Differential changes in SP-A and disaturated phospholipids in the isolated perfused rat lung and in vivo

Alveolar disaturated phospholipids (DSPA) increase in vivo in rats with hyperpnea and in isolated perfused lungs (IPL) in response to either salbutamol or increasing tidal volume (VT). Because surfactant protein-A (SP-A) may play a role in surfactant homeostasis, we have examined the relationship between SP-A and DSP in the alveolus lamellar bodies (LB-A), and in a vesicular (LB-B) lung subfraction. Whereas 2 h swimming increased total DSPA (similar to 48%), it had no effect on alveolar SP-A (SP-A(A)). In the IPL, salbutamol increased total DSPA (similar to 30%) and SP-A(A) (similar to 41%); increasing VT (2.5-fold) only increased DSPA (similar to 22%). SP-A and DSP also varied differentially in the tubular myelin-rich and -poor subfractions. In both the IPL and in vivo, we found inverse relationships between DSPA and SP-A(A)/DSPA, indicating that although SP-A(A) and DSPA are related, they vary independently. Whereas total SP-A(A)/DSPA varied between 0.046 and 0.074, it remained constant in LB-A (similar to 0.015) and LB-B (similar to 0.010), suggesting that DSP and SP-A are secreted differentially and that only a small portion of SP-A(A) is derived from lamellar bodies.