MAMMALIAN CAROTENOIDS 



Function of Cakotenoids in Mammals 



The potential vitamin A activity of certain carotenoids is by far 

 the most important function which can be ascribed to this class of 

 pigments in mammals. It is especially important in herbivorous 

 animals for they never obtain any preformed vitamin A in their diet. 

 This is discussed in Chapter XL 



The preferential accumulation of carotenoids in ovaries, corpora 

 lutea, corpora rubra, and adrenals is a good a priori reason for sug- 

 gesting that the pigments per se take part in the metabolism of these 

 organs. This cannot be a general mammalian function, however, 

 because Goodwin and Gregory ^ could find no carotenoids in the ovaries 

 or adrenals of goats. Reports of similar investigations on other animals 

 which have no carotenoids in their blood, liver, or depot fat are awaited 

 with interest. The fall in the plasma carotenoid levels around par- 

 turition which has been observed in cows does not appear to be of 

 specific importance because similar changes have been observed in 

 other blood constituents {see p. 243). 



Reports have been published in which it is claimed that carotene has 

 a specific effect per se ; none of these has yet been confirmed. It is 

 claimed, inter alia, that carotene possesses antihistamine activity, ^ ^ " 

 sensitizes the action of the gonadotrophic hormone, ^ * ^ potentiates the 

 action of insulin and adrenaline, ^ * ^ takes part in production of volatile 

 fatty acids in liver fat, ^ * 2 depresses arginase activity under aerobic 

 conditions, ^ ^ 3 inhibits pepsin, ^ * * cathepsin and trypsin, ^ * ^ and in- 

 creases the rate of glycolysis in muscle, ^ ^ ^ blood, ^ * '^ and liver. 2 4 e a-c 

 The investigations on blood and liver were carried out on guinea pigs ; 

 as these animals do not contain carotenoids in their liver or blood (see 

 p. 247), the action of carotene cannot be considered to have any in vivo 

 significance. 



Recently it has been suggested that carotenoids are linked with the 

 cytochrome system in transferring oxygen to the macular regions of 

 the human retina which has no blood supply. ^ * ' Denton and 

 Pirenne ^ * ^ and Hartridge ^ * » deny this. Hartridge considers that the 

 presence of a macular pigment in humans is not yet unequivocally 

 proved, whilst Denton and Pirenne, assuming that it does occur, 

 consider that its main function wouH be to improve foveal acuity. 

 Barnicot^^^ inserted very small crystals of vitamin A acetate into 

 small pieces of parietal bone cut from ten days old mice and then 

 grafted these pieces of bone into the cerebral hemispheres of litter 

 mates. The presence of the vitamin A led, within 14 days, to well- 

 marked resorption accompanied by numerous osteoclasts and leading 



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