Renal refractoriness to phosphaturic action of parathyroid hormone in a patient with hypomagnesemia.

A 50-year-old tetanic woman with hypomagnesemia is described. She had partial resection of the stomach and the jejunum at the age of 20 years. Lack of parathyroid hormone (PTH) function was indicated by hypocalcemia, hyperphosphatemia and high tubular reabsorption of phosphate. However, both plasma concentration of PTH and nephrogenous cAMP were normal. Administration of magnesium sulfate completely normalized serum phosphate and tubular transport of phosphate with only a modest increase in nephrogenous cAMP. The present findings suggest that phosphaturic action of PTH is impaired in magnesium deficiency and that steps distal to cAMP production may be responsible for the renal refractoriness to the hormonal action.