Insulin-like growth factor I increases bone formation in old or corticosteroid treated rats.

We studied bone induction in subcutaneous implants of demineralized bone matrix with or without insulin-like growth factor I (IGF-I) in aged or corticos-teroid-treated rats. Each rat carried one pair of implants, one control and one experiment implant, containing IGF-I dissolved in a hyaluronan solution for slow release. The rats were killed after 3 weeks and the results were evaluated by measuring the calcium content of implants. Young (6–7 weeks) and old (19–27 months) rats were used. A group of young rats was treated for 1 week with subcutaneous injections of 140 ng/kg dexamethasone daily. Old rats produced only approximately 1 % as much bone as young rats. Local delivery of IGF-I did not increase bone formation in young rats. In old rats, bone formation was increased by IGF-I, 3000 ng/implant. Corticosteroids reduced bone formation in young rats. This effect was partially reversed by local administration of IGF-I.