Differential distribution of insulin-like growth factor-1 and insulin-like growth factor binding proteins in experimental diabetic rat kidney

Insulin-like growth factor-1 (IGF-1) is a peptide growth factor, and its activity is modulated by interaction with the family of IGF binding proteins (IGFBP-1 to 6). IGF-1 is detected in rat kidney and has metabolic and growth effects. To explore the possible involvement of IGFBPs in glomerular hypertrophy in streptozotocin (STZ)-induced diabetic rat, the immunolocalization of IGF-1 and IGFBPs were investigated. IGF-1 was gradually increased in the glomeruli of diabetic rats and correlated with glomerular hypertrophy. IGFBP-1 was transiently increased at 1 week after the STZ injection and declined to control level during the following period. In contrast, IGFBP-4 was increased in the diabetic glomeruli throughout the observation period. With insulin treatment, the levels of IGF-1, IGFBP-1 and 4 were normalized and glomerular hypertrophy was prevented. Initial glomerular hypertrophy of diabetic nephropathy is a related IGF-1 action, which may be modulated by IGFBP-1 and 4.