Effect of hyperpnea on the cholesterol to disaturated phospholipid ratio in alveolar surfactant of rats

Hyperpnea induced by swimming rats for 30 min decreased the choksterol/disaturated phospholipid ratio (CHOL/DSP) in the tubular myelin-poor fraction (alv-2), but did not affect the tubular myelin-rich fraction (alv-1). The phenomenon was further illustrated by the marked inverse relationship between CHOLIDSP and DSP. Because such a result could reflect differential release, processing, or reuptake within the alveolar compartment, this study further explored the mechanism in the rat isolated perfused lung (IPL), using radiolabeled CHOL (³H) and DSP (¹⁴C). The study also examined whether the decrease in CHOLIDSP with swimming was associated with the increase in either tidal volume (V_T), frequency of breathing (f), or both. It was found that whereas a 2.5-fold increase in V_Tfor 15 min in the IPL increased the CHOL/DSP in alv-1 and decreased it in alv-2, a 3-fold increase in f markedly increased the CHOLIDSP in both alveolar subtractions. In apparent contrast, the increases in both V_T and f markedly depressed the ratio of the sp act of CHOLIDSP, reflecting a large decrease in the sp act of CHOL in the alveolar compartment. In view of the acute nature of these IPL experiments, it is suggested that the changes reflect the differential release of CHOL and DSP. Furthermore, the marked decrease in sp act of CHOL must reflect a second source of CHOL supplying the alveolar compartment with sterol of low sp act. It is concluded that there is differential handling of surfactant CHOL and DSP in the alveolar compartment of the rat and that the decrease in CHOL/DSP with swimming is due to an increase in V_T.