Synthesis of the dipalmitoyl species of diacyl glycerophosphocholine by rabbit alveolar macrophages.

The distribution of radioactivity among the molecular species of diacyl glycerophosphocholine of rabbit alveolar macrophages was determined after incubation with [3H]glycerol and 1-[14C]palmitoyl-sn-glycero-3-phosphocholine. The highest percentage of radioactivity of [3H]glycerol was found in the dipalmitoyl species (35% of the total) followed by the 1-palmitoyl-2-linoleoyl (23.6%) and 1-stearoyl-2-linoleoyl plus 1-palmitoyl-2-oleoyl species (19.7%) during the first 30 min incubation. The radioactivity of the dipalmitoyl species reached a maximum at 120 min incubation and decreased thereafter, although the radioactivities of other molecular species still increased. In contrast to the [3H]glycerol labeling, only 4% of the total radioactivity in diacyl glycerophosphocholine derived from 1-[14C]palmitoyl glycerophosphocholine was found in the dipalmitoyl species; 80% of the radioactivity was located in the 1-palmitoyl-2-arachidonoyl species at 10 min incubation. The present results indicate that the dipalmitoyl species of diacyl glycerophosphocholine are synthesized predominantly via a de novo pathway and not the deacylation-reacylation pathway in rabbit alveolar macrophages.