EFFECTS OF IGF-I, ALONE AND IN COMBINATION WITH 17-BETA-ESTRADIOL, ONBONE REMODELING PARAMETERS IN OVARIECTOMIZED RATS

aaWe studied the effects of recombinant human IGF-I (250 mu g/day) and /or 17 beta-oestradiol (E(2); 5 or 50 mu g/kg/day), s,c., for 28 days, on plasma IGF-I and 1,25-(OH)(2) vitamin D-3 concentrations and on bi ochemical indices of bone remodelling (plasma osteocalcin, urinary pyr idinolines) in 3 month-old rats that bad been ovariectomised (OVX) 6 w eeks before. Ten weeks after ovariectomy, plasma 1,25(OH)(2)D-3 was in creased, but IGF-I and bone remodelling indices were within the normal range. RhlGF-I administration to OVX rats increased both IGF-I and 1, 25-(OH)(2)D-3 concentrations, as well as plasma osteocalcin and urinar y pyridinoline excretion, By contrast, E(2) decreased plasma IGF-I, an d 1,25-(OH)(2)D-3 and the markers of bone remodelling, The combination of rhIGF-I and E(2) resulted in intermediate effects. Multiple regres sion analysis showed that IGF-I correlated with plasma osteocalcin, an d also with the urinary excretion of pyridinolines. The data shows tha t rhIGF-I stimulates bone remodelling in growing OVX rats, and that ci rculating IGF-I is a determinant of bone remodelling in vivo.