Increased urine angiotensin I converting enzyme activity in patients with upper urinary tract infection

Angiotensin converting enzyme (ACE) is present within the brush border of the tubular cell of the kidney. Since it has a high molecular mass, ACE activity of urine most probably derives only from tubular cells, thus suggesting the potential usefulness of ACE determination as an index of tubular damage. When assayed with the method described, ACE is optimally active at pH 8 with a calcium concentration exceeding 0.75 mmol/l urine, and is chloride independent. Urine dialysis has no effect on ACE activity. ACE is stable at 4 degrees C for 10 days, but it is inactivated by repeated thawing and freezing. The presence of leucocytes and bacteria does not interfere with the assay. Urine ACE activity was evaluated in patients with upper and lower urinary tract infection, nephrolithiasis, chronic glomerulonephritis and essential hypertension and was found to be significantly increased only in patients affected by upper urinary tract infection and nephrolithiasis.