Validation of Freeze-Drying to Visualize Percutaneous 3H-Estradiol Transport: The Influence of Skin Hydration on the Efficacy of the Method

A study was made of the validity of freeze-drying to visualize the distribution of 3H-estradiol in human stratum corneum after topical application of a dry dose, a patch or a buffer solution. Each of these donor formulations was applied to human dermatomed skin for 24 h using Franz permeation cells. Subsequently, small pieces of skin were subjected to cryofixation, freeze-drying, osmium tetroxide vapor fixation, Spurr resin embedding and electron microscopic autoradiography. Stratum corneum from dry dose and patch application experiments was well preserved by freeze-drying, allowing an accurate localization of 3H-estradiol. In contrast, stratum corneum from buffer solution experiments suffered from cryofixation artifacts due to excessive hydration of the skin. The corresponding autoradiographs showed strong redistribution of 3H-estradiol. Thus, the visualization method under investigation has its limitations regarding the hydration level of the skin.

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