Glutamine synthetase activity in rat urine as sensitive marker to detect S3 segment-speciflc injury of proximal tubule induced by xenobiotics.

The possibility of detecting segment-specific injury of the proximal tubule by means of urinary enzymes was investigated in rats. Urinary glutamine synthetase, an enzyme exclusively localized in the S3 segment, and N-acetyl-beta-D-glucosaminidase, prevalently a S1-S2, but S3 enzyme also, were determined after single treatment with 100 mg/kg body wt. of hexachloro-1:3-butadiene (HCBD; i.p.), toxic for the S3 segment, or 25 mg/kg body wt. of potassium dichromate (s.c.), toxic for the S1-S2 segments. Excretion of total urinary proteins was also measured. In addition, a dose-response relationship was determined between three doses (50, 100 and 200 mg/kg body wt.) of HCBD and glutamine synthetase activity in urine. Glutamine synthetase activity, measured according to a new assay for urine based on modification of methods developed for organs, increased in the urine only when the S3 segment of the proximal tubule was damaged, as demonstrated by histological findings of the kidneys. HCBD caused early excretion of the enzyme related to the necrosis of the S3 segment, whereas potassium dichromate caused a slight increase only when the resulting lesion to this segment (vacuolization) began to develop. On the contrary, N-acetyl-beta-D-glucosaminidase activity showed the peak of excretion 24 and 34 h after treatment with HCBD or potassium dichromate, respectively, according to the histological findings of necrosis of the S3 segment (the former) and vacuolization of the S1-S2 segments (the latter). Excretion of total urinary proteins reached the peak 24 h (HCBD) and 48 h (potassium dichromate) after treatment. HCBD at 200 mg/kg body wt, caused a peak of glutamine synthetase activity in urine 10 h after injection, whereas the peak caused by doses of 50 and 100 mg/kg body wt. occurred 24 h following treatment. The peak of enzyme activity in urine significantly increased with the dose. The results suggest that the measurement of urinary activity of S3 segment-specific enzyme as glutamine synthetase allows us to detect early S3 segment-specific injury of the proximal tubule. In addition, the method for urinary enzyme activity appears sensitive, simple and fast.