522 IX. CAEOTENOIDS AND VITAMINS A 



from dams fed supplementary vitamin A than in the controls. The vita- 

 min A in the plasma and liver of the calf is closely associated with the caro- 

 tene intake of the dam during the lactation period. 



Vitamin A is consumed during the processes of growth. When subopti- 

 mal amounts of vitamin A are available, the quantity remaining in the 

 liver is greater when growth is restricted than when growth proceeds nor- 

 mally. Thus, Johnson and Baumann^^^ observed increased hepatic vita- 

 min A in rats when the extent of growth was limited by diets inadequate in 

 calories, in thiamine, or in tryptophane, or by the administration of thiou- 

 racil or of thiourea, as compared with that in the normal controls. Gillum 

 and associates^^^ reported that the plasma carotene and vitamin A were 

 moderately reduced in men and women with advancing age. 



b. The Effect of Dosage on the Storage of Vitamin A. No storage of 

 vitamin A occurs in the liver until the dosage is sufficient to meet the mini- 

 mum requirements for growth. Thus, Guerrant^^^ reported that, when in- 

 creasing doses of vitamin A, from 0.73 to 29 I.U., were fed daily to depleted 

 rats over a period of twenty-eight days, relatively small but definite in- 

 creases in hepatic \'itamin A took place, although marked increases in body 

 weight were observed. When the dosages were progressively increased 

 from 44 I.U. to 8,800 I.U., the rise in liver vitamin A with each increment 

 was extremely marked. Between dosage levels of 29 and 3,520 I.U. of 

 vitamin A, the hepatic vitamin A was approximately doubled for each two- 

 fold increase in vitamin A intake. However, when the dosage was in- 

 creased from 17,600 to 75,520 I.U., no further rise in the liver vitamin A 

 level occurred; in fact, at the highest dosage level, the hepatic vitamin A 

 was below the maximum. Table 2 summarizes the data on the growth re- 

 sponse of rats as related to vitamin A intake. 



The average vitamin A recovered was as high as 88% at the lowest 

 dosage; when the doses of vitamin A administered ranged between 14.7 and 

 3520 I.U./day, the average vitamin A recovered averaged about 14% 

 (Range 19 to 9%). Wlien moderately high amounts of vitamin A were 

 given (4,400, 6,600, and 8,800 I.U.), an average of 43% (Range 51 to 38%) 

 of that fed was recovered. When higher amounts of vitamin A were given, 

 the proportion retained was further decreased until, at the two highest dose 

 levels, only 6% and 5%, respectively, were recovered. ^'^^ 



The effect of dosage upon the proportion of vitamin A retained accounts 

 for the variability in the results reported by different workers. Thus, 

 Baumann and co-workers^^^ reported that only 10 to 20% of the vitamin A 

 which they administered to rats was stored, while Golding et al.^'^^ observed 



6« J. Goldins, S. K. Kon, and J. E. Campion, Chem. Ind., 55, 400-401 (1936). 



