The uptake and metabolism of retinol, retinoic acid and methyl retinoate by the early chick embryo

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Abstract
1. Fertile eggs deficient in vitamin A were obtained by feeding hens a diet deficient in retinol (vitamin A alcohol) but containing methyl retinoate.2. Radioactive retinol was injected into the albumen of three of these eggs at a level of 2 μg [6,7-14C]retinol/egg. After 5 days' incubation, 4.6–8.3% of the injected material was recovered in the lipid of the embryo, representing a four- to nine-fold concentration into the embryo from the albumen. Approximately 40–50% of this was unchanged retinol, 15–20% retin-aldehyde and 20–30% probably a long-chain fatty acid retinyl ester. The early embryo can, therefore, metabolize vitamin A very effectively.3. [6,7-14C]Retinoic acid (2 μg) was injected into normal fertile eggs, killing most of the embryos. The eggs with dead embryos were analysed; 0.24% and 0.33% of the injected material was recovered from the embryos. Two embryos which developed contained 0.51% and 0.53% of the injected dose. In no instance was any material identified other than retinoic acid. The extremely low amounts of retinoic acid absorbed by the embryos emphasize the very high toxicity of retinoic acid to the early chick embryo.4. [6,7-14C]Methyl retinoate (0.5 μg) was injected into each of four normal eggs; 8.5–11.6% was isolated as unchanged methyl retinoate after 5 days; no other radioactive substance was detected.
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