https://orcid.org/0000-0002-0193-6316
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Abstract
It has been acknowledged for years that compounds containing sulfur (S) are an important source of endogenous acid production. In the metabolism, S is oxidized to sulfate, and therefore the mEq sulfate excreted in the urine is counted as acid retained in the body. In this study we show that pH in fluids with constant [Na] and [HEPES] declines as sulfate ions are added, and we show that titratable acidity increases exactly with the equivalents of sulfate. Therefore, sulfate excretion in urine is also acid excretion per se. This is in accordance with the down-regulation of proximal sulfate reabsorption under acidosis and the observation that children with distal renal tubular acidosis may be sulfate depleted. These results are well explained using charge-balance modeling, which is based only on the three fundamental principles of electroneutrality, conservation of mass, and rules of dissociation as devised from physical chemistry. In contrast, the findings are in contrast to expectations from conventional narratives. These are unable to understand the decreasing pH as sulfate is added since no conventional acid is present. The results may undermine the traditional notion of endogenous acid production since in the case of sulfur balance, S oxidation and its excretion as sulfate exactly balance each other. Possible clinical correlates with these findings are discussed.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Notes
1 where Sref represents a reference state in terms of temperature, ionic strength and reference pH, here assumed to be pH = 7.4 while S refers to current pH. HBi is any present acid, nt is the total amount, and Ni the average charge of the buffer at actual pH or reference pH.