312 IV. DIGESTION OF LIPIDS OTHER THAN FATS 



Lovern and associates 412 ' 413 suggested that the vitamin A alcohol may 

 mediate in the absorption of the fatty acids. Although the vitamin A 

 may act in this capacity in the case of the halibut and of other fishes in 

 which this vitamin plays a more important role quantitatively than in the 

 higher mammals, Gray et al. 407 were unable to demonstrate any such 

 action in the rat. 



(b) Factors Altering the Kate of Absorption of Vitamin A. a'. The 

 Effect of Age: As in the case of triglycerides, age appears to be an im- 

 portant factor in controlling the rate of absorption of vitamin A. Thus, 

 Sobel and his collaborators 414 reported that vitamin A was absorbed at a 

 markedly diminished rate in the newborn baby, as compared with the 

 rate in children over one year of age, or with that of adults, when it was 

 administered either in an oily medium or in an aqueous dispersion. More- 

 over, the rapidity of absorption of vitamin A, as determined by the vita- 

 min A tolerance test, was shown to be low in normal infants, 415 as con- 

 trasted with that in older children. Clausen 416 reported that the maxi- 

 mum level of vitamin A in the blood was attained three to five hours after 

 its oral administration in older children. This is interpreted as indicating 

 a rapid utilization at this age. On the other hand, Rafsky and Newman 417 

 reported that the absorption of vitamin A proceeds relatively slowly in the 

 aged (69 to 89 years) . 



b'. The Effect of Concentration of Administered Vitamin A: Normally, 

 vitamin A is rapidly absorbed by the rat. It has been shown that the 

 concentration of the vitamin A administered is an important factor which 

 influences the rate of utilization in this species. In the experiments of 

 Reifman et al. im a direct proportionality was found, over a wide range, 

 between the concentration of the material fed and the rate of absorption. 

 Thus, the average absorption of vitamin A (calculated as I.U. per 100 

 sq. cm. of body surface per hour) was as follows for the different dosages: 

 100 I.U. dosage, 4.2 to 6.5 I.U.; 1000 I.U. dosage, 28.5 I.U.; 10,000 I.U. 

 dosage, 369 I.U.; 100,000 I.U. dosage, 2108 I.U.; and 1,000,000 I.U. 

 dosage, 10,140 I.U. 



c'. The Effect of Bile: The importance of bile in the absorption of 



412 J. A. Lovern and R. A. Morton, Biochem. J., S3, 330-337 (1939). 



413 J. A. Lovern, T. H. Mead, and R. A. Morton, Biochem. J., S3, 338-343 (1939). 



414 A. E. Sobel, L. Besman, and B. Kramer, Am. J. Diseases Children, 77, 576-591 

 (1949). 



415 A. E. Sobel, S. P. Gottfried, B. Kramer, and L. Besman, Abstracts, 110th Meeting, 

 Am. Chem. Soc, Div. Biol. Chem., Chicago, Sept. 11, 1946, 28B-29B. 



4,6 S. W. Clausen, J. Am. Med. Assoc, 101, 1384-1388 (1933). 



417 H. A. Rafsky and B. Newman, Gastroenterology, 10, 1001-1006 (1948). 



418 A. G. Reifman, L. F. Hallman, and H. J. Deuel, Jr., J. Nutrition, 26, 33-42 (1943). 



