Lipid Synthesis in Rat Skin

Summary.— Rat dorsal skin was fractionated by means of an electrokeratotome into epidermis and dermis containing the sebaceous glands. These fractions were separately cultured in the presence of 32P‐orthophosphate, 14C‐acetate, 14‐glycerol and 14C‐mevalonate, and the radioactivity incorporated into different classes of lipids was measured. The nature of the labelled products was different in the epidermis compared with the sebaceous glands: in the former, phospholipids and sterols were the major radioactive lipids synthesized, whereas, in the sebaceous glands labelled triglycerides, sterol esters and wax esters predominated. The nature of individual fatty acids labelled from 14‐acetate was studied and it was found that the sterol/wax esters fractions of both epidermis and sebaceous glands contained more radioactive odd‐numbered normal chain and iso‐ and anteiso‐branched chain fatty acids than the phospholipids and triglycerides. Isolated epidermal cells were prepared, and lipogenesis studies with radioactive precursors showed labelling patterns very similar to those of the cultured intact epidermis fractions. The presence of biochemically active sebaceous glands in the dermal residues, after excision of the epidermis fractions, was confirmed by treating skin in vivo with methyl testosterone, a hormone which stimulates the function of sebaceous glands, when a higher rate of lipogenests was observed in the subsequently cultured dermal residue fractions, compared with untreated controls. No such differences were seen in the epidermis after testosterone treatment.