Insulin-like growth factor-I and experimental diabetic kidney disease

Insulin-like growth factor-I (IGF-I) has been implicated in the pathogenesis of experimental diabetic renal growth. In this study, we have examined the serial changes of renal IGF-I, by radioimmunoassay (RIA) and immunohistochemistry, in rats made diabetic by a single intravenous injection of streptozotocin (STZ; 55 mg/kg). The kidney IGF-I content, as determined by RIA, increased within 48 h of the induction of diabetes mellitus, peaked on day 4 and returned to normal levels by day 30. Renal IGF-I correlated positively with the severity of hyperglycaemia on day 7 (r = 0.685, p < 0.001). Immunostaining showed IGF-I to be located within the cortical collecting ducts of normal rats. In diabetic rats, IGF-I also appeared within the cells of the thick ascending limbs of the loops of Henle, in particular those undergoing cytoplasmic vacuolation. The changes in immunoreactive IGF-I assessed stereologically were consistent with the amounts of extractable IGF-I. They were not observed in normoglycaemic, STZ-injected, rats treated with high-dose insulin. This study suggests that IGF-I is involved in diabetic tubular injury and growth.