The molecular basis of pulmonary fibrosis remains unknown. The proposed studies will quantify the rate of collagen synthesis and the types of collagen synthesized in fibrotic rat lung and primary fibroblasts of this tissue. Comparisons will be made with normal lung tissue and primary fibroblasts of this tissue. These studies will quantify the amounts of collagen mRNA s a measure of the cell's ability to synthesize collagen. mRNA Fractions will be isolated and their ability to direct the synthesis of collagen determined. Collagen mRNA will be purified from collagen synthesizing polysomes immunoprecipitated with anti-collagen antibodies Complimentary DNA (cDNA) to purified collagen mRNA will be synthesized using AMV RNA-directed DNA polymerase. This cDNA will be used in RNA-excess hybridization experiments to quantify the amount of collagen mRNA and in DNA-excess hybridization experiments to determine gene dosage. The studies will define the possibility that fibrotic lung tissue has an altered capacity to synthesize collagen which will lead to elucidating cellular pahtogenic mechanisms of fibrosis. The effect of glucocorticoids on collagen synthesis during lung fibrosis will also be examined in the context of literature data indicating that there are antianabolic effects of steroids on collagen metabolism and data from this laboratory indicating that this effect is selective for collagen synthesis.