[Recent findings on the importance of vitamin A and its metabolism in man and laboratory animals].

A survey is given concerning recent realizations of importance and metabolism of vitamin A in man and experimental animals. The transport of vitamin A from the small intestine takes place in form of esters by inclusion in chylomicrons and lipoproteins. A higher content in the blood plasma over a longer period evokes toxic effects. In the liver one part of the vitamin A in form of an ester with binding to lipoproteins is accumulated, one part is - according to the need - associated with a vitamin-A-binding protein, which forms complexes with prealbumin molecules and transports the vitamin to the various places of effect. With the help of the receptor proteins the vitamin A is included in the cells, in which it is effective and is transported into the vitamin-A-aldehyde and the vitamin-A-acid. The vitamin A and the vitamin-A-acid are transported into the cell nuclei with the help of receptor-proteins and play a role in the differentiation of the tissues and in the regulation of the synthesis of RNA. When a deficit or an abundance of vitamin A is present in the early phase of pregnancy malformations in the fetuses appear. The vitamin A and structure-similar connections have an inhibiting effect on the development of tumours.