LOCALIZATION OF MESSENGER-RNAS FOR INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS 1 TO 6 IN RAT-KIDNEY

Insulin-like growth factor-I (IGF-I) is a peptide growth factor whose activity is modulated by interaction with the family of six IGF bindin g proteins (IGFBPs). IGF-I is detected in rat kidney and has metabolic and growth effects. We have used in situ hybridization to localize mR NAs for the IGFBPs in rat kidney. Messenger RNAs for all six IGFBPs we re detected, each with a distinctive distribution. IGFBP-1 mRNA was ex pressed in the distal nephron, from the thick ascending limb of the lo op of Henle to the cortical collecting ducts. IGFBP-2 mRNA expression was confined to epithelial cells of the glomeruli and the thin limbs o f the loop of Henle. IGFBP-3 mRNA was localized to the cortical inters titium while IGFBP-4 was the only IGFBP mRNA found in the proximal tub ule. IGFBP-5 mRNA, the most abundant and widely distributed of the IGF BP mRNAs in the kidney, occurred in the glomerular mesangium and the m edullary interstitium as well as in the epithelial cells of the distal nephron. IGFBP-6 mRNA, the least abundant, was expressed mainly in fi broblasts associated with renal blood vessels and the ureter. This het erogeneous distribution of the IGFBPs may enable IGF action to be regu lated by multiple factors in a site-specific manner.