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 wit h hyperpnea and in isolated perfused lungs (IPL) in response to either salbutamol or increasing tidal volume (VT). Because surfactant protei n-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 swimm ing increased total DSPA (similar to 48%), it had no effect on alveola r 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 i ncreased DSPA (similar to 22%). SP-A and DSP also varied differentiall y in the tubular myelin-rich and -poor subfractions. In both the IPL a nd in vivo, we found inverse relationships between DSPA and SP-A(A)/DS PA, indicating that although SP-A(A) and DSPA are related, they vary i ndependently. Whereas total SP-A(A)/DSPA varied between 0.046 and 0.07 4, it remained constant in LB-A (similar to 0.015) and LB-B (similar t o 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.