STANDARDS FOR VITAMINS D 781 



Activated 7-dehydrostigmasterol is potent only to the extent of 100,000 

 I.U. per gram in the rat, while its activity in the chicken is uncertain.''' 

 The biological response is of such a low order that one may question its in- 

 clusion as one of the D vitamins. 



The effectiveness of mussel vitamin D is equal, in the rat,^^ to that of 

 vitamins Do or Ds; in the chicken it has 100%^^ of the efficacy which it dis- 

 plays in the case of the rat. This represents an activity similar to that of 

 vitamin D2. Activated epi-7-dehydrocholesterol has been found to be 

 10% as active as vitamin D3 in the rat, while its potency in the chicken is as 

 yet undetermined." The activated form of 22,23-oxidoergosterol is only 

 "feebly" active." The potencies of other substances possessing vitamin-D- 

 like activity in the rat are the following (per gram) : activated 5,7-andro- 

 stadiene-3,17-diol, 100,000 I.U.'*'^^'; activated 3-hydroxy-5,7-choladienic 

 acid, 100,000 I.U.s"; and dihydrotachysterol, 200,000 I.U.^i 



3. Standards for the Vitamins D 



Because of the varying potency of different vitamin D preparations, a 

 standard by which to gauge unknown samples is necessary. This is particu- 

 larly advisable inasmuch as no satisfactory chemical methods are avail- 

 able, especially when it becomes essential to differentiate among the dif- 

 ferent types of the vitamin D. 



The International Unit (I.U.) of vitamin D is considered to be the 

 primary universal standard. It was defined by an International Vitamin 

 Conference held by the League of Nations in 1934^^1 as the effect caused by 

 0.025 Mg of pure crystalline vitamin D2 dissolved in one milligram of olive 

 oil. The following properties are ascribed to the preparation used as the 

 standard:" 



Calciferol or vitamin Do, C28H43OH 



(a) Colorless, acioular crystals, odorless. M.p. 114.5-1 17 °C. in open capillary. 



(b) Specific rotation: 



in alcohol, [a]!? = +101° to +102.5° 



[a]L°6i = +119° to +122° 

 in chloroform, [a]v = +52° 

 [a]646i = +62° 



(c) Absorption spectrum. In alcohol or other suitable non-absorbing solvent, it shows a 

 smooth curve with maximum at 265 mu. E {\%, 1 cm.) = 470—485. 



This replaces the earlier International Unit of 1931, which is now reported 

 to be unsatisfactory. 2" 



^* League of Nations Quarterly Bull. Health Organization, 4, No. 3 (Sept., 1935), 540- 

 542. Memorandum on the International Standard for Vitamin D and Its Application. 

 252 N. T. Gridgeman, H. Lees, and II. Wilkinson, Analyst, 65, 493^96 (1940). 



