J. Soc. Cosmet. Chem. 26 485--496 (1975) ¸ 1975 SocieO, of Cosmetic Chemists of Great Britain The role of essential fatty acids (EFA) in the regulatory processes of malpighian cell membranes M. CAMBRAI* Presented at the IFSCC VIIIth International Congress on 'Cosmetics--Quality and Safety', organized by the Society of Cosmetic Chemists of Great Britain at London on 26-30th August 1974. Synopsis--Living cells possess the ability to adjust their MEMBRANE PERMEABILITY in response to various stimulations. The electrical resistance of membranes as a function of current intensity proved a convenient means for studying this property. The non-linearity of membranes, i.e. the sudden change in electrical resistance which occurs beyond a critical current intensity, has been the subject of extensive studies. Evidence is presented showing that, in rats deficient in ESSENTIAL FATTY ACIDS, the membranes of living EPIDERMAL CELLS do not retain their normal, non-linear behaviour. Others have established that, under similar conditions, membrane-bound enzymes lose their ALLOSTERIC PROPERTIES. These findings lead to the conclusion that essential fatty acids are a fundamental requirement for the manifestation of regulatory processes in cell membranes. Possible mechanisms and the influences on hormonal regulation at the level of the skin are discussed. INTRODUCTION The disorders arising from lack of essential fatty acids (EFA) have been extensively studied. As far as the skin is concerned, EFA-deficiency is known to cause dermatosis, hyperkeratosis with epithelial h-yperplasia, decreased sebum secretion and increased water permeability. These effects have been observed in animals, mainly rats and mice. The present paper is * Unilever Research, Saint-Denis Laboratory, 8 impasse de la Montjoie, La Plaine Saint-Denis, 93212, France. 485

486 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS concerned with the changes occurring in the phoreographical response of the skin when animals are made EFA-deficient. When an electrical current is applied to the skin, the voltage-current relationship departs from linearity beyond a critical value of current in- tensity. In 1965, J. Kry•pin (1) suggested that this phenomenon is most likely related to active processes which occur in the skin and might therefore yield valuable information in clinical investigations. He developed a method called 'phoreography' for determining the threshold value of current at which the skin response departs from linearity. The method consists in applying electrical pulses of increasing current intensity and recording the voltage (Fig. 1,). Previous studies (2, 3) have shown that non-linearity originates in the living epidermal cells and should be related to energy-dependent changes in membrane permeability which arise from specific types of active processes. In recent years, the role played by essential fatty acids in membrane pheno- mena has been more clearly recognized. The experiments described here have been carried out in order to know whether EFA-deficiency causes any functional membrane disturbances which might be detectable by phoreo- graphical determinations. To correlate the results with more conventional observations, water-loss measurements and chemical analyses of skin lipids have been performed which are also reported. EXPERIMENTAL The study was aimed at observing progressive changes in the phoreo- graphical skin response from the very beginning of EFA-deficiency in rats and the general pattern of recovery after return to normal diet. Six male albino Wistar litter-mate rats were weaned directly on to the purified diet described below. Food and water were provided ad libitum. Control EFA-deficient diet diet Sucrose 72.6•o 72.6•o Fat and vitamin-free casein 20 20 Jones-Foster salt mixture 5.0 5.0 Water-soluble vitamin mixture 0.05 0.05 Choline chloride 0.10 0.10 Sunflower seed oil 2.20 -- Hardened coconut oil -- 2.20