Tissue-specific regulation of insulin-like growth factors and insulin-like growth factor binding proteins in male diabetic rats in vivo and in vitro

1. Insulin-like growth factors (IGFs) are associated with the development of diabetes mellitus. The liver, kidney and heart have been implicated as important organs in the onset of diabetes mellitus. However, the effect of diabetes on the IGF system in these organs has not been fully described. Thus, we investigated changes in IGF-I, IGF-II and IGF binding proteins (IGFBPs) in male steptozotocin-induced diabetic rats, as well as in a high glucose-induced in vitro model. 2. Serum levels of IGF-I were decreased, but the levels of IGF-II were increased, in diabetic rats compared with controls. The expression of IGFBP-3 in the serum was markedly decreased; in contrast, the expression of IGFBP-1 and -2 was increased in diabetic rats. The expression of IGF-I, IGF-II, IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-4 in the liver of the diabetic group was similar to that in the serum of diabetic rats. 3. In heart tissue of the diabetic group, IGF-I levels were decreased, but IGF-II levels were increased. In addition, the expression of IGFBP-3, IGFBP-1 and IGFBP-2 was decreased in diabetic rats. 4. In the kidney of the diabetic group, IGF-I and IGF-II levels were increased. There was only slight expression of IGFBP-3 in the kidney and this was not altered in diabetic rats. Levels of IGFBP-1 and -2 were markedly increased in the kidney of diabetic rats. 5. Insulin treatment recovered the changes in expression of IGF-I, IGF-II and IGFBPs in the serum, liver, heart and kidney. In the liver, heart and kidney, the expression of the insulin receptor was increased in male diabetic rats. 6. In conclusion, diabetes tissue-specifically alters the IGF system in the liver, heart and kidney in rats; this effect can be recovered by insulin treatment.