DISSOCIATION OF BONE-MINERAL DENSITY FROM AGE-RELATED DECREASES IN INSULIN-LIKE GROWTH-FACTOR-I AND ITS BINDING-PROTEINS IN THE MALE-RAT

We evaluated the possibility that age-related decreases in circulating and/or bone-associated insulin-like growth factor-I (IGF-I) and its b inding proteins (BPs) were associated with the development of osteopen ia in 8-, 16-, and 24-month-old specific pathogen-free Brown Norway/Fi scher 344 male rats. We measured bone mineral densities (BMD) of femur s by dual-energy x-ray absorptiometry. IGFs and IGFBPs were extracted from bone and separated by molecular exclusion HPLC before quantitatio n by specific radioligand assays. BMD did not change significantly bet ween 8 and 24 months of age. IGF-I levels decreased by about 30% betwe en 8 and 24 months ill both serum and bone. Similarly, both circulatin g and bone-derived IGFBPs also declined (30% and 60%, respectively) wi th age. Thus, maintenance of femoral BMD throughout most of the adult rat life span,pas dissociated from the age-related decline in circulat ing and bone-associated IGF-I and IGFBPs.