The diurnal cycle in epidermal mitotic duration and its relation to chalone and adrenalin

Abstract

1. 1. It is shown that in mouse ear epidermis the duration of mitosis follows a diurnal rhythm, ranging between 2.6 hr when the animals are asleep and 3.5 hr when they are awake. 2. 2. With injections of adrenalin into sleeping mice the mitotic rate is decreased and the mitotic duration increased beyond the levels normally found in mice when awake. After adrenalectomy the mitotic rate is increased and the mitotic duration decreased beyond the levels normally found in mice when asleep. Adrenalectomy also destroys the diurnal rhythm in both mitotic rate and mitotic duration. 3. 3. The injection of epidermal chalone also decreases the mitotic rate and increases the mitotic duration, while the reduction in chalone concentration after wounding has the converse effects. 4. 4. The nature of the inverse relation between mitotic rate and mitotic duration is shown in Fig. 1. It is concluded that both rate and duration are determined by the homeostatic mechanism of which adrenalin and chalone form parts.