The use of urinary N-acetyl-β-glucosaminidase in human renal toxicology I. Partial biochemical characterization and excretion in humans and release from the isolated perfused rat kidney

Abstract

Selected biochemical properties and the human excretory pattern of urinary N-acetyl-β-glucosaminidase were characterized. A renal origin of the urinary enzyme was demonstrated by comparison of the release from the isolated perfused rat kidney with excretion from the in situ organ. The rate of activity excretion from both the perfused and in situ organ was 22% of the total organ content per day. The basal enzyme release was into tubular luman only, and contralumenal release into the renal lymphatic system was essentially zero. The human urinary activity exhibited unusual properties which indicated that the rate of excretion is directly proportional to the corresponding rate of release by the tubular epithelium. In urine, 0.2% of the activity is lost per hour at 37°C, and the activity is not denatured by physiologic variations in urine pH and osmolarity. The urinary activity is not associated with cells, is almost entirely soluble and exhibits no latency upon addition of Triton X-100. A cortico-medullary activity gradient exists in the human kidney. The rate of activity excretion in 30 human subjects was constant under maximal variations in urine flow rate. The 3-day excretion in 21 subjects fluctuated around a fairly constant mean rate, which was characteristic of each individual, and subsequent 3-day collections up to 3 weeks later were identical. The rate of excretion was independent of body mass, lean body mass, and sex. The pattern of N-acetyl-β-glucosaminidase excretion fluctuated identically with that of several other acid hydrolases. It is concluded that, with certain restrictions, N-acetyl-β-glucosaminidase excretion can be employed as a marker of the rate of release of at least several acid hydrolases from the human kidney.