REGULATION BY NUTRITION AND AGE OF INSULIN-LIKE GROWTH-FACTOR BINDING-SITES IN-OVINE KIDNEY

The insulin-like growth factors (IGFs) are considered to have a role i n the regulation of renal growth and development. The purpose of the p resent study was to evaluate the effect of nutritional stress on IGF b inding in ovine kidney at different postnatal ages. Binding of IGF-I a nd IGF-II to kidneys of fed and fasted sheep was characterised using h istological autoradiography, competitive binding assays, and SDS-PAGE. Nutritional regulation of IGF-I binding was restricted to cells of th e proximal tubules of two and 14-day-old lambs where we identified an IGF binding protein which was upregulated in response to fasting and w here IGF-II binding was also slightly enhanced. Ontogenetic changes oc curred in the glomeruli where IGF-I binding peaked at 6 months (P less than or equal to 0.001), and IGF-II binding increased to 4 months and then plateaued (P less than or equal to 0.01). In the medulla, IGF-II binding was highest at 4 and 6 months (P less than or equal to 0.05). From these studies, we conclude that the IGF axis may play a role in the regulation of the metabolic response to fasting in the kidney of y oung lambs. Furthermore, the changes with age which are described may reflect a transition period at 4-6 months, from an initial promotion o f kidney growth and development in young lambs to establishment of the metabolic and clearance functions in the adult animal. (C) 1997 Wiley -Liss, Inc.