Renal enlargement precedes renal hyperfiltration in early experimental diabetes in rats

The order of appearance between renal hypertrophy and hyperfunction in early experimental diabetes is still disputed. The reason for previous discrepant results is believed to be methodologic problems, as most previous studies of renal function have been performed in anesthetized animals. In the present study in nondiabetic and streptozotocin-diabetic animals, renal volume was measured by a noninvasive magnetic resonance imaging technique, while renal function parameters were measured in conscious, chronically catheterized animals. To avoid artifacts caused by the procedures associated with induction of streptozotocin-diabetes (fasting, brief anesthesia, and transient hypoglycemia) on renal growth and function, diabetic animals were injected with insulin to obtain euglycemia for 4 d before study start. At day 0, insulin administration was withdrawn and all animals developed hyperglycemia within 12 h. Renal volume and kidney function were measured on days 0, 1, 2, 3, 5, and 7. Renal enlargement was detectable at day 1 (20%) and reached an increase of 40% at day 7. No changes were seen in effective renal plasma flow or effective renal vascular resistance within the first 7 d after development of hyperglycemia. GFR tended to rise on day 5 and was increased by 16% at day 7. The absolute proximal reabsorption showed a pronounced rise (30%) at day 7, whereas no change was seen in the proximal tubular fluid output. It is concluded that renal enlargement precedes renal hyperfunction in the early phase after onset of experimental diabetes.