Comparison of Hypercalcemic Effects of Activated Sterols in the Chick

Abstract

It was first demonstrated by Hess and Supplee 1 that irradiated ergosterol is much less effective, rat unit for rat unit, than cod liver oil in the prevention of rickets in the chick. The number of units of calciferol required to produce the same antirachitic effect as one U.S.P. unit of cod liver oil has been variously reported anywhere from 20 to 400, usually 30 to 50. The literature on this point has been reviewed by Remp and Marshall. 2 This phenomenon has never been satisfactorily explained, although the experiments of Russell and co-workers 3 4 5 have shed considerable light on the question. They have shown, for example, that the phenomenon is not attributable entirely to differences in absorption or to the route of administration. Further studies on the subject are in preparation for publication. 6

The explanation of the remarkable difference of behavior between vitamins D₂ and D₃ in the chick must ultimately be referable to one or more of 3 factors: (1) a difference in the extent of absorption from the digestive tract, (2) a difference in the extent of destruction in the digestive tract, or rate of destruction in the tissues, or (3) a specific difference in the manner in which these substances affect calcium and phosphorus metabolism or the laying down of bone. In order to decide among these possibilities we have considered it advisable to review experimentally some of the previous work, and to add further experimental data.

It has been feld that considerable information about the problem might be gained by a determination of the relative amounts of the activated sterols required to produce an equivalent hypercalcemic effect in the Chick. One would not expect the massive doses required to produce a definite degree of hypercalcemia to be subject to the same differences in absorption or the same extent of destruction as would apply to the relatively small doses needed to prevent rickets.