The incorporation of choline into disaturated phosphatidylcholine in the microsomal, lamellar body, and surfactant fractions of hamster lung tissue

The specific activity of disaturated phosphatidylcholine in microsomes and lamellar bodies prepared from hamster lung tissue and in surfactant obtained by lung lavage was determined at various times following the intraperitoneal administration of Me-3H]choline. The highest specific activity of disaturated phosphatidylcholine in the lung microsomes was attained 1 h after the administration of 3H]choline; thereafter, the specific activity declined. The specific activity of disaturated phosphatidylcholine in lamellar bodies increased steadily for 12 h after 3H]choline administration. The specific activity in lamellar bodies ater 12 h exceeded the maximum specific activity achieved in the microsomal fraction (p less than 0.005). The specific activity of the disaturated phosphatidylcholine in the alveolar lavage increased after an initial lag period of approximately 3 h, attaining the same specific activity as that of the lamellar bodies at the 12-h time point. The reported results are discussed in relation to the biosynthesis, storage, and secretion of the disaturated phosphatidylcholine associated with the lipoprotein, surfactant.