PSORIASIFORME REACTION OF GUINEA-PIG EPIDERMIS AFTER TOPICAL APPLICATION OF VITAMIN A-ACID

1. Local application of Vitamin A-acid produces psoriasiforme hyperplasia of the ear-epidermis in guinea-pigs. 2. 3 phases of development can be distinguished, which are very similar to the morphogenesis of psoriasis vulgaris. Phase I: Structural alterations of the subcorneal epidermal cells with nuclear pyknosis, foamy-vacuolated degeneration of the cytoplasm and appearance of mucoid substances. Phase II: Bandlike thickening of the epidermis with parakeratosis. Phase III: Psoriasiforme akanthosis and papillomatois with ortho-hyperkeratinization after prolonged treatment. 3. In the dermis a fibroplastic-histiocytic reaction with esterase-positiv lipophages (as in psoriasis vulgaris) takes place. The capillaries seem to be more elongated than simply due to papillomatosis. 4. Histochemically the qualitative and quantitative behaviour of enzymes of the glycolysis, of the pentosephosphate cycle, the citric acid cycle, the respiratory chain, of hydrolytic enzymes as well as of lipids and nucleic acids in the hyperplastic epidermis indicate remarkable similarities to the psoriasis-vulgaris-pattern. It is demonstrated that none of the alterations in psoriasis vulgaris are specific. 5. The number of DNA-synthesizing epidermal cells is increased by the factor 10 from the 2. day of treatment and remains at this level during the course of treatment even when papillomatosis develops and keratinization becomes normal. 6. From these observations it is concluded that disturbances of the subcorneal zone coincide with an increased proliferative activity of the epidermis. © 1969 Springer-Verlag.