Urinary Excretion of N-acetyl-β-D-Glucosaminidase and Its Isoenzymes in Cats with Urinary Disease

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The present study was designed to assess the clinical usefulness of measurement of urinary N-acetyl-β-D-glucosaminidase (NAG) activity and its isoenzymes in cats with urinary disease. Thirty-five healthy cats and 9 cats with renal disease were used. Furthermore, a 5-year-old female cat was administered a large amount of sulfonamide in order to induce acute renal failure, and urine samples were collected for the assay of NAG activity and its isoenzymes. Urinary NAG activity was measured using p-nitrophenyl N-acetyl-β-D-glucosaminide, and expressed as units per gram of urinary creatinine (NAG index). Urinary NAG isoenzymes were assayed by use of the mini-column method and electrophoresis. The overall mean value of urinary NAG index in healthy cats was 1.6 ± 1.5 U/g. Urinary NAG index varied from 6.2 to 35.5 U/g in cats with chronic renal failure. There was no significant correlation between BUN, serum creatinine concentration and urinary NAG index. In cats with feline lower urinary tract disease, normal values of urinary NAG index were observed. In the urine samples of healthy cats, the proportions of NAG isoenzyme A (NAG-A) and isoenzyme B (NAG-B) were 79.1 ± 4.4 % and 21.0 ± 4.4 %, respectively, as assayed by the mini-column method. In the assay of NAG isoenzymes by electrophoresis, the proportions of NAG-A and NAG-B in healthy cats were 66.6 ± 5.8 % and 33.4 ± 5.8 % , respectively. The proportion of NAG-B as measured by electrophoresis was significantly larger (p<0.05) than that obtained with the mini column method. A feline case of acute renal failure experimentally-induced by sulfonamide showed elevation of urinary NAG index, NAG-A and NAG-B after injection of sulfonamide. The increase in NAG-B was larger than that of NAG-A. From the results reported here, measurement of urinary NAG and its isoenzymes seems to yield information about tubular damage at an early stage in cats with urinary disease.