Estradiol distribution and penetration in rat skin after topical application,studied by high resolution autoradiography

Summary Transdermal pathways and targets in the skin for estradiol were investigated using dry-mount autoradiography.³H-estradiol-17 was applied at doses of 30.1 pmol, 120.4 pmol and 301 pmol/cm² to shaved rat skin in the dorsal neck region. Vehicles were DMSO, ethylene glycol or sesame oil. After 2 h of topical treatment with 30.1 pmol³H-estradiol×cm^–2 dissolved in DMSO a distinct cellular distribution was apparent. Target cells with concentrations of radioactivity were found in epidermis, sebaceous glands, dermal papillae of hair and fibroblasts. After treatment with 120.4 and 301 pmol/cm², a penetration gradient of radioactivity was recognizable however it masked specific cellular and subcellular uptake. The stratum corneum accumulated and retained radioactivity, apparently forming a depot for the hormone. Strong concentration and retention of the hormone was conspicious in sebaceous glands for more than 24 h, suggesting that sebaceous glands serve as a second storage site for the hormone. In all autoradiograms two penetration pathways to the dermis were visible: one through the stratum corneum and epidermis, the other through the hair canals and hair sheaths.This work was supported by US PHS grant NS09914