CAROTENOIDS 



to justify the assumption that the liver was the site always produced 

 equivocal results. Ahmad, " ^ Olcott and McCann, " * Parienti and 

 Ralli ^ ^ and Euler and Klussmann ^ ® using various techniques claimed 

 to have produced traces of vitamin A by incubating a colloidal sus- 

 pension of [3-carotene with minced liver. Woolf and Moore • ' critically 

 discussed these results and pointed out the uncertainty in detecting 

 vitamin A in the small amounts in which it was claimed to have been 

 produced, Rea and Drummond, ^ ^ and Drummond and Mac Walter ^ ^ 

 were unable to demonstrate the conversion, and later experiments of 

 Ahmad ' ^ were also negative. 



Vitamin A, but not carotene, stimulates the growth of fibroblasts ; ' ^ 

 Willstaedt ' ^ claimed that carotene in the presence of liver tissue was 

 active in improving growth rate of the fibroblasts and concluded that 

 the liver tissue had converted carotene into vitamin A. 



In vivo experiments in which carotene was administered parenterally 

 have been almost equally inconclusive. Wolff, Overhoff and van 

 Eekelen ^ ^ and Ahmad, Grewal amd Malik, ' '' noted an increase in the 

 liver vitamin A levels of rabbits after the intravenous injection of caro- 

 tene colloidally suspended in isotonic dextrose ; Ahmad et al, could 

 not, however, repeat the observations using rats and dogs. Similar 

 experiments by Rea and Drummond ^ "^ were also negative. Drummond, 

 Gilding and MacWalter'^ showed that carotene introduced intra- 

 venously is stored in the liver primarily in the Kupfer cells. In further 

 experiments in Drummond's laboratory, a colloidal solution of carotene 

 was injected directly into the portal vein and the disappearance of 

 the stored carotene from the liver was followed by partial hepatectomy ; 

 the disappearance of carotene was not accompanied by a concomitant 

 rise in vitamin A levels in the liver. ' • Similar experiments recently 

 carried out by Vinet, Plessier and Raoul" did not produce results 

 sufficiently significant to warrant the authors' conclusion that vitamin 

 A was produced from carotene in the liver. 



The results of intramuscular injections of carotene can usually be 

 given a negative interpretation ; in manmials any vitamin A effects 

 noted being very considerably less than the effects produced by a 

 similar dose given per os. ' s, 7 9 'pj^jg jg ^\^q ^^ug foi- chickens. * " 

 Similarly, subcutaneous administration of carotene is ineffective ; 

 Greaves and Schmidt ^^ failed to elicit a " 100 per cent, biological 

 response," and Rokhlina, Balakhovski, and Bodrova®^ found that the 

 vitamin A activity of subcutaneously injected carotene was nil. irrespec- 

 tive of whether the vehicle was oil or water. Using the technique of 

 fluorescence microscopy. Popper ^^ never detected vitamin A in livers 

 of depleted rats after parenteral administration of carotene. It should 



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