THE RELATIONSHIP BETWEEN VITAMIN D AND PARATHYROID HORMONE*

Abstract

Over three decades ago, it was established that deficiency of either vitamin D or parathyroid hor- mone may lead to tetany and hypocalcemia (1, 2). Since then, there has been continued interest in the relationship between the biologic effects of these two agents. At one time it was believed that the D vitamins exerted their effects by stimulating the parathyroid glands, but this concept be- came untenable after it was established that vita- min D could induce hypercalcemia in hypopara- thyroid organisms. More recently it has been proposed that the hormone exerts its characteristic effects only in vitamin D-fed animals (3), and that the basis of this action depends upon a chemical interaction between the two (4). These proposals are not satisfactory because there is considerable clinical and pathological evidence (5) suggesting that parathyroid hyperfunction exists in vitamin D deficiency. Certainly complete synergism of action seems most unlikely because of the well-established difference in the syndromes produced by their separate deficiencies (5). On the other hand, there is no satisfactory explana- tion for the persistent hypocalcemia in D-deficient animals, in spite of apparent parathyroid over- function, nor for the observations of Harrison, Harrison, and Park (3) that the administration of a standard dose of parathyroid hormone to a D-deficient rat results in little or no change in the concentration of either calcium or phosphate in the plasma.