Comparison of the Effects of Crystalline Dihydrotachysterol, Vitamin D2and Parathyroid Extract on Calcium and Phosphorus Metabolism in Man

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Abstract
Metabolic balance studies of calcium, phosphorus and nitrogen were carried out on two “normal” patients while they were receiving intramuscular parathyroid extract (PTE) and were compared with similar studies in 2 hypoparathyroid subjects receiving crystalline dihydrotachysterol (DHT) orally. In one of the hypoparathyroid patients, the effects of intravenously administered PTE, DHT and vitamin D2 were also studied. Oral DHT, like vitamin D, increased the intestinal absorption and urinary excretion of calcium and phosphorus. The phosphaturia induced by intravenous DHT and vitamin D2, as contrasted with PTE, appeared more slowly, was not characteristically associated with a fall in serum phosphorus, and, in balance studies, prolonged oral administration of DHT was not followed by post-treatment phosphorus retention. It is concluded that DHT has effects on calcium and phosphorus metabolism which are virtually identical with those induced by large doses of vitamin D and only superficially resemble those of PTE. This is in keeping with the hypothesis that the fundamental hypercalcemic action of all vitamin D isomers (as opposed to antirachitic activity) is the same. Differences do exist potency and rapidity of action. Both orally and intravenously administered DHT caused a decrease in urinary phosphorus excretion on the first day of treatment, followed by a pronounced phosphaturia. These findings are discussed in the light of the previous suggestion that vitamin D has a direct action on the kidney.