The interaction of vitamin D and parathyroid hormone on calcium phosphorus and magnesium homeostasis in the rat

Abstract

The effects of a single injection of 100 units of purified parathyroid hormone (Aurbach) were compared in vitamin D-deficient and vitamin D-primed rats. The rats of the latter group received 500 units of vitamin D 18 hours before the injection of parathyroid hormone. Injection of parathyroid hormone produced no significant alterations of serum calcium, phosphate or magnesium concentrations in the vitamin D depleted rats and only a questionable phosphaturic effect. Vitamin D by itself raised the serum calcium concentration to normal, depressed the serum magnesium level and possibly raised the serum phosphate concentration. This latter effect occurred in one series of rats but not in another. The injection of parathyroid hormone into vitamin D-primed rats produced the characteristic effects of this hormone: elevation of serum calcium concentrations to hypercalcemic levels, decrease of serum phosphate concentrations with associated increase of urinary phosphate excretion, and increase of the concentration of serum magnesium. The concentration of serum magnesium was inversely related to the concentration of phosphate. There is an interrelation between the functions of parathyroid hormone and vitamin D so that in the absence of vitamin D there is little or no response of rats to amounts of parathyroid hormone which produce a marked effect in vitamin D-treated animals. This failure of response involves both the calcium mobilizing and phosphaturic actions of parathyroid hormone.