Comparison of Activity of 25-Hydroxycholecalciferol and Dihydrotachysterol 2 in the Thyroparathyroidectomized Rat 1

Summary

Assays of the activty of synthetic 25-hydroxycholecalciferol in the thyropara-thyroidectomized rat indicate that it is no more potent than ergocalciferol. These and other data (1) indicate that both 25-hydroxycholecalciferol and erygocalciferol are only 1/5 as active as dihydrotachysterol₂ in this assay. These results suggest that the pharmacologic action of vitamin D as a substitute for parathyroid hormone operates through a mechanism different from the physiologic action of this sterol derivative.