Dependence of renal protein reabsorption on glomerular filtration rate and infusion time

Egg-white-lysozyme was infused into rats intravenously to achieve plasma concentrations of lysozyme (PLy) in the range of 10-3,500 mg X l-1. Concentrations of inulin and lysozyme in plasma and urine samples were determined spectrophotometrically. The glomerular filtration rate (GFR) was measured as clearance of inulin. The lysozyme reabsorption rate (TLy) was calculated as the difference between the filtered load and excreted amount of lysozyme. TLy increased with increasing filtered loads of lysozyme up to 1,000 micrograms X min-1 whether the increase in load was caused by an increase in PLy or GFR. These TLy were not dependent upon lysozyme infusion time. At lysozyme loads above saturation of reabsorption (1,000 micrograms X min-1) TLy was dependent on GFR and on the passed time after onset of lysozyme infusion. The results of this study indicated that the transport rate of lysozyme is a function of PLy, GFR and duration of lysozyme delivery to tubular cells.