COMPARATIVE STUDY OF SOME EFFECTS OF ADMINISTRATION OF DIHYDROTACHYSTEROL AND CALCIFEROL TO RATS1

Abstract

The action of dihydrotachy-sterol (AT-10) were studied in normal and parathyroidectomized rats. Only when given orally was the drug effective at the dose levels used. In normal rats, it raised serum Ca levels and renal Ca excretion markedly. However, only minor increases in phosphate excretion were produced. When given prior to parathyroidectomy, dihydrotachysterol prevented the fall in serum Ca but did not prevent the temporary increase in renal Ca excretion which follows the loss of circulating hormone. Conversely, while the drug was able to prevent the fall in renal phosphate excretion it was unable to prevent the rise in serum phosphate levels which follows removal of these glands. When given at the time of or following parathyroidectomy, it was able to raise serum Ca levels without any marked effect on serum phosphate levels or renal excretion rates of these two ions. In the rat, equal or double amounts of calciferol (Vitamin D2) were unable to replace dihydrotachysterol in its effect on these physiological functions. Dihydrotachysterol functions in the rat by removing Ca and phosphate from bone.