CAROTENOIDS 



No carotenoids have been detected in human sweat * *, spermatozoa * ' 

 or cerebro-spinal fluid. * ^ Drigalski * ' found no carotenoids in bile but 

 Willstaedt and Lindquist^* claimed to have isolated two new caro- 

 tenoids from bile (and, incidentally, from plasma) which they con- 

 sider to be metabolic products of ^-carotene. 



Carotenoid Metabolism in Humans 



(i) Metabolism of Carotenoids during reproduction and lactation. It is 

 now well established that foetal blood contains a much lower concen- 

 tration of carotenoids than does the corresponding maternal blood, 

 and that the placenta acts as partial barrier to the transfer of carotenoids 

 to the foetus. * 9- « o 'y^q relative amounts of carotenes compared with 

 xanthophylls is also lowered. Typical values for the total carotenoids 

 in maternal venous cord (placental) and arterial cord (foetal) blood are 

 96-9 and 90 (xg. per 100 ml. plasma respectively. ^ ^ Lewis and Bodansky 

 and their collaborators^*'^' and Neuweiler^^ agree that there is no 

 difference between arterial and venous cord blood for they do not 

 confirm Clausen and McCoord's ^ ^ claim that owing to the utilization 

 of carotene by the foetus, venous cord blood contains more than does 

 arterial cord blood. Lund and Kimble'^' found a direct correlation 

 between concentration of foetal and maternal plasma carotenoids but 

 not between their vitamin A levels. This led them to believe that the 

 placenta is permeable to carotenoids but not to vitamin A, the foetal 

 vitamin A being produced in situ from carotenoids. This is a possi- 

 bility in humans, in whose blood (3-carotene normally occurs, but it 

 cannot be applicable to those mammals whose blood is devoid of 

 carotene but whose foetal livers contain vitamin A. Examples of such 

 animals are pigs and goats, and in these species Thomas, Loosli and 

 Williams, • ^ have demonstrated transference of vitamin A across the 

 placenta. 



It is now well established that there is a fall in carotenoid concentra- 

 tion of blood at or just after parturition in cattle (see p. 240) ; it has 

 been reported only once "^ ^ in humans, but there is no reason to believe 

 that it is not a normal occurrence. 



The ability of the newly born infant to absorb xanthophylls must be 

 slight for compared with birth values, the blood xanthophylls only begin 

 to increase, when the child is two years old whilst the carotene levels 

 begin to increase immediately after birth. 



A number of observers have noted that the carotenoid concentration 

 decreases rapidly as the colostrum changes into mature milk 2 2, 5 3, e 3- « e 

 and this has been confirmed by intensive investigations carried out by 

 Lescher et al. ^ ^ in America, by Kon and Mawson ^ ' in England and 



232 



