Effect of ACTH on circadian periodicity of nuclear volume and mitotic division in the zona fasciculata externa of the adrenal cortex of mice.

In cells of the zona fasciculata externa of the adrenal cortex of mice, the maximal value of nuclear volume is observed in evening and night time, while the mitotic peak occurs in the early part of the day. Ten day subcutaneous injection of 1.5 units of ACTH twice in 24 hr produced nuclear hypertrophy and stimulation of mitotic activity of cells of the zona fasciculata externa. The circadian periodicity of nuclear volume in mice injected with ACTH is disturbed, while the circadian rhythm of mitotic activity is retained.