Biochemical basis of hyaline membrane disease.

Pulmonary function in a normal fetus is dependent upon maturation and maintenance of the biochemical synthesis of a distinct surface-active lipid. Two major pathways for the biosynthesis of this major surface-active lipid, dipalmitoyl lecithin, are described and relative activities of each pathway in human lung are discussed. In normal human lung, the CDP-choline path­ way is quantitatively most important for total lecithin synthesis. Infants with idiopathic respiratory distress syndrome (RD S) are usually prematurely bom. Their lungs lack adequate surface activity and are deficient in the principle surface-active component lecithin. Stress (hypoxia, acidosis, and hyper­ thermia) may induce respiratory distress in the fetus. Biochemical methods are available to detect and characterize pulmonary surfactant in amniotic fluid. Studies show that developmental changes in phospholipids in lungs are reflected by the phospholipids in amniotic fluid, and it is possible to predict the fetus whose lung is too prematurely developed for delivery and who may develop RDS.