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In most animal tissues, lipogenesis converts excessive dietary carbohydrate or protein into storage lipids and this process must obviously be under the control of homeostatic regulatory mechanisms related to dietary intake and composition. The lipids of the skin, both sebaceous and epidermal, however, are formed for a specific biological function, to maintain the integrity of the integument. Lipogenesis, on another hand, in skin regulated by the same mechanisms that operate in other tissues poses a problem.

Following topical treatments of rat dorsal skin with soap solutions (under greatly exaggerated conditions compared with normal usage) to invoke a primary irritation response, keratotome sections of pure epidermis free from sebaceous glands, and dermis free from epidermis were incubated with 11C glycerol, acetate, thymidine, and glucose in order to measure skin metabolism. In the epidermis. DNA synthesis was stimulated soon after treatment, and this was rapidly followed by increased incorporation of both labelled glycerol and acetate into glycerolipids (phospholipids and triglycerides). No such changes were seen in the dermis. Of these altered lipids, the proportion of the total radioactivity incorporated into phospholipids fell drastically, but rose in triglycerides. The frequency of soap treatment was more important than its duration for the development of irritation and changes in liquid synthesis. The activity of the pentose phosphate shunt pathway, as measured by 1-14C- and 6-14C- glucose oxidation was unchanged after soap treatment, as was the synthesis of epidermal fatty acids. The altered glycerolipid metabolism was reversible if the animals were allowed to recover following mild irritation by soap. Cell fractionation and autoradiography suggested that the germinative (stratum basale) cells of the epidermis were the locus of the observed effect, and not the differentiated cells. [ABSTRACT FROM AUTHOR]

Fixation or epidermis with osmium zinc iodide (OZI) for 24 hr at room temperature renders keratinosomes (lamellar granules of epidermis), the Golgi region, and mitochondria preferentially impregnated with heavy material while the remainder of the epidermal cell merely shows background staining. OZI fixation intensifies the heavy metal staining of the lamellae and of the envelope of keratinosomes. Extraction of epidermis with hexane prior to fixation with OZI abolishes the intensified impregnation of the lamellae and of the envelope of keratinosomes with the osmium zinc iodide stain. Because hexane theoretically extracts nonpolar lipids only and does not cause tissue disruption, it is suggested that the OZI-positive materials in keratinosomes are largely nonpolar lipids. [ABSTRACT FROM AUTHOR]

This study was directed towards the mechanisms by which solutions of some ionic surfactants increase the permeability of human skin. Ionic surfactants of three n-alkyl homologous series (R-COONa, R-OSO3Na, R-NH3CI) were selected. The low frequency, low voltage, alternating current (A.C.) conductance of isolated epidermal membranes is related to the permeability constant for water and was suitable for following effects of surfactant solutions below the critical micelle concentrations. Solutions and conditions were compared by observing differences in the induced rates of increase of A.C. conductance. A similar pattern of relative surfactant activity was shown for each series of surfactants. C8 compounds showed no effect, C10 slow but distinct increases in conductance, maximal effects occurred at C12 and C14 and less at C16. The induced changes were reversible to widely varying degrees up to a maximum of 90 percent. Members of the two anionic series were similar in effect but the alkylamine hycirochlorides produced more rapid conductance increases shortly after contact than did corresponding anionic molecules. The reversibility of the permeability changes excludes extraction of molecules as the mechanism of action for the surfactants. The absence of any similarity between the relative surfactant activities and changes in hydrophillipophil balance or detergency indicates an action against the protein rather than the lipid components of the stratum corneum. [ABSTRACT FROM AUTHOR]

Ultrastructural techniques were used to study alterations of rat-tail epidermis 24 and 72 hours after x-irradiation with 2, 4, 8, and 16 Krads. Twenty-four hours after irradiation the tissue showed changes in mitochondrial membranes. Intracellular and extracellular edema and nuclear inclusions also were observed. Seventy-two hours after irradiation cellular structure appeared even more affected. Most cells showed perinuclear lipid vacuoles, nuclear fragmentation, and severe mitochondrial changes. An attempt was made to relate these ultrastructural alterations with those induced by other sources of irradiation and other forms of injury. [ABSTRACT FROM AUTHOR]

Anterior tibia! skin of 12-day chick embryos was grown in organ culture in the absence and presence of serum and in Vitamin A to achieve varying degrees of cornification and mucous metaplasia. Morphogenesis was correlated with ongoing lipogenesis as assessed by short term in vitro incorporation studies with C14 acetate. Shifts in the patterns of lipogenesis similar to those previously described during embryonic differentiation of chick skin suggest that organ culture provides a useful and relevant model for studies of the biochemical events in differentiation. Results further indicated that the non-specific lipogenic effects of serum on cultured skin may be distinguished horn the changes in the intrinsic lipid pathways of differentiating epidermis. [ABSTRACT FROM AUTHOR]

Epidermal slices can produce ATP by both glycolytic and respiratory reactions. Via glycolysis, ATP is produced at a maximal rate of about 0.1 μmole/hr/mg of fresh tissue when slices are incubated in the presence of glucose at concentrations equivalent to normal blood levels. Most of the glucose is converted to lactate, and only a small percentage of the glucose metabolites are oxidized. Respiration generates the majority of the energy for the epidermis, producing ATP at a rate of 0.5 μmole/hr/mg of tissue. The main respiratory reactions of the epidermis in vitro are β-oxidation of lipids and the Krebs cycle. Slices of human epidermis in culture show a relatively constant rate of respiration for several hours in the absence of added substrate, and endogenous components are the main substrates of respiration even in the presence of added nutrients. Cellular phospholipids are probably the major endogenous nutrients for this oxidation. The constant rate of epidermal respiration, the limited oxidation of glucose metabolites, and the Pasteur effect indicate that epidermal energy metabolism is subject to a strong and complex control by biochemical factors. These factors are more prominently expressed in the intact epidermis than in homogenates or extracts. Data are cited which suggest that nucleotide cofactors, particularly ATP, play an important part in energy control by modifying key enzymes of the energy pathways. In light of these data and current concepts of biochemical regulation, an hypothesis is presented in which nucleotides and other intermediates synchronize the rates of glycolysis and respiration, markedly limiting the oxidation of pyruvate by the Krebs cycle. They also may contribute to the accumulation of glycogen, which is observed in wounds and psoriatic epithelium. [ABSTRACT FROM AUTHOR]

The aerobic microflora of the scalp, predominantly cocci, was virtually eliminated by the daily application of 1% aqueous neomycin for one month. This was done to test whether these organisms are an important source of the lipases which liberate fatty acids from the sebaceous triglycerides. This treatment had no effect on the proportion of free fatty acids in the surface lipids as determined by thin layer chromatography. The follicle-residing anaerobic C. acnes, was not attacked by neomycin and the yeast-like fungus P. ovale increased somewhat. The percentage of free fatty acids in any individual's sebum before and after treatment was positively correlated with the density of C. acnes. The latter organism is probably mainly responsible for lipolysis of triglycerides. [ABSTRACT FROM AUTHOR]