Relationship between the sulfur content of total parenteral nutrition and sulfoester excretion in low-birthweight infants.

Inorganic sulfate is an end product of sulfur amino acid metabolism but it is also the cosubstrate for the biosynthesis of a wide array of complex sulfoesters. In vitro studies have shown that SO4 availability may be the primary determinant of sulfoconjugation rates for specific substrates but the relationship between S intake and sulfoester formation in vivo is not known. By substituting MgCl2 for MgSO4 in an amino acid infusate for parenteral nutrition, we were able to examine prospectively the effect of an altered SO4 load on S metabolism. In comparing 21 low-birthweight infants on the experimental MgC2 infusate with 14 subjects on the control MgSO4 infusate, we observed a 40% decrease in urinary excretion of free SO4 and a 31% decrease in excretion of total acid-labile sulfoesters. There was a significant correlation (r = 0.44; p less than 0.02) between total S intake and sulfoester excretion, suggesting that S intake influences sulfoconjugation in the low-birthweight infant requiring total parenteral nutrition.