DIGESTION, ETC. OF CAROTENOIDS IK THE G.I. TRACT 307 



able to demonstrate growth in vitamin A-deficient rats when carotene 

 was given in as small an amount as 1.6 ng. daily by intramuscular injec- 

 tion. However, for maximum growth, approximately four to six times as 

 much carotene was required when given parenterally as when admin- 

 istered orally. Carotene in aqueous solution was also found to be well 

 utilized when given subcutaneously. However, in confirmation of the 

 results of Sexton et a/., 361 oil solutions of the pigment were essentially non- 

 utilizable when given by the parenteral route. 249 In a later paper by 

 Bieri and Pollard, 379 it was noted that an aqueous suspension of /3-carotene 

 solubilized with Tween 40 provided greater growth and longer survival 

 when given by a single intravenous injection than when administered 

 orally. However, the oral route was found to be superior to the intra- 

 venous when tocopherol was incorporated in the carotene preparation. 

 Moreover, when vitamin A-deficient rats from which the small intestine 

 had been surgically removed were injected with 0-carotene, the vitamin A 

 content of the serum four to six hours after the injection varied from 24 to 

 107 microgram per cent. Since this is considerably higher than the 

 normal plasma content of vitamin A, the results are taken as evidence 

 that a considerable formation of vitamin A from carotene can take place 

 in tissues other than the small intestine. According to Samaras and 

 Hingerty, 380 the conversion of carotene to vitamin A takes place in about 

 two hours in normal rats. The reticuloendothelial system plays a role 

 in this change; this was shown by the fact that the injection of trypan 

 blue, which blocks the reticuloendothelial system, increased the ability of 

 the normal rat to change carotene, administered eighteen hours after the 

 dye, to vitamin A. In the vitamin A-deficient rat, in which this trans- 

 formation of provitamin A to vitamin A is markedly diminished, the in- 

 jection of trypan blue further inhibited the transformation of carotene to 

 vitamin A. In the case of the normal rat it is believed that the trypan 

 blue stimulated the RE system, while, in the case of the vitamin A-deficient 

 animals, the dye caused a further deterioration of the already deficient 

 organism. In another communication, these workers 381 proved that the 

 vitamin A-deficient rat is unable to utilize carotene, and will die, even 

 when carotene is available in its tissues as a source of vitamin A. 



c. The Effect of the Thyroid Gland on the Transformation of Carotene 

 to Vitamin A. In addition to playing an important role in the absorption 

 of carotene from the gastrointestinal tract, there seems to be some evidence 



379 J. G. Bieri and C. J. Pollard, Federation Proc, hi, 409 (1953). 



380 S. C. Samaras and D. J. Hingerty, Am. J. Physiol, 159, 588-589 (1949). 



381 S. C. Samaras and D. J. Hingerty, Am. J. Physiol, 159, 588 (1949). 



