Localization and characterization of IGF-I receptors in fetal and adult human kidneys.

Human insulin-like growth factor I (IGF-I) is a growth and differentiating factor produced by various adult and fetal tissues. In the kidney, it has been linked to the proliferative response of renal tubular and glomerular cells, following unilateral or partial nephrectomy, in acromegaly, in diabetes mellitus and in glomerulonephritis. To gain insight into the potential effects of IGF-I in human kidney, a quantitative analysis of IGF-I-binding sites was performed in fetal and adult tissue using 125I-IGF-I. The ligand consistently labelled renal cortex, medulla, and glomeruli while renal vessels were not uniformly marked. The highest affinity of binding sites was found in glomeruli (adult kidneys: Kd 24.7 +/- 5.1 pM; Bmax 5.2 +/- 0.5 fmol/mg tissue equivalent (TE); n = 4; fetal kidneys: Kd 17.0 +/- 2.5 pM; Bmax 4.5 +/- 0.7 fmol/mg TE; n = 4) and cortical tubules, while vessels and renal medulla (adult kidneys: kd 47 +/- 3.9 pM, Bmax 2.6 +/- 0.3 fmol/mg TE; n = 4; fetal kidneys: kd 41.6 +/- 9.2 pM, Bmax 3.5 +/- 0.4 fmol/mg TE; n = 3) had only about half the affinity of binding and a significantly reduced maximal capacity. The strong binding of 125I-IGF-I to glomeruli supports the view that IGF-I may be involved in modulating glomerular structure and function. Fetal renal growth may depend on the action of IGF-I on glomerular cells and tubular epithelia of the kidney.