Renal Reabsorption of Low Molecular Weight Proteins in Adult Male Rats: α2u-Globulin

Abstract Urinary proteins are reabsorbed by the renal tubule cells by two processes, the first for high molecular weight (HMW) and the second for low molecular weight proteins (LMW). The purpose of this report is to establish that α2u-globulin, the sex-dependent, major urinary protein of the adult male rat, is reabsorbed in the kidneys by the general mechanism for LMW proteins. Parameters such as clearance rates were determined to show that α2u is reabsorbed by a process comparable to that for lysozyme. The aminoglycoside, gentamicin, was observed to inhibit the reabsorption of α2u in a dose-dependent fashion. It increased the α2u excretion rate from 4.2 to 13.5 μg/min; the clearance was increased from a normal of 0.33 to 0.91 ml/min. The excretion rate for α2u was also increased by the injection of lysozyme from a normal of 7.4 to 18.1 μg/min. The effect of lysozyme was dose-dependent and reversible. Although gentamicin and lysozyme each increased the excretion of α2u, they had no effect on albumin. Both were equally effective as inhibitors of α2u reabsorption and were 80% as effective as sodium maleate. It is suggested that α2u is reabsorbed by a mechanism which is shared with other LMW proteins. Furthermore, this process is independent of the one which serves to translocate HMW proteins such as albumin.