Changes in lung tissue fibronectin content and synthesis during postnatal lung growth.

We studied changes in lung tissue fibronectin content and synthesis during postnatal lung growth in rats. We reasoned that fibronectin, which is important in cell differentiation, migration, and adhesion, and in the organization of the extracellular matrix, might play a role in the rapid cell proliferation and alveolar septal formation that occurs postnatally in mammalian lungs. Newborn rats were sacrificed at 4, 7, 11, 14, and 21 days after birth. The lungs were perfused and lavaged, tissue fibronectin was extracted using urea and heparin (Bray et al, Science 1981; 214:793) and the extracted fibronectin was measured by enzyme-linked immunoassay. Tissue fibronectin synthesis was measured by the in vivo incorporation of 35S-methionine into fibronectin that was extracted from lung tissue and immunoprecipitated. Lavage fibronectin and albumin content and lung tissue collagen (hydroxyproline) content were also determined. Lung tissue fibronectin content per g dry lung almost doubled between days 4 and 7 after birth, was slightly higher at day 14 than at day 7, and decreased sharply between days 14 and 21. Lung tissue fibronectin synthesis per g dry lung increased steadily between days 4 and 14 to reach a peak value of about 2.5 times the 4-day value; it then decreased sharply between days 14 and 21. The period of increased fibronectin content and synthesis (4 to 14 days) coincided with the period during which lung cell proliferation and secondary alveolar septa formation are known to be the most active, and the sharp decrease in fibronectin content and synthesis (between 14 and 21 days) coincided with the period during which lung growth and remodeling markedly decrease.(ABSTRACT TRUNCATED AT 250 WORDS)