Loss of kidney IGF-1 receptors in experimental long-term diabetic rats

The present study was undertaken to assess the long-term effects of streptozotocin-induced diabetes mellitus on insulin-like growth factor-1 (IGF-1) receptors in rat kidneys. Morphological changes were also evaluated using light and electron microscopy. Using receptor autoradiography the levels of IGF-1 were investigated in rat kidneys diabetic for eight months and controls. Sections from both diabetic and control rats were stained with haematoxylin and eosin for morphological studies. Ultra-thin kidney sections were examined using a transmission electron microscope. IGF-1 receptors were significantly lower in the cortex and the medulla of the diabetic rats compared with controls. Morphological differences between normal and diabetic kidneys were observed in both the cortex and medulla. Glomerular changes and necrosis of the renal cortical and medullary parenchyma were demonstrated in the diabetic rats. Necrosis of cells of the collecting ducts and loops of Henle could explain the loss of IGF-1 receptor concentration in the medulla. Shrinkage of glomeruli and normal proximal convoluted tubules of diabetic kidneys were also observed. Our results also revealed extensive damage to the distal convoluted tubules that have not been reported to possess any insulin-like growth factor-1 receptors. Our results demonstrate a reduction of kidney IGF-1 receptors after long-term diabetes mellitus possibly because of the extensive morphological loss of renal tissue. It could be speculated that early administration of IGF-1 might be useful in longterm diabetes mellitus to prevent the degeneration and/or help regeneration of damaged renal tissue.