Renal Tubular Maximum for Magnesium in Normal, Hyperparathyroid, and Hypoparathyroid Man*

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Abstract
Magnesium infusions were carried out in normalsubjects and patients with hypoparathyroidism and primary hyperparathyroidism in order to determine if a tubular maximum for magnesium (TmMg) existed in man and what influence ndogenous parathyroid hormone played in renal magnesium handling. The increase in the serum ultrafiltrable magnesium concentration during the magnesium infusions resulted in an increase in urinary magnesium excretion. A TmMg of 1.4 mg/100 ml GF/1.73 m2 was found in the normal subjects under basal conditions. Similarly, TmMg values of 1.4 and 1.3 mg⁄100 ml GF⁄1.73 m2, were found in hypoparathyroid and primary hyperparathyroid subjects, respectively. Both were present under basal conditions and neither differed significantly from normal. It is concluded that a TmMg is present in man and that endogenous parathyroid hormone does not appear to play a significant physiological role in renal magensium homeostasis.