Urinary N-acetyl-β-D-glucosaminidase activity in rabbits with experimental hypercalciuria

Abstract.

Routinely used renal function tests remain normal in uncomplicated hypercalciuria. The aim of this study was to assess the value of N-acetyl-β-D-glucosaminidase (NAG), a sensitive marker of renal proximal tubular damage, in experimental hypercalciuria. Oral calcium providing 75 mg/kg per day elementary calcium and 20,000 IU/day vitamin D₃ was administered for 15 days to 7 rabbits (Orytolagus cuniculus-New Zealand white) and 7 rabbits were given placebo as a control group. Serum calcium, phosphorus, and alkaline phosphatase, daily urinary calcium excretion and NAG/creatinine ratio were measured before and after drug administration. Kidneys were examined macroscopically and microscopically following the study period. Serum calcium, phosphorus and urinary calcium excretion increased, while alkaline phosphatase decreased significantly in response to drug treatment [10.8±1.5 vs. 12.2±1.3 mg/dl, 4.6±0.6 vs. 6.7±0.7 mg/dl, 22.3±8.3 vs. 46.8±22.5 mg/kg per day, and 138.0±57.1 vs. 70.1±33.1 IU/l, respectively (P <0.05)]. The NAG/creatinine ratio prior to the study (0.5±0.1 mU/mg) was significantly different from that after the study (5.4±1.5 mU/mg, P <0.01). In the control group, changes in serum and urinary parameters were not significant (P >0.05). The relationship between the urinary NAG/creatinine ratio and the daily urinary calcium excretion was statistically significant (r = 0.67, P <0.05). In the study group, nephrocalcinosis was present in all rabbits except 1 (85.7%), whereas none of the control group rabbits had nephrocalcinosis. In conclusion, in rabbits urinary NAG excretion increases significantly in nephrocalcinosis induced by hypercalciuria.