REVERSIBILITY OF RENAL TUBULAR DYSFUNCTION IN STREPTOZOTOCIN-INDUCED DIABETES IN THE RAT

Enzymuria and specific proteinuria were examined over a period of 19 days in 4 groups of 5 rats: a control group, a nondiabetic polyuric group, a group of streptozotocin-induced diabetic rats treated with insulin as of the 10th day after the injection of the drug, and a similar group of untreated diabetic rats. Increased urinary excretion of beta-N-acetyl-D-glucosaminidase, lactate dehydrogenase, and alanine aminopeptidase was observed shortly after the induction of diabetes. It was partly or totally reversible following insulin treatment. Nondiabetic polyuria had a slight effect on the excretion of alanine aminopeptidase only. The urinary excretion of beta2-microglobulin also rapidly increased after the onset of diabetes to a level approximately 50 times the control values. This effect was largely reversible with insulin treatment and was absent in the nondiabetic polyuric group. A small but significant 3-fold increase in albumin excretion was also noted but was not affected by insulin treatment. We conclude that streptozotocin-induced diabetes causes all early tubular dysfunction that is unrelated to polyuria and is reversible upon insulin treatment. This tubular dysfunction is best revealed by the urinary excretion of the low molecular weight protein beta2-microglobulin. Our results suggest that it would be of interest to further examine the usefulness of sensitive markers of tubular dysfunction, especially low molecular weight proteinuria, in the detection of early stages of diabetic nephropathy.