Pulmonary uptake of liposomal phosphatidylcholine

Liposomes prepared with phosphatidylcholine (PC) labeled with [1-14C]-dipalmitoyl-PC, dicetylphosphate, cholesterol (molar ratio 7:2:1) were injected into the right ear vein of 2-month-old male rabbits. At 5, 60, and 120 min after injection, organs were removed and analyzed for [14C]-PC. Lung, liver, and spleen took up the [14C]-PC by 5 min. Spleen accumulation of [14C]-PC increased steadily, liver plateaued from 1--2 hr, and lung fell rapidly. The uptake of liposomal [14C]-PC by lung and liver was dependent on the concentration of iv injected liposomal [14C]-PC. All lung subcellular fractions (lamellar bodies, mitochondria, and microsomes) took up [14C]-PC. Lamellar body [14C]-PC was highest at 5 min, and then decreased. Still, on a nmole/mg protein basis, uptake of [14C]-PC by lamellar bodies was higher than other organelle fractions. Of the radioactivity in lung, 95% was [14C]-PC even after 2 hr, whereas by 1 hr, 28% of liposomal PC absorbed by liver had been degraded.