Effects of experimental diabetes on renal IGF/IGFBP system during neonatalperiod in the rat

Changes in the renal synthesis and concentration of insulin-like growth fac tors (IGFs) and their serum-binding proteins (IGFBPs) reported in insulin-d eficient diabetes mellitus may be implicated in the alterations of the kidn ey function and morphology accompanying this disease. Most research on this subject has been carried out in adult animals, as well as in peripubertal rats, when the regulation of the IGF system is fully dependent on serum gro wth hormone (GH). However, relevant differences in the regulatory pathways of IGFs between adult and neonatal periods have been described. To examine the response of the IGF/IGFBP system of neonatal kidney to diabetes, renal IGF-I and -II and IGFBP-1, -2, and -3 concentration and mRNA expression wer e determined in streptozotocin-induced diabetic rat neonates. Diabetic neon ates exhibited a kidney weight-to-body weight ratio higher than that of con trol rats, together with decreased IGF-I and increased IGF-II renal concent ration. Because kidney mRNA expression of both IGFs decreased, the elevated renal IGF-II might result from increased uptake from circulation. Insulin treatment recovered the altered IGFs to control values, indicating the insu lin-dependent regulation of IGFs in the neonatal kidney. Elevated levels of the IGFBP-1 and -2 in the kidney of diabetic neonates did not result from changes in their kidney mRNA transcript expression, suggesting also a possi ble uptake from circulation.