The nonpolar lipids of pig epidermis

Epidermis was removed from several sites on the intact bodies of each of seven pigs and the lipids were extracted and analyzed by thin-layer chromatography. The principal nonpolar components were cholesterol, free fatty acids and cholesteryl esters. Small and variable amounts of paraffin hydrocarbons, triglycerides, and an unidentified lipid were noted. In a series of time-course experiments, epidermal lipids were labeled by intradermal injection of [1-14C] acetate at varying times up to 21 days before removal of the epidermis. The hydrocarbons never acquired radioactivity, while the triglycerides retained label only for about 1 day after injection. Squalene and lanosterol retained considerable radioactivity for up to 12 h after labeling. Radioactivity appeared in free fatty acids and cholesteryl esters 2-3 days after labeling and began to decline after 21 days. Epidermis from uninjected sites did not acquire significant radioactivity. From these results it was concluded that cholesterol, cholesteryl esters and free fatty acids are synthesized locally in the epidermis and remain until lost by desquamation. Triglycerides are also synthesized but do not persist into the stratum corneum, so the small amounts found there may be environmental contaminants. Alkanes are not synthesized, and are most probably derived from petroleum waxes.