The effect of hydropenia and oral water loading on renal lysozyme handling and N-acetyl-beta-D-glucosaminidase excretion in man.

To substantiate the effects of urine flow rate on renal lysozyme handling and N-acetyl-beta-D-glucosaminidase (NAG) excretion, experiments were performed in normal human subjects. Urine flow rate was varied by overnight fluid deprivation and progressive diuresis induced by oral water loading. Lysozyme measurements were made using an improved turbidimetric method and NAG determinations using a modified fluorometric assay utilising individual recovery techniques. Fractional lysozyme clearance and lysozyme excretion demonstrated a nearly linear relationship with urine flow rate (r = 0.78, r = 0.80, P less than 0.0005), and both were elevated significantly in samples obtained during diuresis. NAG excretion, however, demonstrated a significant but weak correlation (r = 0.47, P less than 0.005) with fractional urine flow rate. A significant (P less than 0.05) difference in NAG activity occurred only during the period of hydropenia, when a decrease in excretion was observed. These findings suggest that the effect of diuresis on lysozyme excretion should be considered in studies utilising this enzyme as a marker of renal injury.