Insulin-Like Growth Factor I Regulates Type I Procollagen Messenger Ribonucleic Acid Steady State Levels in Bone of Rats*

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Abstract
RNA extracted from parietal bones of rats was analyzed for the abundance of type I procollagen mRNA by a dot hybridization assay using specific cDNA probes. Hypophysectomized rats, deficient in IGF I, have 4.1-fold lower steady state levels of mRNA encoding the .alpha.1 chain of type I collagen when compared to normal rats of the same weight (120 g). Administration of recombinant human insulin-like growth factor I (IGF I) for 6 days restores bone collagen mRNA levels to normal, and a single sc injection of 100 .mu.g IGF I results in a 1.9-fold increase of both .alpha.1(I) and .alpha.2(I)chain mRNAs after 8 h. Studies with calvaria cells in primary culture and with a bone-derived cell ine. PyMS, yielded similar results: IGF I treatment of these osteoblast-likecells for 24 h increased steady state levels of type I procollagen mRNAs. Thus, IGF I appears to contribute to osteoblast mRNA expression for both chains of type I collagen.

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