Relationship between lung intra and extracellular DSPC in fetal and neonatal rats

Using lamellar bodies (LB) as an index of intracellular disaturated phosphatidyl choline (DSPCin) and biochemical measurements of the total lung DSPC, we studied the relationship between the intra and extracellular DSPC (DSPCex) in the lungs of fetal and neonatal rats. A linear correlation was found between the number of LB and the amount of DSPC in fetal lungs. A similar correlation was found in fetal lungs after lung lavage. The difference between the two corresponded to the DSPCex, which was greater than anticipated. Prior to birth there was a massive release of DSPC, into the extracellular space, which was lost from the lungs during labor and upon initiation of respiration at birth. The DSPCin, however, continued to increase during labor and the first 5 min after birth. Thereafter release of DSPCin and accumulation in extracellular space occurred. After age 12 hours, there was a gradual reduction in DSPCex till 24 hours. Thereafter, a linear correlation between number of LB and total DSPC resumed. The results suggest that lung lavage promotes release of DSPCin and that excess DSPCex, from birth to 24 hours, is removed by two different mechanisms: initially through the airways and subsequently by alveolar macrophages.