STORAGE OF CAROTENOIDS AND OF VITAMINS A 517 



when the total \'itamin A storage is greatest; this relationship is, in fact, 

 borne out by the above results. The wide variations noted must be a reflec- 

 tion of widely varying nutritional conditions insofar as vitamin A is con- 

 cerned. 



The distribution of vitamin A in the several tissues of the normal rat 

 (reported in I.U./g. moist tissue) is reported by Williams^*^ as follows: 

 adrenal, 49; liver, 7.G; lung, 3.3; kidney, 2.7; muscle, 0.7; heart, 0.2; 

 and brain, 0.0. Clausen and McCoord, in unpublished studies cited by 

 Williams, ^^^ found the following tissues devoid of vitamin A: lung (dog, 

 guinea pig) ; small intestine (rabbit) ; large intestine (cat) ; stomach (cat, 

 guinea pig) ; spleen (guinea pig, rabbit) ; pancreas (rabbit) ; ovaries (rab- 

 bit); thyroid gland (rabbit) and adrenal gland (gopher). 



(2) Comparative Distribution of Carotenoids 

 and of Vitamins A in Different Tissues 



The distribution of carotenoids in the invertebrates has a certain similar- 

 ity to that in the higher forms. The gonads are among the most common 

 sites for the storage of carotenoids in these forms. Thus, the eggs of 

 Asteroidea contain carotenoids, and their presence in the gonads of the 

 Holothuroidea, Echinoidea, Mollusca, and Gastropoda has been demon- 

 strated. The integument provides another storage site for carotenoids in 

 the lower forms (Asteroidea, Crustacea, Mollusca). The coloring matter in 

 the skin of tropical fishes and of other highly colored specimens of this 

 group consists mainly of carotenoids. The pigmentation of the plumage 

 of birds is also attributable to carotenoids. An accumulation of carote- 

 noids has been noted in the digestive glands of the Asteroidea and Echinoidea, 

 as well as in the digestive diverticula of some Mollusca. Lovern and co- 

 workers^'*^ demonstrated that substantial amounts of vitamin A were 

 present in the gastric and intestinal tissues of halibut. Later, Lovern and 

 Morton 1°" found that the pyloric caeca in the halibut (Hippoglossus hippo- 

 glossus) was very rich in vitamin A; the main concentration was in the 

 tunica propria. In an extension of this work. Glover and Morton^^* cor- 

 roborated the finding that the vitamin A was largely concentrated in the 

 tunica propria and mucosa. A larger porportion of the vitamin A in the 

 mucosa was in the form of the free alcohol than was the case with that pres- 

 ent in the tunica propria. It is believed that a lipase effects alternate syn- 

 thesis and hydrol^'sis of the esters during absorption ; this condition would 

 account for variations in the proportion of free alcohol. Grangaud and co- 



6" J. Glover and R. A. Morton, Biochem. J., 42, IxiiHxiv (1948). 



