Kidney tissue insulin-like growth factor I and initial renal growth in diabetic rats: relation to severity of diabetes

The initial renal hypertrophy in experimental diabetes is dependent on the prevailing blood glucose level and is associated with renal accumulation of insulin-like growth factor I. To investigate the relationship of blood glucose to kidney IGF-I, a graded range of diabetic aberration was established in young rats by iv injection of increasing amounts of streptozotocin (25-80 mg/kg) at day 0. In 30 diabetic rats the mean of day 1 and day 2 blood glucose concentrations ranged from 6.2 to 32.0 mmol/l and 24-h urinary glucose excretion (24-48 h) from 0.04 to 43.3 mmol/24 h. The right kidneys were removed after 48 h, weighed and their IGF-I concentration analysed by radioimmunoassay. Kidney IGF-I was positively correlated to blood glucose (r = 0.66, p less than 0.0001) as well as to 24-h urinary glucose output (r = 0.54, p less than 0.005). At this early stage, kidney weight already correlated to blood glucose (r = 0.60, p less than 0.0005). No relationship between kidney IGF-I and kidney weight was found. However, if animals with severe diabetes were excluded, a significant correlation could be established (r = 0.51, p = 0.01, N = 24). The results support the hypothesis that IGF-I plays a causal role in the initial renal hypertrophy of experimental diabetes.