Abstract
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.