The mechanism of the diurnal periodicity of mitosis

Abstract

Inversion of the alternation of light and darkness during the 24-hour period resulted in a complete inversion of the diurnal rhythm of mitotic activity in the epithelium of the skin, cornea, tongue and esophagus. After removal of the adrenal or thyroid glands the diurnal fluctuations of the number of mitoses were preserved, but their range in the morning and evening hours was somewhat reduced. Diurnal fluctuations of mitotic activity, absent in control animals, were noted in mice fed only at night. When mice were fed only in the morning the diurnal fluctuations were changed in the interstinal and tongue epithelium. The diurnal fluctuation of the RNA and DNA content noted in the cells of different organs corresponded to the mitotic rhythm. When the animals were illuminated at night the time of the maximum nucleic acid content changed from the morning to the evening.