[Urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) and its isoenzyme B as a marker of the nephrotoxicity of gentamicin: re-test from an animal model].

A high level of NAG urinary excretion with marked isoenzyme B excretion are commonly considered as an indicator of aminoglycoside nephrotoxicity. The urinary excretion of NAG following gentamicin treatment was studied in rabbit. The rabbits received gentamicin at equivalent therapeutic (5 and 20 mg/kg/j) or toxic (50 mg/kg/j) doses during four days. Activities were measured daily and isoenzyme patterns were determined on the day of maximal urinary enzyme excretion. Isoenzyme patterns of kidney cortex, urinary control, and urinary gentamicin treated rabbits were compared. As compared with control rabbit, no changes in isoenzyme profiles appeared following the administration of gentamicin at 5-20 mg/kg/j. Thus, NAG enzymuria is constituted almost exclusively by isoenzyme A. Surprisingly, the high level of NAG excretion following the administration of gentamicin at 50 mg/kg/j is not accompanied by a marked excretion of isoenzyme B. The present results confirm controversy still exists regarding the clinical significance of urinary NAG excretion. These data indicate that increases in urinary NAG and isoenzyme B excretion following gentamicin treatment in Human are not always reliable indicators of renal tubular cell lysis.