Comparison of the Pulmonary Surfactant Content in Alveolar Macrophages of Newborn, Young, and Adult Rats

Abstract

The phospholipid composition of the 150-g pellet containing macrophages from neonatal lung lavages resembles that of surfactant. To study whether this composition reflects the surfactant content of the macrophage, we isolated the alveolar phospholipids and macrophages from the lavage fluids of fetal, newborn, young, and adult Wistar rats. The alveolar surfactant phospholipids increased from fetal levels of 2.8 nmol/mg dry lung weight (DLW) to 39 nmol/mg DLW at day 1, decreased sharply within the first week, and stabilized at a level of 2-4 nmol/mg DLW after day 15. The number of alveolar macrophages increased significantly during the first postnatal day from approximately 750 to more than 5000 (per mg DLW), decreased during the next 4 days, and varied strongly at older ages. We estimated the surfactant content in the macrophages semiquantitatively by polarization microscopy. Birefringence augmented significantly during the first 1.5 days after birth and decreased after that concurrently with the amount of alveolar surfactant. However, only cells without birefringent inclusions sedimented at 150g, whereas the phospholipid composition of the pellets falsely suggested that large amounts of intracellular surfactant were present in its cells. At least two populations of macrophages (surfactant-rich and surfactant-poor) are present in the growing animal. We suggest that differences in function of these various types of macrophages also might depend on surfactant congestion.

Ultrastructural features of alveolar epithelial cells in the late fetal pulmonary acinus: A comparison between normal and hypoplastic lungs using a rat model of pulmonary hypoplasia and congenital diaphragmatic hernia

“…The same holds true for the relative amounts of phospholipid components: There is no difference between the Nitrofen-exposed group and the control group. The phospholipid composition in bronchoalveolar lavage fluid from these groups is roughly the same as that described for normal newborn, young, and adult rats (Egberts et al, 1992). However, the total amount of phospholipid (nmol) recovered from Nitrofen-exposed rat fetuses by bronchoalveolar lavage is significantly less than that recovered from control rats.…”

Perinatal Immunotoxicity: Why Adult Exposure Assessment Fails to Predict Risk

“…Surfactant protein A signals amniotic fluid macrophages to migrate to the uterus and initiate the parturition process (Condon et al 2004; Mendelson and Condon 2005). Complicating the age issue is the fact that surfactant content varies with age (Egberts et al 1992). Obviously, such perinatal alterations in macrophage activities are difficult to evaluate using adult-only exposure to potential immunotoxicants.…”

Perinatal expression of genes that may participate in lipid metabolism by lipid-laden lung fibroblasts

“…Because the number of LF decreases by postnatal day 16 and the concentration of ALBP mRNA in LF decreases, it is likely that another type of cell, in addition to the LF, contains ALBP mRNA. Two candidate cells, that approximately double in number in the rat lung between postnatal days 7 and 14 are the alveolar type II (AT2) cell and the alveolar macrophage (36,37). As fatty acid trafficking in the cytoplasm generally occurs while it is associated with a fatty acid binding protein, it is reasonable to expect that these cells may also contain one or more FABP family members, such as ALBP.…”