Local infusion of IGF-I into the kidney of pituitary intact rats induces renal growth

Abstract

To determine whether insulin-like growth factor I (IGF-I) exerts growth-promoting actions on the kidneys of pituitary-intact animals IGF-I was infused into the kidney via two different routes using osmotic pumps. In a first set of experiments IGF-I was infused directly into the tissue by the use of an implanted catheter traversing the kidney. It was found that a dosage of 50 micrograms IGF-I wk-1 but not 20 micrograms wk-1 caused a gain in weight of the kidney. The growth was accompanied with morphological alterations among the cortical distal tubules. As a marker for hyperplasia, a monoclonal antibody directed against the M1 subunit of ribonucleotide reductase (RR) was used. The altered cells stained with RR, as also did the tubule cells of the medullary thick ascending limb (mTAL). No RR staining was found in the bulk of renal mass, i.e. the proximal tubules, indicating that possible growth in these cells did not involve cell division. In a second set of experiments IGF-I at 50, 100 and 300 micrograms wk-1 was infused into the renal circulation via a side branch of the renal artery, the suprarenal artery. In these experiments, no growth response or morphological alterations of the tissue were found. These findings demonstrate that IGF-I, when administered directly into the parenchyma, causes growth of the kidney in normal animals. The data are compatible with a causative role for IGF-I in the course of renal growth.