MEASUREMENT OF LIPID SYNTHESIS IN MOUSE AURICULAR SKIN CULTURED IN VITRO

— Split‐thickness mouse auricular skin has been cultured in vitro for up to 48 hours in the presence of 14C‐sodium acetate, 14C‐leucine, 14C‐isoleucine and 14C‐valine, and the incorporation of radioactivity into various tissue fractions measured in the heat‐separated epidermis and dermis. Lipid fractions were analysed by chromatography. It was found consistently that the epidermis contained higher proportions of labelled sterol esters and lower proportions of labelled triglyceride than the corresponding dermis. The radioactive acyl moieties of certain lipid classes were further studied by gasliquid radiochromatography. With 14C‐acetate as the tracer, sterol esters of both epidermis and dermis were seen to be enriched with respect to branched chain and odd‐numbered chain fatty acids compared with triglycerides and phospholipids. With 14C‐leucine, which is the specific precursor of odd‐numbered chain iso‐branched acids, sterol esters contained the majority of this type of fatty acid, although the major part of the radioactive substrate was metabolized to 14C‐acetate and incorporated into normal, even‐number chain saturated and unsaturated acids. With 14C‐valine, a specific precursor of even‐number chain iso‐branched acids, epidermal and dermal sterol esters again contained the majority of these acids, although there was evidence of some degradation of the valine to acetate, and incorporation into normal fatty acids. With 14C‐isoleucine, a specific precursor of odd‐numbered chain anteisobranched acids, virtually all of the precursor was degraded to 14C‐acetate, and the resultant radioactivity patterns were quite similar to those obtained with 14C‐acetate cultures per se. Slight traces of radioactive anteiso acids were detected in certain lipid classes, however.