INSULIN-LIKE-GROWTH-FACTOR-I INCREASES BONE-FORMATION IN OLD OR CORTICOSTEROID-TREATED RATS

We studied bone induction in subcutaneous implants of demineralized bo ne matrix with or without insulin-like growth factor I (IGF-I) in aged or corticosteroid-treated rats. Each rat carried one pair of implants , one control and one experiment implant, containing IGF-I dissolved i n 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 inject ions of 140 mu g/kg dexamethasone daily. Old rats produced only approx imately 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 wa s increased by IGF-I, 3000 ng/implant. Corticosteroids reduced bone fo rmation in young rats. This effect was partially reversed by local adm inistration of IGF-I.