On circadian rhythms in human epidermal cell proliferation.

The ascertainment of consistent diurnal variations in human epidermal cell proliferation may have important implications for the treatment of many skin diseases. For the evaluation of diurnal rhythms in the growth of human epidermis, skin biopsies were taken every 4th hour for 48 h from each of two persons under synchronized living conditions. The epidermal cell proliferation was assessed by the fraction of cells in S and in G2-M phase as determined by measurements of the DNA content in the individual cells in single-cell suspensions. The existence of diurnally consistent body functions in the test persons was verified by monitoring the excretion of cortisol by urine. The fraction of cells in G2-M phase indicated circadian rhythmicity for the first 32 h of the test period. No regular variation according to time of day could be established in the fraction of cells in S-phase.