URINARY N-ACETYL-BETA-D-GLUCOSAMINIDASE ACTIVITY IN RABBITS WITH EXPERIMENTAL HYPERCALCIURIA

Routinely used renal function tests remain normal in uncomplicated hyp ercalciuria. The aim of this study was to assess the value of N-acetyl -beta-D-glucosaminidase (NAG), a sensitive marker of renal proximal tu bular damage, in experimental hypercalciuria. Oral calcium providing 7 5 mg/kg per day elementary calcium and 20,000 IU/day vitamin D-3 was a dministered for 15 days to 7 rabbits (Orytolagus cuniculus-New Zealand white) and 7 rabbits were given placebo as a control group. Serum cal cium, phosphorus, and alkaline phosphatase, daily urinary calcium excr etion and NAG/creatinine ratio were measured before and after drug adm inistration. Kidneys were examined macroscopically and microscopically following the study period. Serum calcium, phosphorus and urinary cal cium excretion increased, while alkaline phosphatase decreased signifi cantly 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, respectivel y (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 urina ry parameters were not significant (P >0.05). The relationship between the urinary NAG/ creatinine ratio and the daily urinary calcium excre tion was statistically significant (r = 0.67, P <0.05). In the study g roup, nephrocalcinosis was present in all rabbits except 1 (85.7%), wh ereas none of the control group rabbits had nephrocalcinosis. In concl usion, in rabbits urinary NAG excretion increases significantly in nep hrocalcinosis induced by hypercalciuria.