Investigation of the drug-binding defect in plasma from rats with glycerol-induced acute renal failure.

The binding defect in plasma from rats with glycerol-induced acute renal failure has been studied. The protein binding of phenytoin, salicylic acid, o-methyl red and methyl orange in uremic rat plasma, measured by equilibrium dialysis at 37 degrees C, was significantly decreased. Analysis of the data by a modified Scatchard plot revealed that in uremic plasma the total binding capacity (nkP) was decreased mainly as the result of a decrease in apparent association constant (k). Charcoal extraction significantly increased the ability of uremic rat plasma to bind the four ligands and restored the binding to about that of the control plasma. Extraction with organic solvents or silicic acid and pre-dialysis against defatted human albumin produced no significant removal of the binding defect. The thiol concentrations of male rat plasma and female rat serum were significantly decreased in uremia. Dithiothreitol decreased the binding of o-methyl red to both control and uremic rat plasma and thereby largely removed the pretreatment difference in unbound fraction of dye. The results suggest the presence of endogenous binding inhibitors.