CAROTENOIDS AND VITAMINS A IN THE BLOOD 473 



placenta limits the access of vitamin A to the fetus. Williamson"' dem- 

 onstrated that this does not result from a general inhibition of the trans- 

 fer of lipids to the fetus, but is specific for vitamin A. When pregnant rats 

 were fed high-cholesterol diets, the lipid content of the placentae was 

 found to be about twice that of the controls ; however, the placentae of the 

 experimental rats had significantly less vitamin A than in the case of the 

 control placentae. 



Sex is another important factor which one must consider in relation to 

 blood vitamin A. The level of plasma vitamin A in the male usually ex- 

 ceeds that for the female by a significant amount. On the other hand, the 

 sex differences for plasma carotene are reversed. In the case of infants 

 and of young children, the plasma vitamin A has been found to be higher in 

 girls than in boys."^- However, in studies of the adult, Getz and Koerner,'^* 

 Kimble,-*^ Popper and Steigmann,'^* Abels et al.-^* and Week and Sevigne^^* 

 consistently found higher values for plasma vitamin A in men than in 

 women. Moreover, Week and Sevigne^^^ observed that the plasma vita- 

 min A was consistently lower in females than in males after they were sub- 

 jected to a vitamin A tolerance test by the administration of 134,000 jug. 

 of vitamin A in 50 g. margarine. However, Ivirk and Chieffi*^^ demon- 

 strated that there are no definite sex differences in plasma vitamin A values 

 in the case of aged men and women, respectively. 



Hormones, particularly those associated ■\^'^th sex changes, influence 

 plasma vitamin A le^'els. Changes in the estrogenic hormones are pre- 

 sumably responsible for the sharp decrease in plasma vitamin A in cows 

 following parturition.'^^ A decreased plasma vitamin A level was observed 

 when large doses of estradiol benzoate were injected into thyroidectomized 

 rabbits, although no effect was noted in the case of unoperated animals. '^^ 

 On the other hand, this hormone evoked an increase in the level of vitamin 

 A esters in the plasma when injected into pullets. '^^ Testosterone, one of 

 the male hormones, was found to be without effect on the amomit of blood 

 vitamin A in pullets,'''^ although it has been reported to increase plasma 

 vitamin A levels in the case of man.'^'' 



Young and Wald"^ stated that an increase in the amount of vitamin A 

 occurred in the blood of rabbits following the injection of adrenalin, but 



3" M. B. Williamson, /. Biol. Chem., 174, 631-636 (1948). 

 "^ H. R. Getz and T. A. Koerner, Am. J. Med. Set., 202, 831-847 (1941). 

 3's M. B. Williamson, Proc. Soc. Exptl. Biol. Med., 68, 621-623 (1947). 

 "6 V. E. Gardiner, W. E. Phillips, W. A. Maw, and R. H. Common, Nature, 170, 80-81 

 (1952). 



3" A. Danish and T. C. Klopp, Cancer Research, 10, 211 (1950). 

 ^^ G. Young and G. Wald, Am. J. Physiol, 131, 210-215 (1940). 



