Local and systemic expression of insulin-like growth factor-I (IGF-I) mRNAs in rat after bone marrow ablation

Local and systemic expression of insulin-like growth factor-I (IGF-I) durin g bone formation was studied using the rat bone marrow ablation model. The temporal expression pattern of IGF-I mRNA in rat femurs was examined. The I GF-I mRNA level was enhanced rapidly after ablation reaching a level threef old greater than basal by day 3 (P < 0.01) and declined to basal or below b asal level by day 5. Histological analysis showed that IGF-I immunoreactivi ty was predominantly associated with the mesenchymal cells at the bone/conn ective tissue interface and osteoblastic cells at active sites of bone form ation. Serum level of IGF-I increased 50 and 130%, respectively (P < 0.005) , over the basal level at days 3 and 6. We also investigated the systemic e xpression of IGF-I in liver and kidney. In contrast, hepatic IGF-I gene exp ression decreased 37 and 48%, respectively, at days 3 and 6 after marrow ab lation (P < 0.001). Kidney IGF-I mRNA levels also fell 13 and 27%, respecti vely, at days 3 and 6 (P < 0.005). The present findings suggest that locall y produced IGF-I during bone formation may not only serve as an autocrine/p aracrine factor but also influence systemic expression of IGF-I in other or gans. (C) 2001 Academic Press.