LIPIDS PRESENT IN SKIN AND ITS APPENDAGES 779 



tionship between the cholesterol level of the skin and the frequency of 

 skin tumors. Gould and Taylor, 414 and Srere et al., 1 making use of C 14 - 

 acetate, demonstrated that the skin possesses the ability to synthesize 

 cholesterol at a rate comparable with that of the liver. 



In addition to cholesterol, several other sterols have been identified as 

 components of the skin. The most important of these is 7-dehydrochole- 

 sterol, or provitamin D 3 . Although this compound has been shown to be a 

 constant contaminant of cholesterol, 415 it usually occurs in a higher propor- 

 tion in the skin lipids than in those obtained from inner tissues. 16 Windaus 

 and Bock 416 were able to separate it in amounts as high as 3 to 6% of the 

 total sterols in pigskin. Rosenberg 16 reported the following percentages 

 of provitamins D in the sterols obtained from the skin of several species: 

 man, 0.15 to 0.43; cattle, 0.18; calf, 0.68; mouse, 0.87; and chicken 

 (feet) 1.0 to 4.0. Rosenberg 417 recently confirmed the presence of high 

 concentrations of 7-dehydrocholesterol (provitamin D 3 ) in the feet of the 

 chicken. However, no evidence could be obtained indicating the presence 

 of this or of any other provitamin D in the preen gland (glandula uro- 

 pygialis) of ducks, geese, or chickens. It is therefore evident that our 

 concept of the synthesis of vitamin D from the secretion of the preen 

 gland of fowl must be revised. 



It is generally believed that 7-dehydrocholesterol originates from chole- 

 sterol in the skin, and that it can be further transformed to vitamin D 3 by 

 ultraviolet radiation. The latter transformation can readily be demon- 

 strated in an in vitro system ; it is believed that the protection from rickets 

 afforded to rats by sunlight or ultraviolet light is to be traced to a similar 

 activation of the provitamins D within the skin, resulting in the in vivo 

 production of vitamin D. 



Moore and Baumann 418 have reported evidence for the presence of sterols 

 other than cholesterol in the cholesterol fraction obtained from rat skin. 

 Whereas the sterols isolated from most tissues of the body reacted with 

 the modified Schoenheimer-Sperry reagents in a manner similar to the re- 

 action of pure cholesterol, those isolated from the skin formed an intense 

 blue color almost immediately. 7-Dehydrocholesterol and 7-hydroxy- 

 cholesterol are known to react with this reagent at a rapid rate. The skin 

 was found to contain 22 to 36% of a fast-reacting sterol, although spectro - 



414 R. G. Gould and C. B. Taylor, Federation Proc, 9, 179 (1950). 

 416 A. G. Boer, E. H. Reerink, A. van Wijk, and J. van Niekerk, Proc. Acad. Set., 

 Amsterdam, 39, 622-632 (1936). 



416 A. Windaus and F. Bock, Z. physiol. Chem., 245, 168-170 (1936). 



417 H. R. Rosenberg, Arch. Biochem. Biophys., 42, 7-11 (1953). 



418 P. R. Moore and C. A. Baumann, J. Biol. Chem., 195, 615-621 (1952). 



