Effects of growth hormone and insulin-like growth factor I in men with idiopathic osteoporosis

Injections with growth hormone (GH) or insulin-like growth factor I (IGF-I) have been proposed for anabolic therapy in osteoporosis. In a cross-over study, 12 men with idiopathic osteoporosis received daily subcutaneous injections of GH (2 IU/m2) or IGF-I (80 micrograms/kg) for 7 days with 12 weeks of wash-out. Serum levels of procollagen type I increased by 29% following treatment with GH (P < 0.001) and by 43% with IGF-I (P < 0.001 compared with pretreatment levels; P < 0.05 compared with GH injections), whereas both treatments rendered a 20% increase in osteocalcin concentrations (P < 0.001), indicating enhanced bone formation. There was also evidence of stimulated bone resorption, as the urinary levels of deoxypyridinoline increased by 44% following GH injections (P < 0.001) and by 29% following IGF-I (P < 0.001), and there were 28% higher serum concentrations of IGF-I after GH than after IGF-I injections. Although markers of bone metabolism increased under both treatments, comparison of the treatments suggests that IGF-I enhanced formation of collagen type I more than did GH. Furthermore, the stimulation of bone resorption was detected as soon as 4 days after the initiation of GH injections. Some of the differences might be dose-dependent, but could also indicate separate mechanisms at the cellular level.