Renal Mechanisms for the Excretion of Inorganic Sulfate in Man *

The sulfur contained in plasma is derived from sulfalipids, sulfatides, amino acids, and glycoproteins as well as from ionizable inorganic sulfate. The plasma concentration of inorganic sulfate is partially determined by the kidneys, since the ion is freely filterable at the glomerulus (1, 2) and reabsorbed by the renal tubules. In dogs (3) the excretory processes have been fairly well defined and the tubular reabsorptive mechanism has been shown to be characterized by a maximal transfer rate (Tmso4). The present study was under- taken to ascertain if similar mechanisms are op- erating in man. To elucidate this problem, the filtered load, tubular reabsorption, and urinary excretion of inorganic sulfate were measured prior to and during the infusion of sodium sulfate solution. Further, the readily exchangeable sulfate mass was determined using isotope dilution techniques. The results of this study show that the tubular reabsorption of inorganic sulfate in man is limited by a maximal transfer rate (Tm).