Extensive changes in collagen synthesis and degradation during compensatory lung growth.

Unilateral pneumonectomy in rats causes compensatory growth of the remaining lung. This growth involves rapid production of collagen and noncollagen proteins, but the mechanisms for these changes have not been fully investigated. Rates of collagen metabolism were measured using previously validated in vivo methods. Six days after pneumonectomy, a threefold increase in the fractional rate of collagen synthesis was observed (control 11.8 +/- 0.9%/day, pneumonectomy 30.0 +/- 4.6%/day). Collagen degradation rates also increased but returned to normal more rapidly than the synthesis rates. These changes in synthesis and degradation resulted in a 75% increase in collagen content by 28 days. Although degradation of extracellular collagens was apparently increased, the fraction degraded intracellularly decreased by approximately 30%. Noncollagen protein synthesis and degradation rates both increased by approximately 80% (control 44.3 +/- 3.4%/day, pneumonectomy 80.3 +/- 10.2%/day) with a slightly greater increase in synthesis that led to an 85% increase in noncollagen protein content 28 days after pneumonectomy. The data obtained show dramatic changes in protein synthesis and degradation during compensatory lung growth and indicate extensive remodeling of structural elements in lung tissue. The changes for intracellular collagen degradation provide further evidence that this pathway may have an important role in regulating collagen deposition.