Stress and adrenaline in relation to the diurnal cycle of epidermal mitotic activity in adult male mice

Abstract

With mice starved to the point at which epidermal mitotic activity had almost ceased, a study has been made of the subsequent recovery of mitotic activity in vitro, using a simple phosphate-buffered saline medium. The results obtained suggest that the suppression of epidermal mitotic activity during starvation is due primarily to the increasing concentration of a mitotic inhibitor. It is suggested that this inhibitor is adrenaline secreted in excess during the stress of starvation. After both starvation and adrenaline treatment mitotic activity recovers rapidly when the skin is separated and placed in a saline medium, even when no nutrients are present. Further it is evident in both cases that during the course of the inhibition epidermal cells continue to prepare for division so that, when the inhibitor is washed out, mitoses appear in abnormally large numbers. It was also found that adrenalectomy is followed by a considerable rise in the epidermal mitotic rate and by the elimination of the diurnal mitotic rhythm. It is suggested that this rhythm is normally based on the hour-by-hour variations in the rate of adrenaline secretion. A mouse when awake and active evidently had a raised adrenaline blood content and thus a low epidermal mitotic rate; a mouse when asleep or resting has a reduced adrenaline blood content and thus a high epidermal mitotic rate. The epidermal mitoses developing when a mouse sleeps are partly those for which preparation was made when the mouse was awake and partly those which then complete their preparation. Thus it is possible to show that the longer a mouse remains awake the higher is the number of epidermal mitoses subsequently developing.