Effect of magnesium depletion on responsiveness to parathyroid hormone in parathyroidectomized rats

Hypocalcemia and resistance to exogenous parathyroid hormone have been reported in several clinical states associated with magnesium deficiency. On the basis of such observations, it has been suggested that magnesium depletion per se may result in impaired responsiveness of the adenyl cyclase-adenosine 3',5'-monophosphate (3',5'-AMP) system. To test this hypothesis, 4 wk old male parathyroidectomized rats were maintained on normal or magnesium-deficient diets for 4 wk and their responses to parathyroid hormone compared. Serum magnesium and calcium fell progressively in the magnesium-deficient group. Despite clinical and biochemical evidence of severe magnesium deficiency in these animals, renal production and excretion of 3',5'-AMP in response to parathyroid hormone was normal both in vitro and in vivo. Additionally, administration of either dibutyryl 3',5'-AMP or parathyroid extract to fasting magnesium-depleted rats produced a normal increase in serum calcium. Parathyroid hormone infusion studies demonstrated normal renal and skeletal responsiveness as measured by urinary excretion of calcium, magnesium, phosphate, and hydroxyproline. These data show that the effect of parathyroid hormone on 3',5'-AMP formation and excretion, the responsiveness of skeletal tissue to 3',5'-AMP, and the renal and skeletal system responses to parathyroid hormone are not altered by pure magnesium deficiency in the parathyroidectomized rat.