INSULIN-LIKE GROWTH FACTOR-I AND EXPERIMENTAL DIABETIC KIDNEY-DISEASE

Insulin-like growth factor-I (IGF-I) has been implicated in the pathog enesis of experimental diabetic renal growth. In this study, we have e xamined the serial changes of renal IGF-I, by radioimmunoassay (RIA) a nd 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 diab etes mellitus, peaked on day 4 and returned to normal levels by day 30 . Renal IGF-I correlated positively with the severity of hyperglycaemi a on day 7 (r = 0.685, p < 0.001). Immunostaining showed IGF-I to be l ocated within the cortical collecting ducts of normal rats. In diabeti c rats, IGF-I also appeared within the cells of the thick ascending li mbs of the loops of Henle, in particular those undergoing cytoplasmic vacuolation. The changes in immunoreactive IGF-I assessed stereologica lly were consistent with the amounts of extractable IGF-I. They were n ot observed in normoglycaemic, STZ-injected, rats treated with high-do se insulin. This study suggests that IGF-I is involved in diabetic tub ular injury and growth.