The diurnal variation of epidermal metabolism

In previous studies, the rates of epidermal glycolysis and amino acid incorporation were found to parallel rates of mitosis in both the hypoplasia associated with starvation and the hyperplasia produced by treatment with hexadecane. To examine whether similar changes in epidermal metabolism accompany the known diurnal variation in epidermal mitotic activity, the rates of glycolysis and incorporation of amino acids in epidermal sheets from skin samples at various times during a 24-hr period were assayed. These activities were found to parallel the diurnal variation of mitosis demonstrated by metaphase counts. Diurnal variation of metabolism in the suprabasal layers was investigated by examining the relative rates of incorporation of histidine and leucine: it was found that histidine showed a broader peak of activity than that seen for the other measured activities. When epidermal samples were prepared form tissue treated with hexadecane to induce hyperplasia, an increase in metabolic activity and decrease in the amplitude of diurnal variation was observed. The results indicate that the general metabolic activities of the epidermis follow a diurnal pattern similar to that found for mitosis.