Effects of feeding on plasma concentrations of vitamin A in captive African penguins (Spheniscus demersus)

抄録

Vitamin A comprises vitamin A₁ and vitamin A₂; vitamin A₁ is retinol and its fatty-acid esters and vitamin A₂ is 3,4-didehydroretinol and its fatty-acid esters. Although vitamin A₁ is generally recognized as the major vitamin A, vitamin A₂ is found in some birds and mammals that eat fish containing vitamin A₂. Plasma concentration of retinyl esters, but not retinol, is known to increase postprandially in humans. The objectives of this study were to confirm the presence of vitamin A₂ in fish fed to penguins, and in penguin plasma, and the postprandial changes in vitamin A concentration in penguin plasma. Blood was collected from six male African penguins (Spheniscus demersus) before and after feeding on jack mackerels (Trachurus japonicus) along with a vitamin premix containing vitamin A₁. Vitamin A₁ concentration in fish was much higher than the requirement, and was 5-fold higher than the vitamin A₂ concentration. Vitamin A₂ was present in plasma but its concentration was at least 100-fold below that of plasma retinol, suggesting that vitamin A₂ is much less bioavailable than vitamin A₁ in penguins. Plasma retinol and retinyl palmitate concentrations were found to be stable after the meal. Plasma retinol concentration is suggested to be homeostatically controlled in penguins against the rapid flow of vitamin A₁ after meal. The absorbed vitamin A₁ is thought to be transported to the liver via the portal vein for storage in penguins, resulting in stable retinyl palmitate concentration in plasma after meal.