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

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 micrograms 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 line, PyMS, yielded similar results: IGF I treatment of these osteoblast-like cells 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.