524 IX. CAROTENOIDS AND VITAMINS A 



that the percentage of storage increased with the magnitude of the dose 

 up to the optimum point, but decUned when very heavy doses were given. 

 Davies and Moore"'' obtained essentially similar results when varying 

 dosages of halibut liver oil were given to rats. They indicated that the 

 following three principles govern storage under these conditions: 



(1) At low dosages, about 100 I.U. is "lost," or apphed to other pur- 

 poses, before storage commences in the liver. The proportion "lost" de- 

 creases as the dose is raised, until a toxic level is reached. 



(2) Following toxic overdoses a high proportion of the dose may dis- 

 appear, and less storage occurs than would have been the case had the dos- 

 age been just below the toxic level. 



(3) With prolonged massive dosing, without obvious toxic symptoms, 

 the percentage of the vitamin stored may be low, even when a high con- 

 centration is attained in the liver. This is considered to be due to the 

 "saturation" of the liver with vitamin A. 



Frey et a/."^ reported that the hepatic stores of vitamin A in cattle in- 

 creased in practically a linear relationship with intake throughout the 

 range of vitamin A supplement fed. An intake of 100 I.U./lb. of body 

 weight was found to maintain nearly maximum serum vitamin A levels. 



c. The Effect of Sex on the Storage of Vitamin A. The sex of the animal 

 plays such an important role in the metabolism of lipids in general that it 

 is not surprising that it should likewise be concerned with the metabolism 

 of carotene and of vitamin A. It was reported earlier that sex differences 

 exist in the plasma levels of carotene and of vitamin A in man. Thus, 

 the figures for /S-carotene in the blood are uually higher in the female than 

 in the male, and those for plasma vitamin A show exactly the reverse 

 relationship between the sexes. 



Sex also constitutes an important factor in relation to the storage of 

 vitamin A in the liver and kidneys. A number of workers have reported 

 higher vitamin A values for hepatic vitamin A in females, as compared with 

 males, under normal feeding conditions, not only in rats"^-^^" but also in 

 cattle. ^^^ The same phenomenon has been shown to obtain in rats after 

 the feeding of shark and halibut liver oils,^"-^**-'^^^ as well as after the ad- 



6" A. W. Davies and T. Moore, Biochem. J., 4^, Ixiii (1948). 



«'8 P. R. Frev, R. Jensen, and W. E. Connell, J. Nutrition, 34, 421-430 (1947). 



"9 E. C. Caliison and V. H. Knowles, A7n. J. Physiol., US, 444-452 (1945). 



680 T. Moore and I. M. Sharman, Biochem. J., 47, xliii-xliv (1950). 



681 F. Ender, Z. Vitaminforsch., 3, 247-253 (1934). 



682 A. R. Bult and C. J. Sorgdrager, Acta Brevia Need. Physiol. Pharmacol. Microbiol., 

 8, 114-116 (1938). 



683 H. Popper and S. Brenner, /. Nutrition, 23, 431-443 (1942). 



