Studies on Carotenoid Metabolism XII. The Effect of Dietary Carotenoids on the Carotenoid Distribution in the Tissues of Chickens

Abstract

It was shown that, in chickens on a farm diet, considerable amounts of lutein are present in the blood, liver, ovaries, and in the yolks of the eggs which they produced. On the other hand, only small amounts of β-carotene were found in these biological materials. The adventitious origin of the carotenoids in the tissues of chickens was proved by the fact that they could be completely removed from the tissues when the birds were maintained on a carotenoid-free diet over a prolonged period. When pure cryptoxanthin or zeaxanthin was fed to carotenoid-depleted chickens, considerable amounts of the carotenoids were present in the blood, liver and ovaries. Blood levels as high as 526 μg % were noted for zeaxanthin and 213 μg % in the case of cryptoxanthin. On the other hand, when α- or β-carotene was given, only traces, if any, appeared in the blood, and minimum quantities were present in the liver, ovaries, or egg-yolks. After lycopene was fed, the average blood value was 7.4 μg %, while the amounts in the liver and in the ovaries were 1.4 and 1.2 μg per gram, respectively. Proof that the small amounts of material reported as α- or β-carotene in the tissues of the chickens and in the eggs of the hens actually were these carotenoids was obtained by mixed chromatograms and by extinction maxima in several solvents. When colloidal solutions of zeaxanthin, α-carotene or β-carotene were given intravenously to chickens, no trace was present in the blood after 24 hours, although considerable proportions were found in the liver. A suggested interpretation of these results is the hypothesis that carotenoids in normal blood are neither in colloidal form nor merely in solution in lipids, but instead are combined with a specific blood constituent.