222 ASCORBIC ACID 



these conditions there is an actual increase in both the concentration of 

 sucrose and ascorbic acid. Conditions which promote the synthesis of su- 

 crose therefore appear also to favor an increase in the concentration of 

 ascorbic acid. It is still not clear, however, whether the action is one of 

 increased synthesis or one in which the rate of loss of ascorbic acid is re- 

 duced. A direct chemical relationship between sucrose and ascorbic acid is 

 difficult to visualize; it is conceivable that some essential component in the 

 synthesis of sucrose may be concerned either directly in the synthesis of 

 ascorbic acid, or in a sequence of reactions which stabilize the vitamin in 

 the cell. 



4. Synthesis of Ascorbic Acid in Vitamin-Deficient Animals 



Work over the past ten years has suggested the possibility that vitamin 

 A is necessary for the synthesis of ascorbic acid in animals. Single or re- 

 peated depletion of vitamin A caused a fall in the ascorbic acid content of 

 the tissues of rats,^^ and with rats fed with graded doses of vitamin A it 

 was found that the ascorbic acid concentration in the plasma ran parallel 

 with the vitamin A intake. ^^ The observation that animals deficient in 

 vitamin A excrete less ascorbic acid than the non-deficient animals^ was 

 in line with the above results and suggested that the absence of vitamin A 

 decreases the concentration of ascorbic acid in the tissues by interfering 

 with its synthesis and not by causing an excessive loss from the kidney. 

 Observations with calves and horses suffering from vitamin A deficiency 

 showed that the lowered level of ascorbic acid in plasma and cerebrospinal 

 fluid could be raised by the administration of vitamin A.^^ These observa- 

 tions on the rat were generally confirmed, but the interpretation that this 

 represented a decreased synthesis of ascorbic acid due directly to a lack of 

 vitamin A per se was negatived.'^** It was shown that the lowered concen- 

 tration of ascorbic acid in the tissues of animals deprived of vitamin A 

 could be accounted for solely by their lowered food intake. Moreover the 

 rise in the urinary excretion of ascorbic acid following the administration 

 of chloretone, although less in vitamin A-deficient rats than in non-de- 

 prived rats, was eliminated if the food intake of the latter was restricted 

 to that of the deficient animal. No specific relationship was found between 

 the rat's resources of vitamin A and its capacity to synthesize ascorbic acid. 



Observations that a deficiency of vitamin produces scurvy -like alterations 



68 B. Sure, R. M. Theis, and R. T. Harrelson, J. Biol. Chem. 129, 245 (1939). 



67 T. S. Sutton, H. Kaeser, and S. Hansard, J. Biol. Chem. 144, 183 (1942). 



68 P. D. Boyer, P. H. Phillips, W. D. Pounden, C. Jenson, I. W. Rupel, and M. E. 

 Nesbit, J. Nutrition 23, 525 (1942). 



69 P. H. Phillips, N. S. Lundquist, and P. D. Boyer, J. Dairy Sci. 24, 977 (1941). 

 ^o L. W. Mapson, and S. E. Walker, Brit. J. Nutrition 2, 1 (1948). 



