Differential response of urinary N-acetyl-beta-D-glucosaminidase to two osmotic diuretics in the dog

Urinary N-acetyl-beta-D-glucosaminidase (NAG), a lysosomal hydrolase located the proximal tubule of the kidney, has been used as a marker for subtle renal injury. In humans and other animals with diabetes mellitus, urinary NAG activity has been shown to increase within 12 hours of the onset of hyperglycemia and glycosuria. Whether the rise in urinary NAG activity is in response to the hyperglycemia or to the osmotic diuresis associated with glycosuria is not known, nor has the time course of the rise in enzyme activity been determined. A study was designed using four groups of dogs to examine these possibilities: group 1 (n = 5), control dogs; group 2 (n = 5), mannitol-infused dogs; group 3 (n = 5), low-glucose dogs; and group 4 (n = 5), high-glucose dogs. In groups 2 and 4, mannitol and glucose, respectively, were infused at a rate to double urine flow from the left ureter without altering the contralateral urine volume. In group 3, sufficient glucose was infused to elevate left renal vein glucose level without producing glycosuria. In the control dogs infused with normal saline solution at a constant rate throughout the control and study periods, no differences were found in urinary NAG excretion when data from individual clearance periods were compared for the right and left kidneys. In the low-glucose dogs, urinary NAG/creatinine ratios were significantly increased (P less than 0.01) when the left and right kidneys were compared for the duration of the infusion.(ABSTRACT TRUNCATED AT 250 WORDS)