Variations in lipids in different layers of porcine epidermis.

Frozen cryosections, 8 microns thick, were cut parallel to the surface of porcine skin so as to provide separate samples representing various epidermal layers. These samples were dried, extracted with chloroform-methanol mixtures, and the lipids chromatographed on silica gel plates in different solvent systems. After spraying with sulfuric acid and charring, lipids were quantified using a scanning densitometer. It was thus possible to determine lipid concentrations in 12 consecutive epidermal layers, extending 96 microns into the skin. The phospholipids that were characterized all decreased in concentration toward the surface, whereas the neutral lipids and ceramides all increased. Glucosylceramide and acylglucosylceramide reached a peak concentration in the stratum granulosum and then decreased in the surface layers. Cholesterol sulfate reached a maximum concentration in the deeper stratum corneum and then abruptly decreased in the surface layer. These changes in patterns of lipid concentration are consistent with current theories regarding the formation of a water barrier in the stratum corneum that is composed mainly of neutral lipids, and with a possible function of cholesterol sulfate in cellular adhesion in the stratum corneum.