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 cholestero l/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 invers e relationship between CHOL/DSP and DSP. Because such a result could r eflect differential release, processing, or reuptake within the alveol ar compartment, this study further explored the mechanism in the rat i solated perfused lung (IPL), using radiolabeled CHOL (H-3) and DSP (C- 14). The study also examined whether the decrease in CHOL/DSP with swi mming was associated with the increase in either tidal volume (V-T), f requency of breathing (f), or both. It was found that whereas a 2.5-fo ld increase in V-T for 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 increase d the CHOL/DSP in both alveolar subfractions. In apparent contrast, th e increases in both V-T and f markedly depressed the ratio of the sp a ct of CHOL/DSP, reflecting a large decrease in the sp act of CHOL in t he alveolar compartment. In view of the acute nature of these IPL expe riments, it is suggested that the changes reflect the differential rel ease of CHOL and DSP. Furthermore, the marked decrease in sp act of CH OL must reflect a second source of CHOL supplying the alveolar compart ment with sterol of low sp act. It is concluded that there is differen tial handling of surfactant CHOL and DSP in the alveolar compartment o f the rat and that the decrease in CHOL/DSP with swimming is due to an increase in V-T.