A histochemical investigation on the percutaneous absorption of vitamin D synthesized into the mammal epidermis.

The vitamin D transepidermis absorption was studied by means of a histochemical technique suitable to detect this vitamin and to discriminate it from cholesterol and its esters. Such technique shows vitamin D inside the mast cell granules. As the mast cell granules contain metachromatic substances its own histochemical reactivity must be previously blocked by methylation. After this treatment the mast cell granules do not stain by toluidine blue and do not react to the peracetic acid-toluidine blue reaction. However, the granules remains reactive to alkaline permanganate-toluidine blue and to alkaline permanganate-Schiff reactions. These results show that the mast cell granules do not contain cholesterol but they contain vitamin D. The lack of cholesterol suggests that vitamin D is not synthesized inside the granules. As the mast cells may appears within the epidermis or in close relationship with the epidermis, although it is placed into the superficial dermis, it was admitted that the mast cells uptake vitamin D contained inside the epidermis intercellular compartment. In such instances, the vitamin D synthesized by the keratinocytes enter the intercellular compartment, where its synthesis accomplishes, and migrate towards the basement membrane. At the basal epidermis layer or after passing through the basement membrane the vitamin D is taken up by mast cells, where it is stored inside its granules.