Rates of replacement of lecithins and alveolar instability in rat lungs

Abstract

To determine half-lives of radioactivity in different lecithins of the lungs, palmitate-I-Cl4 and uniformly labeled (u.1.) glucose-H^ were injected into rats. Mixed lecithins were degraded to diglycerides by phospholipase C and the mixed diglycerides were separated into saturated, monoenoic, dienoic, and polyenoic fractions by thinlayer chromatography. Biological half-life of radioactivity in these fractions was approximately 14 hr. except for the polyenoic fraction whose half-life was more than 20 hr. The half-life in each fraction was similar for tritium and C14, which were in the glycerol and fatty acid moieties of the lecithins, respectively. One hr. and 24 hr. after injection of palmitate-I-C^, specific activities of saturated lecithin in a surface-active lipoprotein from lung and in whole lung were similar. The short half-life of saturated lecithin is concordant with the rate of turnover of surface-active alveolar lining calculated from observations of alveolar instability.