Acute effects of streptozotocin diabetes on rat renal function

Renal clearance studies were performed on rats both during the administration of streptozotocin and sequentially during the following 8 days as hyperglycemia progressed. Although GFR was depressed 30 min after the drug administration, GFR steadily rose during the following days to become 52% greater than control levels. Renal size did not change during this short period, and it is suggested that glomerular hemodynamic changes are responsible. A maximal tubular reabsorptive capacity for glucose (TmG) could not be satisfactorily demonstrated in normal rats, although glucose reabsorption was significantly depressed at high-filtered loads. At comparable filtered loads, glucose reabsorption in diabetic rats was almost complete in contrast to normal rats, and the increases in GFR and renal tubular sodium reabsorption are presumed to be the major factors. The administration of insulin to normal and diabetic rats was followed by a significant diuresis as well as an increase of 1% to 4% in the fraction of filtered sodium excreted although GFR was unaltered. This shows that even a 35% to 60% reduction in the filtered load of glucose can significantly depress renal sodium reabsorption. It is concluded that this is a good animal model in which to study the effects of diabetes on renal function as well as the in vivo interrelationships of sodium and glucose reabsorption.