VITAMINS D 771 



bers of the vitamin D group may only occur as minor constituents in a mix- 

 ture containing the other vitamins D. 



Ten different provitamins D are known, as determined by the fact that, 

 on irradiation, antirachitic substances originate. There must therefore be 

 ten different vitamins D which correspond to these provitamins D. Of 

 these, only four vitamins have been prepared in pure form. The composi- 

 tion of the others can be surmised by analogy in those cases in which the 

 structure of the provitamin is known. 



As indicated earlier, vitamin Di is not a true vitamin, since it is a molecu- 

 lar compound of vitamin D2 and lumisterol2. Vitamin D2, also referred 

 to as calciferol or \'iosterol, is derived from the irradiation of ergosterol. 

 On activation of 7-dehydrocholesterol, vitamin D3 originates. Vitamin D4 

 consists of activated 22-dihydroergosterol, while vitamin D5 is generally 

 considered to be the vitamin originating from the irradiation of 7-dehy- 

 drositosterol. Of these, only vitamins D2 and D3 have been isolated^"^ in 

 pure form from fish liver oils. On the basis of molecular distillation of cod 

 liver oil, it has been suggested^^' that six different vitamins D are present. 

 These consist of two which occur in major amounts, two others in lesser 

 amounts, and the remaining two in traces. Rosenberg^^ refers to one of the 

 latter as vitamin De, but it has not been further identified. Other fish liver 

 oils, such as those from spearfish (Tetrapturus spp.) and from white sea 

 bass {Cynoscion nobilis), show elimination curves differing from each other 

 and also varying from that of cod liver oil. It is therefore presumed that 

 these oils contain distinct types of vitamin D. 



One factor which has helped qualitatively in the study of the vitamins D 

 is the difference in their physiological behavior when administered to var- 

 ious species of animals. Although diverse cod liver oils are not entirely 

 uniform in composition, an especially prepared sample has been used for 

 many years as the reference standard in the United States. This is as- 

 sumed to possess maximum activity in the case of the test animals com- 

 monlj'- used, namely the rat and the chicken. On the other hand, although 

 vitamin D2 is very effective in curing rickets in the rat, it possesses very 

 little potency in this respect for the chicken. Pure vitamin D3, prepared 

 from irradiated 7-dehydrocholesterol, is equally active in the case of the 

 rat and of the chicken, and compares favorably with the vitamin D in cod 

 liver oil. However, Bills and co-workers^^ reported that the vitamin D 

 isolated from the white sea bass {Cynoscion nobilis) is 300% more active in 

 the chick than is cod liver oil, while that from the Pacific spiny dogfish 

 (Squalus suckleyi) is about 230% more active. It has been suggested'^ 

 that such unusually high potencies may be due to the presence of an un- 

 known vitamin D rather than to some hypothetical synergistic factor. 



Turkeys and chickens do not necessarily respond in the same manner to 



21' K. C. D. Hickman and E. Lt; li. Cray, Ind. Eiuj. Vliem., 30, 790-802 (1938). 



