Human sulfate kinetics

Abstract

Electrospray tandem mass spectrometry was used to determine steady-state serum and urinary inorganic sulfate and sulfate ester kinetic profiles of nine normal men after intravenous injection of the stable isotope sodium [34S]sulfate. Sulfate ester appearance was traced by eliminating inorganic sulfate from samples, followed by hydrolysis of sulfate esters to inorganic sulfate for analysis. Whole body inorganic sulfate turnover in steady state was calculated using standard tracer techniques. Rate of appearance and disappearance of inorganic sulfate was 841 ± 49 μmol/h. Average urinary inorganic sulfate excretion was 609 ± 41 μmol/h, and the whole body sulfation rate (total rate of disappearance minus rate of urinary excretion) was 232 ± 36 μmol/h. Tracer-labeled sulfate esters appeared in serum and urine within 1 h of tracer injection. The kinetics of inorganic sulfate and sulfate esters were linked by means of a compartmental model. The appearance and excretion of sulfate esters accounted for ∼ 50% of the total sulfation rate. These results indicate that human whole body sulfation accounts for ∼ 27% of inorganic sulfate turnover and that extracellular inorganic sulfate is an important pool for intracellular sulfation. A substantial fraction of newly synthesized sulfate esters promptly enters the extracellular space for excretion in the urine.