Disposition of 4-methylbenzoylglycine in rat isolated perfused kidney and effects of hippurates on renal mitochondrial metabolism

Hippurates tend to accumulate within proximal tubule cells during renal sec retion. High intracellular concentrations can alter proximal tubular functi on or lead to tubular toxicity. In this study we examined the renal disposi tion of the hippurate 4-methylbenzoylglycine, a compound known for its high renal intrinsic clearance in-vivo. The effect of intracellular accumulatio n on mitochondrial respiration was also measured in-vitro and compared with that of the 2-methyl and LC-amino analogues. Experiments were performed with either 2.5% pluronic or a combination of 2. 2% pluronic and 2% bovine serum albumin (BSA) as oncotic agents. Within the concentration range studied (1-200 mu g mL(-1)) tubular secretion seemed t o be a function of the amount of unbound drug in thp perfusate. Renal excre tion data were best fitted by a model in which a term was used to describe active secretion. Parameters obtained after the analysis of renal excretion data were the maximum transport velocity (T-M = 55 +/- 2 mu g min(-1)) and the Michaelis-Menten constant for tubular transport (K-T = 4.2 +/- 0.8 mu g mL(-1)). The compound accumulated extensively in kidney tissue, ratios up to 600 times the perfusate concentration were reached. Accumulation could be explained by active tubular uptake and data were analysed best by a mode l similar to the model used to describe renal excretion. Calculated paramet ers were theoretical maximum capacity (R-M = 300 +/- 210 mu g g(-1)) and af finity constant for renal accumulation (K-A = 5.0 +/- 4.4 mu g mL(-1)). The high intracellular concentrations of 4-methylbenzoylglycine had no effect on kidney function and mitochondrial oxygen consumption. The 2-methyl analo gue reduced mitochondrial respiration slightly, but 4-aminobenzoylglycine ( p-aminohippurate) caused a significant reduction. In conclusion, this study shows that renal accumulation of a hippurate is d etermined by the efficiency of its tubular secretion. Whether the high intr acellular concentrations affect tubular cell functioning depends on the ana logue involved.