Effectiveness of insulin therapy on altered renal calcium transport in diabetic rats

The uptake of 45Ca was measured in slices of kidney cortex from normal rats, streptozotocin-diabetic rats, and streptozotocin-diabetic rats treated early and late with insulin. Insulin therapy was performed such that blood glucose levels were controlled in half the treated diabetic animals but not in the others. Considerably earlier than evidence of nephropathy (i.e., proteinuria and increased BUN levels) in streptozotocin-diabetic rats, there was a significant decrease in active uptake of calcium by the kidney. Insulin therapy, begun immediately upon diagnosis of diabetes, maintained normal calcium transport even when blood glucose levels were not controlled. On the other hand, insulin therapy, begun 1 mo after diabetes was confirmed but before evidence of nephropathy, did not restore calcium transport to normal whether or not blood glucose was controlled. We conclude that this biochemical mechanism, which possibly may be implicated in the pathophysiology of diabetic nephropathy, is clearly influenced by duration of insulin deficiency and not by the degree in hyperglycemia.