Lung collagen composition and synthesis. Characterization and changes with age

In the lung, collagen is found associated with bronchi, with blood vessels, and with the alveolar interstitium; it is known to be fundamental in the maintenance of lung structure and function. Two collagen chains, α₁ and α₂, can be extracted from rabbit lung homogenates; each chain has an approximate molecular weight of 100,000 and is composed of amino acids that are characteristic of collagen, but are not specific for lung. Lung slices incubated in vitro synthesize α₁ and α₂ chains, as demonstrated by carboxymethylcellulose chromatography, by sodium dodecyl sulfate acrylamide gel electrophoresis, by acidic acrylamide gel electrophoreis, by sensitivity to collagenase, and by sensitivity to trichloroacetic acid at 90°. As a percentage of dry weight, lung protein does not change significantly during maturation, but the content of collagen increases 5 fold from the late stages of gestation to adult life. The average rate of collagen synthesis per cell decreases slowly 10 fold from fetal to adult life whereas the average rate of noncollagen protein synthesis per cell rapidly decreases to adult levels before birth. The rate of collagen synthesis relative to the rate of total protein synthesis is low in fetal life, rises from 2 to 15 % in the first month of life, and then declines by 2 mth of age to the fetal level throughout adult life. The maturing lung, therefore, has significant changes in genetic expression during a period of rapid growth as the lung converts to a gas exchanging organ.