Urinary angiotensin I-converting enzyme activity is increased in experimental acute renal failure

The angiotensin I-converting enzyme (ACE) activity was studied in 2 experimental models of acute renal failure: (a) rats treated with a single injection of mercuric chloride (1.5 mg/kg) and (b) rats treated with a single injection of potassium dichromate (15 mg/kg). Rats were sacrificed 24 and 48 h after mercuric chloride or potassium dichromate injection. ACE activity was measured in urine, serum, and kidney. These data were compared with vehicle-treated rats. Rats with acute renal failure had proteinuria, polyuria, and decreased creatinine clearance. The damage to the kidney proximal tubule was evident by (a) the histological analysis at light and electron microscopy, (b) the augmentation in the urinary excretion of dipeptidyl aminopeptidase IV and N-acetyl-beta-D-glucosaminidase, and (c) the low molecular weight proteinuria pattern. In addition, the histological analysis at the ultrastructural level showed normal glomeruli appearance. The above data suggest that the increased urinary excretion of enzymes and proteins in rats with acute renal failure is a consequence of tubular injury. Urinary and serum ACE activities increased and kidney ACE activity decreased. Our data suggest that the increase in urine ACE activity may be due to the kidney proximal tubule damage. This work supports the contention that an increase in urine ACE may be an indicator of injury to the proximal tubule.