Urinary excretion of GAA in diabetic nephropathy
Urinary guanidinoacetic acid (GAA) is a sensitive marker for gentamicin nephrotoxicity in rats. This study assesses the usefulness of GAA concentrations in the diagnosis of renal tubular injury in diabetic nephropathy. Serum, urine, and renal cortex samples were obtained from rats 1, 2, and 3 weeks after streptozotocin injection (65 mg/kg body weight). Guanidinoacetic acid levels were measured by high-performance liquid chromatography. N-acetyl-beta-D-glucosaminidase (NAG) activity in urine was determined by an enzymatic method. GAA levels in serum, urine, and renal cortex were significantly decreased in diabetic rats compared with those in control rats. In contrast, urinary NAG activity was significantly increased in diabetic rats. Decreases in serum, urine, and renal cortical GAA levels were attenuated by insulin treatment. These results indicate that a high serum glucose level may affect GAA synthesis in the renal cortex and that urinary GAA may be a clinically useful indicator of renal tubular injury in diabetic nephropathy.