Rat lung surfactant contains glycoproteins with molecular weights of about 38,000,32,000 and 26,000, which are not of serum origin and appear to form an integral part of surfactant as its apoproteins. An enzyme-linked immunoassay for these apoproteins has been developed, in which the antigen is sandwiched between specific antibodies raised in two different species. The assay is capable of measuring 10-160 ng of the apoproteins per ml of lung homogenate or amniotic fluid with a coefficient of variation of less than 5%. The immunoassay has been used to quantitate apoproteins in rat lungs during pre and postnatal development, as well as in amniotic fluids at different stages of pregnancy. The apoproteins become detectable in the lungs of 18-day-old fetuses. The lung content of apoproteins increases 4-fold in 19-day-old fetuses, 18-fold in 20-day-old fetuses and 38-fold in 21-day-old fetuses. The lungs of newborn rats contained twice as much apoproteins as the lungs of 21-day-old fetuses. During the postnatal period, the apoprotein content of the lung showed a 3-fold increase in adults as compared to newborn rats. Apoproteins could be detected for the first time in the amniotic fluids of 19-day-old pregnant rats, and their concentration rose 2-3-fold at 20 and 21 days of pregnancy. Our results in this study show that surfactant apoproteins, like pulmonary surfactant lipids, appear in fetal lungs during the late stages of gestation and their amounts increase rapidly as gestation progresses. Furthermore, presence of surfactant aproproteins in fetal lungs can be monitored by quantitation of apoproteins in amniotic fluids during late stages of pregnancy.
ASJC Scopus subject areas
- Pediatrics, Perinatology, and Child Health