DIABETES-RELATED RENAL GROWTH AND IGF-I ACCUMULATION IN CASTRATED RATS

The effects of castration on diabetes-related renal growth and IGF-I regulation were studied. In the rat, prepubertal castration is associated with a normal or increased surge in plasma insulin-like growth factor I (IGF-I) at the time of 'puberty'. In order to determine the role of sex steroids in the development of diabetes-related kidney growth and IGF-I regulation, Sprague-Dawley rats were castrated at the age of 4 weeks and streptozotocin diabetes was induced at the age of 13 weeks. The development of renal enlargement and kidney IGF-I levels was studied over the following 7 days. Kidney weight in diabetic animals was significantly greater than in controls, and by day 7, had increased by 27% (1.20 +/- 0.03 vs 0.94 +/- 0.03 g, P < 0.001). Kidney IGF-I content was significantly elevated in diabetic rats, peaking on day 1 (diabetic, 1159 +/- 302 ng/g vs control, 237 +/- 53 ng/g, P < 0.001) and remaining higher than control levels throughout the 7 days of the experiment. The pattern of diabetes-related kidney growth and IGF-I regulation in castrated rats resembles that of age matched intact postpubertal controls, suggesting that sex steroids do not have a direct role in these phenomena.