[The mechanism of action of vitamin A acid]

Although vitamin A acid has been used successfully in medicine for several years, the mode of action is still unknown. Clinical investigations have shown, that the application of vitamin A acid is associated with elevation of serum levels of vitamin A and after high dosage side effects develop similar to hypervitaminosis A. Several possibilities regarding the mode of action of vitamin A acid are discussed; it seems to be most likely: 1. The vitamin A depots of the body are mobilized by vitamin A acid. 2. The release of lysosomal enzymes is dependent on the serum level of vitamin A. 3. The unlimited DNS and RNS syntheses are inhibited by the action of lysosomal enzymes. 4. Disturbances in this control mechanism cause anomalies in the process of keratinization and the cellular turnover of epithelial tissues.