title: Evidence of diurnal variation of human epidermal cell proliferation. II. Duration of epidermal DNA synthesis.
abstract: In the epidermis of six healthy male volunteers the DNA synthesis time was measured by in vitro double labeling technique in a longitudinal study (48 h) with taking skin punch biopsies every 6 h. The external conditions of the experiments and one group of volunteers were identical to those of a previous study on LI of the epidermal keratinocytes. 14C-thymidine and 3H-thymidine were used for double labeling the DNA-synthesizing nuclei of keratinocytes. The duration of DNA replication time proved to be nearly constant, with minor fluctuation, during the entire time span of experiments (mean 6.19 +/- 0.3 h). Thus, the present results are in accordance with the conception that a periodically changing entrance rate of G1-cells into the S-phase of the generation cycle of keratinocytes is predominantly responsible for circadian variations in the number of DNA-synthesizing epidermal keratinocytes.
mesh_terms: D000328:Adult; D001345:Autoradiography; D002455:Cell Division; D002940:Circadian Rhythm; D004247:DNA / Q000096:biosynthesis*; D000078404:Epidermal Cells; D006801:Humans; D008137:Longitudinal Studies; D008297:Male
chemical_list: D004247:DNA