Effects of the Intravenous Administration of Magnesium Sulfate on Corrected Serum Calcium Level and Nephrogenous Cyclic AMP Excretion in Normal Human Subjects

The effect of intravenous magnesium sulfate infusion on corrected serum calcium level and parathyroid function assessed by determination of nephrogenous cAMP (NcAMP) excretion were studied in normal human subjects. Significant hypermagnesemia induced by the magnesium sulfate infusion for 120 minutes was accompanied by a gradual and progressive decrease in the corrected serum calcium level. NcAMP excretion fell rapidly, reaching a nadir between 60 and 120 minutes after the infusion began, and after that rose above the baseline excretion. Urinary calcium excretion gradually increased, reaching a peak between 120 and 180 minutes after the infusion began and then gradually decreased. Since magnesium was given as the sulfate, it is not clear whether these changes were attributable to magnesium or sulfate or both. As a control study, we performed intravenous sodium sulfate infusion. The sodium sulfate infusion caused slight hypocalcemia, slight hypercalciuria, and a significant increase in NcAMP excretion. These findings indicate that the hypocalcemia and the hypercalciuria caused by the magnesium sulfate infusion is mainly due to the effect of magnesium, and that the decrease in NcAMP excretion during the infusion is due to the effect of magnesium alone. We conclude that the hypocalcemia caused by the magnesium sulfate infusion is mainly due to the renal calcium loss, and that the inhibition of parathyroid function caused by hypermagnesemia may be only partially involved in the early phase of this hypocalcemia.