Early phase collagen synthesis in lungs of rats exposed to bleomycin

Skin wound healing exhibits type III collagen synthesis occurring transiently as early as 10 h after injury, with subsequent synthesis of type I to form a scar. We hypothesized that similar collagen type switching also occurred in the bleomycin model of lung fibrosis in the rat. We could measure elevated lung collagen synthesis rates as early as 4 days after administration of bleomycin. Collagen type I:III ratios in whole lung remained constant for the first 7 days at the control level of 2:1, then increased to as high as 5:1 at day 21. Procollagen mRNA content, expressed as a ratio of type I:III mRNAs, was consistent with the protein synthesis data and the observed ratio of collagen types bring made by the lungs at the various time points evaluated. We conclude that a transient increase in type III relative to type I collagen does not occur in the bleomycin rat lung model. Therefore, the sequence of type-specific collagen expression and deposition in the skin wound healing model is not entirely analogous to this widely used animal model of pulmonary fibrosis. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.