The Treatment of Experimental Hypoparathyroidism

In subtotal thyroidectomy in human subjects, a significant amount of the parathyroid tissue is frequently removed, so that some of these patients show the characteristic symptoms of hypoparathyroidism. Although preparations of parathyroid hormone are available for the treatment of this condition, administration of dihydrotachysterol -(Hytakerol) has become largely the method of choice, and clinical experience with it has been almost entirely favorable (1 to 3). A review of the chemical and biological properties of this preparation has been published by another investigator (4). Vitamins D2 and D3 are calcemic and therefore might also be satisfactory for the treatment of these patients on theoretical grounds. In fact, there are clinical reports which indicate that the substitution may be made (5 to 8). It has been pointed out (9) that the chief bar to such substitution is psychological, i.e., there is a fear of overdosage (since adequate therapy may require millions of units) or of toxicity (since the early preparations of vitamin D2 did actually contain toxic irradiation by-products). A comparative study of the effects of adequate doses of the 3 preparations on the calcium and phosphorus metabolism of the normal dog has been reported from this laboratory (10). Since data on human subjects are accumulated very slowly, it seemed worth while to carry out a study of the treatment of parathyroid insufficiency in dogs, comparing the methods of treatment now commonly used; namely, the administration of calcium salts, parathyroid extract, vitamin D2, vitamin D3, and dihydrotachysterol. The purpose of this work has been (a) to determine the doses of these preparations required to bring dogs from the borderline of tetany to normal or slightlyelevated serum calcium values, (b) to determine the duration of action of therapeutic doses, and (c) to compare the calcium and phosphorus metabolism of normal and thyroid-parathyroidectomized dogs. It was hoped that the principles which might be developed would facilitate and stimulate further comparative trials of the 3 principles in the treatment of human parathyroid insufficiency.