofactors protects the lung against the negative effects of phosphatidylglycerol on endogenous surfactant and alveolar macrophages. This study indicates that the phosphatidylglycerol concentration may play a fundamental role in the surfactant function and metabolism depending on the presence of so-called cofactors like calcium and magnesium; further study is needed to clarify the mechanisms involved. lung; surfactant; metabolism THE ALVEOLUS IS LINED WITH a thin layer of lipids and proteins, called surfactant, and this surface active agent has an essential role in maintaining normal lung function. Pulmonary surfactant is produced by alveolar type II cells. By weight, ϳ90% of surfactant consists of lipids. Although the lipid composition varies in different species, its major component is phosphatidylcholine (70 -80%