The roles of the microtubular system in the transport and secretion of surfactant phospholipids in the lung were studied using colchicine-treated rats, who were administered in vivo by (methyl-3H) choline and (2-3H) glycerol. The radioactivities of phosphatidylcholine, disaturated phosphatidylcholine and phosphatidylglycerol were measured in four lung fractions, i.e., lung parenchyma, microsomes, lamellar bodies and alveolar wash, of colchicine-treated animals. The prior injection of colchicine resulted in marked increases in the labels of the phospholipids in microsomes as well as in lamellar bodies, and in the decrease in alveolar wash. These findings suggest that the microtubular system participates not only in the secretion of lamellar bodies into the alveolar space, but also in the translocation of surfactant phospholipids from the synthetic site, i.e., microsomes to lamellar bodies of the store house
